2025-11-05 シカゴ大学
A new study finds that many “mini-Neptunes”—perhaps the most common planets in the galaxy—are under so much pressure from their heavy atmospheres that the surface is likely compressed solid. Illustration courtesy NASA/JPL-Caltech/R. Hurt (IPAC)
＜関連情報＞
- https://news.uchicago.edu/story/new-study-revises-our-picture-most-common-planets-galaxy
- https://iopscience.iop.org/article/10.3847/2041-8213/ae0c07
海王星より下の太陽系外惑星の全てがマグマオーシャンを持つわけではない Not All Sub-Neptune Exoplanets Have Magma Oceans
Bodie Breza, Matthew C. Nixon, and Eliza M.-R. Kempton
The Astrophysical Journal Letters Published: 2025 November 5
DOI:10.3847/2041-8213/ae0c07
Abstract
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.
