Labeled top to bottom, the tiny pinpricks of light above bright Jupiter are the four Galilean moons; Callisto, Europa, Ganymede, and Io. Callisto, Ganymede, and Io are physically larger than Earth’s Moon, while water world Europa is only slightly smaller. In fact, of the Solar System’s six largest planetary satellites, only Saturn’s moon Titan is missing from the scene.
In this composite image from near-infrared light, two of Jupiter’s moons are visible against the planet. The white circle in the middle of Jupiter is Io, and the blue circle at upper right is Ganymede. The three black spots are shadows cast by Io, Ganymede, and another moon, Callisto.
Image Credit: NASA, ESA, and E. Karkoschka (University of Arizona)