Science: Mercury Unveiled

As the innermost planet of the solar system, Mercury is almost always obscured by the sun's harsh glare. Under the best viewing conditions, it never appears as more than a hazy disk in earth-bound telescopes. Last week, as the Mariner 10 passed only 400 miles from the planet, some of the mystery about Mercury was finally dispelled. Radioing back the first close-up pictures of the Mercurian surface, the robot ship unveiled a bleak, cratered and totally forbidding world.

"It's like the moon and it isn't," said Donald E. Gault, one of the scientists monitoring...

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