Mercury's moon

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A moon orbiting Mercury was, for a short time, believed to exist.

On March 27, 1974, two days before Mariner 10 made its flyby of Mercury, instruments on Earth began registering large amounts of ultraviolet radiation in the vicinity of Mercury which, according to one astronomer, "had no right to be there".^{[citation needed]} By the next day, the radiation had disappeared; it reappeared three days later, appearing to originate with an object which was, seemingly, detached from Mercury.^{[citation needed]} Some astronomers speculated that they had detected a star, but others argued that the object must be a moon, citing the two different directions the radiation had emanated from and the belief that such high-energy radiation could not penetrate very far through the interstellar medium.^{[citation needed]} Adding to their arguments, the object's speed was calculated to be 4 kilometers per second (2.4 miles per second), which matched the expected speed of a moon.^{[citation needed]} The object was even given a name: in an interview, the discoverer said if it was confirmed, he'd like to name it 'Charley'.^{[citation needed]} When asked why, he said "I once had a dog named that, and I've always wanted to name something after the dog".^{[citation needed]}

Soon, however, the "moon" was detected moving away from Mercury, and was, eventually, identified as a star, 31 Crateris. The origin of the radiation detected on March 27 is still unknown.^{[citation needed]}

Mercury's moon, although non-existent, did spark an important discovery in astronomy: ultraviolet radiation, it was found, was not as completely absorbed by the interstellar medium as was formerly thought.

[edit] In popular culture

In Eric Rücker Eddison's 1922 novel The Worm Ouroboros, Mercury is mentioned as having a moon.

The Buck Rogers Sunday strips feature a visit to Mercury's moon in "Exploring the Water Moon of Mercury" (1/13/35 to 3/17/35) (Series I, Strips 251 to 260)