Europa is one of the Galilean moons of Jupiter, along with Io, Ganymede, and Callisto. It is the most intriguing satellites.

Europa is the smallest of the four Galilean moons. It is slightly smaller the Earth’s moon. Its surface is smooth and bright, consisting of water ice crisscrossed by long, linear fractures.

Europa has a frozen surface and is covered with a layer of ice. Because of the icy surface, this moon is one of the most reflective in the solar system.

Astronomers believe that Europa has an iron core just like Earth. And just like our planet, this moon has a rocky mantle and astronomers believe it has an ocean of salty water beneath its icy crust. While evidence for this internal ocean is quite strong, its presence awaits confirmation by a future mission.

However, unlike Earth, this ocean would be deep enough to extend from the moon’s surface to the top of its rocky mantle.

In 2013, Hubble Telescope spotted water plumes jetting from the moon.

Europa could be the most promising place in the solar system to search for signs of present-day life.

Pioneers 10 and 11 and Voyagers 1 and 2 have done flybys of Europa in the 1970s. The Galileo spacecraft did a long-term mission to Jupiter and its moons between 1995 and 2003. As for the future missions, both NASA and the European Space Agency plan to visit Europa and other moons in the 2030s.

Europa orbits Jupiter every 3.5 days and gravity locks it to Jupiter. This means that the same hemisphere of the moon always faces the planet.

Europa’s orbit is elliptical. So, its distance from Jupiter varies, thus, creating tides that stretch and relax its surface.

Discovery

In 1610, Galileo Galilei turned its telescope upwards and discovered the Jovian moons, thus finding Europa. This was the first time a moon was discovered orbiting a planet other than Earth. It’s thought that Galileo had observed Europa on 7 January 1610 but had been unable to differentiate it from Io until the next night.

This was a controversial discovery in the religious world. At the time, the Catholic Church supported the idea that everything orbited the Earth, an idea supported in ancient times by Aristotle and Ptolemy. Galileo’s observations of Jupiter’s moons — as well as noticing that Venus went through “phases” similar to our own moon — gave compelling evidence that not everything revolved around the Earth.

Facts About Europa

Name: Europa’s name came after a woman in Greek mythology who was the daughter of a king. She was supposedly one of Zeus’ many lovers and was made the queen of Crete.

Life: Because Europa is water-rich and has a warm interior, scientists think it could be hospitable to life.

Magnetic Field: There is a magnetic field at Europa, caused by its interaction with the Jupiter’s massive magnetic field. The existence of a magnetic field means that something beneath the ice is conductive.

Age: Astronomers estimate that Europa is about 4.5 billion years old, about the same age of Jupiter.

Thumbnail credits: NASA/JPL-CalTech