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運営者ブログ - 太陽風によって剥ぎ取られた火星の大気

太陽風によって剥ぎ取られた火星の大気

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admin_mb 2015-11-16 23:02
NASAの火星探査機「メイブン」の観測データから、火星の大気は太陽風による侵食で毎秒約100gの割合で宇宙空間に放出されていることがわかったそうです。毎秒100gですから、1時間だと3600秒で360,000、24時間で8,640,000g、1,000gで1Kgですから1日あたり8.64tになります。メイブンの観測によると、大気の散逸には3つの異なる領域があるとのこと。まず、太陽風が火星の夜の側から約75%、火星の両極の上空から25%、残りを火星を取り巻くガス雲から剥ぎ取られているそうです。

億年単位だと大量の大気が失われたことになりますが、逆に考えると、数十億年前には今より遥かに厚い大気があったということですね。水が大量存在したと考えられる痕跡がありますので、過去には大気も水も十分にあったということでしょう。ただ、地球と比べて水と大気が豊富にある環境が短期間しかなかったことから、生命が生まれなかったのでは、という説もあるそうです。地球の方が火星よりも太陽に近いわけですから、遥かに多くの大気が太陽風により剥ぎ取られていることになります。それでも地球の大気が薄くならないのは地球の重力が火星よりも大きいためですが、それでもやはり徐々に減ってはきているようです。数十億年未来には地球も火星のような姿に成るのかもしれませんね。

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