Europa’s Enigmatic Ice: Juno’s Insight and What Lies Beneath

Juno’s Revelatory Data on Europa

New data from the Juno spacecraft has allowed for an assessment of the ice thickness concealing Europa’s subsurface ocean, a crucial element in the scenarios for searching for life in the subsurface ocean. The solar-powered probe provided new information on the thickness and structure of the ice crust, using a microwave radiometer (MWR). NASA scientists determined that the crust’s thickness averages around 29 kilometers in the region observed during the flyby of Europa in 2022. Previous estimates ranged from less than one kilometer to tens of kilometers. Europa, which is slightly smaller than the Moon, is a priority object in the search for extraterrestrial life. Under its icy crust is believed to be a salty ocean containing the elements necessary for life. Determining the characteristics of the ice crust, including its thickness, is essential for understanding the potential habitability of the moon.

The MWR instrument was originally intended for studying the atmosphere of Jupiter below the cloud cover but turned out to be useful for studying the icy and volcanic moons of the gas giant. On September 29, 2022, Juno approached the surface of Europa at a distance of about 360 kilometers. During the flyby, the MWR collected data on approximately half of the moon’s surface, measuring temperatures at various depths.

“The measurement of 29 kilometers is based on a scenario with a cold and rigid outer ice shell composed of pure water ice,” stated Juno project manager Steve Levin. “If there is an internal, warmer convective layer, the total thickness of the ice crust could be even greater.”

If the ice crust contains a small amount of dissolved salt, as leading models suggest, the crust thickness could decrease by about 5 kilometers. Previous MWR data also provided new information about the composition of the ice just below Europa’s surface. The instrument detected the presence of “scatterers”-inhomogeneities in the near-surface ice, such as cracks, pores, and cavities that scatter microwaves reflected from the ice. The size of these “scatterers” does not exceed 10 cm in diameter, and they extend to a depth of up to 30 meters beneath Europa’s surface. The small size and shallow depth of these structures, according to models, suggest that they are unlikely to be a significant pathway for the transfer of oxygen and nutrients from Europa’s surface into its salty ocean.

The information obtained is important for the missions Europa Clipper (NASA, arriving at Jupiter in 2030) and Juice (European Space Agency, arriving at Jupiter in 2031), which are heading to the Jupiter system. Furthermore, advances in technology have enabled more comprehensive exploration, improving the potential for detecting biological signatures.

On February 25, Juno will complete its 81st flyby of Jupiter.