Io at Sunset . ... Credit Copyright: Galileo Project , JPL , NASA Explanation: How tall are mountains on Jupiter 's moon Io ? One way to find out is to view them at sunset . ... The above image highlights Mongibello Mons on the far left, a sharp ridge rising so high it would rank among the highest mountains on Earth . ... The grayscale image was taken two years ago by the robot spacecraft Galileo currently orbiting Jupiter . ... NASA Web Site Statements, Warnings, and Disclaimers . ...