Research press release


Nature Astronomy

Astronomy: Hydrogen- and helium-rich exoplanets may provide habitable conditions for billions of years

水素ガスとヘリウムガスを主成分とする大気を持つ岩石質の系外惑星は、数十億年にわたる表面の温和な環境と液体の水を維持できることが、Nature Astronomy に発表されるモデル化研究で示された。今回の発見は、地球とは全く異なる大気を持つ惑星でも、その歴史の長期間にわたって生命が存在できる可能性があることを示唆している。


Marit Mol Lousたちは、そのような惑星の進化を調べた。研究チームは数値モデルを用いて、水素とヘリウムに富む系外惑星がその表面に液体の水を保持できる期間を予測した。著者たちは、惑星の質量と星からの距離に依存するが、大気が十分に厚い(地球の大気厚の100倍から1000倍)という条件で、これらの惑星は80億年もの間にわたって温和な表面環境を保つことができると明らかにした。


Rocky exoplanets with atmospheres dominated by hydrogen and helium gases can sustain temperate conditions and liquid water on their surface for billions of years, according to a modelling study published in Nature Astronomy. These findings suggest that even planets with very different atmospheres from ours can be potentially habitable for long periods of their history.

As hydrogen and helium gases were readily available in the planet-forming disk of materials around young stars, all planets accumulated atmospheres that were dominated by these two elements. In our Solar System, rocky planets lost this primordial atmosphere in favour of heavier elements, such as oxygen and nitrogen on Earth. However, large rocky exoplanets at some distance from their star could retain their hydrogen and helium-dominated atmospheres.

Marit Mol Lous and colleagues investigated the evolution of such planets. The team used a numerical model to predict the duration that hydrogen and helium-rich exoplanets could host liquid water on their surface. The authors reveal that, depending on the mass of the planet and how far away it is from its star, these planets could keep a temperate surface environment for as long as 8 billion years, provided that the atmosphere is thick enough (between 100 to 1,000 times thicker than the Earth’s).

The authors highlight that although future research is needed to address many remaining questions — such as the likelihood of these planets forming or how liquid water would get there — these results suggest that habitable conditions may be very different from what we are used to on Earth. We therefore, they state, need to remain open-minded when investigating habitability on other planets.

doi: 10.1038/s41550-022-01699-8


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