Lesson 7: Life in the Solar System 7.1 Modern Views of Mars It is surely ironical that Mars, that desert planet of red dust storms and dry ice caps, might have answers for us regarding the origin of Life. Yet, Mars is our best bet to go beyond the main problem that we face in this connection: The problem of a Sample of One. With only one sample of Life to go by (and with the discovery that modern living forms are closely intertwined) we keep on getting the same story. Alternative possibilities do not emerge. We need a second sample if we are to seriously deal with the question whether there is only one kind of Life. The presence of the gullies on Mars suggests that Mars has warm events or warm climate periods at times. From analogy with the ice ages on Earth, we might expect astronomically driven alternations of cold and mild periods, since Mars' axis is tilted and since Mars' orbit has substantial eccentricity. (Both tilt and eccentricity produce ice age fluctuations on Earth.) Perhaps, periodically, ancient dormant life forms protected deep within Mars come to life. If so, what kind of carbon chemistry governs their existence? Is there, was there ever, life on Mars? Here is one of the more optimistic answers, from the people who know Mars best: "Early environments were apparently sufficiently similar on Earth and Mars, and life arose so rapidly on Earth once conditions became clement, that emergence of life on both planets at that time is scarcely less plausible than emergence on only one." "Exobiological Strategy for Mars Exploration", NASA SP-530 (April 1995) "Scarcely less plausible" is about the best we can do at the moment. It is a cautious scientific statement, but hopeful at the same time. The stakes are high: "...[finding extraterrestrial life] would change everything - no human endeavor or thought would be unchanged by that discovery." Dan Goldin, NASA Director Studying Mars as the second test bed after the Earth most likely to have hosted life, even in a primitive form . . . is an obvious step in understanding the development of life in the whole Universe." Roger Bonnet, Director of Science, ESA The point is, we don't have many options and Mars is our best bet at this time. For reasons already discussed, we agree that liquid water is a strong requirement for life. So we have to ask (again): Is there now, or was there ever, water on Mars? Finding evidence for water will greatly increase our chances that Life on Mars, past or present, is a reality. Figure 7.1.2 North pole of Mars with elevations taken with the Mars Global Surveyor Altimeter. Blue is low, red is high. The massive depression at the center of the image may have been an ocean basin. See our student Mars project pages: http://calspace.ucsd.edu/marsnow/