Both Jupiter and Saturn have very extensive systems of moons.
There are, however, differences. Jupiter has four fairly large moons, called the Galilean moons, that are comparable in size to Earth’s moon.
Saturn, on the other hand, has one large moon, Titan, and a number of middle-size moons.
Both Jupiter and Saturn also have dozens of small moons.
Titan is comparable in mass to Jupiter’s Galilean moons, but because Jupiter is more massive than Saturn Titan is more massive compared to Saturn than the Galilean moons are compared to Jupiter.
Titan, in fact, has more mass relative to the central planet than all Jupiter’s Galilean moons combined.
Jupiter and Saturn: Similar Yet Different
As planets Jupiter and Saturn are fairly similar, so why do their moon systems differ so much? Astronomers think that the moon systems of Jupiter and Saturn both formed by the same accretion process around the planets as the planets formed. This accretion process is similar to the process that formed the solar system of planets orbiting the Sun.
Erik Asphang of UC Santa Cruz and Andreas Reufer of the University of Bern has proposed a new theory to explain this difference, the origin of Saturn’s middle-sized moons, and Titan’s larger mass relative to its planet. Asphang and Reufer proposed this theory at the American Astronomical Society’s Division for Planetary Sciences meeting on October 19, 2012. Their theory will also be published in the journal Icarus.