NASA recently announced $6,000,000 (£495,000) in financing for research into the feasibility of sending swarms of miniature swimming robots (also known as independent micro-swimmers) to explore oceans beneath the frozen shells of our Solar System’s numerous “ocean worlds”.
But don’t imagine metal humanoids swimming underwater like frogs. They’ll most likely be simple triangular wedges. Pluto is one such possible ocean world. However, the worlds with the closest oceans to the surface, making them the most accessible, are Europa, a Jupiter moon, and Enceladus, a Saturn moon.
Scientists are interested in these oceans not only because they contain so much liquid water (Europa’s ocean likely contains about twice as much water as the entire Earth’s oceans), but also because chemical interactions between a rock and ocean water could support life. In fact, the environment in these oceans could be very similar to that on Earth when life first evolved.
These are the environments in which water that has seeped into the rock of the ocean floor becomes hot and chemically enriched before being expelled back into the ocean. This chemical energy can be used by microbes, which can then be eaten by larger organisms.
There is no need for sunlight or an atmosphere. Since their discovery on Earth’s ocean floors in 1977, many warm, rocky structures of this type, known as “hydrothermal vents,” have been documented. Chemosynthesis (energy from chemical reactions) rather than photosynthesis supports the local food web in these locations (energy from sunlight).
The energy that heats the rocky interiors of our Solar System’s ocean worlds and keeps the oceans from freezing all the way to the bottom is primarily provided by tides. This contrasts with the primarily radioactive heating of the Earth’s interior. The chemistry of water-rock interactions, however, is similar.
Cassini has already sampled Enceladus’ ocean by flying through plumes of ice crystals that erupt through cracks in the ice. There is also hope that Nasa’s Europa Clipper mission, which will begin a series of close flybys of Europa in 2030, will find similar plumes to sample. Getting inside the ocean to go exploring, on the other hand, could be far more informative than sniffing at a freeze-dried sample.