Water and Life on Mars
Mars perhaps first caught public interest in the late 1870s, when Italian astronomer Giovanni Schiaparelli reported using a telescope to observe canali, or channels, on Mars. By the turn of the century, popular songs told of sending messages between Earth and Mars by means of huge signal mirrors. On a darker side, H.G. Wells' 1898 novel The War of the Worlds portrayed an invasion of Earth by technologically superior Martians desperate for water. (1) In the early 1900s novelist Edgar Rice Burroughs, who is best known his creation of the jungle hero Tarzan, also entertained young readers with tales of adventures among the exotic inhabitants of Mars, which he called Barsoo. (2) It was hoped that Mars had ample liquid water and perhaps even irrigation channels of liquid water. Of all the planets in our solar system other than Earth, Mars is the most likely to have harbored liquid water and perhaps even life. Mars' rotational period and seasonal cycles are similar to those of Earth, although they are twice as long due to its greater rotational period around the sun. (see table 1) (3) Fact began to turn against such imaginings when the first robotic spacecraft was sent to Mars in 1965. Pictures from the first flyby and orbiter missions showed a desolate world, (see figure 1) blemished with craters like Earth's Moon. The first wave of Mars exploration ended after the Viking mission. This mission sent two orbiters and two landers to the Red Planet in 1975. The landers conducted experiments including chemical tests in search of life. Most scientists interpreted the results of these tests as negative, diminishing hopes of a world where life is widespread. (3) Several new developments in studies occurred over the next few decades and changed the way that scientists thought about life and Mars. One of these developments was the 1996 announcement by a team from Stanford University, NASA's Johnson Space Center and Quebec's McGill University that a meteorite, ALH84001, believed to have originated on Mars contained what might be the fossils of ancient microbes (see figure 2). This rock and other apparent Mars meteorites that were discovered on several continents on Earth are believed to have been blasted away from the red planet by asteroid or meteor impacts. They are thought to come from Mars because gases trapped in some of the rocks match the composition of Mars' atmosphere. Not all scientists agree with the conclusions of the team announcing the discovery of fossils, but it reopened the issue of life on Mars. (4) A fundamental requirement for life as we know it is liquid water. In the 1980s and 1990s, biologists found that microbial life has an amazing flexibility for surviving in extreme environments, areas of the world that are extraordinarily hot, or cold, or dry, or under immense pressure, conditions that could not sustain human life. In June of 2000, NASA announced that it had found evidence of water on Mars. The tremendous discovery fueled hope for finding microbiological life on the Red Planet. This discovery also made a human mission to Mars more practical. This discovery led many researchers to wonder if Red Planet could have ever supported life. (5) Many scientists believe that water may have thrived billions of years ago in an underground thermal spring, or it might still exist in some form in niches below the frigid, dry, windswept surface. Mars today is too cold, with an atmosphere that is too thin to support liquid water on its surface. Yet scientists who studied images from the Viking orbiters kept encountering features that appeared to be formed by flowing water, among them deep channels and canyons. There is conclusive evidence that liquid water existed at one time on the surface of Mars, even though some scientists dispute it. Key discoveries leading to this conclusion include the detection of various minerals such as hematite and goethite which usually only form in...
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