On April 13th 2017, NASA held a press conference that began with a single question, “is there life elsewhere?” The Oceans Beyond Earth conference investigated whether Europa and Enceladus; two ocean worlds could harbor life in the vast liquid oceans shielded by their icy surfaces.
These moons were chosen because they contain vast liquid oceans beneath the ice on their surface. The thick ice layer acts somewhat like our own atmosphere, allowing the water to exist below the surface. In theory, there should be heat vents at the bottom of these oceans, heating the water and providing potential energy for life.
There are four primary ingredients for life, Water, Time, Energy and CHNOPS, or the six most important chemical elements that make up the majority biological molecules here on Earth. The Cassini mission has demonstrated that Enceladus has all of these elements. Ocean worlds are more likely to harbor life because they have one of these categories in abundance, water.
Dives into our own oceans have proven that life does not need access to sunlight to survive. In fact the deep-ocean heat and methane vents on earth are teeming with tiny organisms. This discovery turned the search for life on its head. Rather than turning sunlight into energy, these organisms convert chemicals into energy. No longer were we looking for worlds that could have sunlight, but worlds with water that were geologically active.
When Cassini drifted through the great water plumes of Enceladus enough data was collected to allow scientists to make the first calorie count on an alien world. They estimate that the plume gas mixtures have roughly 300 pizzas per hour (their measurement, not mine) in energy content, which should be plenty to help stimulate to the growth of life.
These findings are significant because they also imply that there is some kind of “ice tectonics” at work on Enceladus and Europa. Both moons are heavily affected by the gravity of their respective gas giants. In Europa’s case the entire surface moves by as much as 30 meters every 2-3 days due to Jupiter’s influence. This movement is important because it creates an active shell that helps to move energy around and distribute the nutrients necessary for life.
So potentially, both Europa and Enceladus and other ocean worlds could harbor life. The question, which one more likely to? When asked this , Mary Voytek, Astrobiology senior scientist for NASA, answered that she believed Europa is still the best candidate in our solar system for finding extra-terrestrial life.
Her primary argument for this was the amount of energy found in Enceladus’ plumes. If there were life, you would expect it to use this energy, instead it is fired off into space. She believes that even if there were life on Enceladus, it would likely be quite primitive compared with any potential life on Europa. This is primarily down to time. Europa is older than Enceladus so there have simply been more chances for life to develop beneath it’s icy crust.
While any life on these ice sheathed moon is likely to be quite primitive, they offer our best shot at finding extra terrestrial life in our own solar system.
The Cassini Mission has proven that life can exist on ocean worlds. It is now up to the Europa Clipper to find out whether it does exist.