Check this out:
That's a Hubble image of Jupiter and its moon Ganymede, just before the satellite dips behind the planet's disk. It was taken in April of 2007 but just released today (which is good, because I would've been ticked it missed my Top Ten this year). Look at the detail you can see on Ganymede! What kills me here is the scale of this: Ganymede is about the same size as Mercury! If Jupiter weren't there, Ganymede might be considered a planet on its own. It would be visible to the naked eye, too. There's science lurking here as well. As Ganymede goes behind Jupiter, we see it through more and more of the giant planet's atmosphere. We know how Ganymede normally looks when it's not being obscured by Jupiter, so we can observe it as it goes behind the planet to get a measurement of the atmospheric ...
