New data from NASA’s Juno spacecraft suggest that the icy shell of Jupiter’s moon Europa is significantly thicker than previously thought – potentially several tens of kilometers – complicating the search for liquid water and possible life beneath its surface.
The findings, published in Nature Astronomy, utilized microwave readings taken during a close flyby to map the temperature of Europa’s ice at varying depths. This “thermal scanning” allowed scientists to infer the structure of the ice shell and estimate the thickness of its most rigid layer, which acts as a barrier to the ocean below.
Europa, slightly smaller than Earth’s Moon, has long been considered a prime candidate in the search for extraterrestrial life due to strong evidence of a global ocean of saltwater hidden beneath its icy crust. This ocean is believed to be heated by tidal forces generated by Jupiter’s gravity. However, the thickness of the ice layer has remained a key uncertainty in assessing the potential for chemical exchange between the ocean and the surface, and the moon’s habitability.
The new measurements indicate that the conductive outer layer of Europa’s ice shell is substantially thicker than models had predicted. While the possibility of warmer, more deformable regions existing below this layer hasn’t been ruled out, the data suggest reaching the liquid water ocean would be a formidable technological challenge.
The observations also revealed that Europa’s surface isn’t a solid, inert block. The first few hundred meters of ice contain pores, small cracks, and voids that scatter microwave signals, indicating a fractured and constantly reorganizing crust. However, these imperfections don’t appear sufficient to facilitate a significant exchange of oxygen or nutrients between the surface and the deep ocean.
This finding challenges scenarios that envision a subsurface ocean regularly “fed” by processes occurring on the surface. According to NASA, Europa’s surface composition is primarily water ice, a discovery made through spectroscopic observations in 1972. Subsequent missions, including Voyager 1 and 2 in the 1970s, provided more detailed images of the moon’s surface.
The scale of Europa’s ice shell dwarfs that of Earth’s Antarctic ice, which reaches thicknesses of several kilometers. Comparing the two, scientists say, is akin to comparing a hill to a mountain range. This vast icy barrier underscores the challenges inherent in exploring subsurface oceans beyond Earth.
NASA’s upcoming Europa Clipper mission is designed to conduct dozens of flybys of Europa to further investigate its potential habitability. The Clipper will build upon these recent findings, studying the moon’s structure, ice, ocean, and surface chemistry in greater detail. The mission aims to determine if Notice locations beneath the surface that could support life, but the new data on ice thickness suggest that accessing those locations will be even more difficult than previously anticipated.
As of now, the question of whether Europa’s ocean is habitable remains open, protected by a formidable icy shield that will require significant technological advancements to penetrate.
