Another World.(NASA Mars rover)

Morton is author of "Mapping Mars."

If you saw this patch of rock-studded wasteland in the Mojave Desert, a few hours from Pasadena, California, you wouldn't look twice. After a trip of 300 million miles, though, it's a sight for sore eyes. The ecstatic reception that greeted the pictures that Spirit, NASA's Mars rover, sent back to the Jet Propulsion Laboratory in Pasadena was in part an expression of simple relief. Four years ago all three NASA Mars landers failed, and an orbiter, too. So for the people at JPL, who run America's Mars Exploration Program, even a bad picture would have been bliss; the excellent ones they got--far and away the best yet taken on the surface of Mars-- were heaven.

Apart from the difficulty of getting there and the relief that comes with success, what makes this desert so exciting? What makes it so exciting that scientists see it through tears of joy, so exciting that NASA's Web servers strain to send the pictures to eager viewers around the world? What makes it so exciting that U.S. President George W. Bush thinks sending humans to walk in Spirit's tire tracks, at a cost in the hundred-billion dollar range, will turn the public on in an election year?

The answer is partly that Mars, a mere planet, has many attributes that make a star--a movie star, that is. For a start, it has a famous face. It's a face we've had a long time to get to know, because its features are discernible from earth with just a modest telescope. That unique attribute--no other planet's surface is so open to inspection--means that for centuries idle thoughts about life elsewhere have settled on Mars just a bit more easily than on the other planets. It's why "the man from Mars" became and remains the archetypal extraterrestrial, and why this planet was the one chosen by the great writers of science fiction and planetary romance, like H. G. Wells, Edgar Rice Burroughs and Ray Bradbury. The space-age revelation that Mars's features--its mountains and craters and polar ice caps--look pretty good up close, too, hasn't hurt.

Mars also has an easily identifiable character: redness. This may seem trivial (and it borders on the untrue--to instruments up close Mars is more a yellowish brown). Redness, though, is something simple that everyone can ...