Europa's ice shell is about 18 miles thick, NASA study finds

Data from Juno's 2022 flyby and its Microwave Radiometer indicate the outer, rigid layer of Europa's ice shell is about 18 miles (29 km) thick in the surveyed region, and small near-surface scatterers such as cracks and pores were detected.

Researchers report a new estimate for the thickness of Europa's ice shell based on data from NASA's Juno spacecraft. The spacecraft passed about 220 miles (360 km) above the moon on September 29, 2022, and collected data with its Microwave Radiometer. Analysis focuses on the cold, rigid, conductive outer layer of a pure water ice shell. The work is relevant to questions about Europa's subsurface ocean and potential habitability. Key findings: - The estimated thickness of the outer, rigid water-ice layer is about 18 miles (29 km) in the region surveyed. - If an inner, slightly warmer convective layer exists, the total shell would be thicker; a modest amount of dissolved salt would reduce the estimated thickness by about 3 miles (4.8 km). - Data were recorded by Juno's Microwave Radiometer during the September 29, 2022 flyby, when the spacecraft passed within roughly 220 miles (360 km) and sampled about 50% of Europa's surface. - The flyby identified small near-surface "scatterers"—cracks, pores and voids—likely no larger than a few inches, which alter microwave reflections. - A thicker rigid shell implies that oxygen and nutrients would need a longer route between the surface and any subsurface ocean, and the study indicates scatterers are probably not a major transport pathway. Summary: A thicker outer ice shell changes expectations about how surface materials might reach Europa's subsurface ocean, with the observed small scatterers unlikely to form an efficient pathway. The study was published in December in Nature Astronomy and provides context for future observations. NASA's Europa Clipper and ESA's Juice missions are on their way to the Jovian system to gather more detailed data.