When you hear the word ocean, I assume you think of the massive body of saltwater that covers over 70% of the Earth’s surface. What if I told you there is another saltwater ocean, more than twice the size of Earth’s oceans combined, that is intense and even more unexplored than our own? This is the ocean thought to be under the icy surface on Europa, one of Jupiter’s moons. Europa is one of Jupiter’s 95 moons and just a little smaller than Earth’s moon. It’s made of silicate rock and, importantly, has an ice crust. As a surface covered in cracks and small craters, Europa has the smoothest exterior of any object in the known Solar System, implying that water exists beneath the surface. The possible ocean under Europa’s icy crust is estimated to be up to 100 miles deep and potentially habitable for life. While Europa is still a target for exploration, scientists think its ocean is a possible place for life beyond Earth.
The curiosity about oceans on Europa dates back to the 1970s, when the Voyager 1 and 2 spacecraft took photos of Jupiter’s surface, revealing more than the expected cratered and old exterior. Instead, Europa was found to have an extremely icy surfice, smooth because itlacks craters and mountain formations. These photos were of high enough quality that scientists analyzed the moon’s line patterns and discovered that predicted fractures didn’t align. The only way the patterns seen on the European surface could be possible was if the surface was separate from the interior, something only possible if a warmer form of ice was present between the surface and interior — water.
Beyond these explorations, studies and observations from other spacecraft, like Galileo, have also produced evidence for the existence of an ocean beneath Europa’s surface. First, evidence that there is conductive material underneath the surface, which could likely be saltwater, has been seen in studies of Jupiter’s magnetic field. Evidence for a larger magnetic field under the crust suggests that conductive fluid exists, probably in the form of a liquid, like an ocean. Secondly, the gravitational pull from Jupiter that is projected onto Europa would generate tidal forces, similar to the ocean tides on Earth. These forces would create the ocean on Europa, known as tidal heating, suggesting that underneath the icy surface, liquid water may be present. Lastly, a more in-depth analysis of Europa’s surface, including cracks and shelves, indicates that there must be some sort of movable layer beneath the ice, suggesting the possibility of an ocean.
Exploring an ocean beyond our own may seem premature, as Earth’s oceans are still largely unexplored. But, we know that the Earth’s ocean contains a wide variety of sea life, ranging from large to microscopic organisms, giving hope that Europa could also support life. The possible water, energy, and chemicals of this subsurface ocean are important for scientists to investigate. These essential features and elements, including nitrogen, oxygen, and hydrogen, are building blocks for life, potentially giving insight into the future of biological life and evolution. The research done on Europa could apply to other oceans in space and help scientists understand what’s needed for life on other planets or in other habitats. Exploring Europa’s ocean could also help us better understand our ocean, as the chemicals and structures found on Earth may have mirrored those on our planet billions of years ago when life first formed.
A significant plan for exploring the oceans of Europe and the moon, in general, is NASA’s Europa Orbiter mission, which would use wavelength radars similar to those used on Mars to look through the ice and learn about the possible ocean. The Europa Orbiter aims to determine if there is an ocean below the surface of the icy moon and if, furthermore, it could support life. The mission has three main goals: to understand the icy crust, gain insight into the ocean beneath the surface, and learn about the potential for life. Specifically, one of the goals of the mission would be to measure Europa’s shape, which changes during an orbit accurately. The shape changes due to tidal deformation, which is influenced by whether or not there is an ocean below the surface. Measurements of the shape, done by an altimeter, would provide insight into possible oceans. This data would help scientists determine if Europa’s ocean exists and if it could support life like Earth’s oceans do.
In Orbit 