Triton, Neptune's largest moon, is the coldest place in our solar system. It has an average temperature of minus 315 F. Triton has a weird, backward orbit and has been inching closer to Neptune each year. When the two finally collide, in about 10 million to 100 million years, the moon will be shredded into rings perhaps as beautiful as those of Saturn.
Voyager 2 image of Jupiter's moon Calisto. This image was taken from over 2 million km away as the spacecraft approached Jupiter. The bright spots peppering the surface are meteorite impact craters which have excavated through the dark surface and exposed the lighter material below. Callisto is 4,800 km in diameter
Researchers suggest they may know why the Uranus moon Miranda resembles Frankenstein's monster, a jumble of mismatched parts: Constant squeezing and stretching from Uranus caused the moon to heat up and churn.