Juno’s New Data Suggests Europa’s Ice Shell is Thicker Than Previously Thought, Complicating the Search for Life

Recent analysis of data from NASA’s Juno probe indicates that the ice shell of Jupiter’s moon Europa may be significantly thicker than many previous models suggested, a finding that has profound implications for the moon’s potential habitability. The spacecraft, which has been orbiting Jupiter since 2016, uses its extended mission to study the gas giant’s major moons, including Europa, Callisto, and Ganymede. Europa is of particular scientific interest due to strong evidence of a vast liquid water ocean beneath its surface, making it a prime candidate in the search for extraterrestrial life.

A Microwave Peek Beneath the Ice

During a close flyby on September 29, 2022, the Juno spacecraft passed just 360 km (about 220 miles) from Europa’s surface. In this brief window, it activated its Microwave Radiometer (MWR), an instrument originally designed to probe Jupiter’s deep atmosphere. This marked the first time such technology was used to study Europa’s icy crust, allowing scientists to measure the temperature at various depths beneath the surface. The MWR data enabled researchers to distinguish between competing theories on the shell’s thickness, which ranged from less than a kilometer to tens of kilometers.

The Thick Shell Conundrum

The calculations based on the MWR data revealed that the cold, rigid outer layer of the ice shell is approximately 29 km (about 18 miles) thick on average. Steve Levin, a Juno project scientist at NASA’s Jet Propulsion Laboratory, noted that this estimate pertains only to the conductive outer layer. If a warmer, convective ice layer exists beneath it, the total thickness of the shell could be even greater. This result favors the “thick shell” models and presents a significant challenge for the moon’s potential to harbor life. A thicker barrier makes it more difficult for chemical compounds essential for life, such as oxygen and other nutrients produced on the surface by radiation, to reach the subsurface ocean.

Cracks and Voids: A Complex Interior

Beyond measuring thickness, the Juno data also shed light on the internal structure of the ice. The MWR detected the presence of “scatterers”-irregularities like cracks, pores, and voids within the ice that disperse microwave radiation. These features appear to extend hundreds of feet down from the surface but are estimated to be only a few inches in diameter. According to models, their small size and shallow depth make them an unlikely pathway for transporting vital nutrients from the surface to the ocean below. This complex internal structure paints a picture of a dynamic and fractured, yet largely impenetrable, ice shell.

A Look to the Future: Europa Clipper and JUICE

Juno’s findings provide a crucial foundation for upcoming missions specifically designed to investigate Jupiter’s icy moon. NASA’s Europa Clipper, which launched in 2024 and is set to arrive in 2030, will perform dozens of close flybys to study the moon’s habitability in unprecedented detail. Similarly, the European Space Agency’s JUICE (Jupiter Icy Moons Explorer) mission will also observe Europa as part of its broader survey of the Jovian system. Scott Bolton, Juno’s principal investigator, stated that understanding the ice shell’s thickness and structure is part of the complex puzzle of Europa’s potential habitability and that Juno’s data provides critical new information for these future missions. These dedicated probes will use instruments like ice-penetrating radar to map the shell and search for subsurface water, building on the new constraints provided by Juno.