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Mars Odyssey “火星奥德赛”的太空之旅
2002 sees the start of one of the most exciting missions in almost half a century of space exploration, as the 2001 Mars Odyssey space probe begins its final journey to uncover the secrets. The 2001 Mars Odyssey is not the first probe to visit Mars. Since 1964 the US National Aeronautics and Space Administration (NASA)1 has sent several probes to orbit and land on the planet, and all have made significant observations. However, it is hoped that 2001 Mars Odyssey will make the most thorough exploration yet, possibly even marking our first ever discovery of extraterrestrial life!2 The Mars Odyssey mission began on April 7, 2001, when the probe was launched from Cape Canaveral,3 Florida. Because Earth and Mars have very different orbits around the Sun, the timing of the launch was crucial, and was carefully planned to take place at the moment when the journey between the two planets would be at its shortest.4 In January 2002, three months after going into orbit around Mars, the Odyssey embarked on5 its ultimate mission—a three-year-programme to search for life. Significantly, the name "2001 Mars Odyssey" is a tribute to science fiction author and visionary, Arthur C. Clarke, and his most celebrated work 2001: A Space Odyssey, a story of evolution and contact with extraterrestrial intelligence.6 The probe will begin by studying the chemical elements (e.g. carbon, silicon,7 iron etc.) and minerals that make up the geology of Mars, and will help to explain how the planet's landforms8 have developed over time. This will provide clues to the climatic history of Mars and, in particular, may point to evidence of water, the key to life. The planet today is too cold and has an atmosphere that is too thin to support liquid water on the surface, but it is hoped that the probe will find evidence of water trapped under the surface, either as ice or possibly in liquid form if near a heat source. Although today Mars is a windswept desert, the Mars Global Surveyor (1996) discovered numerous channels on the surface that resemble valleys eroded by liquid water billions of years ago.9 So, has there ever been life on Mars? Life on Mars People have argued that there is life on Mars since 1877 when Italian astronomer Giovanni Schiaparelli claimed to have seen a huge system of canals10 on the surface of the planet. This was later popularized as evidence of an advanced civilization by the American astronomer Percival Lowell. Of course, we now know that no such civilization exists, but what about microscopic life?11 The Viking 1 and 2 (1976) and Mars Pathfinder (1997) landers all concluded that the Martian soil contains no organic material, and when a meteorite believed to be from Mars was discovered in Antarctica, suggestions that it contained fossil traces of bacteria-like organisms were soon discounted.12 Yet, given the evidence that billions of years ago both water and a warmer, thicker atmosphere existed on Mars, we cannot discount the notion that life may have existed in the past...and may still exist if you look hard enough. Perhaps the new probe will discover some current "hot spots" where hydrothermal vents provide nooks and crannies where life may still persist.13 Evidence of energy sources other than sunlight will be sought, since life on the surface is unlikely given the presence of so-called "superoxides" that break down organic molecules on which life is based.14 On Earth, chemical and geothermal energy causes microscopic life to exist in places where sunlight never reaches—ocean depths, within rocks, and below the surface—and the same may be the case on Mars. The presence of carbonates would be another possible sign of life as it would indicate that chemical reactions have taken place between the carbon dioxide atmosphere and water over a long period of time,15 perhaps long enough for life to develop. However, the signs of life on another planet may be very different from those on our own. The only way to know for sure is to go there. Manned Mission to Mars NASA is hopeful of a manned expedition to Mars later this century, and research conducted by 2001 Mars Odyssey will play an essential role in preparing such a future mission. In particular, the effects on astronauts of high doses of solar ultraviolet radiation, caused by Mars lacking an ozone layer to protect it, will need to be studied.16 There are also great extremes of atmospheric pressure at the surface of Mars, as well as average daily temperatures that do not exceed -33� C (-27), and the means of surviving both must be discovered. The next few months will play a crucial role
in increasing our understanding of the red planet, and whether or not
signs of life are found, the Mars Odyssey mission represents another
giant leap forward in the history of space exploration. |