2023-06-29 ブラウン大学
◆研究者たちは、火星の気候条件が一時的に液体の水を可能にするような状態になる「スイートスポット」をモデル化しました。火星が傾いた35度のとき、大気が十分に濃密になり、渓谷の場所で一時的に融解が起こることがわかりました。
◆この研究により、火星で液体の水が存在し、渓谷が形成される可能性があることが示されました。これにより、火星における生命の存在可能性や将来の探査ミッションの重要な対象となる渓谷の重要性も明らかになりました。
＜関連情報＞
- https://www.brown.edu/news/2023-06-29/mars-meltwater
- https://www.science.org/doi/10.1126/science.abk2464
火星のガリーは、斜度が高い時期に水の氷が溶けて形成された可能性がある。 Gullies on Mars could have formed by melting of water ice during periods of high obliquity
J. L. Dickson,A. M. Palumbo,J. W. Head,L. Kerber,C. I. Fassett, and M. A. Kreslavsky
Science Published:29 Jun 2023
DOI:https://doi.org/10.1126/science.abk2464
Editor’s summary
Some steep slopes on Mars have gullies with morphologies suggesting that they were formed by a fluid. However, the planet’s current climate is not conducive to the melting of water ice at those locations, and mechanisms involving carbon dioxide ice do not explain the distribution of the gullies. Dickson et al. simulated how the climate of Mars differed when its axis tilted by different amounts over the past few million years. At a tilt of 35 degrees, the ice caps partially melted, raising the atmospheric pressure, and there were higher summer temperatures. Under these conditions, the atmospheric pressure at the gullies would be above the triple point of water, so it could melt to form a liquid. —Keith T. Smith
Abstract
Gullies on Mars resemble water-carved channels on Earth, but they are mostly at elevations where liquid water is not expected under current climate conditions. It has been suggested that sublimation of carbon dioxide ice alone could have formed Martian gullies. We used a general circulation model to show that the highest-elevation Martian gullies coincide with the boundary of terrain that experienced pressures above the triple point of water when Mars’ rotational axis tilt reached 35°. Those conditions have occurred repeatedly over the past several million years, most recently ~630,000 years ago. Surface water ice, if present at these locations, could have melted when temperatures rose >273 kelvin. We propose a dual gully formation scenario that is driven by melting of water ice followed by carbon dioxide ice sublimation.
