New measurements from NASA's Juno spacecraft suggest that the ice covering Jupiter's moon Europa is thicker than previously thought, potentially isolating its subsurface ocean from the surface. This thick barrier may complicate efforts to detect life, though alternative nutrient transport mechanisms could still exist. The findings highlight challenges for upcoming missions like the Europa Clipper.
Jupiter's moon Europa has long been a prime candidate for hosting extraterrestrial life, thanks to its vast subsurface ocean of liquid water. However, recent analysis of data from the Juno spacecraft indicates that this ocean might be more isolated than scientists anticipated.
A team led by Steven Levin at the California Institute of Technology examined observations collected during Juno's close approach to Europa on 29 September 2022. The probe, orbiting Jupiter since 2016, passed within 360 kilometres of the moon and used its microwave radiometer to scan the surface. This instrument detected heat emissions from the ice shell, revealing its temperature profile and any irregularities.
The study estimates the ice thickness at around 29 kilometres on average, with a possible range of 19 to 39 kilometres—thicker than many prior models, which varied from under 10 kilometres to nearly 50 kilometres. Previous assumptions suggested that surface cracks, fissures, and pores could allow nutrients to exchange between the icy exterior and the ocean below. But the new data shows these features penetrate only hundreds of metres deep, with pores just a few centimetres wide.
"It means that the imperfections which we see with the microwave radiometer don’t go deep enough, and aren’t big enough, to carry much of anything between the ocean and the surface," Levin explained. He noted that while this limits direct transport, other pathways might still deliver essential materials, and unexplored regions of Europa could differ.
Experts like Ben Montet from the University of New South Wales point out that the robust ice could shield potential life forms over time but hinders human exploration. Helen Maynard-Casely from Australia's Nuclear Science and Technology Organisation added that without surface-ocean links, the ecosystem would rely solely on its original resources.
NASA's Europa Clipper mission, launched in 2024, is set to arrive in 2030 and provide clearer insights into the ice's structure. The research appears in Nature Astronomy (DOI: 10.1038/s41550-025-02718-0).
