Steve’s Virtual Planet

Galilean Moon Orbital Periods

A common question comes up now and then about the period of the moon’s orbits. I’ve been sort of giving round numbers until recently but I thought I’d better look up the periods to get an exact number. So, off to Wikipedia for this page on Jupiter’s Moons and a chart of all of them! The values have nine significant digits so I thought I’d round them a little so I could remember them more easily. Here they are in the order of decreasing orbital size.

Callisto, the second largest moon, takes a little over 16.5 days

Ganymede, the largest and most massive moon, takes a little over 8 days

Europa, is the least massive of the four and takes about 3 days and 13 hours (so, make that about 3.5 days)

Io, almost twice as massive as Europa, takes about 1 day and 18.5 hours (this would be 1.75 days)