For as long as the written word has existed, there are records of people discussing the possibility of alien life. Whether it is little green men or UFOs, the possibility of alien existence has been one explored by comic books and scientists alike. Each time a new planet is discovered, scientists analyze its physical properties in order to determine if life could exist on it. Many people believe that because the universe is so large, there must be life somewhere else besides Earth. In recent years, scientists have been looking closer to home to investigate the possibility of extraterrestrial life. Discovered in 1610 by Galileo Galilei, Europa, Jupiter’s sixth closest moon, was a mystery for centuries. However, as space exploration technology improved throughout the twentieth and twenty-first centuries, so too did our knowledge of Europa. The more we learn about Europa, the more favorable this moon seems for being able to inhabit life.
Most of the information we have on Europa was obtained during the Galileo mission in 1989. Nevertheless, no spacecraft has yet landed on the moon. Europa is slightly smaller than the Earth’s moon in size and is made primarily of silicate rock. Its crust is made of water-ice and is predicted to have an iron-nickel core. In between the crust and the core, there is believed to be a subsurface ocean. Its weak atmosphere is composed mainly of oxygen. Because Europa is about 485 million miles from the sun while Earth is only 92.95 million miles, the intensity of the sunlight and the heat that reaches Europa is much lower than that on Earth; its temperature ranges from -369.67 degrees Fahrenheit to -234.67, so this moon is far colder than Earth. The surface of Europa has many cracks and streaks but very few craters. Europa’s surface is actually the smoothest of any known solid object in our solar system, and scientists believe that the smoothness could suggest the presence of a water ocean underneath. On Earth, there are billions of living organisms in the ocean, so could the same be true for Europa?
Just as there are tidal forces between Earth and the Moon, there are forces between Jupiter and Europa. In fact, the same hemisphere of Europa is always facing Jupiter, as the moon orbits the planet every three and a half days. Depending on where Europa is in its orbit around Jupiter, sometimes it is a little closer to or a little farther from the planet. When Europa comes slightly closer to Jupiter, the gravitational attraction between the two bodies increases, which causes Europa to stretch towards and away from Jupiter. When Europa moves slightly away from Jupiter, the gravitational force is lower, and Europa returns to a more spherical shape. Supposedly, this process creates tides in Europa’s subsurface ocean. This type of tidal flexing movement kneads Europa’s interior and also acts as a source of heat. The heat produced by tidal flexing could potentially be warm enough to cause the ocean to remain in liquid form. All of the crisscrossing cracks on Europa’s surface also point to the stresses exerted on the moon’s surface by massive tides in the ocean underneath. Scientists believe that the tidal flexing activity also produces geological activity that has a similar effect to the plate tectonics on Earth. In 2014, NASA reported evidence that supports the theory of plate tectonics within Europa’s thick shell of ice. This was the first sign of plate-tectonic geological activity on a planetary body other than Earth.
In addition to the tidal flexing, scientists also point to active volcanoes that could be heating the water in Europa’s salty ocean. The heat from these underwater volcanoes would provide vents where bacterial life could thrive, just as it does on Earth. In 2015, scientists revealed that sea salt from an ocean under Europa’s surface could be serving as a coating for some of the moon’s geological features. This suggests that the ocean could be interacting with the seafloor, which scientists believe is significant when determining whether or not Europa could be a habitat for life.
The curiosity and intrigue that surrounds Europa has prompted several exploration proposals. The European Space Agency’s Jupiter Icy Moon Explorer is a mission to Ganymede, Jupiter’s largest moon. This mission is expected to launch in 2022 and will conduct two flybys of Europa, hopefully providing us with more information on this icy moon. NASA has also planned the Europa Multiple-Flyby mission that will be launched in the middle of the following decade. After these two missions, scientists should be able to gather additional data that allows them to more accurately determine whether or not Europa could be habitable for living organisms.
