Jupiter’s Galilean moons

Jupiter and its Galilean moons
(Io / Europa / Ganymede / Callisto)

Jupiter’s Galilean moons

Galileo spotted Jupiter’s four biggest moons in the 17th century,
their names from left to right; Io, Europa, Ganymede, Callisto.

  • they were discovered in January 1610 by the Italian astronomer, Galileo Galilei.
  • Ganymede is the biggest of the Galilean moons – 3,289 miles across, it is larger than the planet Mercury!
  • Ganymede looks solid, but under its shell of ice is 563 miles slushy ice and water.
  • Callisto is the second biggest moon – 3,004 miles across.
  • Callisto is scarred with craters from bombardments early in the Solar System’s life.
  • Io is the third biggest moon –  2,276 miles.
  • the surface of Io is a mass of volcanoes caused by it being stretched and squeezed by Jupiter’s massive gravity.
  • the smallest of the Galilean moons is Europa – 1,961 miles.
  • Europa has a smooth icy surface full of cracks, but the Galileo space probe discovered an ocean of water under the ice where there might be living creatures.

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