Jupiter Week: Wednesday: Delinquent moons

November 17, 2010

Jupiter has been taunting, bright in middle of the southern sky for—what? months now?—from our latitude. Only the moon and Venus can hold a candle to its magnitude, and Venus is off being coy somewhere below the horizon. So there is a bold Jovian dot up there, and we’ve been pointing David’s telescope at it. And trying to attach cameras to it. With mixed success.

In honor of our feeble attempts, here is Jupiter week! Each day a little snippet of astronomical wonder about the biggest planet we’ve got.

Wednesday: Delinquent moons

At last count, Jupiter has 63 moons. It has some nice, chubby ones—the moon Ganymede is larger than the planet Mercury. Pleasingly spherical, these bigger moons keep us occupied while the littler ones get up to mischief.

55 of Jupiter’s moons exhibit some level of delinquency. The majority of them go around Jupiter backwards (retrograde) and have wobbly or weird orbits. A tracing of theirs paths ends up making Jupiter look like an atomic nucleus, the moons like a buzzing electron cloud.

Some of them are ridiculously small. Themisto, an underwhelming rock eight kilometers in diameter, was found in 1975. Then no one could really remember where they’d last seen it and it took until 2000 for someone to look in the right drawer or whatever and find it again (oh, that’s where I left the Themisto! shouted the scientists).