OUR planet seems to be in just the right spot to sport a mild climate. Not too near the sun's heat, not too far from its warmth, in a narrow habitable zone in which water is liquid and life can thrive. But Earth could still support life even if it were as far from the sun as Saturn, claim two scientists in the US, as long as the air abounded with hydrogen. If they are right, then billions of life-bearing planets may exist much further from their host stars than astronomers had thought possible.
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