A prototype of a robot designed to explore the subsurface oceans of icy moons glides through a pool at Caltech in September 2024, its reflection visible below the water's surface. The prototype was built at NASA's Jet Propulsion Laboratory in Southern California to demonstrate the feasibility of a mission concept called SWIM, short for Sensing With Independent Micro-swimmers.

SWIM envisions a swarm of dozens of self-propelled, cellphone-size robots exploring the waters of icy moons like Jupiter's Europa and Saturn's Enceladus. Delivered to the subsurface ocean by an ice-melting cryobot, the tiny robots would zoom away to look for chemical and temperature signals that could point to life.

The prototype used in most of the pool tests was about 16.5 inches (42 centimeters) long, weighing 5 pounds (2.3 kilograms). As conceived for spaceflight, the robots would have dimensions about three times smaller – tiny compared to existing remotely operated and autonomous underwater scientific vehicles.

In this image, commercial acoustic modules are mounted to the robot for testing: on top, one for communication, and on the bottom, one for underwater GPS. These devices were used during pool testing as stand-ins for what would be a novel wireless underwater acoustic communication system used both to transmit data between the cryobot and the swarm and to help each robot determine its position without the benefit of GPS.

Led by JPL, work on SWIM took place from spring 2021 to fall 2024. The project was supported by Phase I and II funding from NASA's Innovative Advanced Concepts program under the agency's Space Technology Mission Directorate. JPL is managed for NASA by Caltech in Pasadena, California.