Mercury is the closest planet to the Sun, and the second-smallest
planet in the Solar System. Mercury ranges from −0.4 to 5.5 in apparent
magnitude, and its greatest angular separation from the Sun (greatest
elongation) is only 28.3°, meaning it is only seen in twilight. The planet
remains comparatively little-known: the only spacecraft to approach Mercury was
Mariner 10 from 1974 to 1975, which mapped only 40–45% of the planet's surface.
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Color image
(Mariner 10)
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Mercury from
Mariner 10
(NASA)
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