Summary
nasa’s juno spacecraft used its Microwave Radiometer (MWR) during a September 29, 2022 flyby (within ~360 km) of Jupiter’s moon europa to produce the first measurement that discriminates between thin- and thick-shell models of Europa’s ice crust. The study, published in Nature Astronomy (Dec 17, 2025), estimates Europa’s cold, rigid, conductive ice shell averages about 29 km (18 miles) thick in the observed region. The finding has direct implications for ocean-worlds habitability research and provides critical context for europa-clipper (arriving 2030) and ESA’s juice mission (arriving 2031).
Key Claims
- Juno MWR provides the first observational constraint distinguishing thin-shell (<1 km) from thick-shell (tens of km) models of Europa’s ice; the data favor a thick shell averaging ~29 km for a pure water-ice conductive layer
- If a warmer convective inner layer exists beneath the conductive crust, total shell thickness would be even greater
- If the ice contains modest dissolved salt (as some models suggest), the thickness estimate decreases by about 5 km (~3 miles)
- MWR detected near-surface scatterers — cracks, pores, and voids a few inches in diameter extending to hundreds of feet deep — that scatter microwaves
- The small size and shallow depth of these scatterers make them unlikely to be significant pathways for transporting surface oxygen and nutrients to Europa’s subsurface ocean
- A thick ice shell implies a longer route for oxygen and nutrient transfer from the surface to the ocean, which is relevant to Europa’s habitability assessment
Notable Quotes
“The 18-mile estimate relates to the cold, rigid, conductive outer-layer of a pure water ice shell. If an inner, slightly warmer convective layer also exists, which is possible, the total ice shell thickness would be even greater.” — Steve Levin, Juno project scientist, NASA JPL
“How thick the ice shell is and the existence of cracks or pores within the ice shell are part of the complex puzzle for understanding Europa’s potential habitability. They provide critical context for NASA’s Europa Clipper and the ESA Juice spacecraft.” — scott-bolton, Juno principal investigator, Southwest Research Institute