Using The Earth to Understand Other Planets
How do scientists test their ideas of how life can survive in harsh conditions or what kind of geochemistry would be present on Mars? They use locations on Earth called “analogs," places that approximate conditions on other planets either in environmental or geological terms. One of the most well known analog sites for studying the characteristics of Mars, for example, is the Atacama Desert in Chile.
So essentially, scientists are looking to processes on Earth and their causes to try to understand what is going on in the rest of the universe. For example, recently scientists have discovered plumes of methane spewing forth from Mars. On Earth, these kinds of plumes are either caused by life itself or some kind of volcanic activity. Methane is a relatively unstable gas, and there must be some kind of ongoing process to continuously produce it.
The presence of these plumes leads scientists to believe that there could be bacteria beneath the Martian soil producing methane; they could be feeding off the minerals in subterranean rocks to survive. From the study of extremophiles, we know that this is not a far-fetched assumption. If the plumes are instead caused by volcanic activity (though scientists have long considered Mars to be geologically inactive), that would still be an important find, as it is believed that a planet must be geologically active in order to create the necessary geochemical processes to support life.
Looking at other places in the universe, Europa, one of Jupiter’s moons, is covered in ice that seems to display cracks that form, close up and then re-form continuously. This could mean that there is liquid water under the ice, as this is how Earth’s polar ice caps behave due to the presence of water. And, again, from the study of extremophiles, we know that simple forms of life can live below the surface of icy conditions. Enceladus, one of Saturn’s moons, has plumes of water vapor, hydrocarbons, sodium and ammonia spewing from its surface. The sodium especially leads scientists to believe that the plumes originate from some kind of deep-sea salty cavern; life is present under those conditions on Earth today.