Its surface is very smooth - no surface feature is higher than one kilometerItHas a relatively low density, about 2/3 that of the Earth
It OrbitsJupiter once every 3.55 Earth days and rotates on its axis with the same period.
The Europa Orbiter is a probe that will try to determine whether or not there is liquid water under the planet's icy surface. It will use sub-surface radar imaging to try and find the boundary between ice and water. Also, an altimiter in conjunction with gravity measurements will be able to detect the tidal movements of the surface. If there truly is an ocean of liquid water under the surface of the planet the movements should be rather large.
I think the biggest question is whether Europa's energy source is great enough to support life. There is strong evidence for liquid water and available organic materials on Europa, but not enough is known about the satellite's energy potential to decide whether it is adequate to power life.
The thickness of Europa's hard ice shell is a hot scientific debate. Some argue the crust must be only one or two kilometers (six-tenths mile to 1.2 miles) thick, given ridges, cycloid cracks and other geological features. Others contend the ice crust must be 10 times thicker, and that it includes a warm convecting ice layer that shapes observed surface features.
