Astronomy Picture of the Day . Io: Moon Over Jupiter . ... Credit Copyright: Cassini Imaging Team , SSI , JPL , ESA , NASA Explanation: How big is Jupiter's moon Io ? ... 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 . ... Publications with keywords: Io - Jupiter - cassini spacecraft . ...