Santa Cruz -
A new study says the Earth may have had two moons in the past. According to the study, the two moons crashed into each other to form the Moon we have today. Scientists say this may explain why the two sides of our Moon are so different from each other.
This global view of Jupiter's moon, Io, was obtained during the tenth orbit of Jupiter by NASA's Galileo spacecraft. Io, which is slightly larger than Earth's Moon, is the most volcanically active body in the solar system.
NASA/JPL/University of Arizona
Saturn's rings and moons from 2013 space probe
The moons of Pluto
Jupiter's moon Ganymede, the largest in the solar system, has layered ocean subsurface which may indicate it harbors life.