Research press release


Nature Geoscience

Giant impacts ended early on Mars



今回Desmond Moserたちは、火星南部高地由来と考えられている隕石から得た、知られている限り最古の鉱物粒子を分析した。その結果、粒子のほぼ全てで、衝突による変成はごくわずかであることが明らかになった。一方、地球と月の衝突地域で分析された粒子の80%以上は、高温や高圧への曝露といった、衝突に関連した特徴を持っていた。このことからMoserたちは、火星の重爆撃期は分析した鉱物が形成されるよりも前に終了したと示唆している。その結果、火星の表面は、水が豊富に存在していたと考えられている時期までに、生命が存在できる条件になったと考えられる。


Giant, life-inhibiting meteorite impacts ended on Mars by 4.48 billion years ago, according to a paper published online this week in Nature Geoscience. These findings suggest that conditions under which life could have potentially developed may have occurred on Mars from around 4.2 to 3.5 billion years ago.

The number and size of meteorite impacts on Mars and Earth gradually declined after the planets formed. Eventually, impacts became small and infrequent enough that the near-surface conditions could allow life to develop. However, when the heavy meteorite bombardment waned is debated. It has been proposed that there was a ‘late’ phase of heavy bombardment of both planets that ended around 3.8 billion years ago.

Desmond Moser and colleagues analysed the oldest-known mineral grains from meteorites that are believed to have originated from Mars’s southern highlands. The authors found that almost all of the grains had only been slightly modified by impacts. In comparison, over 80% of the grains studied from impacted areas on the Earth and Moon contained features associated with impacts, such as exposure to high pressures and temperatures. Therefore, the authors suggest that heavy bombardment of Mars ended before the analysed minerals formed. Consequently, the Martian surface would have become habitable by the time it is believed that water was abundant there.

The authors suggest that if giant impacts ended early on Mars, it is also plausible that Earth did not experience late heavy bombardment either, and that habitable conditions may have developed here earlier than previously thought.

doi: 10.1038/s41561-019-0380-0


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