Study Findings: Not All Sub-Neptune Exoplanets Have Magma Oceans

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Credit: Image by Enrique from Pixabay

The Astrophysical Journal Letters abstract of the study findings:

The evolution and structure of sub-Neptunes may be strongly influenced by interactions between the outer gaseous envelope of the planet and a surface magma ocean. However, given the wide variety of permissible interior structures of these planets, it is unclear whether conditions at the envelope–mantle boundary will always permit a molten silicate layer or whether some sub-Neptunes might instead host a solid silicate surface. In this work, we use internal structure modeling to perform an extensive exploration of surface conditions within the sub-Neptune population across a range of bulk and atmospheric parameters. We find that a significant portion of the population may lack present-day magma oceans. In particular, planets with a high atmospheric mean molecular weight and large envelope mass fraction are likely to instead have a solid silicate surface, since the pressure at the envelope–mantle boundary is high enough that the silicates will be in solid postperovskite phase. This result is particularly relevant given recent inferences of high-mean molecular weight atmospheres from JWST observations of several sub-Neptunes. We apply this approach to a number of sub-Neptunes with existing or upcoming JWST observations and find that in almost all cases, a range of solutions exist that do not possess a present-day magma ocean. Our analysis provides critical context for interpreting sub-Neptunes and their atmospheres.

Citation: Bodie Breza et al. Not all sub-Neptune exoplanets have magma oceans. ApJL 993 L46 (2025).

https://doi.org/10.3847/2041-8213/ae0c07

Study-related stories:

Universe Today – “It Looks Like All Mini-Neptunes Aren’t Magma Oceans After All”

University of Chicago – “New Study Revises Our Picture of the Most Common Planets in the Galaxy”

Space.com – “Is Our Dream of Finding Ocean-Covered Exoplanets Drying Up?”

Study Findings: A Less Terrifying Universe? Mundanity as an Explanation for the Fermi Paradox

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Credit: Image by Angela from Pixabay.

Abstract of the pre-publication study findings:

Applying a principle of “radical mundanity”, this paper examines explanations for the lack of strong evidence for the presence of technology-using extraterrestrial civilizations (ETCs) in the Galaxy – the Fermi paradox. With this principle, the prospect that the Galaxy contains a modest number of civilizations is preferred, where none have achieved technology levels sufficient to accomplish large-scale astro-engineering or lack the desire to do so. This consideration also leads to the expectation that no ETC will colonize a large fraction of the Galaxy, even using robotic probes, and that there are no long-duration high-power beacons. However, there is a reasonable chance that we may make contact on a short, by historical standards, timescale. This event would be momentous, but could still leave us slightly disappointed. Such a Universe would be less terrifying than either of the two possibilities in the quote generally attributed to Arthur C. Clarke on whether we are alone or not. Also, if there is a modest number of ETCs in the Galaxy, that would suggest that there is a large number of planets with some form of life.

Citation: Robin H.D. Corbet. A less terrifying universe? Mundanity as an explanation for the Fermi Paradox. arXiv.org (2025).

https://doi.org/10.48550/arXiv.2509.22878

Study-related stories:

Times of India – “Aliens Got Bored: NASA Scientist Gives Bizarre Reason Why Aliens Have Stopped Contacting Us”

The Guardian – “‘Bored Aliens’: Has Intelligent Life Stopped Bothering Trying to Contact Earth?”

Futurism – “NASA Scientist Proposes Theory of Alien Civilizations Throughout Milky Way”

Space Quote: Surmising Planetary-mass Bodies in the Outer Solar System

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Image (Credit): Illustrations of the Kuiper Belt and the Oort Cloud. (European Space Agency)

“One explanation is the presence of an unseen planet, probably smaller than the Earth and probably bigger than Mercury, orbiting in the deep outer solar system…This paper is not a discovery of a planet, but it’s certainly the discovery of a puzzle for which a planet is a likely solution.”

-Statement by lead author Amir Siraj, an astrophysicist and a doctoral candidate in the department of astrophysical sciences at Princeton University, as quoted by CNN News. The presence of a new, distant planet attempts to address the tilted orbits of some distant objects in the Kuiper Belt. The issue is discussed in a recent paper by Siraj and his fellow authors titled Measuring the Mean Plane of the Distant Kuiper Belt and found in the journal Monthly Notices of the Royal Astronomical Society: Letters.

Study Findings: Lunar Surface and Subsurface Water Revealed by Chang’e-6

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Image (Credit): Artist’s rendering of the Chang’e-6 probe. (China Daily)

Nature Astronomy abstract of the study findings:

The processes driving the formation and distribution of lunar water (OH/H2O), particularly in the subsurface, remain poorly understood. An opportunity to study subsurface water comes from lander plumes, which can displace and expose millimetre- to centimetre-sized regolith during the descent of the lander. Here we analyse data from the Chang’e-6 landing site and find that plume-disturbed areas exhibit distinct temperature and water-content patterns, which are driven by the redistribution of fine regolith. The average water content of the exposed fine regolith of the shallow subsurface is ~76 ppm, which is lower than the surface abundance of ~105 ppm measured at the surface. The Chang’e-6 landing site also contains on average approximately twice the water content than the Chang’e-5 one. Temporal variations of water content are observed at identical locations but different local times, exhibiting a minimum at local noon. We suggest that the differences in water content are correlated with the regolith glass abundance, particle sizes, depths and local times, reinforcing the hypothesis that solar wind implantation and impact gardening govern lunar water formation and distribution.

Citation: Liu, B., Zeng, X., Xu, R. et al. Lunar surface and subsurface water revealed by Chang’e-6. Nat Astron (2025).

https://doi.org/10.1038/s41550-025-02668-7

Study-related story:

Chinese Academy of Sciences – “Chang’e-6 Probe Data Reveal Water Distribution on Moon”

Study Findings: The Variety and Origin of Materials Accreted by Bennu’s Parent Asteroid

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Image (Credit): The asteroid Bennu produced by the OSIRIS-REx spacecraft. (NASA, Goddard and University of Arizona)

Nature Astronomy abstract of the study findings:

The first bodies to form in the Solar System acquired their materials from stars, the presolar molecular cloud and the protoplanetary disk. Asteroids that have not undergone planetary differentiation retain evidence of these primary accreted materials. However, geologic processes such as hydrothermal alteration can dramatically change their bulk mineralogy, isotopic compositions and chemistry. Here we analyse the elemental and isotopic compositions of samples from asteroid Bennu to uncover the sources and types of material accreted by its parent body. We show that some primary accreted materials escaped the extensive aqueous alteration that occurred on the parent asteroid, including presolar grains from ancient stars, organic matter from the outer Solar System or molecular cloud, refractory solids that formed close to the Sun, and dust enriched in neutron-rich Ti isotopes. We find Bennu to be richer in isotopically anomalous organic matter, anhydrous silicates, and light isotopes of K and Zn than its closest compositional counterparts, asteroid Ryugu and Ivuna-type (CI) carbonaceous chondrite meteorites. We propose that the parent bodies of Bennu, Ryugu and CI chondrites formed from a common but spatially and/or temporally heterogeneous reservoir of materials in the outer protoplanetary disk.

Citation: Barnes, J.J., Nguyen, A.N., Abernethy, F.A.J. et al. The variety and origin of materials accreted by Bennu’s parent asteroid. Nat Astron (2025).

https://doi.org/10.1038/s41550-025-02631-6

Study-related stories:

Rowan University – “Connolly: Bennu Samples Reveal Clues to Solar System Origins, Water-rock Chemistry, Space Weathering”

Science Alert – “Asteroid Bennu Samples Contain Stardust Older Than Our Solar System”

Astrobiology – “Asteroid Bennu Is A Time Capsule Of Materials Bearing Witness To Its Origin And Transformation Over Billions Of Years”