Io: Moon Over Jupiter

Explanation: How big is Jupiter's 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 above 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 center of Jupiter . That puts Io 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.