Scientists believe that three moons in our solar system are similar enough to Earth to possibly house extraterrestrial life. Experts have speculated this based on the Earth Similarity Index, which measures many characteristics including radius, density, escape velocity, and surface temperature of a planet or moon against that of Earth’s. Jupiter’s moons Europa and Ganymede, and Saturn’s moon Enceladus are regarded as prospects for alien life in our universe.
The presence of liquid water is considered one of the most important factors in supporting life. Europa is likely to have a sub-surface ocean that may contain up to 3 times the amount of water found on Earth, despite it’s smaller size. Enceladus was found to have geysers of water vapor spouting from it’s surface and a warm, sub-surface ocean. Scientists say they have detected many elements important to life in Enceladus’ ocean including nitrogen, carbon dioxide, and methane. Ganymede was also found to have a sub-surface, saltwater ocean, underneath the moon’s icy surface. All three of these moons have been determined to have at the least harshly habitable conditions in addition to the presence of water. Don’t go “phoning home” right away, as extraterrestrial life has yet to be found on these moons or anywhere else, but these are important findings that may lead us to those discoveries.