The Galileo mission discovered an amazing thing: Callisto seems to have its own atmosphere, although it is very, very thin, and may come and go with time. The atmosphere is created when molecules from the magnetosphere, moving very fast, hit the surface and knock out a water molecule. The surface may also evaporate, or ‘sublimate’ when the sun is shining, the way the surface of a comet
One of the instruments on the spacecraft measured the presence of an Ionosphere, a part of the atmosphere that is filled with ions. But it wasn’t always there.
Even though Ganymede and Callisto have thin atmospheres, there does not seem to be a Ganymede or Callisto torus, as there is at Europa and Io.
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A satellite which has an atmosphere, such as Jupiter's moon Io, and which also is inside a magnetosphere (unlike the Earth's moon), will leave a cloud of particles behind as it orbits the planet. This...more
Callisto was first discovered by Galileo in 1610, making it one of the Galilean Satellites. Of the 60 moons it is the 8th closest to Jupiter, with a standoff distance of 1,070,000 km. It is the 2nd largest...more
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Amalthea was discovered by E Barnard in 1872. Of the 17 moons it is the 3rd closest to Jupiter, with a standoff distance of 181,300 km. Amalthea is about the size of a county or small state, and is just...more
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