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Galilean satellite
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Jupiter's four Galilean moons Callisto Europa Ganymede Io volcanic eruption on Io
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Galilean satellite

astronomy
Also known as: Galilean moon, Medicean star
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Jupiter's four Galilean moons
Jupiter's four Galilean moons Montage of Jupiter's four Galilean moonsā€”(left to right) Io, Europa, Ganymede, and Callistoā€”imaged individually by the Galileo spacecraft, 1996ā€“97. The images are scaled proportionally and arranged in order of the moons' increasing distance from Jupiter.

The Galilean satellites are the four largest moons of Jupiter: Io, Europa, Ganymede, and Callisto. They were first observed by Galileo Galilei in 1610 using a telescope. Galileo's discovery of these moons orbiting Jupiter, rather than Earth, provided significant evidence supporting the Copernican model of the solar system, which placed the Sun at the center.12

These moons are considered "regular" satellites due to their nearly circular orbits around Jupiter's equatorial plane. Their composition varies, with Io and Europa being rocky, while Ganymede and Callisto are composed of significant amounts of water ice. Ganymede is notable for having its own magnetic field and evidence of a subsurface ocean.13

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4 Britannica Sources
  1. Jupiter - Ganymede
  2. Jupiter - Other satellites
  3. universe - The Copernican revolution
  4. Gian Domenico Cassini

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