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TRAPPIST-1 is an M8 dwarf hosting seven known exoplanets and is currently one of the most frequently observed targets of the James Webb Space Telescope (JWST).

However, it is notoriously active, and its surface is believed to be covered by magnetic features that contaminate the planetary transmission spectra. The radiative spectra of these magnetic features are needed to clean transmission spectra, but they currently remain unknown.

Here, we develop a new approach for measuring these spectra using time-resolved JWST/NIRISS observations. We detect a persistent post-flare enhancement in the spectral flux of TRAPPIST-1.

Our analysis rules out lingering flare decay as the cause of the flux enhancement and, thus, points to structural changes on the stellar surface induced by flares. We suggest that the flaring event triggers the disappearance of (part of) a dark magnetic feature, producing a net brightening.

This suggestion is motivated by solar data: flare-induced disappearance of magnetic features on the solar surface has been directly detected in high spatial resolution images, and our analysis shows that this process produces changes in solar brightness very similar to those we observe on TRAPPIST-1.

The proposed explanation for the flux enhancement enables, to our knowledge, the first measurement of the spectrum of a magnetic feature on an M8 dwarf. Our analysis indicates that the disappearing magnetic feature is cooler than the TRAPPIST-1 photosphere, but by at most a few hundred kelvins.

Valeriy Vasilyev, Nadiia Kostogryz, Alexander I. Shapiro, Astrid M. Veronig, Benjamin V. Rackham, Christoph Schirninger, Julien de Wit, Ward Howard, Jeff Valenti, Adina D. Feinstein, Olivia Lim, Sara Seager, Laurent Gizon, Sami K. Solanki

Comments: accepted for publication in The Astrophysical Journal Letters
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2508.04793 [astro-ph.EP] (or arXiv:2508.04793v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2508.04793
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Submission history
From: Valeriy Vasilyev
[v1] Wed, 6 Aug 2025 18:09:01 UTC (4,502 KB)
https://arxiv.org/abs/2508.04793
Astrobiology, Space Weather,

Giant impacts were common in the early evolution of the Solar System, and it is possible that Venus also experienced an impact. A giant impact on Venus could have affected its rotation rate and possibly its thermal evolution.

In this work, we explore a range of possible impacts using smoothed particle hydrodynamics (SPH). We consider the final major collision, assuming that differentiation already occurred and that Venus consists of an iron core (30% of Venus’ mass) and a forsterite mantle (70% of Venus’ mass). We use differentiated impactors with masses ranging from 0.01 to 0.1 Earth masses, impact velocities between 10 and 15 km/s, various impact geometries (head-on and oblique), different primordial thermal profiles, and a range of pre-impact rotation rates of Venus.

We analyse the post-impact rotation periods and debris disc masses to identify scenarios that can reproduce Venus’ present-day characteristics. Our findings show that a wide range of impact scenarios are consistent with Venus’ current rotation. These include head-on collisions on a non-rotating Venus and oblique, hit-and-run impacts by Mars-sized bodies on a rotating Venus.

Importantly, collisions that match Venus’ present-day rotation rate typically produce minimal debris discs residing within Venus’ synchronous orbit. This suggests that the material would likely reaccrete onto the planet, preventing the formation of long-lasting satellites – consistent with Venus’ lack of a moon.

We conclude that a giant impact can be consistent with both Venus’ unusual rotation and lack of a moon, potentially setting the stage for its subsequent thermal evolution.

Mirco Bussmann, Christian Reinhardt, Cedric Gillmann, Thomas Meier, Joachim Stadel, Paul Tackley, Ravit Helled

Comments: Accepted for publication in A&A, 12 pages, 9 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2508.03239 [astro-ph.EP] (or arXiv:2508.03239v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2508.03239
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Submission history
From: Mirco Bussmann
[v1] Tue, 5 Aug 2025 09:12:48 UTC (5,186 KB)
https://arxiv.org/abs/2508.03239
Astrobiology,

A tidy textbook definition of life has never existed, yet most biology lessons still lean on the idea that living things must grow, make energy, and reproduce on their own.

That simple checklist leaves viruses outside the club, since their genetic shells activate only inside another organism and go dormant again when drifting alone.

Ryo Harada of Dalhousie University and colleagues discovered a creature that forces us to redraw those lines on the fly.

Their oddball microbe, provisionally named Sukunaarchaeum mirabile, was hiding in DNA scraped from a single plankton species off the Japanese coast.

Sukunaarchaeum virus line blurs

Biologists once leaned on André Lwoff’s dictum that “an organism is constituted of cells.” That rule pushed viruses into a separate realm of particles.

That neat boundary already looked wobbly when giant viruses surfaced in the early 2000s, flaunting genomes larger than some bacteria.

Sukunaarchaeum muddies the waters further. It is undeniably cellular, yet its playbook borrows many viral tricks. It retains the genes for building its own ribosomes and messenger RNA – parts no virus carries – but appears to outsource nearly every other task to a host cell.

A record-breaking small genome

The new organism’s entire genome fits into 238,000 base pairs – roughly the length of a medium-sized magazine article.

For comparison, the minimalist archaeon Nanoarchaeum equitans holds the previous cellular record at about 490,000 base pairs, already microscopic by prokaryotic standards.

Viruses can be both larger and smaller, yet they never lug around the full toolkit for protein synthesis. That is why Harada’s team calls Sukunaarchaeum “a cellular entity retaining only its replicative core.”

A virus-like microbe emerges

“Its genome is profoundly stripped-down, lacking virtually all recognizable metabolic pathways, and primarily encoding the machinery for its replicative core: DNA replication, transcription, and translation,” wrote Harada and co-authors in their report.

The code resembles a viral instruction manual more than a self-sufficient microbe.

Yet the creature sits within Archaea, one of the three great domains of life – not among viruses. Phylogenetic trees place it on a deep branch so distant from known groups that the authors propose creating a new phylum.

Sukunaarchaeum and borrowed genes

The team stumbled on the microbe while sequencing DNA from the dinoflagellate Citharistes regius. Nested in that plankton’s genetic debris was a tight loop of foreign DNA that refused to match any catalogued species.

Marine symbiosis can be intimate: some plankton rely on bacterial partners for vitamins, while others house entire algal cells that photosynthesize for them.

Sukunaarchaeum appears to take this intimacy to the extreme, shaving off every gene it can afford to lose and leaning on its host for nearly everything else a cell needs to stay alive.

Redrawing the tree of life

Because its ribosomal genes remain intact, the organism qualifies as cellular under the classic molecular litmus test.

Yet its pared-down metabolism likely prevents it from harvesting nutrients, producing ATP, or fixing carbon without help – behaviors normally reserved for viral passengers.

Scientists debate whether life is a binary label or a spectrum; Sukunaarchaeum pushes the spectrum view to the forefront.

The find suggests that many other stealth lineages may be hiding in environmental sequencing data, dismissed as contaminants or viral oddities.

Defining the meaning of “alive”

Words such as “alive” steer funding, public health policy, and even planetary protection rules for space probes.

If more organisms like Sukunaarchaeum exist, biosecurity protocols that screen only for free-living microbes could miss entire classes of symbiotic parasites.

The discovery also sharpens a practical question: What genetic load is the bare minimum for a cell to function? Synthetic biology groups pursuing engineered minimal cells may mine this archaeon’s blueprint for clues.

“The discovery of Sukunaarchaeum pushes the conventional boundaries of cellular life and highlights the vast unexplored biological novelty within microbial interactions,” wrote the researchers.

Harada’s team suspects that extreme genome pruning evolved because the host environment guaranteed nutrients, letting redundant pathways decay. 

Paleobiologists see a glimpse of early evolution, when ancient cells likely shared genes and resources more freely than today.

If so, today’s viruses and streamlined symbionts may echo an ancient lifestyle rather than representing biological outliers.

Sukunaarchaeum may not be alone

Scientists plan to investigate whether similar organisms exist in other marine ecosystems or symbiotic relationships.

These searches may involve reanalyzing existing metagenomic databases that could contain overlooked sequences resembling Sukunaarchaeum.

Another goal is to identify the specific host that enables Sukunaarchaeum to survive.

Without knowing its exact partner, researchers can’t fully explain how the symbiosis functions or what evolutionary pressures shaped such an extreme dependency.

The study is published in bioRxiv.

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