Mission Possible
Why go to Mars? Part of the answer, of course, is to explore the unknown. The Pathfinder mission, the first landing on Mars in over 20 years, is the spearhead of a series of exploratory flights to be launched about every two years, designed to answer important questions about our neighboring planet. But it may come as a surprise that one of the main reasons to study Mars is to gain a better understanding of our own planet.
Mars resembles Earth in many respects (length of day about 24 hours, annual seasons, polar ice caps, geological features), but its climate is very different. Although the diameter of Mars is about half that of Earth, its atmospheric pressure is less than 1
percent as much. In an atmosphere as thin as that of Mars, water cannot exist in a liquid state. It goes directly from a solid (ice) to a gas (water vapor) in a process called "sublimation." Without liquid water, there can be no life as we know it on the surface of Mars.
Today, Mars is a vast, frozen wasteland with an atmosphere consisting almost entirely of carbon dioxide. Its surface features, however, show traces of a time when it was subject to conditions similar to those on Earth today. Features that look like
immense flood plains and dry riverbeds suggest that water once flowed over the planet. If that is true, the atmosphere must have been denser at one time. Surface conditions may, therefore, have been able to support life.
If Mars was once a watery and life-sustaining planet, what happened to make it change? It now appears to be in the grip of a global ice age, though we don't know how long it has lasted and whether the "big freeze" will ever end. Global surveys from
orbit, surface exploration, and probes beneath the surface may provide answers. But how does looking into the Martian past help us understand the history of Earth? Mars has been frozen in time (as well as in temperature) while Earth's surface has been subjected to changes caused by weather and climate, geological upheavals, and the footprints of humans and other living things, both animals and plants. It is hoped that in-depth studies of Mars will show scientists what our own planet was like
before these changes made the Earth we know today.
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