Callisto

Figure obtained from Astronomy Picture of the Day

           This is a picture of Callisto which is one of the Galilean satellites that orbits around Jupiter. This picture was posted on Astronomy picture of the day on July 31^st, 2001. It is the third largest moon in the Solar System and is close to the size of Mercury. Callisto is the Galilean moon that is furthest away from Jupiter and is thought to have a large body of water under the icy surface. It is also thought to be one of the satellites in the solar system where life could form. I will discuss the evidence that shows that this is possible. There are three factors that need to be present in order for life to evolve. One is that there needs to be source of elements and molecules from which to build living organisms. Second is the need for a source of energy for metabolism and growth and the last is the need for a liquid medium for transporting the molecules of life.  The outer three Galilean moons are thought to be areas of interest for finding life. As mentioned earlier there is evidence that there are vast bodies of water that is under the ice.  Callisto itself does not have a strong magnetic field but it does have an induced magnetic field which is evidence of the presence of salty water under the surface. Another factor is the energy that is needed. It is thought that the warmth and energy needed from can be formed by radioactive decay that is occurring on the satellite. Of the two other Galilean moons Callisto has the least amount of energy available. It is thought that to would not have the energy needed to create and sustain life. Because of this Europa and Ganymede is thought to have a better opportunity for life.