Juno finds Europa's ice shell averages about 18 miles thick

Data from NASA's Juno Microwave Radiometer show Europa's ice shell averages about 18 miles (29 km) thick in the region observed during a Sept. 29, 2022 flyby, and reveal small near-surface irregularities extending to depths of hundreds of feet.

NASA's Juno mission has provided new measurements of the thickness and near-surface structure of Europa's icy shell. The spacecraft's Microwave Radiometer (MWR) made the observations during a close flyby on Sept. 29, 2022. Scientists report the shell averages about 18 miles (29 kilometers) thick in the region sampled. The result was published Dec. 17 in Nature Astronomy. Key findings: - MWR data from the Sept. 29, 2022 flyby indicate an average ice-shell thickness of about 18 miles (29 km) in the region observed. - The 18-mile estimate applies to the cold, rigid, conductive outer layer; an inner, warmer convective layer would increase total thickness, while a modest amount of dissolved salt could reduce the estimate by about 3 miles, as noted by mission scientists. - The instrument detected "scatterers" — small irregularities such as cracks, pores and voids — that are modeled as no larger than a few inches across and reaching depths of hundreds of feet below the surface. - Modeling in the study suggests these small, shallow features are unlikely to serve as a major pathway for oxygen and nutrients from Europa's surface to its subsurface ocean. - MWR was designed to probe Jupiter's atmosphere but has been used successfully to study icy and volcanic moons; during the flyby it collected subsurface data over roughly half of Europa's surface. Summary: The Juno MWR measurement narrows the range of previously competing thin- and thick-shell models and adds detail about near-surface structure. A thicker conductive outer layer implies a longer route for surface-derived oxygen and nutrients to reach the subsurface ocean, which is relevant to assessments of Europa's potential habitability. The findings also provide context for upcoming missions, including NASA's Europa Clipper (arriving in 2030) and ESA's Juice (arriving the year after). Juno will continue science operations with an additional flyby on Feb. 25.