Originally Posted by
d1spenser
Has it been proven that extraterrestrial life exists? No. Is there a possibility that extraterrestrial exists? Yes, it is very likely.
Our own existence is a very good argument. If life can exist on Earth, then out of billions of planets there must be some with similar conditions where life could form too. Not only that, but in our own solar system there are a few potential habitable worlds:
1) Mars. Life hasn't been found there so far, but at least some evidence was found showing that in the past it was a much more hospitable world. Evidence of liquid water that once flown there were found. I've also read about possibilites of origins of methane that could be either produced naturally or through breathing of primitive organisms. However, the fact that this planet has no magnetic field and very tiny atmosphere to protect its surface from sun radiation greatly reduces a chance of anything surviving there. So if any life exists there, it has better chances to survive underground.
2) Icy moons of gas giants. There are lots of them, the most well known candidates are Enceladus (Saturn moon) and Europa (Jupiter moon). Below the ice shell of these frozen worlds it is believed that there is an ocean of liquid water. Tidal forces from their massive gas neighbours heat these moons from the inside. There is no sunlight, but it was proven that sunlight is actually not crucial component of life: deep in the oceans of Earth where sun rays couldn't reach anything exotic life forms still exist. Enceladus and Europa are probably the best candidates to look for extraterrestrial life in solar system.
3) Titan (Saturn's moon). This one is quite mysterious: it is the only world that has liquid on its surface besides Earth. There are rivers, lakes, oceans... but they are not made out of water! They are actually filled with gazoline-like liquids, it even rains there with them. The atmosphere is actually similar to Earth's (most of it is nitrogen) but instead of oxygen there is lots of methane (which may indicate life presence too). In addition, it may contain a liquid ocean of water under it's surface.
