In this illustration, a NASA space exploration concept called Probe using Radioisotopes for Icy Moons Exploration, or PRIME, is depicted being deployed from a lander on the frozen surface of an ocean world. The nuclear-powered probe, also called a cryobot, glows red in the subsurface ocean while connected via a communications tether to a lander miles above on the icy crust. Wedge-shaped, cellphone-size robots – another concept, called Sensing With Independent Micro-Swimmers, or SWIM – are seen traveling off underwater to conduct science beyond the heat of the probe.

About four dozen SWIM robots would fit compactly within a cryobot like PRIME, which would take years to tunnel through the frozen crust.

Both PRIME and SWIM are in development at NASA's Jet Propulsion Laboratory in Southern California.

PRIME is one of several cryobot concepts being developed through the agency's Scientific Exploration Subsurface Access Mechanism for Europa (SESAME) program, as well as through other NASA technology development programs.

SWIM received funding in 2021 and 2022 through the NASA Innovative Advanced Concepts (NIAC) program. Run by the agency's Space Technology Mission Directorate, NIAC fosters exploration by funding early-stage studies to evaluate technologies that could support future aeronautics and space missions.