How many moons does Jupiter have?
Q: How many moons does Jupiter have?
A: Jupiter has 79 known moons.
Q: Who discovered the four Galilean moons of Jupiter?
A: The four Galilean moons of Jupiter were independently discovered in 1610 by Galileo Galilei and Simon Marius.
Q: What are the names of the four Galilean moons?
A: The four Galilean moons are Io, Europa, Ganymede and Callisto.
Q: How do the sizes of the Galilean Moons compare to Earth's moon?
A: The Galilean Moons are roughly the same size as Earth's moon, some are a bit bigger, some are smaller.
Q: How big is each of the other 75 Jovian moons?
A: All 75 Jovian moons are less than 250 kilometres (160 mi) in diameter, with most barely exceeding 5 kilometres (3.1 mi).
Q: What is their orbital shape like?
A: Their orbital shapes range from nearly perfectly circular to highly eccentric and inclined. Many revolve in the direction opposite to Jupiter's spin (retrograde motion).
Q: What is their orbital period like compared to that of Jupiter?
A: Orbital periods range from seven hours (taking less time than Jupiter does to spin around its axis), to some three thousand times more (almost three Earth years).
