Almost two million kilometers away from Jupiter, Callisto is the most distant of the Galilean satellites and has a diameter of 4 850 kilometers. Though it is almost entirely covered with craters, it is not very similar to our Moon and has almost no relief formations. However, the most interesting structure is a system of concentric rings in the center of which is a brilliant circular region with a diameter of 600 kilometers. This structure, called Walhalla, was probably generated by a gigantic shock wave. A large meteorite probably collided with Callisto when the moon was still young: at the time of the impact, the monstrous block of rock must have melted a vast zone of the icy crust producing clouds of steam and forming a kind of small semi-fluid sea. The icy remains make up the ringed basin that we can observe today.
Almost two million kilometers away from Jupiter, Callisto is the most distant of the Galilean satellites and has a diameter of 4 850 kilometers. Though it is almost entirely covered with craters, it is not very similar to our Moon and has almost no relief formations. However, the most interesting structure is a system of concentric rings in the center of which is a brilliant circular region with a diameter of 600 kilometers. This structure, called Walhalla, was probably generated by a gigantic shock wave. A large meteorite probably collided with Callisto when the moon was still young: at the time of the impact, the monstrous block of rock must have melted a vast zone of the icy crust producing clouds of steam and forming a kind of small semi-fluid sea. The icy remains make up the ringed basin that we can observe today.
