This is an drawing of the Galileo probe exploring Jupiter's environment.
Click on image for full size
Image from: The Jet Propulsion Laboratory
The Atmosphere of Icy Moons
It is unlikely that the icy moons have an atmosphere. The reason they have no atmosphere is because they do not have enough gravity. Gravity depends upon the amount of substance (mass) contained in a body. The smaller the body is the lower its gravity, so moons have much less gravity than a planet has. The icy moons are made of ice, and because ice contains less substance than rock, icy moons have even less gravity than a rocky moon of the same size. Because there is little gravity, an icy moon cannot hold onto an atmosphere for very long.
An atmosphere can come from inside a moon. Some icy moons may have active surfaces, such as Europa, where the surface may "crack" and release molecules for an atmosphere from inside the moon.
An atmosphere can also come from the magnetosphere. The icy moons are usually inside a magnetosphere, and magnetospheres contain energetic particleswhich can knock molecules loose from the surface of a moon.
Whether they come from inside the moon or from the magnetosphere, molecules may float around a moon for a while, but because of the low gravity, whatever "atmosphere" may be created rapidly drifts away.
You might also be interested in:
The picture to the left shows examples of the many amazing different surface features of Europa. Many exciting discoveries were made about Europa during the Galileo mission. The surface of Europa is unusual,
...more
Since it has been determined that the composition of the moons is mostly ice, there is probably not enough magnetic material for these to have a magnetosphere of their own. Nevertheless, because of the
...more
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
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
Most of the moons and planets formed by accretion of rocky material and volatiles out of the primitive solar nebula and soon thereafter they differentiated. Measurements by the Galileo spacecraft have
...moreMany examples of the differing types of terrain are shown in this image. In the foreground is a huge impact crater, which extends for almost an entire hemisphere on the surface. This crater may be compared
...more
The surface of Callisto is deeply pockmarked with craters. It looks to be perhaps the most severely cratered body in the solar system. There are also very large craters to be found there. The severity
...more
