Europa, one of Jupiter’s 95 moons, is encased in a shell of water ice, and researchers have just re-estimated its thickness.
In 2022, NASA’s Juno spacecraft zoomed close to the moon’s surface. Information from this flyby has led researchers to conclude that, in the area where the flyby collected data, the moon’s layer of ice is on average around 18 miles thick (29 kilometers). The new measurement, along with other new information about certain ice features, could inform our understanding of the moon’s potential habitability.
A 2022 flyby
“The 18-mile estimate relates to the cold, rigid, conductive outer-layer of a pure water ice shell,” Steve Levin, Juno project scientist and co-investigator from NASA’s Jet Propulsion Laboratory (JPL), said in an agency statement. “If an inner, slightly warmer convective layer also exists, which is possible, the total ice shell thickness would be even greater. If the ice shell contains a modest amount of dissolved salt, as suggested by some models, then our estimate of the shell thickness would be reduced by about 3 miles [4.8 km].” The JPL manages the Juno mission.
Juno recorded this data on September 29, 2022, using its Microwave Radiometer (MWR). The flyby took the spacecraft within roughly 220 miles (360 km) of Europa, with the MWR gathering information from around 50% of its surface. In the search for other habitable worlds within our solar system, scientists are particularly interested in Europa, which is thought to have a salty ocean (which might hold the ingredients for life). Learning more about the ice shell above it helps us figure out what goes on beneath the moon’s surface and how likely it is to host an environment where life could exist.
Shallow ice features
Furthermore, Juno’s flyby also identified features called “scatterers,” such as cracks, pores, and voids, in ice close to the surface—traits that, as the name suggests, scatter the MWR’s microwaves as they bounce off the ice. The researchers theorize them to be at most a few inches in diameter.
The team’s estimate of a thick shell suggests that oxygen and nutrients would have to embark on a longer journey between the moon’s surface and its potential ocean, and the study indicates that the scatterers are probably not an important route within this context. Understanding this connection could be important for future research into Europa’s habitability.
Habitability, habitability, habitability
“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,” explained Scott Bolton, Juno’s principal investigator from the Southwest Research Institute. He and Levin are co-authors of a study published in December in the journal Nature Astronomy. “They provide critical context for NASA’s Europa Clipper and the ESA (European Space Agency) Juice (JUpiter ICy moons Explorer) spacecraft—both of which are on their way to the Jovian system.”
So, Europa’s icy crust is thicker than we thought. And with each new data point, scientists are getting a little closer to unlocking the moon’s hidden secrets. Eventually, we may finally solve the mystery of whether life ever existed on this fascinating frozen world—and whether it still might today.
