ＮＡＳＡ火星探査機インサイト、ミッション終了間近に

【ワシントンＡＦＰ＝時事】約４年にわたり火星の内部を調査してきた米航空宇宙局（ＮＡＳＡ）の着陸探査機「インサイト（ＩｎＳｉｇｈｔ）」が、今夏で任務を終える可能性が高まった。太陽電池パネルに積もった塵（ちり、固体微粒子）のせいで、電力が徐々に弱まっているためだ。（写真は米航空宇宙局（ＮＡＳＡ）の火星無人探査機「インサイト」のイラスト。火星の中心部を調査する初のミッションとして、２０１８年５月５日に打ち上げられた。ＮＡＳＡ提供）
　ＮＡＳＡは１７日、インサイトの任務は終了が間近に迫っていると発表。後に残される観測データという財産は、この先何年も世界中の科学者に活用され、惑星形成に関する理解を向上させる助けとなるに違いないと述べた。
　超高感度の地震計を搭載したインサイトは、火星の地震活動（火震）を１３００回以上記録した。今月４日には、これまでで最大規模のマグニチュード（Ｍ）５の揺れを観測した。 　
　だが、地震計の電源は７月頃に切れると考えられており、その後２０２２年末までに探査任務が完全に停止する見通し。?

■「宝の山」
?　原因は、２枚の太陽電池パネルの上に何か月にもわたって降り積もった火星の塵だ。
?　インサイトは、２０１８年１１月に火星に到着した。現在、火星上では同機を含めて４件の探査ミッションが進行している。残る３件は、ＮＡＳＡの探査車「パーシビアランス（Ｐｅｒｓｅｖｅｒａｎｃｅ）」と「キュリオシティー（Ｃｕｒｉｏｓｉｔｙ）」、中国の探査車「祝融号（Ｚｈｕｒｏｎｇ）」だ。
　インサイトに搭載されたフランス製の地震計は大きな進歩を成し遂げた。インサイトの調査責任者を務めるＮＡＳＡジェット推進研究所（Ｊｅｔ Ｐｒｏｐｕｌｓｉｏｎ Ｌａｂｏｒａｔｏｒｙ）のブルース・バネルト（Ｂｒｕｃｅ Ｂａｎｅｒｄｔ）氏は「史上初めて、火星の内部を地図化することができた」と語る。
　地震波は通過する物質によって変化するため、火星の内部構造を調べるのに利用できる。
　科学者チームはこれまでの調査で、火星の核が液体であることの確認と、地殻の厚さの測定に成功している。火星の地殻はこれまで考えられていたより低密度で、三つの層で構成される可能性が高いことも明らかになっている。
　観測されたマグニチュード５の地震は、地球では巨大地震とは見なされないものの、過去に記録された火星のどの地震よりもはるかに規模が大きく、火星で起こると考えられる最大規模に近かった。
　バネルト氏は「この地震を詳細に分析すれば、きっと科学的データの宝の山になるだろう」と話している。【翻訳編集ＡＦＰＢＢＮｅｗｓ】
〔ＡＦＰ＝時事〕（2022/05/23-13:44）

After some four years probing Mars' interior, NASA's InSight lander will likely retire this summer as accumulated dust on its solar panels saps its power.
The lander will, however, leave behind a legacy of data that will be tapped by scientists around the world for years to come, helping to improve our understanding of planet formation, NASA said, while announcing on Tuesday the imminent end to InSight's science operations.
Equiped with an ultra-sensitive seismometer, InSight recorded more than 1,300 marsquakes, including a magnitude 5 quake on May 4, the largest so far.
But around July, the seismometer will be turned off.
The lander's energy level will then be checked about once a day, and some pictures may still be taken. Then by the end of 2022, the mission will be completely stopped.
The cause: the accumulation over months of Martian dust on the lander's two solar panels, each measuring about seven feet (2.2 meters) wide.
InSight, which is already running on only a tenth of the energy it had at the beginning, will soon find its batteries drained.
The speed at which dust accumulated corresponded more or less to what had been estimated by NASA.
The lander got a new lease on life around a year ago, when its robotic arm was put to new and unplanned use to remove some dust from the solar panels, extending the mission.
The maneuver -- employed six times successfully -- saw the arm use dust itself to clear the panels, as it scooped up some martian soil and gently dropped onto the robot so the dirt was blown across the solar panels, clearing parts of their surface.
Adding something to the lander specifically to clean the panels was forgone due to costs, explained Bruce Banerdt of NASA's Jet Propulsion Laboratory, during a press conference Tuesday.
Such a mechanism would leave less to put into the science instruments, he said.
- 'Treasure trove' -
InSight, one of four missions currently on the Red Planet -- along with the US rovers Perseverance and Curiosity, and China's Zhurong -- arrived on Mars in November 2018.
Its seismometer, made in France, has since paved the way for great advances.
The interior was kind of just a giant question mark, said Banerdt, who has worked on the InSight mission for more than a decade.
But thanks to InSight, we've been able to map out the inside of Mars for the very first time in history.
Seismic waves, varying based on the materials they pass through, offer a picture of the interior of the planet.
For example, scientists were able to confirm that the core of Mars is liquid and to determine the thickness of the Martian crust -- less dense than previously thought and likely consisting of three layers.
The magnitude 5 quake in early May was much larger than all those previously recorded and close to what scientists thought would be the maximum on Mars, though it would not be considered a huge tremor on Earth.
This quake is really going to be a treasure trove of scientific information when we get our teeth into it, Banerdt said.
Earthquakes are in particular caused by plate tectonics, he explained. But, they can also be triggered when the Earth's crust moves due to temperature anomalies caused by its mantle.
It is this type of vibration that scientists think they are dealing with on Mars.
Not all of InSight's scientific operations have gone smoothly, however, such as when its heat probe had trouble being successfully buried below the surface to take the planet's temperature because of the composition of the soil where the robot landed.
Regardless, in light of the seismometer's success, NASA is considering using the technique elsewhere in the future, said Lori Glaze, director of NASA's Planetary Science Division.
We'd really like to set up a complete network on the moon to really understand what's going on there.