... Moon . ... What can astronomers tell us about the different colors on the surface of Jupiter's moon Europa? ... We can use the colors of Europa s surface to tell us about the chemical compounds that make up the surface and subsurface of the jovian moon. Even before the first spacecraft made a close visit to Europa, astronomers on Earth used telescopes to study the moon and were able to use a technique called spectroscopy to determine that Europa s surface is composed mostly of water ice. ...