Io: Moon Over Jupiter

How big is the Jovian moon Io? The most volcanic body in the Solar System,
Io (usually pronounced "EYE-oh") is 3,600 kilometers in diameter, about the
size of planet Earth's single large natural satellite. Gliding past Jupiter at
the turn of the millennium, the Cassini spacecraft captured this awe inspiring
view of active Io with the largest gas giant as a backdrop, offering a stunning
demonstration of the ruling planet's relative size. Although in the picture Io
appears to be located just in front of the swirling Jovian clouds, Io hurtles
around its orbit once every 42 hours at a distance of 420,000 kilometers or so
from the centerof Jupiter. That puts it nearly 350,000 kilometers above Jupiter's
cloud tops, roughly equivalent to the distance between Earth and Moon. The Cassini
spacecraft itself was about 10 million kilometers from Jupiter when recording the image data.