Prokaryotes create adaptive immune memories by acquiring foreign DNA snippets, known as spacers, into the CRISPR array1. In type II CRISPR-Cas systems, the RNA-guided effector Cas9 also assists the acquisition machinery by selecting spacers from protospacer adjacent motif (PAM)-flanked DNA2,3. Here, we uncover the first biological role for Cas9 that is independent of its dual RNA partners. Following depletion of crRNA and/or tracrRNA, Neisseria apoCas9 stimulates spacer acquisition efficiency. Physiologically, Cas9 senses low levels of crRNA in cells with short CRISPR arrays – such as those undergoing array neogenesis or natural array contractions – and dynamically upregulates acquisition to quickly expand the small immune memory banks. As the CRISPR array expands, rising crRNA abundance in turn reduces apoCas9 availability, thereby dampening acquisition to mitigate autoimmunity risks associate with elevated acquisition. While apoCas9’s nuclease lobe alone suffices for stimulating acquisition, only full-length Cas9 responses to crRNA levels to boost acquisition in cells with low immunity depth. Finally, we show that this activity is evolutionarily conserved across multiple type II-C Cas9 orthologs. Altogether, we establish an auto-replenishing feedback mechanism in which apoCas9 safeguards CRISPR immunity depth by acting as both a crRNA sensor and a regulator of spacer acquisition.
Category: 7. Science
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Spatial joint profiling of DNA methylome and transcriptome in tissues
Tissue slide preparation
Mouse C57 embryo sagittal frozen sections (MF-104-11-C57 and MF-104-13-C57) were purchased from Zyagen. Freshly collected E11 or E13 mouse embryos were snap frozen in optimal cutting temperature (O.C.T.) compounds and sectioned at 7–10 μm thickness. Tissue sections were collected on poly-l-lysine-coated glass slides (Electron Microscopy Sciences, 63478-AS).
Juvenile mouse brain tissue (P21) was obtained from the C57BL/6 mice housed in the University of Pennsylvania Animal Care Facilities under pathogen-free conditions. All procedures used were approved by the Institutional Animal Care and Use Committee.
Mice were euthanized at P21 using CO2 inhalation, followed by transcranial perfusion with cold Dulbecco’s PBS (DPBS). After isolation, brains were embedded in Tissue-Tek O.C.T. compound and snap frozen on dry ice and a 2-methylbutane bath. Coronal cryosections of 8–10 μm were mounted on the back of Superfrost Plus microscope slides (Fisher Scientific, 12-550-15).
Preparation of transposome
Unloaded Tn5 transposome (C01070010) was purchased from Diagenode and the transposome was assembled following the manufacturer’s guidelines. The oligonucleotides used for transposome assembly were: Tn5ME-B, 5′-/5Phos/CATCGGCGTACGACTAGATGTGTATAAGAGACAG-3′; Tn5MErev, 5′-/5Phos/CTGTCTCTTATACACATCT-3′.
DNA barcode sequences, DNA oligonucleotides and other key reagents
DNA oligonucleotides used for PCR and library construction are shown in Supplementary Table 1. All DNA barcode sequences are provided in Supplementary Tables 2 (barcode A) and 3 (barcode B) and all other chemicals and reagents are listed in Supplementary Table 4.
Fabrication of the polydimethylsiloxane microfluidic device
Chrome photomasks were purchased from Front Range Photomasks, with a channel width of either 20 or 50 μm. The moulds for polydimethylsiloxane (PDMS) microfluidic devices were fabricated using standard photolithography. The manufacturer’s guidelines were followed to spin-coat SU-8-negative photoresist (Microchem, SU-2025 and SU-2010) onto a silicon wafer (WaferPro, C04004). The heights of the features were about 20 and 50 μm for 20- and 50-μm-wide devices, respectively. PDMS microfluidic devices were fabricated using the SU-8 moulds. We mixed the curing and base agents in a 1:10 ratio and poured the mixture onto the moulds. After degassing for 30 min, the mixture was cured at 66–70 °C for 2–16 h. Solidified PDMS was extracted from the moulds for further use. The detailed protocol for the fabrication and preparation of the PDMS device can be found in our previous research24.
Spatial joint profiling of DNA methylation and RNA transcription
Frozen tissue slides were quickly thawed for 1 min in a 37 °C incubator. The tissue was fixed with 1% formaldehyde in PBS containing 0.05 U ml−1 RNase inhibitor (Enzymatics) for 10 min and quenched with 1.25 M glycine for another 5 min at room temperature. After fixation, tissue was washed twice with 1 ml of DPBS–RNase inhibitor and cleaned with deionized H2O.
The tissue was subsequently permeabilized with 100 μl of 0.5% Triton X-100 plus 0.05 U ml−1 RNase inhibitor for 30 min at room temperature, then washed twice with 200 μl DPBS–RNase inhibitor for 5 min each. After permeabilization, the tissue was treated with 100 μl of 0.1 N HCl for 5 min at room temperature to disrupt histones from the chromatin, then washed twice with 200 μl of wash buffer (10 mM Tris-HCl pH 7.4, 10 mM NaCl, 3 mM MgCl2, 1% BSA and 0.1% Tween 20) plus 0.05 U ml−1 RNase inhibitor for 5 min at room temperature. Next, 50 μl of transposition mixture (5 μl of assembled transposome, 16.5 μl of 1× DPBS, 25 μl of 2× Tagmentation buffer, 0.5 μl of 1% digitonin, 0.5 μl of 10% Tween 20, 0.05 U ml−1 RNase inhibitor (Enzymatics) and 1.87 μl nuclease-free water) was added and incubated at 37 °C for 60 min. After 60 min incubation, the first round of transposition mixture was removed and a second round of 50 μl of fresh transposition mixture was added and incubated for another 60 min at 37 °C. To stop the transposition, 200 μl of 40 mM EDTA with 0.05 U ml−1 RNase inhibitor was added with incubation for 5 min at room temperature. After that, 200 μl 1× NEB3.1 buffer plus 1% RNase inhibitor was used to wash the tissue for 5 min at room temperature. The tissue was then washed again with 200 μl of DPBS–RNase inhibitor for 5 min at room temperature before proceeding with the in situ reverse transcription reaction.
In situ reverse transcription
For the in situ reverse transcription, the following mixture was added: 12.5 μl 5× reverse transcription buffer, 4.05 μl RNase-free water, 0.4 μl RNase inhibitor (Enzymatics), 1.25 μl 50% PEG-8000, 3.1 μl 10 mM dNTPs, 6.2 μl 200 U μl−1 Maxima H Minus Reverse Transcriptase, 25 μl 0.5× DPBS–RNase inhibitor and 10 μl 100 μM reverse transcription primer (biotinylated-dT oligo). The tissue was incubated for 30 min at room temperature, then at 45 °C for 90 min in a humidified container. After the reverse transcription reaction, tissue was washed with 1× NEB3.1 buffer plus 1% RNase inhibitor for 5 min at room temperature.
In situ barcoding
For in situ ligation with the first barcode (barcode A), the first PDMS chip was covered at the tissue ROI. For alignment purposes, a 10× objective (KEYENCE BZ-X800 fluorescence microscope, BZ-X800 Viewer Software) was used to take the bright-field image. The PDMS device and tissue slide were clamped tightly with a custom acrylic clamp. Barcode A was first annealed with ligation linker 1 by mixing 10 μl of 100 μM ligation linker, 10 μl of 100 μM individual barcode A and 20 μl of 2× annealing buffer (20 mM Tris-HCl pH 7.5–8.0, 100 mM NaCl2 and 2 mM EDTA). For each channel, 5 μl of ligation master mixture was prepared with 4 μl of ligation mixture (27 μl T4 DNA ligase buffer, 0.9 μl RNase inhibitor (Enzymatics), 5.4 μl 5% Triton X-100, 11 μl T4 DNA ligase and 71.43 μl RNase-free water) and 1 μl of each annealed DNA barcode A (A1–A50, 25 μM). Vacuum was applied to flow the ligation master mixture into the 50 channels of the device and cover the ROI of the tissue, followed by incubation at 37 °C for 30 min in a humidified container. Then the PDMS chip and clamp were removed after washing the tissue with 1× NEB 3.1 buffer for 5 min. The slide was then washed with deionized water and dried using compressed air.
For in situ ligation with the second barcode (barcode B), the second PDMS chip was covered at the ROI and a bright-field image was taken with the 10× objective. An acrylic clamp was applied to clamp the PDMS and tissue slide together. Annealing of barcode B (B1–B50, 25 μM) and preparation of the ligation mixture are the same as barcode A. The whole device was incubated at 37 °C for 30 min in a humidified container. The PDMS chip and clamp were then removed, and the slide was washed with deionized water and dried using compressed air. A bright-field image was then taken for further alignment.
Reverse crosslinking
For tissue lysis, the ROI was digested with 100 μl of the reverse crosslinking mixture (0.4 mg ml−1 proteinase K, 1 mM EDTA, 50 mM Tris-HCl pH 8.0, 200 mM NaCl and 1% SDS) at 58–60 °C for 2 h in a humidified container. The lysate was then collected in a 0.2-ml PCR tube and incubated on a 60 °C shaker overnight.
gDNA and cDNA separation
For gDNA and cDNA separation, the lysate was purified with Zymo DNA Clean and Concentrator kit and eluted with 100 μl nuclease-free water. Next, 40 μl of Dynabeads MyOne Streptavidin C1 beads were used and washed three times with 1× B&W buffer containing 0.05% Tween 20 (50 μl 1 M Tris-HCl pH 8.0, 2,000 μl 5 M NaCl, 10 μl 0.5 M EDTA, 50 μl 10% Tween 20 and 7,890 μl nuclease-free water). After washing, beads were resuspended in 100 μl of 2× B&W buffer (50 μl 1 M Tris-HCl pH 8.0, 2,000 μl 5 M NaCl, 10 μl 0.5 M EDTA and 2,940 μl nuclease-free water) containing 2 μl of SUPERase In RNase inhibitor, then mixed with the gDNA–cDNA lysate and allowed to bind for 1 h with agitation at room temperature. A magnet was then used to separate the beads, which bind to the cDNA that contains dT, from the supernatant that contains the gDNA.
gDNA library generation
Supernatant (200 μl) was collected from the above separation process for further methylated gDNA detection and library construction. Next, 1 ml of DNA binding buffer was added to the 200 μl supernatant and purified with the Zymo DNA Clean and Concentrator kit again, then eluted in 84 μl (3 × 28 μl) nuclease-free water. The NEBNext enzymatic methyl-seq conversion module (EM-seq) was then used to detect methylated DNA in the sample by converting unmethylated cytosines to uracil; the manufacturer’s guidelines were followed. Then, 28 μl of DNA sample was aliquoted into each PCR tube, TET2 reaction mixture (10 μl TET2 reaction buffer containing reconstituted TET2 reaction buffer supplement, 1 μl oxidation supplement, 1 μl DTT, 1 μl oxidation enhancer and 4 μl TET2) was added to the DNA sample on ice. In brief, 5 μl of diluted 1:1,300 of 500 mM Fe (II) solution was added to the mixture and incubated for 1 h at 37 °C in a thermocycler. After the reaction, the sample was transferred to ice and 1 μl of stop reagent from the kit was added. The sample was then incubated for another 30 min at 37 °C. TET2 converted DNA was then purified with 90 μl of solid-phase reversible immobilization (SPRI) beads and eluted with 16 μl nuclease-free water. The thermocycler was preheated to 85 °C, 4 μl formamide was added to the converted DNA and incubated for 10 min at 85 °C in the preheated thermocycler. After the reaction, the heated sample was immediately placed on ice to maintain the open chromatin structure, then reagents from the kit were added (68 μl nuclease-free water, 10 μl APOBEC reaction buffer, 1 μl BSA and 1 μl APOBEC) to deaminate unmethylated cytosines to uracil for 3 h at 37 °C in a thermocycler. Deaminated DNA was then cleaned up using 100 μl (1:1 ratio) of SPRI beads and eluted in 20 μl nuclease-free water.
Splint ligation
The gDNA tube was heat-shocked for 3 min at 95 °C and immediately put on ice for 2 min. Then, 10 μl of 0.75 μM pre-annealed Splint Ligate P5 (SLP5) adapter was added. This adapter was diluted from a 12 μM stock, which contained 6 μl of 100 μΜ SLP5RC oligo, 8.4 μl of 100 μΜ SLS5ME-A-H10 oligo, 5 μl of 10× T4 RNA Ligase Buffer and 30.6 μl nuclease-free water in a PCR tube that was incubated at 95 °C for 1 min, then gradually cooled by −0.1 °C s−1 to 10 °C on a thermocycler. Next, 80 μl of ligation master mixture was added to the gDNA tube at room temperature. The mixture contained 40 μl preheated 50% PEG-8000, 12.5 μl SCR buffer (666 mM Tris-HCl pH 8.0 and 132 mM MgCl2 in nuclease-free water), 10 μl of 100 mM DTT, 10 μl of 10 mM ATP, 1.25 μl of 10,000 U ml−1 T4 PNK and 6.25 μl of 400,000 U ml−1 T4 ligase. The splint ligation mixture was then splinted into five 0.2-ml PCR tubes, 20 μl per tube. The tubes were shaken at 1,000 rpm for 10 s and spun down, then incubated for 45 min at 37 °C, followed by 20 min at 65 °C to inactivate the ligase. For splint ligation indexing PCR, 80 μl of the PCR reaction mixture was mixed in each splint ligated tube. The mixture contained 20 μl 5× VeraSeq GC Buffer, 4 μl 10 mM dNTPs, 3 μl VeraSeq Ultra Enzyme, 5 μl 20× EvaGreen dye, 2 μl of 10 μM N501 primer and 2 μl of 10 μM N70X-HT primer (Supplementary Table 1). The mixture was then aliquoted into a clean PCR tube with 50 μl volume and run on a thermocycler with the setting below, 98 °C for 1 min, then cycling at 98 °C for 10 s, 57 °C for 20 s and 72 °C for 30 s, for 13–19 cycles, followed by 72 °C for 10 s. The reaction was removed once the quantitative PCR (qPCR) signal began to plateau. The amplified PCR products were pooled and purified with a 0.8× volume ratio of SPRI beads (bead-to-sample ratio) and the completed DNA library was eluted in 15 μl nuclease-free water.
cDNA library generation
The separated beads containing cDNA were used for cDNA library generation. In brief, 400 μl of 1× B&W buffer with 0.05% Tween 20 was used to wash the beads twice. Then, the beads were washed once with 400 μl of 10 mM Tris-HCl pH 8.0 containing 0.1% Tween 20 for 5 min at room temperature. Streptavidin beads with bound cDNA molecules were placed on a magnetic rack and washed once with 250 μl nuclease-free water before being resuspended in a template switching oligonucleotide solution (44 μl 5× Maxima reverse transcription buffer, 44 μl of 20% Ficoll PM-400 solution, 22 μl of dNTPs, 5.5 μl of 100 mM template switch oligo, 11 μl Maxima H Minus reverse transcriptase, 5.5 μl of RNase inhibitor (Enzymatics) and 88 μl nuclease-free water). Resuspended beads were then incubated for 30 min with agitation at room temperature and for 90 min at 42 °C, with gentle agitation. After the reaction, beads were washed with 400 μl of 10 mM Tris pH 8.0 containing 0.1% Tween 20 and washed without resuspension in 250 μl nuclease-free water. Water was removed on the magnetic rack and the beads were resuspended in the PCR solution (100 μl of 2× Kappa Master mix, 8.8 μl of 10 μM primers 1 and 2 and 92.4 μl nuclease-free water). Next, the beads were mixed well and 50 μl of the PCR mixture was split into four 0.2-ml PCR tubes. The PCR programme was run as follows: 95 °C for 3 min and cycling at 98 °C for 20 s, 65 °C for 45 s and 72 °C for 3 min, for a total of five cycles, followed by 4 °C on hold. After five cycles of PCR reaction, four PCR tubes were placed on a magnetic rack and 50 μl of the clear PCR solution was transferred to four optical-grade qPCR tubes, adding 2.5 μl of 20× Evagreen dye to each tube. The sample was run on a qPCR machine with the following conditions: 95 °C for 3 min, cycling at 98 °C for 20 s, 65 °C for 20 s and 72 °C for 3 min, for 13–17 cycles, followed by 72 °C for 5 min. The reaction was removed once the qPCR signal began to plateau. The amplified PCR product was purified with a 0.8× volume ratio of SPRI beads and eluted in 20 μl nuclease-free water.
A Nextera XT DNA Library Prep Kit was used for cDNA library preparation. In brief, 2 μl (2 ng) of purified cDNA (1 ng μl−1), 10 μl Tagment DNA buffer, 5 μl Amplicon Tagment mix and 3 μl nuclease-free water were mixed and incubated at 55 °C for 5 min. Then, 5 μl NT buffer was added to stop the reaction with incubation at room temperature for 5 min. PCR master mix (15 μl 2× N.P.M. Master mix, 1 μl of 10 μM P5 primer (N501) and 1 μl of 10 μM indexed P7 primer (N70X) and 8 μl nuclease-free water) was added. The PCR reaction was run with the following programme: 95 °C for 30 s, cycling at 95 °C for 10 s, 55 °C for 30 s, 72 °C for 30 s and 72 °C for 5 min, for a total of 12 cycles. The PCR product was then purified with a 0.7× ratio of SPRI beads and eluted in 15 μl nuclease-free water to obtain the cDNA library.
Library quality check and next-generation sequencing
An Agilent Bioanalyzer D5000 ScreenTape was used to determine the size distribution and concentration of the library before sequencing. Next-generation sequencing was conducted on an Illumina NovaSeq 6000 sequencer and NovaSeq X Plus system (150 bp paired-end mode).
Data preprocessing
For RNA-sequencing data, Read 2 was processed to extract barcode A, barcode B and the UMIs. Using the STARsolo pipeline56 (v.2.7.10b), these processed data were mapped to the mouse genome reference (mm10). This step generated a gene matrix that captures both gene-expression and spatial-positioning information, encoded through the combination of barcodes A and B. The gene matrix was then imported into R for downstream spatial transcriptomic analysis using Seurat package (v.5.1.0)57.
For DNA-methylation data, adaptor sequences were trimmed before demultiplexing the FASTQ files using the combination of barcodes A and B. We used the BISulfite-seq CUI Toolkit (BISCUIT) (v.0.3.14)58 to align the DNA sequences to the mouse reference genome (mm10). Methylation levels at individual CG and CH sites were stored as continuous values between 0 and 1, representing the fraction of methylated reads after quality filtering. These processed CG–CH files were then analysed independently using the MethSCAn pipeline18 to identify VMRs59, defined as fused genome intervals with methylation-level variance in the top 2%. We used default parameter settings when running MethSCAn, and the MethSCAn filter min-sites parameter was determined from the read coverage knee plot (Extended Data Fig. 3a). The methylation levels and residuals of VMRs were then imported into R for downstream DNA-methylation analysis.
Clustering and data visualization
We mapped the exact location of pixels on the bright-field tissue image using a custom Python script (https://github.com/zhou-lab/Spatial-DMT-2024/tree/main/Data_preprocess/Image), before removing additional empty barcodes on the basis of read-count thresholds determined by the knee plot (Extended Data Fig. 3a). Clustering and data visualization were conducted using R in RStudio.
For RNA data, we used the SCTtransform function in the Seurat package (v.5.1.0), built using a regularized negative binomial model, for normalization and variance stabilization. Dimensionality reduction was performed using RunPCA function with the SCTtransformed assay. We then constructed the nearest-neighbour graph using the first 30 principal components with the FindNeighbors function and identified clusters with the default Leiden method in the FindClusters function. Finally, a UMAP embedding was computed using the same principal components with RunUMAP function.
Owing to the inherent sparsity of DNA-methylation data, it is impractical to analyse methylation status solely at the individual CpG level. Binary information at sparse loci cannot be used directly to construct a feature matrix suitable for downstream analysis. In our study, we adopted the VMR framework, which divides the genome into variable-sized tiles and calculates the average methylation level across CpGs in each tile for each pixel18. This approach results in a continuous-valued matrix, in which rows correspond to pixels and columns represent genomic tiles, with values ranging from 0 to 1. VMR methylation levels and residuals were then imputed using the iterative principal component analysis approach as suggested in the MethSCAn instructions. Initially, missing residual values were replaced with zero and missing methylation levels were replaced with the average values for that VMR interval. The principal component analysis approach was iteratively applied until updated values stabilized to a threshold. The imputed residual matrix for VMRs was then imported into the existing Seurat object as another modality. Similar to the RNA-clustering pipeline, dimensionality was reduced using the RunPCA function. The first ten principal components from the residual matrix were used for clustering and UMAP embedding.
To visualize clusters in their spatial locations, the SpatialDimPlot function was used after clustering on the basis of gene expression or VMR residuals. UMAP embedding was visualized with the DimPlot function. The FindMarkers function was applied to select genes and VMRs that were differentially expressed or methylated for each cluster. For spatial mapping of individual VMR methylation levels or gene expression, we applied the smoothScoresNN function from the FigR package60. The SpatialFeaturePlot function was then used to visualize VMR methylation levels and gene expression across all pixels. To illustrate the relationships between clustering results from different modalities, we generated the confusion matrix and alluvial diagram using the pheatmap and ggalluvial R package61.
Integrative analysis of DNA methylation and RNA data
To integrate spatial DNA methylation and RNA data, WNN analysis in Seurat was applied using the FindMultiModalNeighbors function19. On the basis of the WNN graph, clustering, UMAP embedding and spatial mapping of identified clusters were performed for integrated visualization.
For the integration of spatial transcriptomics data of E11 and E13 mouse embryos, the top 3,000 integration features were selected, followed by the use of PrepSCTIntegration and IntegrateData functions to generate an integrated dataset. Similarly, to integrate with public single-cell transcriptomic data25,44, we first identified anchors using the FindIntegrationAnchors function in Seurat, followed by data integration using the IntegrateData function. To integrate DNA-methylation data, common VMRs between both developmental stages were obtained and the integrated CCA method from the IntegrateLayers function was used to join the methylation data from the two developmental stages. A Wilcoxon signed-rank test was performed to compare the methylation levels and gene-expression differences between the two time points.
TF motif enrichment
To perform TF motif enrichment, we first used the MethSCAn diff function on distinct groups of cells to identify differentially methylated VMRs on the basis of the clustering assignment. The HOMER62 findMotifsGenome function was then applied to analyse the enrichment of known TF motifs using its default database. We followed the same parameter settings used in MethSCAn, with motif lengths of 5, 6, 7, 8, 9, 10, 11 and 12.
CpGs enrichment analysis
Enrichment analysis of individual CpGs in the differential regions (Fig. 5a,b) was performed using knowYourCG (https://github.com/zhou-lab/knowYourCG), which provides a comprehensive annotation database for each CpG, including chromatin states, TF binding sites, motif occurrences, PMD annotations and more. To avoid inflated odds ratios for high-coverage data, genomic uniformity was quantified using fold enrichment, defined as the ratio of observed overlaps to expected overlaps. The expected number of overlaps was calculated as: (number of CpGs sequenced × number of CpGs in the chromatin state feature)/total number of CpGs in the genome.
Correlation and GO enrichment analysis
Correlation analysis was performed for different clusters. We first used the findOverlaps function in GenomicRanges package (v.4.4)63 to map VMRs to overlapped genes. Then, the Pearson correlation test was applied to obtain the correlation between mapped genes and corresponding VMRs. The Benjamini–Hochberg procedure was used to adjust all P values.
GO enrichment analysis was conducted using the enrichGO function from clusterProfiler package64 (v.4.2). For GO enrichment in the comparative analysis of E11 and E13 mouse embryos, the FindMarkers function in Seurat package was used to find differential genes and VMRs in the same cluster from integrated data across two developmental stages. Differentially upregulated genes (false discovery rate ≤ 0.05) with demethylated VMRs were used for the GO analysis.
Reporting summary
Further information on research design is available in the Nature Portfolio Reporting Summary linked to this article.
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Treat carbon storage like 'scarce resource': scientists – France 24
- Treat carbon storage like ‘scarce resource’: scientists France 24
- A prudent planetary limit for geologic carbon storage Nature
- Study: There is less room to store carbon dioxide, driver of climate change, than previously thought The Washington Post
- Safe underground carbon storage would only reduce warming by 0.7°C, analysis finds Phys.org
- Carbon Storage Potential Seen at Just 10th of Industry Estimates Bloomberg.com
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expert reaction to study of limits to underground carbon storage
A study published in Nature looks at planetary limit for geologic carbon storage.
Dr Robert Sansom, a member of the IET’s Sustainability and Net Zero Policy Centre, said:
“The installation of carbon capture and storage (CCS) can substantially reduce fossil fuel carbon emissions, however, as this latest study shows, it is a powerful tool in the fight against climate change, but it’s not a bottomless solution. We must treat it as a strategic and finite resource, and with this, comes an urgent need to reassess the role of CCS within national and global climate strategies.
“We should prioritise its use for long-term carbon removal, not just as a way to delay the transition away from fossil fuels. Engineers have a vital role to play in making sure storage sites are safe, effective, and used responsibly. We also need to invest in alternative technologies, build public trust, and ensure that countries with fewer resources aren’t left behind.
“We are not going to be able to stop using fossil fuels overnight, so it’s important that the UK has a fossil fuel strategy on how we manage their use going forward and which supports the transition to Net Zero.”
Dr Jen Roberts, Senior Lecturer in Civil and Environmental Engineering at the University of Strathclyde, and Deputy Director of the UK Carbon Capture & Storage Research Centre (UKCCSRC), said:
“There has been a real need for updated and realistic global CO2 storage capacity estimates, so I wholly welcome this new research. Previous global estimates are quite old and outdated now and didn’t consider risk-based spatial constraints that this new work incorporates. As a result, previous work has often framed storage resources as plentiful or unlimited, and this is simply not the case in some geological conditions and contexts. This new research finds more conservative values and thus presents global CO2 storage as a ‘limited intergenerational resource’, which I know many in the CO2 storage community will welcome.
“The pace of global emissions reduction has been too slow, with a range of ramifications including the potential need for carbon removal – both to balance carbon budgets and to prevent temperature rise. This places additional reliance on CO2 geological storage, and this new study explores questions around prioritising CO2 storage.
“It is important to note that global assessments like this may be useful to understand constraints and guide policy, but they have limitations. They are typically very simplified and have big uncertainties. This large-scale, low-resolution analysis takes a highly simplified approach to calculating storage potential, and the estimates of capacity essentially assume the same amount of CO2 can be stored in every cubic metre of sedimentary basin around the world. We still need detailed regional and basin scale analyses which underpin assessments for CO2 geological storage development. The storage calculations from a more granular analysis might be quite different.
“Overall the research brings a nuanced viewpoint on CO2 geological storage; while developing CO2 storage is absolutely necessary for our climate, the constraints are not simple, storage resource is not unlimited, and how the technology scales up is laced with justice implications for generations to come.”
Prof Sam Krevor, Professor of Subsurface Carbon Storage and Royal Academy of Engineering Senior Research Fellow at Imperial College London, said:
“The authors suggest that they have identified that the prudent resource base for CO2 storage globally is far lower than previously estimated because past efforts, largely led by government geological surveys and national laboratories, have not considered important physical and socio-political risks. What the authors fail to acknowledge is that the physical limitations that comprise the vast majority of their identified reductions (ocean depth, sedimentary depth, locations in polar circles) are already incorporated into past assessments, and that when a nearly identical approach was taken to estimate the global storage resource base1, a similar result was obtained, i.e., 2,000 Gt of CO2 storage resource estimated compared with the 10,000+ Gt when compiling detailed regional estimates produced by geological surveys.
“Thus, rather than having identified important considerations that were previously ignored, it is apparent that the authors have implemented a modelling approach that is simply pre-disposed to estimate the resource base for CO2 storage far below estimates arising from established standards developed by government and academic groups over the past 20 years. Whether this systematic bias arises from some fundamental error in the approach can only be assessed once the full dataset can be scrutinised, but it is notable that established methods make use of far more detailed data and analyses of regional geological systems than was used in this work or the previous work1.
“It is a shortcoming of this work that the authors do not validate their modelling approach, or explain major and systematic differences as compared with alternative and established methods. The bias in the estimates would have been revealed immediately by comparison of the authors’ estimates of ‘geological potential’ to any number of detailed regional analyses that have been carried out by government geological surveys, for example in the United Kingdom, Norway, and the United States. Indeed it can be seen in the open peer review documentation that this and many of the issues above were pointed out by the reviewers, but not addressed in the rebuttals. It will be a valuable exercise to understand where the differences arise when using the coarse and imprecise global sedimentary basins and thickness datasets, as is done in this paper, as compared with the established methods that use detailed regional information about local geological systems.
“Ultimately, whether it is 1,200 Gt, 2,000 Gt, or 10,000 Gt, there is far more potential storage resource than is needed for CO2 storage to play a major role in emissions mitigation. Approaching even 1,000 Gt of CO2 stored underground would be a signal achievement in our fight against climate change. Thus even if 200 years from now we are needing to find alternatives to the use of CO2 storage for want of geology, this will be a problem that we can welcome.”
1 Wei, Y. M., Kang, J. N., Liu, L. C., Li, Q., Wang, P. T., Hou, J. J., … & Yu, B. (2021). A proposed global layout of carbon capture and storage in line with a 2 C climate target. Nature Climate Change, 11(2), 112-118
Prof Naomi Vaughan, Professor of Climate Change at the University of East Anglia, said:
“This is a valuable and timely study that quantifies a feasible estimate of geological storage potential. This more conservative estimate of global CO2 storage capacity raises important questions for governments and global society about how this unique resource should be used in the coming decades to reach net zero. Some argue it could be used to extend the life of fossil fuels, or to reduce emissions from the trickier sectors; or it could be prioritised for methods that take existing CO2 out of the atmosphere, allowing us to lower greenhouse gas concentrations more than through emissions reduction alone. We will have to decide.”
Prof Jon Gibbins, Professor of CCS at the University of Sheffield and Director of the UK CCS Research Community network, but commenting in a personal capacity, said:
“This paper seems to state nothing new with respect to the minimum expected amount of global CO2 geological storage capacity. The IPCC Special Report on CCS1 published in 2005 estimated that the lower limit on total global storage capacity is around 1,680 billion tonnes of carbon dioxide vs the estimate of 1,460 billion tonnes of carbon dioxide in this paper, essentially the same number for approximations of this type. The paper cites the seminal and very widely-authored IPCC report as general evidence for the period of global interest in CCS but the authors do not seem to have made this obvious acknowledgement.
“Then, given that the authors’ assumed ‘prudent’ limits are already significantly exceeded by hard evidence from well-established carbon dioxide storage projects, their headline storage capacity number obviously needs to be viewed with some scepticism. And, because these assumed limits have already been demonstrably broken within just the first, relatively few, current injection projects, it is likely that they are not such a big deal. The authors do note that ‘When we apply exclusion layers in the order presented here, we find that that the largest increase in storage would be realized if our assumptions regarding storage and ocean depth were relaxed.’ The authors’ own data suggests that, with more realistic assumed limits, global carbon dioxide storage capacity would be at least doubled.
“The limit on sub-surface injection depth of 2,500 metres used to arrive at the headline value for minimum global CO2 storage capacity is at variance with actual practical evidence from the Aquistore project in Canada, where 620,000 tonnes have been successfully stored at a depth of around 3300 metres2. The Aquistore project, used as a backup ‘overflow’ for the Boundary Dam capture project, is monitored extensively for learning purposes, has been running for ten years and is well-covered in the literature. But the Aquistore evidence does not appear to have been referenced directly in this paper, although the maximum feasible upper depth limit in their sensitivity analyses is reported to be 3,500 metres.
“The paper’s authors also assume a limit of 300 metres of ocean depth for offshore CO2 storage in their headline estimate of global storage potential. Again this is at variance with actual practical experience over about ten years in the Brazilian offshore oil fields, where, just in 2024, over 10 million tonnes of CO2 were reinjected into four different oil fields at a water depth of around 2,000 metres (and a further rock depth of several kilometres) from multiple floating capture units. This paper says ‘drilling for hydrocarbons has been achieved down to water depths of 2,000 metres’ and cites a 2017 reference on Brazilian oil production history but does not appear to include any mention of the extensive subsequent CO2 injection experience described in more up-to-date publications. It then goes on to cite the Deepwater Horizon disaster, involving oil exploration not CO2 injection, as evidence for why CO2 storage in locations with more than 300 metres water depth is unlikely (headline estimate limit) and more than 500 metres (the authors’ maximum contemplated limit) should be considered impossible.
“There is also an error in the Grantham press release: ‘disused mines are the most efficient type of geological storage’ is very definitely not true. You don’t mine for oil and gas and it is reservoirs for these hydrocarbons – some in use, some new, as well as some disused ones – that will be used for CO2 storage, and not old mines. It would be entirely incorrect to suggest that people living in old mining areas need to worry about stored CO2 leakage as a result of this sloppiness.”
1 https://www.ipcc.ch/report/carbon-dioxide-capture-and-storage/
2 https://discoverestevan.com/articles/ptrc-receives-prestigious-award-for-southeast-ccs-project
Brazilian CO2 injection references include:
22 FPSOs in Brazil’s pre-salt enable Petrobras to break C02 reinjection record
https://pure.tudelft.nl/ws/portalfiles/portal/220693591/1-s2.0-S1750583624001750-main.pdf
https://www.energy.gov/sites/default/files/2023-07/6a.%20CCUS%20at%20Petrobras%20-%20CSLF%20meeting%202023%20_%20final%20version%20PDF.pdf
Dr Wei He, a Senior Lecturer in the Department of Engineering at King’s College London, said:
“The headline message is that geologic carbon storage is finite when assessed prudently. This reframes storage potential in terms of usability and risk, which should stimulate further work in both risk assessment and engineering mitigation to refine the global limit or recover the resource via engineering innovations. The equity dimension also matters: linking responsibility for emissions with access to readily usable storage could help accelerate deployment through international collaboration.
“This is a transparent, spatially explicit global assessment that layers multiple risk and feasibility filters on sedimentary basins, then benchmarks results against IPCC scenario demand. The central conclusion—that “easy-to-use” (low-risk) storage is far more limited than raw technical capacity—is well supported by the mapping, sensitivity tests and scenario comparisons. The authors are appropriately cautious about uncertainties and report ranges throughout.
“This research shifts the debate from “How much storage space exists?” to “How much high-quality storage should we carefully plan to use? This study shows that quality screens and socio-environmental constraints cut that figure substantially, consistent with recent feasibility concerns and the difficulty of scaling CCS in practice. Importantly, in my opinion, this does not say “there is no capacity.” It says the readily deployable, low-risk subset is scarce relative to demand in strong-overshoot scenarios—arguing for prioritisation, not abandonment, of CCS for the high-quality storage for climate.
“The practical takeaway is: treat geologic storage as a limited, intergenerational resource reserved for the highest-value uses—hard-to-abate industrial point sources and durable removals (e.g., DAC/BECCS)—rather than offsetting emissions that can be avoided through electrification or renewables.
“CCS is viable and needed, but over-reliance or non-strategic use can be a policy risk. If we lean too heavily on CCS—especially to prolong fossil use—we deplete a scarce resource and still risk breaching the sensible limit this or next century. In short, pursue CCS as part of a portfolio, not as a substitute for rapid mitigation, and use it strategically to maximise the impact of limited high-quality storage.”
Prof Stuart Gilfillan, Professor of Geochemistry at the University of Edinburgh, said:
“Gidden and colleagues offer a useful, science‑based budget for carbon capture and storage (CCS): a “prudent” global limit of about 1,460 billion tonnes of CO2 (over a range 1,290–2,710) within porous sedimentary formations. That is still a very large resource, which is equivalent to several decades of today’s emissions and enough for CCS to play a central role alongside rapid emissions cuts. If devoted to storage of CO2 removed from the atmosphere, it could trim global warming by around 0.4–0.7°C. Rather than downgrading CCS, this work helps target it where it delivers the most climate benefit. It is important to remember that CCS remains the only tool to cut emissions directly from industrial sources.
“The authors calculate this number by mapping where storage makes sense after accounting for earthquake risks, protected and populated areas, and cross‑border issues. This prudence reduces the headline potential, but it also boosts confidence that stored CO2 will remain safely underground, as the climate benefits are preserved if leakage remains below about 0.01% per year. Experience from well‑chosen sites shows this standard is attainable with modern well integrity and monitoring. Hitting 1.5–2°C pathways will still require a major scale‑up from today’s small base, meaning that there is a need to build shared CO2 transport and storage hubs now and there is a need to advance other storage options, such as CO2 mineralization in reactive rocks.
“The policy takeaway is optimistic but disciplined: treat storage as valuable and use it where it matters most, to tackle hard‑to‑abate industrial emissions and high‑durability carbon removals, backed up by strong measurement and long‑term stewardship. As storage opportunities are uneven across countries and some basins cross borders, fair international rules and finance are critical. This paper doesn’t close the door on CCS; it provides the guardrails to deploy it safely, credibly, and to maximum climate effect.”
Dr Tom Kettlety, Research Fellow in Geological Carbon Storage in the Department of Earth Sciences & Oxford Net Zero, University of Oxford, said:
“The Grantham press release and the associated quotes are fundamentally misleading in their framing of this paper’s findings. ‘Industry’ estimates of accessible storage capacity are already aligned with the capacity estimates this paper finds (in the order of thousands of gigatonnes). Framing this work as a ‘game changer’ and positioning this against an ‘overly optimistic’ industry estimate is exaggeration in my view, and destructive to broader understanding around a small but vital part of stopping climate change.
“No one credible thinks that storage resources are an ‘unlimited solution’, and it’s irresponsible to characterise it this way. The paper’s analysis is reasonable, albeit pessimistic; but this press release appears to be arguing against a position that no credible voice in the CO2 storage industry or policy sphere is taking — these are clear straw man arguments.
“It’s agreed that massive emissions reductions are needed, and that geological storage is necessary in the near-term to cover for sectors that will be very hard to decarbonise. This is necessary to achieve the rapid transition to net zero required to stop climate change. This is also infrastructure that needs to be constructed and scaled up right now, otherwise it won’t be ready in time for when it’s needed.
“These new storage capacity estimates do not change that conclusion. This paper’s results still support — even with their pessimistic assumptions — that there are many decades worth of storage resources that can be used to get to net zero. But these findings will be used to stoke controversy where none should exist.”
Prof Carrie Lear, Professor of Past Climates and Earth System Change at Cardiff University’s School of Earth and Environmental Sciences, said:
“Carbon capture and storage can either decarbonise industrial processes or remove CO₂ from the atmosphere to reverse climate change. We’ve assumed we could do both, storing CO₂ underground where we have extracted fossil fuels. But this study challenges that assumption, showing that if we avoid risks to people and sensitive environments like the Arctic, the safe storage potential drops by a factor of ten.
“If future generations will depend on CCS to maintain net-zero emissions, then we must act now to preserve that option. That means cutting CO₂ emissions rapidly today. We cannot afford to use up this finite resource on short-term industrial fixes when its long-term value lies in restoring a safe climate.
“The study makes cautious assumptions, like limiting offshore CCS to shallow waters. But even if deeper sites become viable, it’s clear we should reduce our reliance on fossil fuels rather than expand industrial activity into fragile deep ocean ecosystems.
“There is no single solution to climate mitigation, it is like a pie made up of many slices. The biggest slice has always been cutting our use of fossil fuels, and that remains true today. Other slices include restoring forests, improving energy efficiency, and using technologies like carbon capture and storage (CCS). But this new study shows that the CCS slice is much smaller than we thought. That means the fossil fuel reduction slice just got bigger and also more urgent. We need to act fast to reduce emissions at the source, because we now have even less room to rely on technological fixes later.”
Prof Myles Allen FRS, Head of Atmospheric, Oceanic and Planetary Physics, University of Oxford, said:
“The paper correctly notes ‘incumbent industry actors must be appropriately incentivized to become net injectors, rather than extractors, of subsurface carbon’. That’s spot on: if you want to dig it up, you need to put it back, and then some. We must make geological CO2 disposal a licensing condition of continued extraction and use of fossil carbon. Only then will we truly discover the scale of this resource.”
Dr Phil Williamson, Honorary Associate Professor at University of East Anglia, said:
“For the past twenty years or so, there has been a plausible escape route from climate catastrophe: we don’t need to stop greenhouse gas emissions just yet, since we will be able to remove CO2 from the atmosphere in future and store it safely underground. Whilst the world seems near-certain to overshoot 1.5C warming, it will be possible to get back to that just-about-liveable level after we have fully experienced the human and economic costs of higher temperatures. Gidden and colleagues question that assumption, by setting limits on the amount of removed CO2 that can be feasibly stored in sedimentary basins. These safe limits are around ten times lower than their initial estimates based on physical storage potential. There may be other storage options, for example in basalt formations or directly in the ocean; however, the former is still highly uncertain, whilst the latter would currently be contrary to international law (as well as having high potential for environmental harm). The new Nature analysis therefore confirms the folly of any policy option other than “stringent near-term gross emission reductions”. It also points out that decisions made in the next few years are likely to have consequences for the human population for at least the next ten generations.”
Dr Injy Johnstone, Oxford University Smith School of Enterprise and the Environment
“This paper provides the most advanced assessment of feasible carbon storage prospects yet – clearly illustrating the critical need to double down on our efforts to cut emissions. The limits to global carbon storage the paper finds mean we must also take carbon removal budgeting seriously so that we can tackle difficult questions head on: such as who should have access to this carbon storage globally and on what terms.”
Prof Kevin Anderson, Professor of Energy and Climate Change at the University of Manchester, said:
“This publication is a welcome intervention, particularly in how it challenges the exaggerated claims and speculative projections associated with carbon capture and storage (CCS). However, its reference to an upper limit of almost 1.5 trillion tonnes of CO₂ storage, while technically feasible, risks legitimising continued “business-as-usual” approaches. Such figures are likely to be used by actors, including much of the integrated assessment modelling (IAM) community, to justify scenarios that rely heavily on CCS and carbon dioxide removal (CDR), while neglecting the possibility of rapid and equitable societal transformation – an omission that significantly distorts the policy pathways they present.
“This is especially concerning given the persistent gap between the promises of CCS and real-world performance. After decades of bold projections, only around 10 million tonnes of CO₂ are captured and permanently stored each year (excluding enhanced oil recovery), representing less than 0.03% of annual global fossil fuel emissions. Rather than serving as a credible mitigation technology, CCS has largely functioned as a rhetorical device to delay robust fossil fuel regulation.
“While there is a legitimate and important role for CCS in cement production, this is typically overshadowed by its broader misuse as a tool to justify continued oil and gas extraction. As such, although the Nature paper makes a valuable contribution, it risks being misread as endorsing the large-scale deployment of CCS and CDR seen in many IAM scenarios – an approach that lacks empirical grounding and continues to undermine serious climate policy and transformative change.”
Dr Ben Caldecott, Director, Oxford Sustainable Finance Group, University of Oxford
“Finite geological storage will need to be stewarded wisely, even more wisely than the paper suggests. The estimates are a very significant overestimate of what geological storage will actually be available as the economics have not been factored in. Only a fraction of that estimated will be accessible at a price society will be willing to pay.”
* ‘A prudent planetary limit for geologic carbon storage’ by Matthew J. Gidden et al. was published in Nature at 4pm UK time on Wednesday 3 September.
DOI: https://doi.org/10.1038/s41586-025-09423-y
Declared interests
Jen Roberts: “I collaborate with Matthew Giddens and Keywan Riahi (two of the authors) through the EU-funded UPTAKE project which is referred to in the acknowledgement statement for this paper.”
Myles Allen: “My group is currently working on a project on Geologically Balanced Fuels for Net Zero Aviation funded by VietJet.”
Injy Johnstone: “No conflicts of interest to declare.”
Ben Caldecott: “No conflicts of interest to declare.”
Phil Williamson: “No conflicts of interest to declare (retired employee of Natural Environment Research Council/UK Research & Innovation).”
Tom Kettlety: “I’ve sat on project scientific advisory boards, provided consulting, and been in research projects with CO2 storage operators, regulators, and associated government departments.”
Naomi Vaughan: “I’ve worked with the lead author on a paper before and published with some of the co-authors. I have no financial or commercial interests in anything.”
Jon Gibbins: “None to declare.”
Stuart Gilfillan: “I have received funding from TotalEnergies in the past, for research related to CO2 origins in the subsurface and reservoir connectivity and Equinor for research related to the subsurface trapping of CO2 in natural CO2 reservoirs. I currently receive funding from the UK Natural Environment Research Council for research related to CO2 mineralisation.”
Wei He: “I recieve industrial funding from Mission Zero Technologies – a company working on direct air capture technology”
Carrie Lear: “I once received some funding from NERC for a PhD studentship that was in collaboration with BG Group. Nothing to do with CCS. We were using BG core material to reconstruct climate in the past.”
Kevin Anderson: “I have no financial interests or formal affiliations with any organisations that support or oppose carbon capture and storage.”
Sam Krevor: “I receive research funding from Shell to carry out research on the geological storage of CO2, although not on the topics that are covered by the paper. I am the Editor-in-chief of the International Journal of Greenhouse Gas Control, the leading scientific journal with a focus on carbon capture and storage, which is published by Elsevier.”
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Earth’s capacity to store carbon could max out surprisingly soon
The planet’s capacity to store carbon-dioxide emissions in rock formations is much smaller than previous estimates suggest and it could run out as early as 2200, according to a study1 published in Nature today.
To meet the goal of the 2015 Paris agreement — limiting global warming to 1.5–2 °C above pre-industrial temperatures — vast amounts of CO2 will need to be removed from the atmosphere. One way to do that is to capture CO2 produced by industry and store it deep underground.
Researchers report that Earth can safely store around 1,460 gigatonnes of carbon dioxide (GtCO₂) — a number much lower than the 10,000–40,000 GtCO₂ often cited in previous studies2.
At present, carbon capture and storage technologies remove only 49 million tonnes of CO₂ annually, with a further 416 million tonnes per year in planned capacity, say the authors of the study. But to stay within the Paris target, annual carbon storage would need to rise to 8.7 GtCO₂ by mid-century — a 175-fold increase over the next three decades.
Low-risk storage
To estimate Earth’s storage capacity, the study — led by scientists at the International Institute for Applied Systems Analysis in Laxenburg, Austria — calculated that the planet has a physical storage reserve of 11,800 GtCO2. But, when the researchers estimated how much of those reserves can be used practically without the risk of carbon leakage triggered by earthquakes, or without access being blocked owing to political decisions, the capacity dropped to 1,460 GtCO₂.
The study focused on the storage capacity of stable sedimentary basins, in which most prospective CO2 storage sites are being considered.
Even if the 1,460 GtCO₂ capacity was used exclusively for removing carbon from the atmosphere, the effort would reverse global warming by only 0.7 °C. Current trends suggest that global warming will increase by up to 3 °C this century, even if all the identified geological storage for reversing climate change is used, it would not reverse warming back to 2 °C, says Joeri Rogelj, a co-author of the study and climate scientist at Imperial College London.
The researchers suggest that if stored CO₂ escapes to the surface, it could lead to the formation of carbonic acid in groundwater. Acidic conditions can dissolve metal-containing minerals, releasing toxic metals, which could harm humans and the environment.
Winners and losers
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A prudent planetary limit for geologic carbon storage
Riahi, K. et al. in Climate Change 2022: Mitigation of Climate Change (eds Shukla, P. R. et al.) Ch. 3 (Cambridge Univ. Press, 2022); https://doi.org/10.1017/9781009157926.005.
Clarke, L. et al. in Climate Change 2022: Mitigation of Climate Change (eds Shukla, P. R. et al.) Ch. 6 (Cambridge Univ. Press, 2022); https://doi.org/10.1017/9781009157926.008.
Kearns, J. et al. Developing a consistent database for regional geologic CO2 storage capacity worldwide. Energy Procedia 114, 4697–4709 (2017).
Google Scholar
Baines, S. et al. CO2 Storage Resource Catalogue—Cycle 3 Report (Oil and Gas Climate Initiative, 2022).
Damon, et al. An integrated approach to quantifying uncertainties in the remaining carbon budget. Commun. Earth Environ. 2, 7 (2021).
Google Scholar
Palazzo, et al. The Zero Emissions Commitment and climate stabilization. Front. Sci. 1, 1170744 (2023).
Google Scholar
Arias, P. A. et al. Technical Summary. In Climate Change 2021: The Physical Science Basis (eds Masson-Delmotte, V. et al.) (Cambridge Univ. Press, 2021).
Metz, B., Davidson, O., de Coninck, H. & Loos, M. IPCC Special Report on Carbon Dioxide Capture and Storage (IPCC, 2005).
Matters Relating to the Global Stocktake under the Paris Agreement (UNFCCC, 2023).
The Global Status of CCS: 2024 (Global CCS Institute, 2024).
Gasos, A., Pini, R., Becattini, V., & Mazzotti, M. Enhanced oil recovery using carbon dioxide directly captured from air does not enable carbon-neutral oil. Preprint at EarthArXiv https://doi.org/10.31223/X55X4S (2025).
Selosse, S. & Ricci, O. Carbon capture and storage: lessons from a storage potential and localization analysis. Appl. Energy 188, 32–44 (2017).
Google Scholar
Steyn, M., Oglesby, J., Turan, G., Zapantis, A. & Gebremedhin, R. Global Status of CCS 2022 (Global CCS Institute, 2022).
Churkina, G. et al. Buildings as a global carbon sink. Nat. Sustain. 3, 269–276 (2020).
Google Scholar
Schleussner, Carl-Friedrich, et al. Overconfidence in climate overshoot. Nature 634, 366–373 (2024).
Lane, J., Greig, C. & Garnett, A. Uncertain storage prospects create a conundrum for carbon capture and storage ambitions. Nat. Clim. Change 11, 925–936 (2021).
Google Scholar
Grant, N., Hawkes, A., Mittal, S. & Gambhir, A. The policy implications of an uncertain carbon dioxide removal potential. Joule 5, 2593–2605 (2021).
Google Scholar
Hepple, R. P. & Benson, S. M. Geologic storage of carbon dioxide as a climate change mitigation strategy: performance requirements and the implications of surface seepage. Environ. Geol. 47, 576–585 (2005).
Google Scholar
Krevor, S. et al. Subsurface carbon dioxide and hydrogen storage for a sustainable energy future. Nat. Rev. Earth Environ. 4, 102–118 (2023).
Google Scholar
Benson, S. et al. in IPCC Special Report on Carbon Dioxide Capture and Storage (eds Metz, B. et al.) Ch. 5 (Cambridge Univ. Press, 2005).
Kazlou, T., Cherp, A. & Jewell, J. Feasible deployment of carbon capture and storage and the requirements of climate targets. Nat. Clim. Chang. 14, 1047–1055 (2024).
Romeiro, V. & Parente, V. Carbon capture and storage and the UNFCCC: recommendations to address trans-boundary issues. Low Carbon Econ. 03, 130–136 (2012).
Google Scholar
Stuart-Smith, R. F., Rajamani, L., Rogelj, J. & Wetzer, T. Legal limits to the use of CO2 removal. Science 382, 772–774 (2023).
Google Scholar
Wei, Y.-M. et al. A proposed global layout of carbon capture and storage in line with a 2 °C climate target. Nat. Clim. Change 11, 112–118 (2021).
Google Scholar
Zhang, Y., Jackson, C. & Krevor, S. The feasibility of reaching gigatonne scale CO2 storage by mid-century. Nat. Commun. 15, 6913 (2024).
Google Scholar
Goodman, A. et al. U.S. DOE methodology for the development of geologic storage potential for carbon dioxide at the national and regional scale. Int. J. Greenh. Gas Control 5, 952–965 (2011).
Google Scholar
Shindell, D. & Rogelj, J. Preserving carbon dioxide removal to serve critical needs. Nat. Clim. Change https://doi.org/10.1038/s41558-025-02251-y (2025).
Bachu, S. Sequestration of CO2 in geological media: criteria and approach for site selection in response to climate change. Energy Convers. Manag. 41, 953–970 (2000).
Google Scholar
Kaldi, J. G. & Gibson-Poole, C. M. (eds.). Storage capacity estimation, site selection and characterisation for CO2 storage projects. Report No. RPT08-1001 (CO2CRC, 2008).
Raza, A. et al. A screening criterion for selection of suitable CO2 storage sites. J. Nat. Gas Sci. Eng. 28, 317–327 (2016).
Google Scholar
Nicol, A., Carne, R., Gerstenberger, M. & Christophersen, A. Induced seismicity and its implications for CO2 storage risk. Energy Procedia 4, 3699–3706 (2011).
Google Scholar
The severity of an earthquake. USGS https://pubs.usgs.gov/gip/earthq4/severitygip.html (1989).
Mehlhorn, J., Byrne, J. M., Kappler, A. & Planer-Friedrich, B. Time and temperature dependency of carbon dioxide triggered metal (loid) mobilization in soil. Appl. Geochem. 74, 122–137 (2016).
Google Scholar
Knauss, K. G., Johnson, J. W. & Steefel, C. I. Evaluation of the impact of CO2, co-contaminant gas, aqueous fluid and reservoir rock interactions on the geologic sequestration of CO2. Chem. Geol. 217, 339–350 (2005).
Google Scholar
Pianta, S., Rinscheid, A. & Weber, E. U. Carbon capture and storage in the United States: perceptions, preferences, and lessons for policy. Energy Policy 151, 112149 (2021).
Google Scholar
Arning, K. et al. Same or different? Insights on public perception and acceptance of carbon capture and storage or utilization in Germany. Energy Policy 125, 235–249 (2019).
Google Scholar
Request for an Advisory Opinion Submitted by the Commission of Small Island States on Climate Change and International Law (International Tribunal for the Law of the Sea, 2024).
Garrett, J. & McCoy, S. Carbon capture and storage and the London Protocol: recent efforts to enable transboundary CO2 transfer. Energy Procedia 37, 7747–7755 (2013).
Google Scholar
Status of IMO Treaties (International Maritime Organization, 2024).
Larson, E., Li, Z. & Williams, R. in Global Energy Assessment: Toward A Sustainable Future Ch. 12 (Cambridge Univ. Press, 2012).
Muratori, M. et al. EMF-33 insights on bioenergy with carbon capture and storage (BECCS). Climatic Change 163, 1621–1637 (2020).
Google Scholar
Bui, M. et al. Carbon capture and storage (CCS): the way forward. Energy Environ. Sci. 11, 1062–1176 (2018).
Google Scholar
Fuhrman, J. et al. The role of direct air capture and negative emissions technologies in the shared socioeconomic pathways towards +1.5 °C and +2 °C futures. Environ. Res. Lett. 16, 114012 (2021).
Google Scholar
Strefler, J. et al. Carbon dioxide removal technologies are not born equal. Environ. Res. Lett. 16, 074021 (2021).
Google Scholar
Gidden, M. J. et al. Fairness and feasibility in deep mitigation pathways with novel carbon dioxide removal considering institutional capacity to mitigate. Environ. Res. Lett. 18, 074006 (2023).
Google Scholar
Gambhir, A. & Tavoni, M. Direct air carbon capture and sequestration: how it works and how it could contribute to climate-change mitigation. One Earth 1, 405–409 (2019).
Google Scholar
Grant, N., Gambhir, A., Mittal, S., Greig, C. & Köberle, A. C. Enhancing the realism of decarbonisation scenarios with practicable regional constraints on CO2 storage capacity. Int. J. Greenh. Gas Control 120, 103766 (2022).
Google Scholar
Smith, S. M. et al. The State of Carbon Dioxide Removal 1st edn (The State of Carbon Dioxide Removal, 2023); https://www.stateofcdr.org.
Crude Oil Production (Indicator) (OECD, 2024); https://doi.org/10.1787/4747b431-en.
den Elzen, M. G. J. et al. Updated nationally determined contributions collectively raise ambition levels but need strengthening further to keep Paris goals within reach. Mitig. Adapt. Strateg. Glob. Change 27, 33 (2022).
Google Scholar
Höhne, N. et al. Wave of net zero emission targets opens window to meeting the Paris Agreement. Nat. Clim. Change 11, 820–822 (2021).
Google Scholar
Rogelj, J. et al. A new scenario logic for the Paris Agreement long-term temperature goal. Nature 573, 357–363 (2019).
Google Scholar
IPCC: Summary for Policymakers. In Climate Change 2021: The Physical Science Basis (eds Masson-Delmotte, V. et al.) (Cambridge Univ. Press, 2021).
Andreoni, P., Emmerling, J. & Tavoni, M. Inequality repercussions of financing negative emissions. Nat. Clim. Change 14, 48–54 (2024).
Google Scholar
Nemet, G. F. et al. Near-term deployment of novel carbon removal to facilitate longer-term deployment. Joule 7, 2653–2659 (2023).
Google Scholar
Khandoozi, S., Hazlett, R. & Fustic, M. A critical review of CO2 mineral trapping in sedimentary reservoirs—from theory to application: pertinent parameters, acceleration methods and evaluation workflow. Earth Sci. Rev. 244, 104515 (2023).
Google Scholar
Azzolina, N. A. et al. CO2 storage associated with CO2 enhanced oil recovery: a statistical analysis of historical operations. Int. J. Greenh. Gas Control 37, 384–397 (2015).
Google Scholar
Clark, D. E. et al. CarbFix2: CO2 and H2S mineralization during 3.5 years of continuous injection into basaltic rocks at more than 250 °C. Geochim. Cosmochim. Acta 279, 45–66 (2020).
Google Scholar
McGrail, B., Spane, F., Sullivan, E., Bacon, D. & Hund, G. The Wallula basalt sequestration pilot project. Energy Procedia 4, 5653–5660 (2011).
Google Scholar
Cao, X., Li, Q., Xu, L. & Tan, Y. A review of in situ carbon mineralization in basalt. J. Rock Mech. Geotech. Eng. https://doi.org/10.1016/j.jrmge.2023.11.010 (2023).
Mace, M. J., Fyson, C. L., Schaeffer, M. & Hare, W. L. Large-scale carbon dioxide removal to meet the 1.5 °C limit: key governance gaps, challenges and priority responses. Glob. Policy 12, 67–81 (2021).
Google Scholar
Medvecky, F., Lacey, J. & Ashworth, P. Examining the role of carbon capture and storage through an ethical lens. Sci. Eng. Ethics 20, 1111–1128 (2014).
Google Scholar
Fyson, C. L., Baur, S., Gidden, M. & Schleussner, C.-F. Fair-share carbon dioxide removal increases major emitter responsibility. Nat. Clim. Change 10, 836–841 (2020).
Google Scholar
Ringrose, P. S. & Meckel, T. A. Maturing global CO2 storage resources on offshore continental margins to achieve 2DS emissions reductions. Sci. Rep. 9, 17944 (2019).
Google Scholar
Zickfeld, K., Azevedo, D., Mathesius, S. & Matthews, H. D. Asymmetry in the climate–carbon cycle response to positive and negative CO2 emissions. Nat. Clim. Change 11, 613–617 (2021).
Google Scholar
Gütschow, J. et al. The PRIMAP-hist national historical emissions time series. Earth Syst. Sci. Data 8, 571–603 (2016).
Google Scholar
Furre, A.-K., Eiken, O., Alnes, H., Vevatne, J. N. & Kiær, A. F. 20 years of monitoring CO2-injection at Sleipner. Energy Procedia 114, 3916–3926 (2017).
Google Scholar
Benedictus, T. et al. Long Term Integrity of CO2 Storage—Well Abandonment (IEAGHG, 2009).
Evenick, J. C. Glimpses into Earth’s history using a revised global sedimentary basin map. Earth Sci. Rev. 215, 103564 (2021).
Google Scholar
Bradshaw, J. et al. The potential for geological sequestration of CO2 in Australia: preliminary findings and implications for new gas field development. APPEA J. 42, 25–46 (2002).
Google Scholar
Development of Storage Coefficients for CO2 Storage in Deep Saline Formations (IEAGHG, 2009).
Laske, G., Masters, G., Ma, Z. & Pasyanos, M. Update on CRUST1. 0—a 1-degree global model of Earth’s crust. Geophys. Res. Abstr. 15, 2658 (2013).
Szulczewski, M. L., MacMinn, C. W., Herzog, H. J. & Juanes, R. Lifetime of carbon capture and storage as a climate-change mitigation technology. Proc. Natl Acad. Sci. USA 109, 5185–5189 (2012).
Google Scholar
Protected Planet: The World Database on Protected Areas (WDPA) (UNEP-WCMC and IUCN, 2024).
Maritime Boundaries Geodatabase (Flanders Marine Institute, 2023); https://doi.org/10.14284/628.
Michie, E. A. H. & Braathen, A. How displacement analysis may aid fault risking strategies for CO2 storage. Basin Res. 36, e12807 (2024).
Google Scholar
Johnson, K. et al. Global seismic hazard map. Zenodo https://doi.org/10.5281/zenodo.8409647 (2023).
Wald, D. J., Quitoriano, V., Heaton, T. H. & Kanamori, H. Relationships between peak ground acceleration, peak ground velocity, and modified Mercalli intensity in California. Earthq. Spectra 15, 557–564 (1999).
Google Scholar
Damen, K., Faaij, A. & Turkenburg, W. Health, safety and environmental risks of underground CO2 storage—overview of mechanisms and current knowledge. Climatic Change 74, 289–318 (2006).
Google Scholar
Gao, J. & O’Neill, B. C. Mapping global urban land for the 21st century with data-driven simulations and Shared Socioeconomic Pathways. Nat. Commun. 11, 2302 (2020).
Google Scholar
O’Neill, B. C. et al. The roads ahead: narratives for shared socioeconomic pathways describing world futures in the 21st century. Glob. Environ. Change https://doi.org/10.1016/j.gloenvcha.2015.01.004 (2015).
Bruhn, C. H. et al. Campos and Santos basins: 40 years of reservoir characterization and management of shallow-to ultra-deep water, post-and pre-salt reservoirs-Historical overview and future challenges. In Offshore Technology Conference Brasil D011S006R001 (OTC, 2017).
Beyer, J., Trannum, H. C., Bakke, T., Hodson, P. V. & Collier, T. K. Environmental effects of the Deepwater Horizon oil spill: a review. Mar. Pollut. Bull. 110, 28–51 (2016).
Google Scholar
Global Oil and Gas Extraction Tracker (Global Energy Monitor, 2025).
Omara, M. et al. Developing a spatially explicit global oil and gas infrastructure database for characterizing methane emission sources at high resolution. Earth Syst. Sci. Data 15, 3761–3790 (2023).
Google Scholar
Sabbatino, M. et al. Global Oil & Gas Features Database (National Energy Technology Laboratory, 2017); https://doi.org/10.18141/1427300.
Global Oil and Gas Extraction Tracker (Global Energy Monitor, 2024).
Zhang, G. et al. Giant discoveries of oil and gas fields in global deepwaters in the past 40 years and the prospect of exploration. J. Nat. Gas Geosci. 4, 1–28 (2019).
Google Scholar
Project, T. T., De Reuck, K., Angus, S. & Armstrong, B. International Thermodynamic Tables of the Fluid State: Carbon Dioxide (Pergamon Press, 1976).
Hasan, M. M., Alam, M. W., Jian, H. & Chowdhury, K. M. A. Protracted maritime boundary disputes and maritime laws. J. Int. Marit. Saf. Environ. Aff. Shipp. 2, 89–96 (2019).
Byers, E. et al. AR6 scenarios database. Zenodo https://doi.org/10.5281/zenodo.5886912 (2022).
Huppmann, D. et al. pyam: analysis and visualisation of integrated assessment and macro-energy scenarios. Open Res. Eur. 1, 74 (2021).
Google Scholar
Gidden, M. & Joshi, S. Supplemental Data for Gidden et al 2025: a prudent planetary limit for geologic carbon storage. Zenodo https://doi.org/10.5281/zenodo.15657542 (2025).
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Uranus revealed: Solving the ice giant’s heat…
Sarah Al-Ahmed:
A long-standing Uranian mystery gets an update, this week on Planetary Radio. I’m Sarah Al-Ahmed of The Planetary Society with more of the human adventure across our solar system and beyond. For decades, Uranus has baffled scientists. Voyager 2’s 1986 flyby suggested that the ice giant wasn’t radiating any extra heat, but new research has finally cracked the case. I’ll talk with Michael Roman, assistant professor at the Universidad Adolfo Ibáñez in Chile, and co-author on a new paper showing that Uranus really is giving off more heat than it receives from the sun. We’ll also celebrate the discovery of a brand new moon around Uranus, in this week’s What’s Up, with our chief scientist, Bruce Betts. If you love Planetary Radio and want to stay informed about the latest space discoveries, make sure you hit that subscribe button on your favorite podcasting platform. By subscribing, you’ll never miss an episode filled with new and awe-inspiring ways to know the cosmos and our place within it.Uranus has a reputation, partly for its name that’s the butt of endless jokes, but mostly because it’s just plain weird. This ice giant spins on its side, tilted nearly 98 degrees. That tilt gives it some of the most extreme seasons in the solar system, with decades of daylight at one pole, while the other one is locked in darkness. Its atmosphere is strangely bland compared to Neptune’s stormy skies, and yet it hides mysteries that we still don’t fully understand. One of the strangest puzzles was uncovered by Voyager 2 in 1986. Unlike Jupiter, Saturn and Neptune, which all radiate more heat than they received from the sun, Uranus appeared to be in perfect balance, giving off no excess heat at all. We would say that this world seemed to be in thermal equilibrium. That made it a definite oddball among the giant planets raising big questions about its history and interior.
We expect our giant planets to radiate more energy than they receive from the sun because they’re still slowly cooling off from their formation, leaking leftover heat from their interiors into space. Now, new research has finally rewritten this story, the paper called Internal Heat Flux and Energy Imbalance of Uranus, which was published in the Geophysical Research Letters on July 14th, 2025, by lead authors, Xinyue Wang and Liming Li, confirms that Uranus is indeed radiating more heat than it receives from the sun. It’s still less than the other giant planets, but definitely more in line with what we would expect from this world. Their work is also reinforced by other recent studies, including by a team led by Patrick Irwin at the University of Oxford.
Joining me now to explain what this means for Uranus, for ice giants in general, and even for our understanding of exoplanets, is Dr. Michael Roman, assistant professor of physics and astronomy at the Universidad Adolfo Ibáñez in Santiago, Chile. He’s one of the co-authors on this study, and an expert on planetary atmospheres, especially when it comes to ice giants like Uranus and Neptune. Hey Michael, thanks for joining me.
Michael Roman:
Hi. Yeah, it’s a pleasure to be here.Sarah Al-Ahmed:
Or should I say bienvenido, you’re coming to us from Chile, right?Michael Roman:
Yes, from Santiago. I started just recently here at the university on the eastern side of the city, Universidad Adolfo Ibáñez, where I’m an assistant professor.Sarah Al-Ahmed:
So, you spent most of your career studying the atmospheres of Uranus and Neptune, what first drew you to these ice giants?Michael Roman:
I suppose, Uranus and Neptune, they kind of occupy a space where they’re at the very edge of our solar system as far as the giant planets are concerned, and they are far less studied than Jupiter and Saturn, so there’s a lot of mysteries that remain about them. They’re sort of enigmatic in that case. But they’re close enough where we can actually see them through telescopes and resolve clouds on their atmospheres. So, yeah, I think they’re just sort of mysterious outer worlds, that we’ve had some idea about, my entire life, and I remember first seeing those Voyager images as a child, and we’re at a position, I suppose, where we really can start to learn a lot about them just due to technology advancing, and telescopes advancing in the last 20 years. So, for me, it’s an exciting place to study, where there’s opportunity to learn a lot about some worlds we’ve known about for a while, but haven’t been able to really explore as much as we would like.Sarah Al-Ahmed:
It just kills me that we’ve only ever flown by these worlds once with the Voyager missions. It was so long ago, and I’m really grateful that now we have instruments like JWST to give us a closer look. What was it like to finally see those images of Uranus and Neptune through JWST’s eyes?Michael Roman:
Oh yeah, that was incredible. I remember some of my older professors talking about their time in the Voyager days, and the excitement of seeing these planets for the first time, and I don’t think anything will ever really catch that same sort of initial excitement of seeing volcanism on Io, and the close-up look of Neptune and its clouds and all that for the first time. But I feel like I got a little hint of it perhaps, of seeing the first spectra from JWST of Uranus and Neptune, because they’re challenging targets, we’ve been trying to observe them from ground-based telescopes for years, and we get some data, but often it can be quite noisy, and to see the precise clean data, that looks almost like a model in some cases, from JWST, given its sort of amazing sensitivity, it really was something I had been waiting years to see. And when it came down, and I was in a room with Lee Fletcher, and some of my other colleagues, and we’re looking at it for the first time, it was exciting. It was really one of those moments I don’t think I’ll forget.Sarah Al-Ahmed:
Really though, it feels like, depending on how the future plays out, there are a lot more nations that are trying to prioritize potentially missions to Uranus someday, and the results coming out of studies like the one that you and your team have done, but also from all the data coming out of JWST, I hope reinforces that incentive for us to go back to these worlds, because there’s just so much we don’t know.Michael Roman:
Oh yeah, absolutely. As you say, Voyager was the only time we really got a close look at these planets, and that was 1986, for Uranus. And there’s only so much you can figure out from far away, from 20 times the distance between Earth and the sun. So, you need to get close to really learn a lot about these planets, and it’s a logical next step in our exploration of the solar system I’d say. We got Jupiter studied pretty well, Saturn, we had the amazingly successful Cassini mission, now it feels like it’s Uranus’ turn.Sarah Al-Ahmed:
Well, can you tell us a little bit about your journey? You’ve gone from Cornell, to Michigan, to Leicester, and now to Chile, how has that shaped your approach to planetary science and international collaboration?Michael Roman:
I suppose it’s given me different perspectives on the world, just living in different places, in a way that’s sort of a perk of the job, to be able to, as a postdoc, have a reliable income for a few years in a new place, and meet new people. I worked on some different things, in Michigan it was more exoplanets than solar systems, so it gave me that sort of perspective on the astrophysics and just planets in general. There’s a great diversity of planets out there, our solar system is just one subset, and in some ways maybe kind of an odd subset of planets. But so to be able to work with different people on different topics over the years has been a great privilege.So, yeah, I’ve enjoyed the process of investigating with different collaborators around the world to some extent. At the same time, yes, of course it has… I don’t know where my home is exactly, in essentially [inaudible 00:08:02], I feel a little divided, and it’s sort of a nomadic lifestyle, but yeah, it is what it is. But the planets, they’re there to kind of give me focus as I look from different perspectives.
Sarah Al-Ahmed:
For decades, Uranus has presented this kind of heat mystery. Early Voyager 2 observations, and you said they were in 1986, which is what, 39 years ago? They suggested that Uranus wasn’t emitting this excess heat that we expected from other gas giants. Could you talk a little bit about this long-standing puzzle, and why it’s perplex planetary scientists for so many decades?Michael Roman:
Yeah, sure. General, Uranus is a bit of an oddball as a planet, it’s the coldest planet in the solar system, and it’s about as cold as any planet we really know of. It gets down to around 50 Kelvin, and so this is colder than the temperatures you see on Neptune, which is farther from the sun. So, there’s already something a little weird there. Uranus, as I guess we’ll talk about in a little more detail, is unlike all the other planets, it’s tilted on its side, essentially… Earth’s axis is tilted about 23 and a half degrees or something, so that it gives you the seasons. Uranus is tilted and it’s something close to 98 degrees, 97.77 or something like this degrees, and as a result, you get these many to high latitudes fall into decades and decades of darkness followed by decades of light.So, you get these cold, dark winter nights, which last 30, 40 years near the pole, and then on the other side, again, daylight for decades. And so, this is sort of extreme setup in terms of sunlight falling on the planet. And even though that sunlight is 19 astronomical units out there, and the edge of the solar system, that sunlight is something like 370 times weaker than we get on Earth. It still adds up, it still provides energy to the planet. But what’s sort of odd, I guess, about Uranus compared to the other planets, aside from these other facts, is that all the other giant planets, Jupiter, Saturn, and Neptune, if you look at the amount of heat that comes off those planets, the amount of heat that they radiate, it exceeds the amount of heat they actually absorb from the sun.
As I say, they’re not an equilibrium, the amount of energy falling from the sun, enters the atmosphere, and it warms the atmosphere, if it was perfectly an equilibrium, the amount of heat it would give off would be equal to that amount. So, it’s not heating or cooling over time, it’s just getting a certain amount of energy from the sun, and then radiating that same amount of energy off into space. But it turns out Jupiter, Saturn, and Neptune all radiate excess heat. And so, it must come from some internal heat source, some sort of theorized that, essentially, primordial heat from their formation or their contraction, or the way they’re still separating, differentiating over time, they’re still evolving, and as they’re evolving, they’re losing energy still, they’re still losing heat and cooling down. And so, we have determined this for the planets to occur, but for Uranus, it seems the case is somewhat different.
When we did the same sorts of studies, when I say we, scientists back in the Voyager, did the same sort of studies, they realized that the amount of heat that Uranus gave off really didn’t exceed the amount it was receiving from the sun by much, if at all. And so, within [inaudible 00:11:34] , it seemed like it was perhaps in equilibrium with the sun. The amount of energy it emitted seemed to be about equal to the amount it received, which was very different than the other planets as we’ve said. And I think the other planets, in the case of Jupiter, something like 1.67 times as much energy is emitted than it receives, Saturn is 1.78, and Neptune, estimates are something like two and a half times, or 2.7 times as much energy is emitted than what it receives. So, there’s a lot of internal energy coming from its interior that’s escaping and being lost to space.
But for Uranus it’s something close to one, where basically it’s the amount of energy it receives is equal to the amount of energy it emits. To make these measurements is not easy, you can’t do it necessarily from Earth alone, because you need to know how much energy is entering the atmosphere, and how much is being scattered back. And from Earth, if you look at Uranus, you’re only really seeing the side of Uranus that is facing Earth in the sun. And so, you know how much light is being scattered directly back towards you, but you don’t know how much light is being scattered in other directions, unless you’re observing Uranus from those other directions. And so, as a result, from Earth, you can only say something about its geometric albedo as we call it, and you don’t really get a full picture as to how much of that sunlight is actually being scattered in other directions.
And so, to get that measurement, you need to observe the planet from a different range of observing geometries, different phases as we say, and the only way to do that is to have something like a spacecraft go out and observe it at these different angles as it’s, in the case of Voyager, flying past Uranus. So, what the Voyager mission did was allow us to get these observations of all the giant planets at different phase angles, over a range of angles, to see how this light from the sun is scattered off into different directions, basically just an accounting problem, the amount of energy in versus the amount of energy out.
Sarah Al-Ahmed:
But what did Voyager actually tell us about how much heat was escaping the planet into space?Michael Roman:
Well, you need to be able to look at the thermal emission from the planet, from all positions on the planet, and so again, with the same problem, if you’re looking at Uranus from Earth, you’re only seeing the heat that’s escaping from Uranus in the infrared directed towards Earth. And in order to know how much heat’s being lost all around the planet, you need to be able to look at it, what’s going on the other side. From Earth, you can’t tell how much heat is escaping on the dark, cold night side of Uranus out into space, you just have no idea from looking at Earth alone. And when Uranus is being tilted on its side, when it’s rotating, you’re not getting any of that night side into your field of view over the course of a day, it’s blocked from your view for 30, 40 years.So, it’s really, it’s a mystery is what’s going on back there without having a spacecraft go right behind and have a look. And so, what Voyager did flying by, gave us those measurements of how the light is scattered as a function of angle going past the planet, but also how much heat was actually escaping from the night side of the planet. And so, Voyager, with this infrared spectrometer was able to measure the thermal emission… I should say, when it flew by in January 1986, I think so we are coming up on just the short of 40 years, it was summer solstice, near summer solstice on Uranus for the hemisphere facing Earth. You had half the planet was in winter solstice, and that winter solstice meant that we couldn’t really see what’s going on there without Voyager. And so, Voyager was able to measure the planet at this time of solstice, for one side is summer, one side is winter.
And what it found was the temperatures were not all that different between the two hemispheres, roughly it was symmetric, or you had sort of warm at the equator and then colder at mid-latitudes, and there was a little difference between the hemispheres, maybe something on order of just a few Kelvin. But it wasn’t dramatic, it wasn’t extreme, which is sort of surprising when you think about… You might expect that that side that hasn’t seen the sun in 30 years, just cooling off, radiating heat, and would be much colder than the day side which is getting baked by sunlight. Weak sunlight out, at that distance in the solar system, but is still getting irradiated, you might expect a significant difference, but in fact it really didn’t seem to be much of a difference. Which has implications, it means that energy is being deposited on one side, not on the other, by the sun, and the fact that they don’t differ by that much in temperature means that that energy is being redistributed somehow, through winds at some height in the atmosphere to equilibrate and give it sort of an average temperature.
But back to the point, is that once you know how much heat is… How much solar energy is coming into the planet, taking into account that that’s scattered off in all different angles, versus that which is absorbed, you can come up with what is called a bond albedo, and that’s what these scientists guys, like Pearl back in the Voyager era, did to determine what the energy balance was of the planet. So, when they do that for Jupiter, and for Saturn, and for Neptune, you find the amount of energy greatly exceeds that which it receives from the sun. So, there’s an internal source of energy that’s quite significant, that’s contributing to all the energy lost into the space.
And that is to say that these planets are losing energy, you can think about maybe in terms of evolution, if the planet’s still cooling down and contracting and it’s not yet reached its sort of steady state, but when you do the same one for Uranus, they found that, well, unlike the others, it doesn’t seem to have much excess energy. It seems that within error bars basically, from those original Pearl paper back in the 90s, that the amount of energy escaping from Uranus was within error bars consistent with the amount that’s being received, statistically significant with it being in equilibrium. And so, that was weird because Neptune, which is a lot ways similar to Uranus, in size, roughly similar size, roughly similar mass, roughly similar composition, out there on the edge, its sister ice giant is giving off more than two and a half times as much energy.
So, something’s weird about Uranus, and people over the years have speculated, well, what’s going on? Did we catch Uranus at some strange time in its history? Is it a clue the fact that Uranus is tilted on side? Perhaps this all is due to one very violent, dramatic collision early in the history of Uranus, that knocked it on its side, but also maybe stirred it up, or mixed in a way, or caused it to dispel some of this internal heat that the others are now just slowly radiating away. So, it’s been a mystery for a while.
Sarah Al-Ahmed:
How does that impact the level of mixing in the atmosphere?Michael Roman:
It contributes to sort of Uranus as being this kind of oddball strange planet. Without that internal heat escaping, the atmosphere then becomes very… You don’t have that extra source of heat from below, and that’s part of the reason Uranus is very cold, and you don’t get the same sort of mixing that we see on Neptune. Neptune, if you look at the atmosphere on Neptune, there’s a lot more methane up high in the atmosphere, because it seems like it’s being mixed up higher. It’s there, therefore it must be getting mixed up higher, whereas on Uranus, you don’t have that same amount of methane up high, which is consistent with it essentially not being mixed upwards.Sarah Al-Ahmed:
But what role does methane actually play in Uranus’s energy balance, or its photochemistry?Michael Roman:
If you don’t have that internal heat leading to that mixing, then Uranus ends up being drier up high, and you don’t have this as rich photochemistry that occurs when methane interacts with sunlight, produces all these other hydrocarbons, the methane gets [inaudible 00:19:41], you end up with carbons and hydrogen floating around, and they recombine, they form all these different hydrocarbons, like ethane, and acetylene, and benzene, and these sorts of things, that then, themselves, are very effective at radiating heat. And so, they affect energy [inaudible 00:19:59] planet too. So, it comes to this complicated picture where an interaction between sunlight, and chemistry, and heating, and where gases are, and internal mixing all comes together to give you this complicated picture as to how the planet evolves, and what sort of composition and temperatures it has. But Uranus, for whatever reason, just has this different tilt, has this lack of internal heat, and it leads to it being cold, and maybe less vigorously mixed, and maybe from an observational point of view, a little more quiescent than the other planets.Neptune, you’re probably well familiar, you see these pictures of clouds moving along Neptune very quickly. In Uranus you have some clouds, but you don’t have the same dynamic, rapidly changing, and frequently seen clouds as you see on Neptune. And we’re starting to unravel this, learn about this, JWST is providing some insight into this. But numerous studies over the last 20 years have really been helping to give us more information on these planets. They’re challenging targets because they are far away compared to Jupiter and Saturn, Neptune is smaller than the great red spot in the sky, than Jupiter. So, it’s a tiny thing. And so, you need a big telescope in order to observe it, and really, we only had telescopes that were big enough to observe it well, with adaptive optics, since maybe 2000, around year 2000, late-1990s, when you start getting these adaptive optics.
The data I worked on in graduate school for my thesis was data from the Palomar 200-inch, the five-meter telescope, which is a telescope from the 1940s and 50s, but adaptive optics, that allows you to correct for the seeing in the atmosphere, was a game changer. It allowed us to really see details on the planet from the ground for the first time. And that only occurred, yeah, in the early 2000s really, you had data like that. In the 1990s you had Hubble, and those gave us some nice views of a Uranus and Neptune for the first time, that you can see the structure in the atmosphere. But those JWST images show for the first time, and if you look at Uranus over time, you start to see there’s a very seasonal cycle to it, because it goes around the sun every 80, 84 years, which means that each season is around 20, 21 years long on Uranus.
Sarah Al-Ahmed:
God, that’s so long.Michael Roman:
Yeah, it’s a long time. But don’t get me started on Neptune. Since that tilt, you get these very extreme seasons, again where you are having 20 years where it’s summer, and the pole is basically facing towards the sun, as we were talking about before. But what we found is when you observe Uranus over time, there is a cyclic pattern to its brightness. There’s a great set of data, a guy named Lockwood was observing Uranus and Neptune from Flagstaff, from the Lowell Observatory since the 1950s, I think, and gave this long period of just annual observations looking at Uranus and Neptune, how they looked each year near their opposition, near where they’re highest in the sky, just recorded their brightness, and when you looked at this over time, you found trends where cyclic almost, where Uranus would get darker and brighter, and darker and brighter.And it really wasn’t clear why this was happening until we really were able to resolve the planet with these bigger telescopes, with Hubble, and then things like Palomar, and the big Keck, and all these telescopes that came on in the last 20 years, that showed that there’s a big difference between Uranus’s low latitudes and its high latitudes in visible light. You see towards the high latitudes in Uranus, which I mean latitudes 45 degrees and north, or 40 degrees and north, it is brighter, it is more reflective than it is near the low latitudes. For reasons we have come to understand, it’s due to the combination of the high latitudes, they seem to have more cloud, there’s clouds around one and a half to two bars, that just seem to be thicker at those high latitudes, and they just reflect more light.
And secondly, very interestingly, if you look at the amount of methane in the atmosphere, and methane is a sort of dominant absorber in Uranus’s atmosphere, you look at the amount of methane, it varies significantly from the equator to the pole. Near the equator you have, when you go down to around a bar level… So, in terms atmospheric pressure, you talk about sort of stratosphere up high, these millibar pressures, and then you go down to around a bar, which is basically around the surface pressure on Earth. And then you’re in the tropopause, where the weather layer, where things are mixing in the atmosphere, in general, and that’s where the thickest clouds are, or hazes are, on these planets. And Uranus… It’s also where methane becomes more abundant. And this is because on Uranus, and the very cold region at the tropopause, where temperatures kind of reach their minimum, the amount of methane just condenses out. You just can’t have a lot of it.
And so, if you look at the amount of methane in the atmosphere of Uranus, it’s some small trace amount, 10 to the -5th, something like this, order of magnitude. As they go down and it gets warmer, you can have more methane, and then you get down to several percent of the atmosphere by mixing ratio, by volume, is methane. And near the equator it seems, there was a paper, I guess in the mid-2000s, 2000 maybe 11 or 2009, I forget. But Erich Karkoschka, one of the great scientists in our field, using some data from Hubble Spectra was able to determine that the amount of methane near the pole differed from the amount of methane near the equator in the tropopause, and the deeper party atmosphere. Something like three or 4% near the equator, and down to 1% or 1.5% near the pole.
So, a factor of two, a significant difference. And what means though is that since methane is the strongest absorber in this atmosphere, the high latitudes have less methane and quite dramatically, changes quite abruptly at these mid-latitudes, and as a result, high latitudes, they’re cloudier and there’s less absorption, so they appear brighter. And the low latitudes in your equator, they have more methane, more of the sunlight’s absorbed, and there’s less clouds, so they appear darker, less albedo is the term we’d sort of use, less reflective. And so, Uranus has reflective poles and less reflective equator, low latitudes. And so, when Uranus, since it’s tilted on its side, there’s points where it’s poles are facing towards you, and points where it’s equator is more or less facing towards you, and then the other pole, and this cycles back and forth over the course of its 84-year orbit.
And so, that leads to some variation in how bright Uranus appears from Earth. And so, what that means is that the amount of sunlight Uranus receives depends on how far Uranus is from the sun, but the amount it absorbs going to depend on how much it’s reflecting back. And so, sometimes in its solstices, it’s going to be reflecting more, and near the Equinox it’s going to be absorbing more. And so, you end up with this change in the amount of heat, that’s sunlight that’s being absorbed in the planet. Also, it turns out, Uranus has an eccentric orbit, it’s not perfectly circular orbit, and so as a result, when it’s at its closest to the sun, the planet’s larger in the sky, it’s subtending a larger arc, and it’s therefore intercepting more sunlight and it’s absorbing more sunlight.
And when Uranus is at this apogee, at the farthest point away of its orbit, then it’s receiving less sunlight. It turns out this is quite a dominant factor, this is actually maybe more important than the change in albedo, just due to the clouds and methane and the orientation of the planet. So, then the question is, how does the amount of energy that it emits over time vary over time? So, that’s what the lead authors, Xinyue Wang and Liming Li looked at in this paper, was basically how the energy balance of Uranus, given the amount of sunlight falling on it, the amount of sunlight being absorbed by it, and the amount of heat it’s radiating away, how it all balances and how that balance changes over time, and that was sort of the crux of this paper.
Sarah Al-Ahmed:
Was it the fact that you had so much time to look at this world over the decades that finally allowed us to realize that it wasn’t in thermal equilibrium? Was it just a matter of getting more data?Michael Roman:
Right, I think that’s precisely the case. And I guess also critically is just in recent years they’ve recalibrated, one of the other authors, Daniel Wenkert, he went ahead and reanalyzed some of the Voyager data, and had found that some of the original estimates for the energy is a function of different phases, how it scattered over different angles, could be improved. And he came up with a revised number, and never revised number was significant, and that sort of changed things to push in favor that maybe it wasn’t quite so close to equilibrium as previously thought. So, the question is, now have a better measurement, a better idea of how sunlight falling on Uranus heats it up over time, how much of that energy is absorbed versus how much is scattered as a function of Uranus’s orbital period and season. So, better accounting, the simple accounting, adding up photons absorbed by the atmosphere over time to give us the energy coming in.And so, now, we know how the input energy from the sun changes in time, how does the output energy from the atmosphere change in time? It turns out that in the last, only in the last 20 years, technology from the ground has allowed us to make infrared measurements of Uranus with some accuracy that was just not possible before the early 2000s. And so guys like Glenn Orton, over at JPL, have been making infrared measurements of the giant planets using big telescopes to measure the thermal emission in the mid-infrared. Most of the energy emitted from Uranus and Neptune, given your cold temperature, is going to be in the far infrared, but the mid-infrared is more easily accessible from the ground, and we can get a sense of, at least sample how much heat’s escaping in some of these wavelengths.
And from that we can relate it to the amount of energy given off in total, just through some careful relationships between that and this paper, Liming and Xinyue have looked at, to say how you can relate the brightness temperatures we call it, these observations of thermal emission from the Earth, to sort of total amount of energy just getting from the planet. Over the years, we had some observations collaborating with Glenn Orton, Lee Fletcher, myself, did infrared observations of Uranus, during the 2000s and again in 2018, and again in a few months time I’ll have some new observations from the VLT, these are using telescopes that are eight and a half meters or so, and diameters are large and they can resolve Uranus, and they’re up high in mountains, and here in Chile, and they can get some pretty good measurements of the thermal heat escaping Uranus reaching Earth.
And with these measurements, with some extrapolating, using this sort of relationship between brightness temperatures observed from Earth and what we saw, for example, Cassini in Saturn, the authors of this paper, we were able to infer what the global thermal emission coming from Uranus was over time. And what we had found, well, there’s a couple things we found. [inaudible 00:32:04] in a paper in 2015, and then a paper again in 2020, Glenn and I looked, Glenn Orton and I looked at the thermal emission we sensed from Earth, of Uranus, and we compared that to what Voyagers gave off, and if you put into, say, the same circumstances, the same geometry, if you’re looking at them, I’d say comparable, it turns out they were pretty much exactly the same. They didn’t vary at all. Which is to say over 30 something years, and a whole season on Uranus from solstice to spring, the atmosphere didn’t really change much in temperature. Let’s just say it seems to be rather invariant over time, at least unto the measurement uncertainties.
Sarah Al-Ahmed:
We’ll be right back with the rest of my interview with Michael Roman after this short break.Jack Kiraly:
This October, NASA needs you. Hi, I’m Jack Kiraly, director of government relations at The Planetary Society. In response to unprecedented proposed budget cuts to NASA Science programs, The Planetary Society and a coalition of our allies and partners are organizing a special day of action to save NASA Science. Join us in person on October 5th and 6th in Washington D.C. You’ll receive training on effective advocacy from our team of space policy experts, then head to the Hill to meet directly with your representatives in Congress to advocate for protecting NASA’s science budget and ongoing missions. If you can’t come to Washington D.C. you can still pledge to take action online. We’ll give you the resources you need to be part of the movement to save NASA Science. This event is open to any US resident, no experience required. Space science benefits all of humanity, let’s stand together to protect it. Registration is open now at planetary.org/dayofaction. We’ll see you in Washington.Sarah Al-Ahmed:
Well, that sounds like a little bit of a paradox, right? Uranus has these huge seasonal swings and sunlight, but the temperature hardly budges. What does that tell us about how the atmosphere works?Michael Roman:
This implies that the time scales for the atmosphere to respond to changes in the amount of sunlight coming in are really long and maybe longer than the time scales of a season and an orbital period of Uranus. So, that even though you’re heating it up one time and then putting it in complete darkness for a while, that doesn’t happen for a long enough period of time to actually cause a change on the planet in terms of its temperature. It seems that there’s very little, despite the great seasonal variation on Uranus, where you have decades of constant sunlight and decades of constant darkness, doesn’t seem to have much effect on the temperatures, at least at these heights in the atmosphere, at these pressures that are most strongly radiating, emitting their heat to space.So, the planet just doesn’t seem to have much in terms of seasons, in terms of temperature swings, despite our sort of… And I say, intuitive, naive expectation, is that you have this planet and it’s going to be pretty extreme, right? You expect it to be freezing, and then getting cooked on one side, but it just doesn’t seem to be the case. It seems that the amount of sunlight falling on it varies greatly over the course of the year. Complete darkness, complete daylight, a eccentric orbit leading to changes over the course of its orbit of the amount of sunlight it’s receiving.
Sarah Al-Ahmed:
Different albedo even.Michael Roman:
Yeah. So, the albedo and its relative distance from the sun changing, that’s leading to a variable amount of solar energy being deposited into the atmosphere of Uranus. Yet, from the thermal point of view, from the amount of energy escaping, it doesn’t seem to be any statistical variation in the amount of energy that actually escapes from the planet. So, the amount coming in varies, the amount going out doesn’t seem to vary much, and so that implies that energy being deposited from the sun is being redistributed in a way, such that you’re ending up with a structure that is insensitive to the seasonal swings in sunlight.Sarah Al-Ahmed:
That seems really weird when you think about it, because what we’re saying here, essentially, there’s not a huge amount of mixing going on because while it’s not in thermal equilibrium, it’s close, and now it’s taking a long time for that heat to go around the world, but in such a way that it’s just keeping static between seasons. That is so weird.Michael Roman:
It is weird. And I guess to also to point that this newest analysis, these new studies with these new measurements and the things that Pearl, that weren’t available back when this first study came out, the revised quantities of this phase function, revised quantity of albedo, and that has allowed for us to revise this energy balance. And what we found is that with smaller error bars also is that the amount of energy that’s emitting is actually in excess of the amount it receives. So, whereas Pearl’s measurement was maybe slightly in excess, but error bars were indicating that it is still statistically consistent with being perfectly in equilibrium with [inaudible 00:37:45], with the amount of energy receives, this new study says no, actually when you look at this a little more carefully, with this new data, in fact, Uranus is giving off more energy than it receives. So, it is closer to, more like the other planets, in that has an internal heat flux that is escaping, and the planet is in fact cooling off still over time.And so, ends up becoming an interesting thermodynamic problem because it’s basically, two things. Now, we know there is some source of internal heat that’s escaping from the planet, that internal heat we can maybe presume is constant over time, but we don’t really know, and the amount of heat that is falling on a planet we know is not constant over time, but it’s being distributed very efficiently, such that you’re not getting these extreme variations in temperature over time, which is all pretty weird. I should also just shout out, there’s another paper that came out basically at the same time, by some of my other co-authors, Pat Irwin leading this one.
He did a very similar analysis, in that case they did some modeling of what the scattering would look like, using a theoretical model, a ready to transfer model, of given what we know the clouds are like, the hazes are like, and the gases are like in the atmosphere, constrained by observations, given that if you take this model of the atmosphere, and its gases and its clouds and hazes, and you shine light on it and you look at how it’s scattered over time, it gives you a numerical model simulation as to how this light scatters over time.
As opposed to what we kind of did in this study, was to look at observational data and extrapolate [inaudible 00:39:31]. But what they found is very consistent, pretty much the same thing. Within the error bars, more or less agreeing, there is an excess heat flux, internal heat flux from Uranus, contrary to what we for the last 30 years have been saying to be the case, based on these original Voyager studies. So, it’s revised our understanding of the heat flux. It’s still really small, and it still needs an explanation, so it doesn’t sort of make everything right and place Uranus right in line with the other planets, it’s still a weirdo planet that needs some explanation. So, it’s a privilege to have been involved in this work.
Sarah Al-Ahmed:
And really wonderful that we now have a long enough timeline on this world that we can try to piece some of this together. But I am wondering, given what we know now about the seasonal variation, is there an optimal seasonal configuration that you would like to see for us to then actually have an orbiter around Uranus during that time? Because we could conceivably go back during same configuration that Voyager had for us and maybe not learn as much.Michael Roman:
Yeah. So, Voyager looked at it was near solstice, it would be great to look at it near equinox, and to be honest, as far as our options, solstice is coming up, the next solstice is coming up pretty soon on Uranus, in 2030. And so, we are not going to get a spacecraft there by then, so a good starting point or a good target would be to observe around equinox. That way we can see both hemispheres in daylight and get a good view of the planet illuminated at all latitudes, as opposed to not being able to see invisible light, what’s going on on the night side, for example. So, yeah, I think these sorts of seasonal milestones, the solstices, the equinoxes are a nice time because you can learn a lot about the planet at these periods. And so, having a spacecraft that, say, launches sometime in the next 10 years, gets to Uranus near the solstice, near 2050, so we can cross our fingers on something like that, but…Sarah Al-Ahmed:
Yeah, it gives us a good reason to be patient for it, other than just waiting for budgets to clear up, right? But also we’re in this interesting phase in our exploration of the universe, where we’re right on the board of almost 6,000 exoplanets at this point, confirmed. We’re getting there, we’re not there yet, but we’re going to be there soon. And so, in some ways I’m really glad that we have this world as an outlier. For whatever reason, maybe it’s tilt, maybe… Who knows what’s actually creating the situation. But that gives us another world that we can look at to compare against some of these other potential ice giants in other exoplanetary systems.Michael Roman:
Yeah. A lot has been said, when you look at these statistical studies, these population studies of exoplanets, the most common size planet is something in the neighborhood of Uranus and Neptune. Basically, it’s something close to that, several Earth masses, that Uranus and Neptune are basically are the closest things in our solar system to the size of the maybe most common size of exoplanet. So, to some of us it makes Uranus and Neptune even more compelling targets because they may be in some way representative of a class of planet that is extremely common across the galaxy, and here they are right in our own backyard. And so, Uranus and Neptune have the potential to give us a greater insight that could be extrapolated, or greater insight into what may be going on on these other planets out there, that are, I want to say, hopelessly far away for this type of detailed studies. So, yeah, I’m optimistic, I’m hoping that I’ll see a Uranus mission someday, because that would be a culmination of a lot of work, and something that I just would love to behold.Sarah Al-Ahmed:
Well, I know the United States is talking about it because it is one of the priorities in the Planetary Science Decadal Survey. But even if that doesn’t pan out, there are some plans from the European Space Agency, there’s some plans from the China National Space Administration, so fingers crossed, I believe it, we can hold out, we’re going to see this mission sooner or later.Michael Roman:
Yeah. Humanity will get to Uranus someday, hopefully sooner than later, and hopefully by equinox at least, because yeah, that’d be great to see. These planets are dynamic, things are changing, seasons in Uranus are changing as we’re approaching solstice. I think it’s a wonderful time to be studying Uranus and Neptune science, which is why I sort of have been obsessively working at it over the past few years, and I hope to continue in the years ahead. But yeah, it’s a privilege. I hope the community agrees, and Congress agrees, and we can start gear up towards the next big mission to look and discover things about it that we’ll never learn any other way.Sarah Al-Ahmed:
Well, for the people who want to learn more, I’ll be sharing this paper and all of the other papers mentioned in this conversation on the website for this episode at planetary.org/radio. Thank you so much, Michael.Michael Roman:
Take care. Thank you.Sarah Al-Ahmed:
See, now I’m doubly convinced that we need a dedicated mission to Uranus. There’s so much left to learn. For example, we just discovered a new Uranian moon. Using the James Webb Space Telescope, a team led by Maryame El Moutamid at the Southwest Research Institute has spotted a previously unknown moon orbiting the ice giant, designated S/2025 U 1. It’s the tiniest and faintest Uranian moon that we’ve discovered so far. The object was detected in February 2025, in a series of long exposure images from Webb’s near infrared camera. Even Voyager 2, which gave us our first close up look of Uranus nearly 40 years ago, completely missed it. This brings Uranus’ known moon count to 29. We’ll talk more about that next, in What’s Up, with our chief scientist Dr. Bruce Betts. Hey, Bruce.Bruce Betts:
Hello, Sarah.Sarah Al-Ahmed:
Man, this is the first time I’ve had a true occasion to talk about Uranus on the show, and I cannot wait to see how many jokey joke emails people send me about it.Bruce Betts:
I used all my really good random space facts years ago about Uranus, but I got some good ones. Yeah, it’s discovering moons, that’s why every time I write about moons in the outer solar system, like in kids’ books, like, hey, don’t worry about memorizing those numbers too closely because we keep discovering them, and it’s impressive. This is a really far away tiny object, that just we, people, discovered using James Webb Space Telescope. Go on, Sarah, tell me more.Sarah Al-Ahmed:
It’s really cool watching the way that we’re progressing in finding new moons, like the war between Jupiter and Saturn, who has more moons I think is really interesting. But because we don’t have these dedicated missions up to Uranus and Neptune, there’s so much that we don’t know. So, in the midst of learning more about this world, and setting up for this interview, suddenly we get the story dropping that we found a new moon of Uranus, which is all the more reason to love these JWST images.Bruce Betts:
Oh, they’re amazing. We’ve had images, but it’s the usual. We got a better telescope, it’s super cool, we can see things better, you can see the rings, you can see everything better, that’s the nutshell.Sarah Al-Ahmed:
What do we know about this moon so far?Bruce Betts:
It is, I think believed to be about 10 kilometers in diameter. So, compared to a city, pretty good size, compared to moons… It’s one of the closer ones to the planet that have been discovered, it’s in a prograde orbit, so it’s gone the same direction as the planet is spinning, is in an equatorial plane along with the five big moons, bigger moons… They’re small for the solar system, but they’re big enough to be round. And then, you got little guys like this. So, moon number 29, and fits in now they’re 14 of the small moons hanging out, closer in equatorial plane, going prograde, and then there are ones farther out that are just wacky, zany, retrograde, and all sorts of craziness. And they usually form in different ways. But at least that’s the guess. It needs a name, but it gets the official designation, S/2025 U 1, which is actually one of the simpler designations since its satellite year was discovered. U for Uranus, and first one discovered in 2025.Sarah Al-Ahmed:
Wow. Yeah, I was wondering why that name was so simple. But really though, I think one of my favorite little random space facts when I was a kid was about the naming of the moons around Uranus. Because I was one of those kids that just loved Shakespeare, not to put aside Alexander Pope, the other author who gets some names around Uranus, but I just love that as a naming mechanic. What would you name this moon? Do you have a favorite Shakespeare character you would name it for?Bruce Betts:
I wouldn’t describe it as a favorite Shakespeare character, but I would describe it as one that I would just enjoy people doing science and having to use the word Bottom. Midsummer Night’s Dream, I’d name it after Nick Bottom, just name it Bottom.Sarah Al-Ahmed:
Name it Bottom.Bruce Betts:
It’s just funny, just stupid. What about you?Sarah Al-Ahmed:
Oh, my favorite Shakespeare play is Much Ado About Nothing. So, if I was being serious about it, I would name it Beatrice, because I love that character. But if I was being funny about it, I would go for Dogberry.Bruce Betts:
Dogberry, that’s awesome.Sarah Al-Ahmed:
It’s a great name and a great character in that play, he is so freaking funny.Bruce Betts:
Somehow I’ve never seen that one or read that one. All my teachers, we always had to read the tragedies, it was a real bummer.Sarah Al-Ahmed:
Oh man. Highly recommend Much Ado About Nothing, if you love shenanigans falling out from totally silly reasons.Bruce Betts:
Shenanigans are one of my favorite things.Sarah Al-Ahmed:
You would love Dogberry.Bruce Betts:
Dogberry. I change my vote, I want to go with Dogberry.Sarah Al-Ahmed:
We’re submitting it to the IAU right now.Bruce Betts:
Yeah, and I’m sure they’ll discover more. Poor Neptune, maybe we can start cranking up the Neptune numbers. Saturn’s just gotten ridiculous, Saturn is just, it decided to just leap forward in the standings. Yeah, I think it has about a billion. Oh wait, that’s only if you count the ring particles, no, never mind.Sarah Al-Ahmed:
I was going to say. But yeah, the moons of Saturn are interesting, I think for me, in that some of them are being created from the ring around it. So, in my brain, something smashed up some moons or something, created this ring around Saturn, and now it’s reforming cute little potato-esque chaos demons inside of the rings.Bruce Betts:
Chaos demon. And don’t forget the ravioli moon, that’s… Anyway, yeah, we like moons. We like moons.Sarah Al-Ahmed:
So, what is our random space fact this week?Bruce Betts:
So, speaking of traveling… Desperate attempt at a segue. So, I was curious, going out to Neptune being way, way out there, it’s 30 AU, with AU being astronomical unit, average Earth-Sun distance, but you don’t go straight to any of those places. So, I was wondering how far did Voyager 2 go to get there, and it went about over 7 billion kilometers. But it got there in a wonderful 12 years, which is one indication of just how very far this is. But what’s really interesting to me is that by using the gravity assists of doing the grand tour, Jupiter, Saturn, Uranus gravity assist, it cut, at the time for what the estimate was, at least with that configuration, 20 years, 20 years off the… It still took 12 years, without the gravity assist, it would’ve taken 32, I guess.Sarah Al-Ahmed:
Oh my gosh.Bruce Betts:
At least that’s what NASA reports.Sarah Al-Ahmed:
That’s crazy. Okay, so I’m in Uranus brain, so it flew by Uranus in 1986.Bruce Betts:
’86, yeah. 89, Neptune-Sarah Al-Ahmed:
When did it go by Neptune? ’89.Bruce Betts:
’89.Sarah Al-Ahmed:
So, if it had taken 20 more years… Whoa. I would’ve been well alive for one, but also… No, that’s just crazy. 2000s. Whoa, whoa.Bruce Betts:
Whoa.Sarah Al-Ahmed:
Whoa.Bruce Betts:
You probably wouldn’t have launched it frankly if you didn’t… And you can do faster, with bigger rockets and with smaller spacecraft. And so the New Horizons was sent out of the Earth-Moon system, going faster than anything else had been at that time anyway, although it’s been slowed now by the pesky Sun’s gravity. So, they flew a small spacecraft and they got it out, they went to Pluto in, what, nine years or so? So, they’re booking it, to use a technical term.Sarah Al-Ahmed:
Yeah. Technically. But no, really, it’s just a great example of the advancement of our technology over time. And yeah, here we are, we haven’t sent one out there yet in a long time, but we can look at it with JWST, this crazy telescope, and learn more like the fact that there are new moons out there that we just didn’t know existed.Bruce Betts:
Yes, they’re new to us, but not to Neptune.Sarah Al-Ahmed:
Yeah, they’ve been out there for a long time.Bruce Betts:
Or Uranus, sorry. Whatever. I’m sure, there got to be more hanging out at Neptune, the Voyager picked up, what, 14, I think? And so, we’re looking for more. Let’s do it. We’ll go out, we can get a three or four inch telescope, I’m sure we’ll do it.Sarah Al-Ahmed:
It’ll be fun.Bruce Betts:
We can hallucinate. All right, everybody, go out there, look up the night sky and think about how long you would take to go to the grocery store if it were on Neptune. Thank you and good night.Sarah Al-Ahmed:
We’ve reached the end of this week’s episode of Planetary Radio, but we’ll be back next week to give you a peek at the upcoming International Observe the Moon Night festivities. We’ll let you know how you can join in no matter where you live or how the weather shakes out in early October. And speaking of celebrating, next week I’m going to be flying off to Philadelphia, Pennsylvania in the United States to host the webcast for NASA’s Innovative Advanced Concept Symposium. This is going to be my third year doing it, and I’m really looking forward to it. So, if you want to watch the webcast, I’m also going to provide a link for that on this webpage, at planetary.org/radio. If you love the show, you can get Planetary Radio t-shirts at planetary.org/shop, along with lots of other cool spacey merchandise. Help others discover the passion, beauty, and joy of space science and exploration by leaving a review or a rating on platforms like Apple Podcasts and Spotify.Your feedback not only brightens our day, but helps other curious minds find their place in space through Planetary Radio. You can send us your space, thoughts, questions, and poetry at our email, [email protected]. Or if you’re a Planetary Society member, leave a comment in the Planetary Radio Space in our member community app. Planetary Radio is produced by The Planetary Society in Pasadena, California, and is made possible by our members who love a good planetary mystery. You can join us as we advocate for future missions to the ice giants at planetary.org/join. Mark Hilverda and Rae Paoletta are our associate producers. Casey Dreier is the host of our monthly space policy edition, and Mat Kaplan hosts our monthly book club edition. Andrew Lucas is our audio editor, Josh Doyle composed our theme, which is arranged and performed by Pieter Schlosser. My name is Sarah Al-Ahmed, the host and producer of Planetary Radio, and until next week, ad astra.
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NASA’s Insight Lander Reveals a Surprise at The Very Core of Mars : ScienceAlert
Scientists peering into the very heart of hearts of the planet Mars have found a deeply unexpected structure.
There, at the innermost core of the planet, InSight seismic data reveals a solid mass about 600 kilometers (373 miles) across. This is not just in contrast to previous findings that the core is squishy all the way through – it doesn’t fit with our current understanding of what the Martian core is made of.
“Having a solid inner core for Mars was something unusual,” a team led by seismologist Huixing Bi of the University of Science and Technology of China told ScienceAlert.
“Early studies suggested that the Martian core contains a significant amount of light elements, which lowers the solidus temperature and makes it unlikely for the core to crystallize given its relatively high temperature.”
Related: In an Incredible First, Scientists Have Discovered What’s at The Core of Mars
frameborder=”0″ allow=”accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share” referrerpolicy=”strict-origin-when-cross-origin” allowfullscreen>It’s only in the last few years that scientists have been able to map the red planet’s interior structure. That’s because NASA’s Insight lander features a seismometer that can record waves generated by quakes and meteorite strikes as they bounce around inside the planet, reacting differently to different matter densities.
The result is somewhat like a planet-sized ‘X-ray’, only made of acoustic waves.
InSight spent four years, from 2018 to 2022, monitoring the trembles in the belly of Mars, collecting data on hundreds of events. This data provided the first detailed internal map of Mars, revealing a structure similar to that of Earth: a hard crust, a molten mantle, and a dense core at the center.
But there are some crucial differences between Earth and Mars that have to do with the planetary interior, and that’s why Bi and colleagues wanted to obtain more information about Mars’s putatively soft and squishy core.
“Unlike Earth, Mars doesn’t have a global magnetic field today,” the researchers explained.
“Instead, parts of its crust are strongly magnetized, which tells us that Mars once had a magnetic field in the distant past. A planet’s global magnetic field is powered by a ‘dynamo’ in its core, which depends on a combination of thermal and compositional convection in the liquid outer core.
“In Earth, light elements preferentially remain in the liquid during core crystallization, leading to residual buoyant liquid at the inner core boundary. This mechanism is believed to play an important role in sustaining the Earth’s magnetic field today. In contrast, for Mars, things seem to work differently.”
Investigations of Earth’s layers rely on quake data from multiple seismic stations. On Mars, InSight spent its time in just a single location. To compensate for this, the researchers relied on impact events, in which large rocks smacking into the Martian surface send acoustic waves rippling through the planet.
They identified 23 high signal-to-noise ratio impact events and used seismic array analysis techniques usually applied to data from multiple stations here on Earth.
“This approach allowed us to pick out specific seismic phases based on how they arrive at the station, with their specified incident angles and arrival times,” the researchers said. “In doing so, we were able to detect waves that travel through the very center of Mars’s core and reflection from the inner core boundary, which provide critical observations for a solid inner core.”
The composition of the Martian core seems to be a little different from that of Earth’s. Mars’s core is also mostly made of iron, but with higher proportions of sulfur, oxygen, and carbon mixed in – lighter elements that should theoretically lower the temperature at which the mixture solidifies, defined by a limit referred to as the solidus.
Since the core of Mars is significantly hotter than this temperature, scientists thought the core should be soft all the way through.
Seismic waves are categorized based on how they move through a planetary interior. P waves are the fastest, traveling through the crust and mantle. K waves are waves that have traveled through a planetary outer core. I waves are those that have traveled through the inner core, while a lower-case i represents a wave that has bounced off the outer boundary of the inner core.
A comparison between the structures of Earth (left) and Mars (right). (Bi et al., Nature, 2025) These letters can be put together to describe a wave’s path; for example, PKiKP waves travel through the mantle, enter the outer core, bounce off the inner core, come back out through the outer core, and then the mantle.
In their data, the researchers found not just one but multiple waves that separately indicated the presence of a solid inner core of Mars.
“Detecting the PKiKP wave is strong evidence on its own, but we also see PKKP arriving earlier than expected, which provides further confirmation. Beyond that, our model predicts – and our data confirm – other inner-core-related phases, including PKiKP at greater distances, PKIIKP, and even a new branch of PKPPKP that travels through the inner core,” they explained.
“These multiple phases are crucial because they cross-validate one another and all consistently point to the same conclusion: Mars really does have a solid inner core.”
Exactly how this can happen is currently unclear. Modeling will need to be done to explore the temperature, pressure, and compositional conditions involved, as well as the way the heavy and light elements are partitioned, to try to replicate what the team’s results have revealed.
The results, nevertheless, are exciting. This further exploration may lead to deeper insights into how Mars lost its dynamo and its global magnetic field. It may also reveal something about the way rocky planets – those scientists believe most likely to host life as we know it – evolve.
“The size and properties of Mars’s inner core serve as a crucial reference for understanding the planet’s thermal and chemical evolution,” the researchers said.
“Gaining a clearer picture of the inner core’s formation – and its implications for the history of Mars’s magnetic field – will require more detailed modeling, ideally within a comparative planetology framework.”
The research has been published in Nature.
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This ancient fish had four sets of teeth instead of two | Northwest & National News
This ancient fish had four sets of teeth instead of two | Northwest & National News | nbcrightnow.com
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Perseid meteors shine with the Milky Way over an ancient Egyptian temple in breathtaking photo
Photographer Osama Fathi has captured a stunning view of Perseid meteors crossing the bright ribbon of the Milky Way over the ruins of an ancient settlement in Egypt dedicated to the worship of the crocodile god Soknopaios.
The image was captured from the Soknopaiou Nesos archaeological site to the north of Qarun Lake in northeastern Egypt on the night of Aug. 12, as the 2025 Perseid meteor shower hit its peak. Sadly, the light of a waning gibbous moon washed out all but the brightest shooting stars this year, though photographers were still able to capture stunning compositions featuring the most brilliant members of the annual shower.
“Despite the presence of the moon this night, we managed to capture a few bright meteors of the Perseid shower above the ancient ruins of Soknopaiou Nesos, known today as Dimeh es-Seba, in the Faiyum Oasis of Egypt,” said Fathi in an email to Space.com.
Fathi’s image captures a swarm of bright Perseid meteors streaking across the dense dust lanes and glowing heart of the Milky Way, framed by the ancient stones and truncated columns of ancient Soknopaiou Nesos.
Perseids captured in the skies over Egypt on the night of Aug. 12. (Image credit: Osama Fathi) Nikon Z8
(Image credit: Jase Parnell-Brookes) The Nikon Z8 excels in just about every department and we rate it as the best overall camera out there. Check out our Nikon Z8 review for a more in-depth look.
“This settlement, founded in the 3rd century BCE during the great Ptolemaic land reclamation of the Faiyum, was once a powerful religious center,” continued Fathi. “It hosted a grand temple dedicated to Soknopaios, the oracular crocodile god with a falcon’s head, from whom the town derived its name.”
The scene is a composite of multiple images taken using a Nikon Z6 camera in conjunction with a Nikkor 14-24 mm wide-angle lens. The sky and Milky Way were captured over a 25 second exposure, while the meteors required a shorter exposure and high ISO of 8000.
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