Astronomy Picture of the Day

Explanation: The robot spacecraft Galileo in orbit around Jupiter has recently photographed the inner moons of Jupiter in greater detail than ever before. These pictures of Thebe, Amalthea, and Metis are shown to scale, and reveal details as small as three kilometres across. Amalthea, by contrast, has a total length of about 200 kilometres. The moons are composed mostly of ice, are much smaller than Jupiter's more famous Galilean satellites (Io, Europa, Ganymede, and Callisto), and orbit between Io and Jupiter's rings. Thebe appears dominated by a huge impact crater 40 kilometres across. Astronomers are uncertain of the origin of the unusual white gash at the bottom of Amalthea.