The Exoplanet Next Door


By M. Darby Dyar /Suzanne E. Smrekar/Stephen R. Kane M. D. ダイアー /S. E. スムレッカー/S. R. ケーン
English 日本語 日本語
In 1982 all anyone could talk about in the planetary science department at the Massachusetts Institute of Technology was the cancellation of NASA’s latest flagship mission, the Venus Orbital Imaging Radar (VOIR). One of us (Dyar) was a graduate student there at the time. (The other two were still in college and elementary school.) Graduate students wept openly in the hallways, and veteran faculty shook their heads. The newly elected Reagan administration had enacted sweeping cuts to space exploration, and VOIR was one of the casualties.  1982年,マサチューセッツ工科大学の惑星科学科では,米航空宇宙局(NASA)の最新の重要ミッションである金星周回撮像レーダー探査機VOIR計画が中止になった話で持ち切りだった。私たち著者の1人ダイアーは当時そこの大学院生だったが(他の2人はまだ大学の学部生と小学生),惑星科学科の大学院生たちは廊下で人目をはばからず涙を流し,ベテラン教員たちは落胆して頭を振っていた。ときのレーガン新政権が宇宙探査費用の大幅削減を含む予算案を立法化し,VOIRはその犠牲となったのだ。
Shortly afterward, though, scientists cobbled together plans for a bargain-priced spacecraft ($680 million) made of leftover hardware and, miraculously, saved the mission. In 1989 the Magellan orbiter launched on a reconnaissance mission to Venus, and by 1990 it was in orbit. Over the next five years the orbiter returned near-global radar images, gravity data and a topographic map of the second planet from the sun. It was the latest in a long line of Soviet and U.S. missions to our neighboring planet, but when Magellan plunged to Venus’s surface in 1994, NASA’s support for Venus spacecraft died with it. Since then, scientists have submitted more than 25 proposals for return missions to Venus, and although some of those received high rankings from review boards, none were approved. Decades-old data gathered by Magellan re­­main the foundation of Venus geoscience to this day.  だが科学者たちは使い残しのハードウエアを使って格安(6億8000万ドル)の探査機を作る計画を急きょ取りまとめ,金星探査は奇跡的に救われた。この「マゼラン探査機」は1989年に打ち上げられ,1990年に金星周回軌道に入った。マゼランはその後5年間で,太陽系第2惑星のほぼ全球にわたるレーダー画像と重力データ,地形図を送ってきた。
But planetary scientists never give up, and we have made progress in uncovering the secrets of this world nonetheless. Since Magellan, the European and Japanese space agencies have sent successful missions to Venus, leading to breakthroughs in understanding its atmosphere. Meanwhile scientists have been busy rewriting the textbooks on our sister planet by performing new analyses of Magellan data. We now think that volcanoes are rampant on Venus, and we have even found hints of the start of plate tectonics, which scientists think is critical for a planet’s habitability. New theoretical models also suggest Venus may have had liquid water on its surface until relatively late in its history—meaning that it may have been hospitable to life much longer than we once thought.  だが惑星科学者たちは諦めず,金星の謎解きは進展してきた。マゼラン以後,欧州と日本の宇宙機関がそれぞれ金星探査ミッションを実行し,金星大気の理解を大きく前進させた。同時に科学者はマゼランのデータを新たに解析し,地球の兄弟惑星に関する教科書の記述を書き換えてきた。