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Since the discovery of the first exoplanet orbiting a Sun-like star, the confirmation of nearly 6000 exoplanets to date – and their diversity – has revolutionized our knowledge of planetary systems in the past three decades.

Nevertheless, the majority of these planets are around mature stars (≳1 Gyr), where the planet birth environments have already dissipated. Indeed, we have only confirmed 2 forming planets (i.e., protoplanets; ≲10 Myr) residing in one single system. In comparison, we have imaged over 200 protoplanetary disks in the past decade, with many of them hosting substructures such as spirals and gaps which suggest the existence of protoplanets.

To understand the early stages of planet formation, the Habitable Worlds Observatory (HWO) – with its high-contrast imaging and integral field spectroscopy capabilities – presents a unique opportunity to explore the demographics of the natal stages of planet formation and their birth environments.

We propose to image protoplanets within substructured protoplanetary disks using HWO via direct imaging, and characterize them (i.e., protoplanets, protoplanetary disks, circumplanetary disks) using integral field spectroscopy and spectropolarimetry. This effort will dramatically extend current population of protoplanets, probing and characterizing over 200 protoplanets.

By expanding the number of protoplanets by two orders of magnitude, these observations will test and refine planet formation theory and planet-disk interaction theory, and further motivate planet migration studies together with existing mature planets. The results will offer critical insight into planetary system formation and evolution, and help understand the origin of our own Solar System.

Bin B. Ren

Comments: 9 pages, 3 figures, 2 tables. HWO Science Case #SCDD-SSiC-8 for HWO25 proceedings
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2506.24129 [astro-ph.IM] (or arXiv:2506.24129v1 [astro-ph.IM] for this version)
https://doi.org/10.48550/arXiv.2506.24129
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Submission history
From: Bin Ren Dr.
[v1] Mon, 30 Jun 2025 17:59:59 UTC (1,388 KB)
https://arxiv.org/abs/2506.24129
Astrobiology,

Extremophilic bacteria from extreme environments, such as the Atacama Desert, Salar de Huasco, and Antarctica, exhibit adaptations to intense UV radiation. In this study, we investigated the genomic and structural mechanisms underlying UV resistance in three bacterial isolates identified as Bacillus velezensis PQ169, Pseudoalteromonas sp. AMH3-8, and Rugamonas violacea T1-13.

Through integrative genomic analyses, we identified key genes involved in DNA-repair systems, pigment production, and spore formation. Phylogenetic analyses of aminoacidic sequences of the nucleotide excision repair (NER) system revealed conserved evolutionary patterns, indicating their essential role across diverse bacterial taxa.

Structural modeling of photolyases from Pseudoalteromonas sp. AMH3-8 and R. violacea T1-13 provided further insights into protein function and interactions critical for DNA repair and UV resistance. Additionally, the presence of a complete violacein operon in R. violacea T1-13 underscores pigment biosynthesis as a crucial protective mechanism.

In B. velezensis PQ169, we identified the complete set of genes responsible for sporulation, suggesting that sporulation may represent a key protective strategy employed by this bacterium in response to environmental stress.

Our comprehensive approach underscores the complexity and diversity of microbial adaptations to UV stress, offering potential biotechnological applications and advancing our understanding of microbial resilience in extreme conditions.

Phylogenetic tree based on the amino acid sequences of UvrA, UvrB, and UvrC proteins (NER system). Multiple sequence alignment was performed using MUSCLE on the Phylogeny.fr platform, followed by tree construction with PhyML and visualization using TreeDyn. The resulting tree was further arranged and refined using the Interactive Tree of Life (iTOL v7) tool. The maximum likelihood method was employed with 1000 bootstrap replicates, where the node sizes reflect the level of bootstrap support. Each label includes the gene name, the bacterial species, and the corresponding NCBI accession number. Three environmental strains are highlighted: Bacillus velezensis PQ-169 (green), Pseudoalteromonas sp. AMH3-8 (yellow), and Rugamonas violacea T1-13 (purple). These strains, along with other extremophilic, UV-resistant, and pathogenic bacteria, were included to compare UvrA (red clade), UvrB (blue clade), and UvrC (green clade) variations under extreme environmental conditions. — Int J Mol Sci via PubMed

Isolation sites, genomic assembly characteristics, and ANI-based taxonomic assignment of three extremophilic bacterial isolates. (a–c) Representative sampling sites of bacterial isolates: (a) Atacama Desert, (b) Salar de Huasco, and (c) Antarctic soil. (d–f) Circular genome representations illustrating variability in genome size, contiguity, and genetic content: (d) Bacillus velezensis PQ169 (76 contigs, 4.18 Mb), (e) Pseudoalteromonas sp. AMH3-8 (single contig, 4.74 Mb), and (f) Rugamonas violacea T1-13 (171 contigs, 6.85 Mb). Rings (outer to inner) represent predicted CDSs, RNA genes (rRNA, tRNA, and tmRNA), GC content, and GC skew. (g–i) Heatmaps depicting average nucleotide identity based on MUMmer (ANIm) analysis between each isolate and closely related reference strains, supporting definitive taxonomic assignment: (g) Bacillus velezensis PQ169, (h) Pseudoalteromonas sp. AMH3-8, and (i) Rugamonas violacea T1-13. Color gradients indicate similarity percentages, with red color representing higher ANI values, and blue lower values. — Int J Mol Sci via PubMed

astrobiology, genomics, extremophiles,