|ＩＳＡＳニュース 1998.10 No.211|
|- Home page|
||- 研究紹介||- お知らせ||- ISAS事情||+ 火星探査入門||- 東奔西走||- 宇宙輸送のこれから||- いも焼酎||- BackNumber|
Japan is on the way to Mars, becoming just the third nation to travel to our most interesting planetary neighbor. Mars is the planet of greatest past and present interest and, I think, will also be the eventual destination of human adventurers.
Mars attracted the attention of early telescope observers with its prominent and sometimes changing markings. Also it rotates with nearly exactly the same period as does earth. What's more, Mars has seasons very similar to Earth with a blanket of white frost covering first one pole and then the other. Mars seemed to be Earth's closest planetary cousin, perhaps even the habitat of alien life!
Indeed, the American astronomer Percival Lowell became convinced by the end of the last century that Mars once had been the home of an intelligent race that perished due to planetary drought, leaving a legacy of dried up canals. His vivid writings inspired H. G. Wells, Edgar Rice Burroughs, Ray Bradbury, Arthur Clarke and other pioneers of science fiction to populate Mars with all manner of beings, hazardous and otherwise. "Martians" became a lasting component of worldwide popular culture.
You can imagine the excitement and anticipation in July 1965 when the primitive spacecraft, Mariner 4, of the United States flew by Mars and collected the first, very poor quality pictures. I was a junior member of that imaging team and still remember how strongly the (then) three main US TV networks pressured us to "Stop hiding the pictures of Mars!" We weren't hiding them. We were simply trying to develop primitive computer techniques to make them comprehensible! And what a shock they were - Mars looked like the Moon with huge barren craters, not the Earth. What's more, neither magnetic field nor radiation belts were detected, and the atmospheric pressure was less than one percent that of Earth. Then, in 1969 Mariner 7 proved that the seasonal white frost at the martian poles was solid carbon dioxide, not water ice. Mars is not the twin of the Earth!
Later, the orbiter Mariner 9 (1971-72) mapped fascinating contradictions, including ancient flood-cut channels winding through a surface environment now so rarefied that liquid water is physically impossible. Mars also is home of the largest volcanic mountains in the Solar System, of canyons far larger and deeper than the Grand Canyon of Arizona, and of vast smooth plains underlain by ice. Finally, in 1976, the Viking landers searched directly for microbial life, pursuing that centuries old popular dream. But a dream is all that it was-the surface of Mars is lifeless, although there still could be microbes living within ground water deep within the crust similar to recently-discovered terrestrial bacteria living in deep ocean volcanic fumaroles.
Then in 1989, scientists on the Soviet orbiting mission Phobos 2 claimed that a small magnetic field was present after all. Even more surprising, the international team of scientists working with Phobos 2 (including some of those now working with Nozomi) deduced that oxygen atoms from the atmosphere of Mars were being stripped away from Mars by the solar wind. One calculation indicated that the entire atmosphere of Mars could be stripped away within a geologically short time! Clearly strange thing is going on at Mars!
Puzzling and important Mars's plasma results like those from Phobos 2 attracted the attention of the world-renown expertise of the scientists and engineers at ISAS. Furthermore, ISAS' new M5 launch system could reach Mars with a modest-sized payload - if everything was designed just right, such as getting a little extra push from the gravity of the Moon along the way. Despite its modest size, Planet B carries fourteen complementary scientific instruments, including five proven standbys jointly developed with scientists from Canada, Germany, Sweden and the US. New approaches are included as well - a lightweight spinning camera led by a Kobe University team and a novel radio-probing instrument from Tohoku University that will study the martian surface at night. Promising young Japanese researchers are being given a chance along with seasoned veterans.
Meanwhile, the Mars surprises continue. When the US Mars Global Surveyor (MGS) went into orbit in September 1997 carrying a magnetometer and electrometer (to help map the magnetic lines of force), the lead magnetometer scientist announced that they too had detected a small martian magnetic field. But after several months he changed his interpretation! Mars has no planetary magnetic field after all. Instead, Mars displays very strong, local magnetic anomalies, stronger than anything similar on Earth. Every time MGS dipped down below the martian ionosphere they detected the strong local anomalies, presumably caused by intensely magnetized lava rocks, although we can't tell until the full magnetic map can be compared with the geological features of Mars' surface. The great thing is that Nozomi is designed to map right through that critical altitude, so it should provide an even richer scientific harvest than had been expected. The Nozomi Mars story will start to unfold in October 1999.
I can hardly wait!