NASA considers sending swimming robots to habitable ‘ocean worlds’ of the solar system

NASA considers sending swimming robots to habitable 'ocean worlds' of the solar system

Realistic color representation of Jupiter’s moon Europa. Credit: NASA/JPL-Caltech/SETI Institute

NASA has recently announced US$600,000 (£495,000) in funding for a study to the feasibility of sending swarms of miniature swimming robots (known as independent microswimmers) to explore oceans beneath the icy shells of our solar system’s many “ocean worlds”. But don’t imagine metallic humanoids swimming frog-like underwater. They will probably be simple, triangular wedges.

Pluto is an example of a probable ocean world. But the worlds with oceans closest to the surface, making them the most accessible, are Europa, a moon of Jupiter, and Enceladus, a moon of Saturn.

Living in Ocean Worlds

These oceans are of interest to scientists not only because they contain so much liquid water (Europe’s ocean probably has about twice as much water like the whole oceans of the earth), but because chemical interactions between rock and the ocean water life could support. In fact, the environment in these oceans can be very similar to that on Earth when life began.

These are environments where water that has seeped into rock from the ocean floor becomes hot 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. There is actually no need for sunlight or atmosphere. Many warm, rocky structures of this kind, known as “hydrothermal vents,” have been documented on Earth’s ocean floors since they were discovered in 1977† At these locations, the local food web is indeed supported by chemosynthesis (energy from chemical reactions) instead of photosynthesis (energy from sunlight).

NASA considers sending swimming robots to habitable 'ocean worlds' of the solar system

Cross-section through the outer zone of Europe’s Antarctic plume, the fractured ice shell, the ocean of liquid water (cloudy at the base near hydrothermal plumes) and the rocky interior. Credit: NASA/JPL

In most of our solar system’s ocean worlds, the energy that warms their rocky interiors and prevents the oceans from freezing down to the base comes mainly from tides. This is in contrast to the largely radioactive heating of the Earth’s interior. But the chemistry of the water-rock interactions is similar.

Enceladus’s ocean has already been sampled by flying the Cassini spacecraft through plumes of ice crystals that erupt through cracks in the ice. And there is hope that NASA’s Europe Clipper Mission may find similar plumes to sample when it begins a series of dense Europa flybys in 2030. However, going out into the ocean to explore could be much more informative than just sniffing a freeze-dried sample.

in swimming

This is where the sensing with independent micro swimmers (Swim) understanding comes. The idea is to land on Europa or Enceladus (which would be neither cheap nor easy) in a place where the ice is relatively thin (not yet located) and use a radioactively heated probe to cut a 25cm wide hole through the ice. ocean – hundreds or thousands of feet below.

NASA considers sending swimming robots to habitable 'ocean worlds' of the solar system

A vent on the floor of the Northeast Pacific. A bed of tube worms feeding on chemosynthetic microbes covers the base. Credit: NOAA/PMEL

Once there, it would release up to about four dozen 12-inch-long, wedge-shaped microswimmers to explore. Their endurance would be much less than that of the 3.6-meter autonomous underwater vehicle of the famous name Boaty McBoatfacewith a range of 2,000 km that has already reached a cruise of more than 100 km under the Antarctic ice.

At this stage, Swim is just one of five “phase 2 studies” into a series of “advanced concepts” to be launched in NASA’s 2022 round. Innovative Advanced Concepts (NIAC) program† So there’s still a good chance that Swim will become a reality, and no full mission has been mapped out or funded.

NASA considers sending swimming robots to habitable 'ocean worlds' of the solar system

A Europa lander uses a probe to melt a hole through the ice, releasing a swarm of swimming robots. Conceptual impression, not to scale. Credit: NASA/JPL-Caltech

The microswimmers would communicate with the probe acoustically (via sound waves), and the probe would send its data via a cable to the lander on the surface. The study will test prototypes in a test tank in which all subsystems are integrated.

Any micro-swimmer might be able to explore only tens of meters from the probe, limited by their battery power and the range of their acoustic data link, but acting as a couple allowed them to map changes (in time or location) in temperature and salinity. They may even be able to detect changes in the turbidity of the waterwhich could indicate the direction to the nearest hydrothermal vent.

NASA considers sending swimming robots to habitable 'ocean worlds' of the solar system

Independent micro-swimmers deployed from a probe that has penetrated the ice crust of a moon. Not to scale. Credit: NASA/JPL

Power limitations of the micro swimmers may mean none of them can carry cameras (these need their own light source) or sensors that can specifically sniff out organic molecules. But nothing is excluded at this stage.

I think finding signs of hot water craters however, is a bull’s eye. The ocean after all, the floor would be many kilometers lower than the release point of the micro swimmer. But to be fair, locating vents is not explicitly suggested in the Swim proposal. To locate and examine the vents ourselves, we’ll probably need Boaty McBoatface in space. That said, swimming would be a good start.

Swarm of tiny swimming robots could search for life on distant worlds

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