Jupiter, a gas giant and the most massive world in our Solar System, has 79 moons. Fourth-largest of these is Europa, at 3,100 kilometers in diameter. The small world is bigger than Pluto but smaller than our own Moon.
What makes Europa truly special is that it very likely may have a huge amount of liquid water hiding beneath its frozen exterior. NASA scientists believe there is some proof of this due to results of density and magnetic field measurements that point to the existence of a great deal of water. Aside from this, there is real evidence that Europa does have water, via spectroscopic analysis that shows water ice covers its ultra-smooth surface.
The icy shell of Europa averages around 22 kilometers deep and is some 50 million years old. Beneath this, however, researchers think an ocean of liquid water some 100–200 kilometers deep could exist, kept relatively warm by its contact with a volcanically active seafloor. All told, Europa might contain more than twice the liquid water volume of Earth’s own oceans, which “only” average about 3.6 km deep.
Pressure at Europa’s seafloor would be somewhere between 130–250 MPa, which would not be out of reach for technology that we’ve already developed to withstand the deepest parts of Earth’s oceans.
Many researchers today believe that Europa holds more promise of potential extraterrestrial life than does Mars, our nearest planetary neighbor. While there has been recent proof of water ice on Mars, and there may indeed be substantial amount of frozen water at its poles and below its surface, the likelihood of liquid water on Mars is almost nil. If there is life on Mars, it will most probably prove to be microbial in nature.
But Europa’s vast ocean holds far more potential. The three requirements for an origin of life as we know it (officially known as “abiogenesis”) are liquid water, an energy source, and the right atoms to serve as chemical “building blocks”. Europa has all three.
Europa is a tidally locked world, with one side always facing its gravitational master Jupiter. This great force holds Europa in an elliptical orbit where at some points the moon is alternately closer and further away from Jupiter. This constant tugging change creates friction within Europa to its very core of solid nickel and iron. This generates a reliable source of geothermal heat, which ultimately keeps Europa’s ocean liquid.
Without sunlight, Europan life would never develop photosynthesis. But that isn’t a requirement. On Earth, plants use energy from the sun to make their own food, rather than eating other living things for nourishment. They are known as autotrophs. There are autotrophs that don’t need the sun: bacteria that thrive on the heat from the mantle bubbling up from hydrothermal vents on the seafloor.
During a recent expedition to hydrothermal vents in the deep sea, researchers from the Max Planck Institute of Marine Microbiology and the Cluster of Excellence MARUM discovered mussels that have their own on-board ‘fuel cells’, in the form of symbiotic bacteria that use hydrogen as an energy source.
Europa also contains the elemental requirements for life. Water itself leads to many other essentials, via various chemical reactions: free oxygen, hydrogen peroxide, carbon dioxide and sulphur dioxide. This, combined with the iron, as well as elements like phosphorus provided by cometary impacts, would ultimately yield all of the needed compounds.
Not all life in Europa’s oceans might be microbial, despite the exceedingly high pressures. On Earth, the eel Simenchelys parasiticus lives over a kilometer deep. The Pacific viperfish hunts prey in 4 kilometers of darkness, and the Mariana snailfish exists at depths greater than 8 kilometers.
Though all of the elements needed for life likely exist in needed quantities on Europa, any multicellular life that does (or did) evolve there would only share very general characteristics with life on Earth. Alien life doesn’t necessarily require DNA, nor does it need to be based on carbon. With the high concentration of silicon seen on Europa’s surface, perhaps Europan life is silicon-based.
Due to the principal of convergent evolution — the idea that living things that are otherwise unrelated will evolve to have similar features as they adapt to what they need to survive in their environment — even silicon-based water life forms would somewhat resemble the fish, crustaceans and mollusks on Earth. Sharks and dolphins are extremely similar in many ways, but are very far apart on the tree of life. We would find fins, tentacles, both rigid and soft skeletal frameworks, varied forms of ballast as that found in whales, an endless variety of eyes, many types of shells, and on and on.
Even if there is life in the darkness on Europa, it will be a true challenge to uncover evidence of it. Seeing such life directly would be the work of years, constructing equipment, tunneling into kilometers of ice and eventually descending into the depths.
And for those of us hopeful that vents ejecting subsurface ocean water above Europa’s ice crust, the thin atmosphere offers little protection from the harshness of Jupiter’s radiation. Using data from both the Galileo and Voyager 1 spacecraft flybys, NASA scientists were able to see that the radiation from Jupiter that hit Europa’s surface was strongest at the moon’s equator and weakest at its poles. If there is a chance to find ejected evidence of life, the poles would be the best bet.
Though the question of Europan life is far from answered and in no way a certainty, we can still consider the chances of actual intelligent, tool-using and/or communicating life having evolved there. It seems, based on our limited experiences on Earth, that fire is needed to develop an extensive level of technology beyond simple tool creation. Without fire, there would be no smelting and manipulation of metals. If life on Europa is limited to an oceanic existence, fire becomes very difficult to tame. However, we might imagine some Europan species evolving the ability to grow shells based on very heat tolerant metals, which they then form into something resembling an oven that can be used to create a bubble-like environment free of water and allow creatures with highly manipulative appendages to experiment with creating and harnessing fire.
Humans touching down on Europa and personally inspecting the surface, and venturing into its mysterious depths, are a likelihood sometime closer to 2100 AD. We will likely settle on Mars, and begin mining asteroids, long before setting foot on Jovian moons. But perhaps we will know if we have alien cousins living in the Solar System with us long before then: NASA is planning a mission in the 2020’s called Europa Clipper that will place a satellite in orbit around Jupiter and conduct extensive study of Europa. After that, there may be missions to Europa’s surface, and, eventually, below.
Hopefully all of us reading this will still be around to share in whatever the answers we find may be.
Thank you for reading and sharing!