Those dates aren't completely random, although they're mostly not 'discovery' dates:
Uranus: Year in which it was determined to be a planet
Mercury: The date we made the first detailed map of its surface
Moon: Roughly the time we started mapping the surface with telescopes
Venus: The year the first detailed map of the surface was made
Sun: Roughly the time when it was first determined that the Earth orbits the sun rather than the other way round
Ganymede: Actually almost correct - An object which was probably Ganymede was spotted by a Chinese astronomer in 365BC
(
Zoroastermouse thinks therefore he am, Wed 4 Mar 2015, 12:00,
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