Moons for Galileo Galilei's observation of Jupiter's four largest moons in 1610: Ganymede and Callisto on January 7, and Europa and Io on January 8.

“I therefore concluded and decided unhesitatingly, that there are three stars in the heavens moving about Jupiter, as Venus and Mercury round the Sun; which at length was established as clear as daylight by numerous subsequent observations. These observations also established that there are not only three, but four, erratic sidereal bodies performing their revolutions round Jupiter… the revolutions are so swift that an observer may generally get differences of position every hour.”

– Galileo Galilei, Sidereus Nuncius (”Starry Messenger”), 1610

A spacecraft named Ganymede II returns back to Earth after its expedition to Jupiter's moons followed by 1500 days stuck in space. The Earth they find, is deserted.