here it comes, here it goes after a lot of other posts I have decided to write again about moons and this time I continue to really cold piece of giantic rock and 2nd biggest moon of Jupiter and 3rd largest in whole Solar System right after Titan. It is Callisto not The Spear of Vengeance.
Callisto was found with other Galilean moons by Galileo Galilei and independently Marius. Marius gave her this name. Instead of Callisto, Jupiter IV was used. I am really glad that it changed.
Callisto was one of many lovers of Zeus or Jupiter for Roman`s.
As you can see on the picture below, Callisto is really just a little smaller than Mercury.
It is smaller just by few kilometers but it has just a third of Mercury`s weight. As you can see it depends a lot on the stuff from which the object is made.
It is actually very important that it is so far away because the rest of the Galilean moons are orbiting in resonance which means that they are creating heat in their interior because of friction of the liquids inside.
Callisto can be described as very cold and hard place. There is no volcanism or tectonic activity on its surface to smooth all the features. But there are also no mountains since they are caused by tectonic activity.
Only things you can find there are craters and there is lot of them. Actually the number can not increase a lot because they will almost always overlap so the ones that are old will erode and disappear.
Crater which you can see on the right is called Valhalla crater and this one is the largest. The middle is only 600 kilometers wide but with the rings from the rest of the collision you can say that Valhalla has 1800 kilometers. Another huge guy is Asgard with 1600 km.
The surface is very old and also very cold with temperatures oscillating between -130 and -190 degrees of Celsius.
Most of the surface is covered by water ice.
Under the surface it is assumed that there is thick salty ocean.
Callisto has really thin atmosphere which is made up of carbon dioxide which is the same for Mars. The atmosphere is actually so thin that it has to be powered from dry ice which is evaporating from surface, otherwise it would disappear completely.
There is mission planned to go for Galilean moons in 2020. It is called Europa Jupiter System Mission and it would be founded by NASA and ESA (European Space Agency). More than Callisto, Europa is the moon of interest since there is much higher probability of live because there is this heat from friction.