Four of Jupiter's moons, Europa, Io, Ganymede, and Callisto, are collectively known by which name?

The planet Jupiter is surrounded by more than 75 moons, the largest four of which are known as the Galilean moons. They are named after Galileo Galilei, who discovered them in 1610. At the time, they were the first objects found to orbit another planet, other than the Earth's moon.

All four of the Galilean moons are some of the largest objects in the solar system. The largest, Ganymede, is over 3,000 miles (4828 km) in diameter, making it bigger than the planet Mercury. The second largest moon, Callisto, is similar in appearance to Ganymede, but orbits Jupiter much farther away at almost 1.5 million miles (2.4 million km). Jupiter has a very strong gravitational field, which is why Callisto is able to orbit the planet from such a distance.

The third largest moon, Io, rotates around Jupiter much more closely and is roughly the same size as Earth's moon. Io contains around 400 active volcanoes that erupt daily, frequently rearranging the surface of the moon. Europa is slightly smaller than Earth's moon and is covered in ice.

Galileo Galilei (1564-1642) was an Italian professor of mathematics and natural science. He is most remembered for his conflict with the Catholic Church, which refused to believe the sun was the centre of the solar system. Galileo initially named his discovery of the four moons of Jupiter 'Cosmica Sidera' ('Cosimo's stars'), but they were later renamed in his honour. Europa, Io, Ganymede, and Callisto get their names from Roman mythology.