Mars Finding Shifts Focus to Inner Planets ; Evidence of Abundant Water Is Whetting Astronomers' Appetites for Future Missions to Mars, Mercury, and Venus

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This week, a mechanical geologist the size of a golf cart and nearly 156 million miles away galvanized the world with news that Mars bears unequivocal evidence of once-watery conditions capable of supporting life as we know it.

Yet for all the excitement surrounding the discovery, the value of the Mars exploration program may lie as much in what it suggests about the early history of Earth and about the prospects for habitable planets around other stars as it does about Mars.

Thus, the results announced Tuesday are whetting astronomers' appetites for coming missions to Mercury, and perhaps later to Venus. These missions are expected to help fill in the outlines of …