Nasa recently announced US$600,000 (£495,000) in funding for a study into the feasibility of sending swarms of miniature swimming robots (known as independent micro-swimmers) out to explore the oceans beneath shells icebergs of the many “ocean worlds” of our solar system. But don’t imagine metallic humanoids swimming underwater like frogs. These will probably be simple, triangular corners.
Pluto is an example of a probable ocean world. But the worlds whose oceans are closest to the surface, making them the most accessible, are Europa, a moon of Jupiter, and Enceladus, a moon of Saturn.
Life in ocean worlds
These oceans are of interest to scientists not only because they contain so much liquid water (Europe’s ocean probably contains about twice as much water as all of Earth’s oceans combined), but because chemical interactions between rock and ocean water could support life. In fact, the environment of these oceans may be very similar to that of Earth when life began.
These are environments where water that has seeped into the rock of the ocean floor becomes warm and chemically enriched – water that is then expelled back into the ocean. Microbes can feed on this chemical energy and can in turn be eaten by larger organisms. No sunlight or atmosphere is actually needed. Many such hot, rocky structures, known as “hydrothermal vents”, have been documented on the Earth’s ocean floors since their discovery in 1977. In these places, the local food web is indeed supported by the chemosynthesis (energy from chemical reactions) rather than photosynthesis (energy from the sun).
On most ocean worlds in our solar system, the energy that heats their rocky interiors and keeps the oceans from freezing all the way down to the base comes primarily from the tides. This contrasts with the largely radioactive warming of the Earth’s interior. But the chemistry of water-rock interactions is similar.
Enceladus’ ocean has previously been sampled by flying the Cassini spacecraft through plumes of ice crystals that burst through cracks in the ice. And it is hoped that Nasa’s Europa Clipper mission can find similar plumes to sample when it begins a series of close flybys of Europa in 2030. However, getting into the ocean to go exploring would potentially be much more informative than just sniffing a freeze-dried snack.
This is where the concept of detection with independent micro-swimmers (Swim) comes in. The idea is to land on Europa or Enceladus (which wouldn’t be cheap or easy) where the ice is relatively thin (not yet located) and use a radioactively heated probe to melt a 25 cm wide to the ocean – located hundreds or thousands of meters below.
Once there, it would release up to about four dozen 12cm-long wedge-shaped micro-swimmers to explore. Their endurance would be much less than that of the 3.6m long autonomous famous underwater vehicle named Boaty McBoatface, with a range of 2,000 km which has already cruised more than 100 km under the ice of Antarctica.
At this point, Swim is just one of five “Phase 2 studies” in a lineup of “advanced concepts” funded under the 2022 cycle of NASA’s Innovative Advanced Concepts (NIAC) program. So there’s still a big chance that Swim will become a reality, and no full missions have been set or funded.
The micro-swimmers would communicate with the probe acoustically (through sound waves), and the probe would send its data via cable to the surface lander. The study will test prototypes in a test tank with all subsystems integrated.
Each micro-swimmer could explore perhaps only a few tens of meters from the probe, limited by the power of its battery and the range of its acoustic data link, but acting as a herd, it could map the changes (in time or location) temperature and salinity. . They may even be able to measure changes in water cloudiness, which could indicate the direction to the nearest hydrothermal vent.
The power limitations of microswimmers may mean that none could carry cameras (these would need their own light source) or sensors that could specifically detect organic molecules. But at this point, nothing is ruled out.
I think finding signs of hydrothermal vents is a long time though. The ocean floor would, after all, be several miles below the micro-swimmer’s release point. But, to be fair, the location of the vents is not explicitly suggested in the Swim proposal. To locate and examine the vents themselves, we likely need Boaty McBoatface in space. That said, swimming would be a good start.
This article by David Rothery, Professor of Planetary Geosciences, The Open University is republished from The Conversation under a Creative Commons license. Read the original article.