... Early Microscopic Life on Mars? ... Europa, the fourth largest moon of Jupiter, was recently discovered to have a thin oxygen atmosphere by scientists using the Hubble Space Telescope. Erupting Volcanoes on Io . ... Jupiter's moon Io has active volcanoes. ... It is, in fact, a Seyfert type 2 spiral galaxy. ... Jupiter's Colorful Clouds . ... What makes the colors in Jupiter's clouds? ... Galileo, Cassini, and the Great Red Spot . ... The Hydra Cluster of Galaxies . ... A Violet Moon . ...