Finding Life on Other Worlds

There is, of course, a direct way of determining whether life can arise under natural conditions: we could try to find it on other planets.221 The SETI activity is one way of doing this, but there is another way. We could look for primitive life elsewhere in the Solar System. If we found life elsewhere — even the simplest microbe — we would at least know that life is not unique to Earth. Finding life on other worlds would almost certainly tell us something about how it arose on this one.222

The key ingredient of life seems to be water: find water and there is a chance of finding life. We know that, in the past, Mars almost certainly possessed water; so there is a chance — no matter how remote — of finding fossil remnants of past Martian life. In the present-day Solar System, at least three bodies besides Earth might have oceans. Two of the moons of Jupiter — Europa and Callisto — might possess subsurface oceans of water. These bodies are far from the warmth of the Sun, of course, and on the surface of these moons there are thick sheets of ice; but geothermal and tidal heating may be enough to maintain liquid water deep beneath the surface. Titan, a moon of Saturn, may possess a subsurface ocean of ammonia-water. Here are three places that maybe — just maybe — are home to alien life. It would not be life with which we could communicate; but if we knew that life arose independently in our Solar System more than once, then how could we reasonably argue that life is rare throughout the Galaxy? Surely, then, missions to Europa and Callisto, and later to Titan, should be a priority.223

figure 70 If there is an ocean beneath the ice ofEuropa, then a hydrobot similar to this artist's impression will probably be used to explore it. nasa scientists are currently examining the details ofhow to send a hydrobot to Europa, have it penetrate the ice and reach the ocean without introducing contamination, and then have it send back information to Earth.

figure 70 If there is an ocean beneath the ice ofEuropa, then a hydrobot similar to this artist's impression will probably be used to explore it. nasa scientists are currently examining the details ofhow to send a hydrobot to Europa, have it penetrate the ice and reach the ocean without introducing contamination, and then have it send back information to Earth.

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