Juno Spacecraft Measures Europa's Ice Shell

Data from NASA’s Juno mission have provided new insights into the thickness and subsurface structure of the icy shell encasing a subsurface liquid ocean within Jupiter’s moon Europa. Using the spacecraft’s Microwave Radiometer (MWR), mission scientists determined that the shell averages about 18 miles (29 kilometers) thick in the region observed during Juno’s 2022 flyby of Europa.

The thick shell suggested by the MWR data implies a longer route that oxygen and nutrients would have to travel to connect Europa’s surface with its subsurface ocean. Understanding this process may be relevant to future studies into Europa’s habitability.

“The thickness of Europa’s icy shell and the existence of cracks or pores within the ice shell are two crucial pieces of the puzzle for understanding Europa’s potential habitability,” said SwRI’s Dr. Scott Bolton, the principal investigator of Juno. “They provide critical new information relevant to the further study of Europa by NASA’s Europa Clipper and the European Space Agency’s Juice (Jupiter Icy Moons Explorer) — both on their way to the Jovian system.”

The new constraints on the ice thickness in the near-surface icy crust were published on Dec. 17, 2025, in the journal Nature Astronomy. Previous models have suggested the ice shell could be less than half a mile to tens of miles thick.

Slightly smaller than Earth’s moon, Europa is one of the solar system’s highest-priority science targets for investigating habitability. Evidence suggests that the ingredients for life may exist in a vast saltwater ocean believed to exist beneath its ice shell. Juno’s determination of the ice shell thickness and the subsurface characteristics provides fundamental new constraints for understanding the moon’s structure, internal processes and potential habitability.

The MWR instrument was invented and designed by SwRI’s Bolton to investigate Jupiter’s atmosphere below the cloud tops. The novel instrument has also proven invaluable for studying Jupiter’s ice-covered and volcanic moons as well.

“The 18-mile estimate relates to the cold, rigid, conductive outer layer of a pure water ice shell,” said Steve Levin, Juno project scientist and co-investigator from NASA’s Jet Propulsion Laboratory in Southern California, which manages the mission. “If an inner, slightly warmer (convective) layer also exists, which is possible, the total ice shell thickness would be even greater.”

The MWR data also provide new insights into the makeup of the ice just below Europa’s surface. The instrument revealed the presence of irregularities in the near-surface ice. These cracks, pores and voids scatter the instrument’s microwaves reflecting off the ice, similar to the way bubbles in ice cubes scatter visible light. These imperfections are estimated to be no bigger than a few inches in diameter and appear to extend to depths of hundreds of feet below Europa’s surface.

The small size and shallow depth of these features, as modeled in this study, suggest they are unlikely to be a significant pathway for oxygen and nutrients to travel from Europa’s surface to its salty ocean.

For more information, visit Planetary Science.