What is the Largest Moon in the Solar System?
Written by Fraser Cain
The largest moon in the Solar System is Ganymede, which orbits Jupiter. It measures 5,268 km across the equator. In fact, Ganymede is so large that it's even bigger than Mercury or Pluto, and almost as big as Mars.
Just for comparison, Mars measures 6,800 km across, and Mercury is only 4,878 km across.
Ganymede is composed mostly of silicate rock and water ice, with an iron-rich, liquid core. Scientist think it might also have a saltwater ocean located about 200 km below Ganymede's surface, crushed between layers of ice.
Astronomers used to think that Titan was the largest moon in the Solar System, but better telescopes showed that it actually has a thick atmosphere that extends for hundreds of kilometers, making it look larger. It's actual diameter is 5,151 km.
So, Titan is the second largest moon in the Solar System, and Jupiter's Callisto is the third largest at 4,821 km across. Our own Moon, at 3,475, is the 5th largest.
Here's another article about Ganymede, and one about Ganymede's lumpy interior.
Here's a list of all the largest moons in the Solar System, and a listing of the largest moons and smallest planets at Solar Views.
We have recorded a whole series of podcasts about the Solar System at Astronomy Cast. Check them out here.
Filed under: Astronomy
