Europa is one of the largest moons of Jupiter in the solar system and is one of only 3 worlds in the Solar System to host life. Europa hosts massive single-cellular anaerobic creatures and minature jellyfish-algae hybrids that use sunlight from cracks in Europa's surface and other organisms for food. Around 6,000 different species have been discovered and an additional 5,000 are believed to be yet to be discovered. It is believed that early in its history when its ice was a liquid it was host to millions of advanced organisms, though most died out when the planet's temperature began to decrease. Some scientists believe that Sapient2 evolved near the end of Europa's warm era. This is because Sapient2 was thought to be a land-aquatic hybrid and several alien settlements believed to be Sapient2 cities have been discovered. Today, Europa is a worldwide nature preserve. Interplanetary laws restrict any cities from being built. The offical population is 126, all rangers or scientists, but several thousand tourists visit the icy moon every year.