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　　There being so many planets in the universe,/the chances are great/that there is life somewhere out there.// But not all planets support life.// Most extra-solar planets are “gas giants,”/which are unsuitable for life/as we know it.// Of course,/that doesn’t mean/that life as we know it/is the only possible kind of life.// There might be life on gas giants,/although I doubt it.// We don’t know/what proportion of planets are rocky like Earth.// But even if the proportion is quite low,/the number will still be high/because the total is so huge.//
　　Scientists searching for extraterrestrial life/regard water as essential.// If there is no water in liquid form,/life can probably not exist.// Ice won’t do,/nor will steam.// Mars shows evidence of liquid water,/in the past if not today.// Europa,/one of the moons of Jupiter,/is covered with ice/and under the ice/there could be a sea of liquid water.//
　　People once thought/Mars was the most likely planet/to have extraterrestrial life/within our solar system.// Now Europa has taken the place of Mars,/but most scientists think/we must keep looking.// Evidence suggests/that water is not particularly rare/on extra-solar planets.//