Galilean Moons

by Max McGaughy

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Galilean Moons

The Galilean Moons are the four largest moons of Jupiter. They orbit the largest planet in our solar system, Jupiter. They are named Ganymede, Callisto, Io, and Europa. All of the moons are very distinctive and different. They were discovered by Galileo Galilei in January 1610 using a telescope that he had modified and improved to increase the magnification. Jupiter is the Roman counterpart of the Greek god Zeus, so all of the Galilean Moons are named after some of Zeus's lovers.
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  • Largest natural satellite in our solar system
  • Relative Size- 3,273 miles in diameter
  • Density- 1,93 g/cm3
  • Mass- 1.4819x10 to the 23rd power kg
  • Has a thin atmosphere
  • Larger than Mercury and Pluto
  • Named after a Trojan Prince
  • Core of metallic iron
  • Rock-like layer above core
  • Crust of ice
  • Has many crater-like spots


  • Third largest moon in our solar system
  • Relative Size-2,995 miles in diameter
  • Density- 1.83 g/cm3
  • Mass- 1.0823x10 to the 23rd power kg.
  • Slightly smaller than Mercury by 60 km.
  • Most heavily cratered natural satellite in the solar system
  • Has a very thin atmosphere
  • Named after the daughter of the King of Arcadia
  • Callisto is composed of water, ice, and rocky material.


  • Most volcanically active moon in our solar system
  • Relative Size- 1,942 miles in diameter
  • Density- 3.52 g/cm3
  • Mass- 8.9319x10 to the 22nd power kg
  • Slightly larger than Earth's moon.
  • Very thin atmosphere that is not always there, and generated by a buildup of volcanic gases
  • Named after the daughter of Inachus.
  • Iron core
  • Brown silicate outer layer which accounts for the splotchy surface.
  • Volcanic activity is due to Io being squeezed and stretched while orbiting Jupiter. The surface can move up and down as much as 100 meters.


  • Can possibly support microbial life in it's deep oceans
  • Relative Size- 1,900 miles in diameter
  • Density- 3.01 gm/cm3
  • Mass- 4.8x10 to the 22nd power kg
  • Smaller than Earth's moon, but larger than Pluto
  • Does have an atmosphere composed solely of oxygen
  • Europa is named after the daughter of the King of Tyre
  • Iron core
  • Rocky mantle
  • Mantle surrounded by layer of ice
  • Surface is covered by a frozen saltwater ocean
Jupiter's Galilean Moons