Most people have looked up at a starry sky and wondered whether there is life beyond our own blue planet. Is our world a unique oasis of life or are there other planets that harbor life? In the past decade astronomers have been searching for planets around other stars. So far they have found over 100. Most of these new worlds are gas giants similar or larger to Jupiter, but as techniques improve in this new science smaller planets are likely to be discovered. All of this means that even in our own galaxy there are likely to be millions of different worlds orbiting their stars and some of them could well contain life.
Mars is the most similar planet to earth in the solar system. It is therefore one of the first places to look when we are considering life on other planets. When the Viking Landers were sent to Mars in the 1970s they found a cold desolate dry world that seemed unlikely to be able to support life. With such cold temperatures, a thin atmosphere and no sign of liquid water the chance of finding even some sort of microscopic life forms seemed remote. Tests performed by both Viking Landers seemed to back this up. However with the advance of astrobiology in recent years it is worth taking another look at those experiments. Results from the Mars Global Explorer indicate that in the past Mars was a very different world. It would have had a denser atmosphere and running water on its surface. This would have made the planet more hospitable to life. The question is, if life did take root, could it have survived until the present day in the more hostile Martian environment? We know there are organisms on our planet deep in the earth’s crust that can exist on hydrogen and carbon dioxide. Could similar organisms be sheltering under the surface of Mars?
Apart from Mars another world that has caught scientists attention is Europe, one of Jupiter’s moons. When the Galileo probe visited Jupiter and its attendant Galilean moons, Europe was thought to be a frozen ball of rock and ice. However pictures taken by the probe clearly revealed a series of cracks and fissures across the moon’s surface. There is only one other place in the solar system that has this appearance, the frozen arctic seas on earth. It appears that deep below the icy surface Europe has a system of giant oceans. The composition of these oceans is unknown but there is a fair chance they support life. How do we know that life could survive below massive permanent layers of ice in oceans with no light reaching them? Because in similar conditions here on earth astrobiologists have also found life.