Destination Mars Read Online Free PDF Page A

plant life gone wild as the moisture from the poles nourished it. We now know that the poles are a mix of a thin layer carbon dioxide ice, or dry ice, and water ice. The CO 2 freezes groundward in the local summer and then is re-released into Martian skies in the summer. This seasonal exchange can account for over a quarter of the atmosphere freezing out, then being released back into the air. The water ice below also melts in the summer; evidence of flowing meltwater, once thought to be very unlikely, is seen in orbital images of the planet.
    In fact, the observation of subterranean and frozen water is becoming relatively common on Mars. At one time thought to be dry, arid, and dead, Mars is turning out to be quite active in terms of weather and erosional processes. Wind is of course the primary agent of erosion today, but water is slowly, stubbornly revealing itself more and more. 4 The southern ice cap alone, the smaller of the two, is thought to have enough water tied up in its frozenreservoir to cover the entire planet to a depth of over thirty feet—but not for long. The atmosphere is so thin, at less than 1 percent of Earth's, that liquid water quickly boils away in the tenuous air. But scratch the surface, literally, and there is plenty of water ice all over the planet.
    That water was far more evident in the past than it is today, slumbering beneath the dust, dirt, and sand of the present Mars. Huge features called outflow channels , about twenty-five of them, litter the surface of Mars, indicating a truly massive and disastrous outpouring of water at some time within the last few million years—and smaller ones are still being formed to this day, via liquid water. There are also areas strongly resembling river deltas, alluvial fans, and channels that speak to a once-watery Mars.
    So what's the big deal about water? Simply this: life as we understand it needs water to exist. Increasingly, extreme forms of life on Earth are discovered that can survive on trace amounts and in hideously difficult environments, but all forms need some water. So when we find water in any form on Mars it is exciting, for it allows us to think, once again, of Martians…microscopic though they might be.
    And why are microbes on Mars so important? It's not like they will be the next explosive market for Big Macs® or directly impacting our daily lives if discovered. But the discovery of some form of life on Mars would be a game changer in other ways. Philosophy, religion, and of course science would all be rocked by such a discovery. The existence of life on Mars would, for some, seem to diminish our special place in the universe as humans. Of course, if this life were something more akin to streptococci than your next door neighbor, it's hard to get too intimidated. But for some, any discovery of life elsewhere would be a threat.
    For others, it would be a delight. The idea that life, that poorly understood miracle of amino acids and organic compounds, could have sprung up independently on another world is a big one. Some scientists have hypothesized that life may not have even begun hereon Earth, that is may have started first on Mars and then hitchhiked a ride to Earth via a meteoric fragment. This idea has gained credibility in the last few decades, when meteors found on Earth (in Antarctica) were definitively traced back to Martian origin. And, since Mars calmed down from its evolutionary throes much sooner than Earth, this idea makes some sense. Life could have slowly evolved there, then come to Earth and survived once our own planet was less volatile. It would certainly give the organisms more time to mature in evolutionary terms. 5
    Of course, there are others who consider this to be hogwash, and still others who consider these ideas blasphemous. The former group will likely come around given sufficient evidence. The latter will never be convinced, regardless of the science; the idea is simply too threatening.
    The important thing