The picture of NASA engineers crouching at the edge of a university swimming pool in Pasadena, California, with one of them holding a fishing rod attached to a 3D-printed plastic robot bobbing through the water below, has a subtly peculiar quality. A laptop, a pool, and a small machine that spells out “J-P-L” with its movements like a child bragging at a science fair—not a rocket launch, not a control room illuminated by mission screens. It sounds almost insignificant. It isn’t.
The robot in that pool is a prototype for a NASA project called Sensing With Independent Micro-swimmers, or SWIM. The plan is to launch a swarm of these palm-sized robots into the subterranean ocean of Europa, one of Jupiter’s moons, where miles of frozen crust are thought to conceal a massive saltwater sea. They would ride inside a nuclear-powered thermal drill that melts through the ice to get there. They would have no human pilot, no real-time guidance, and no rescue line once they were released into that dark, pressurized water. For now, that terrifying autonomy at Caltech is represented by the fishing rod.
The reasoning behind this endeavor is what makes it truly fascinating. The hadal zone, a region of deep trenches and troughs that descends to about 11 kilometers below the surface, is one of the most extreme regions of Earth’s own seas. If Europa’s ocean exists as scientists predict, it would have some physical characteristics in common with these areas. There are crushing pressures down there. No light is present. Life manages to find a way. Scientists’ preconceived notions about the possibility of life anywhere were subtly altered when they discovered hydrothermal vents in the deep ocean decades ago and discovered entire ecosystems surviving on chemical energy instead of sunlight. All of a sudden, Europa seemed less implausible.
Since then, NASA has been focusing on that parallel. In order to practice navigating in complete darkness without a tether, the agency has teamed up with the Woods Hole Oceanographic Institution to send autonomous vehicles like Orpheus into Pacific trenches. A smaller robot named Icefin slipped under the ice shelf in Antarctica, simulating, in a crude but practical manner, the kind of under-ice descent a future cryobot might try on Europa. These analogies are not perfect. There is no claim that the interior of a Jovian moon is the same as the ocean floor of Earth. However, close enough is sufficient for the time being.
Beyond their physical similarities, the oceans serve a practical purpose. It takes hours for radio signals to travel from Earth to Jupiter. Because any robot on Europa must constantly make its own decisions in an unfamiliar environment, real-time control is just not feasible. NASA teaches machines to think for themselves through deep ocean testing. The SWIM prototypes have already shown that they are capable of self-correction and self-directed search patterns. That might sound modest. It’s pretty significant for a gadget headed for a moon 500 million miles away.
Launched in October 2024, Europa Clipper won’t reach Jupiter until 2030. It will conduct 49 flybys to examine the moon from the outside, looking for indications that life may exist in the ocean below. The next generation is represented by SWIM and its offspring. Sending robots straight into that ocean to look for thermal and chemical biosignatures is the ultimate goal. Decades may pass before that occurs. Depending on financing, politics, and what Clipper discovers, it might take longer.
When you observe this from the outside, you are struck by how unglamorous most of it appears in reality. A fishing line. A Caltech pool. On a laptop, engineers are examining sensor logs. The contrast between “searching for life on the moons of Jupiter” and that picture is almost comical. However, that is typically the case. Engineers first calculated trajectories by hand for the moon landings. In parking lots in the California desert, Mars rovers were tested. Somehow, ordinary jobs have a way of taking people to remarkable places.
It is genuinely unclear if these tiny robots will ever discover anything in Europa’s ocean, be it a chemical trace, a temperature anomaly, or anything else. They might descend into nothing but icy, dark water and come back with information that indicates life did not flourish there. That result would also be important. They are still learning to swim, though, for the time being.
