As we consider the other worlds of our solar system, what are the best places to look for life?
Nearly everyone agrees the first rule is... "Follow the Water."
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Well, obviously a world like the Earth would be ideal, but we're it in our solar system. There is no other planet with liquid water at the surface, certainly not with liquid water oceans ...and that means that to look for life elsewhere in our solar system, we have to look for places that are as much like the Earth as we can find. So what are those places? Well, first and foremost there's Mars. We know that liquid water existed on Mars early in its history and it appears that there are still short-lived environments at the surface of Mars where water can briefly exist. It doesn't last long because the Martian atmosphere is too thin and water boils off right away, but for short periods of time you can still have liquid water flowing at the surface of Mars. So you can imagine life having begun at the surface of Mars and then retreated into the subsurface as the surface freeze-dried. So Mars is the best candidate. |
As we've seen, Venus lost all its water...
And if life can't easily exist in gas giant planets, does that mean our search for life has "run dry"?
Not exactly...
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We need to broaden our perspectives and think about uh, some of the other abodes for life. A good example is Jupiter with a series of moons that are on the order of the size of Mars some of them, they're very large habitats for life. |
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The next most interesting place is Europa, one of the big moons of Jupiter. Europa is an ice-covered world that almost certainly has an ocean underneath of that ice, and when I say an ocean, I mean an amount of water that's probably double the amount of water in all of the Earth's oceans. That's potentially a great habitat for life. What we don't know is whether there are the sorts of energy sources available in that ocean either to fuel life if it exists or for life to have begun there. But the high probability that there's liquid water on Europa makes it the other important place to go in our solar system to look for life. |
Beyond Jupiter lies Saturn, to be explored by the Cassini spacecraft starting in 2004.
It too has giant moons, one of which has astrobiologists-scientists who look at life in the cosmic context-very anxious for the new results...
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Titan has an atmosphere in which we know that organic molecules are being produced. That's intriguing, but the surface of Titan is very cold, minus 180 degrees centigrade, so there can't be liquid water at the surface for any length of time. Even so, it's not out of the question that there might be subsurface water on Titan... So if I were looking for life in our solar system, I would begin with Mars and Europa, because in both those cases we have good evidence for liquid water, even if not yet quite yet definitive proof... And I might even think about Titan first of all ...and at least in the case of Titan, we have evidence for the sort of carbon-based organic molecules that we also know are important for life. |
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...we have to remember that life doesn't require abundant water, it just requires enough to sustain itself. 20 years ago I dismissed organisms that could grow at 100 degrees C and I was wrong. So I think we have to keep an open mind in this business when we're looking for life especially on planets with different gravity and magnetic fields and other properties than Earth. |
For millennia, humans have looked up to the skies and speculated about the possibility of life beyond Earth.
Now we have the tools and techniques, new spacecraft and new scientific concepts, that just might enable us to find out...
Stay tuned... success in looking for life might perhaps be just around the corner...
