NASA’s Juno Reveals Key Insights into Europa’s Ice Shell and Its Potential for Life

Recent observations made by NASA’s Juno orbiter have shed light on the intricate structure of Europa’s ice shell, essential for understanding the potential of this enigmatic moon to harbor life. Since Juno entered Jupiter’s orbit in July 2016, it has been instrumental in studying not only Europa but also Jupiter’s other icy moons, Ganymede and Callisto. The findings, derived from new measurements taken by Juno’s Microwave Radiometer, are the first to firmly differentiate between existing theories regarding the ice shell’s thickness.

Europa, which is slightly smaller than Earth’s moon, features a subsurface ocean that many scientists consider one of the most promising candidates for extraterrestrial life. Gaining insight into the composition and thickness of its ice layer is vital in unraveling the moon’s geological and potentially biological secrets.

Using its Microwave Radiometer, tailored for examining Jupiter’s atmosphere beneath its vibrant cloud cover, Juno can also gather data during moon flybys. This sophisticated instrument is equipped with six antennas designed to capture electromagnetic waves at various microwave frequencies. On September 29, 2022, during a flyby that brought it within 360 kilometers of Europa’s surface, Juno successfully collected temperature data from different depths beneath the moon’s icy exterior. The results indicated that, on average, Europa’s ice shell measures around 29 kilometers—or approximately 18 miles—thick.

According to lead author Steve Levin, a project scientist with Juno at NASA’s Jet Propulsion Laboratory, this thickness estimate pertains to a rigid, cold outer layer of pure water ice. If there exists a warmer, convective layer below, the total thickness could be even greater. Conversely, models proposing the presence of salt in the ice could decrease the thickness estimate by about three miles. The implications are significant; if the ice shell is particularly thick, this would demand a longer journey for life-sustaining materials to reach the ocean beneath.

Moreover, the data also unveiled intriguing irregularities in Europa’s surface, including cracks and voids that can scatter microwaves—functioning somewhat like ice cubes refracting light. While earlier hypotheses suggested these features might act as conduits to the ocean below, the latest findings indicate that they may not extend deep enough to connect with the subsurface waters.

Understanding the ice shell’s thickness and the structure within it contributes greatly to the ongoing discourse about Europa’s habitability. This knowledge is essential for NASA’s upcoming Europa Clipper mission, as well as ESA’s Jupiter Icy Moons Explorer, or JUICE, both of which are set to further investigate the Jovian system. Scott Bolton, the principal investigator for Juno, noted that the characteristics of Europa’s ice shell are crucial for assessing its potential to support life.

Though Juno is scheduled to conclude its second mission extension in September 2025, it continues to perform flybys of Jupiter, with its latest encounter occurring in January. The forthcoming Europa Clipper, designed specifically to examine Europa’s ocean, is slated to launch in October 2024, while JUICE was launched in April 2023. The groundbreaking ice measurements reported will play a vital role in shaping the scientific goals of these missions.

Recent research findings by Levin and colleagues were published in Nature Astronomy on December 17, adding to the growing body of knowledge about one of the solar system’s most intriguing bodies.