Why is Europa considered one of the best places to search for alien life?

Europa's icy crust shows cracks, ridges and disrupted terrain that suggest an ocean beneath the surface. Jupiter's gravity flexes Europa, producing internal heat that can keep that ocean from freezing solid. Scientists think the ocean may be in contact with a rocky seafloor, which could supply chemicals useful for life. NASA's Galileo mission and later observations have strengthened the case for this hidden ocean. Because it has water, energy and chemistry, Europa is one of the most promising places in the Solar System to look for habitability.