The Hot Rock: Mysterious Mercury

Mysterious Mercury, the planet closest to the sun, is

Mercury ain't for sissies. Say what you will about the difficulty of sending a spacecraft to a distant place like Saturn, it's Mercury, the first rock from the sun--with its crush of solar gravity and its inferno of solar heat--that presents the greatest challenges. NASA has dared go to Mercury only once before, 30 years ago, when Mariner 10 made three flybys. Now NASA is set to try again, with a spacecraft called MESSENGER, which is scheduled to take off as early as this week on a mission to become the first probe to orbit the planet.

Even to astronomers,...

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