How could the ingredients necessary for life reach the ocean hidden beneath the ice of Europa, this moon of Jupiter? This question has been driving scientists for years, because without an efficient vector, this promising environment would remain sterile despite its abundance of water.
Around Jupiter, Europa stands out for its icy and cracked surface. Beneath this shell lies a vast ocean of saltwater, possibly containing twice as much as all Earth's water. This ocean is deprived of light and oxygen, meaning any form of life would have to draw its energy from chemical reactions. Jupiter's intense radiation generates oxidizing substances on the surface, potentially catalytic for life, but their passage through the thick ice layer constitutes an obstacle.
Illustration of NASA's Europa Clipper probe flying over the icy moon Europa. Launched on October 14, 2024, it will reach Europa in April 2030.
Credit: NASA/JPL-Caltech The surface ice on Europa is perceived as rigid and not very mobile, forming a stagnant layer that blocks the passage of materials. Visible geological movements are mainly horizontal, such as fractures, offering few opportunities for vertical displacement. This configuration limits the descent of chemicals toward the ocean, and thus its seeding, except during major events.
A recent study, however, proposes a new mechanism: pockets of salt-rich ice, denser and more fragile, could detach and sink slowly through the ice shell. This process, called lithospheric foundering, recalls a terrestrial phenomenon where portions of the crust sink into the mantle. On Europa, it would allow for constant transport on geological timescales.
Computer simulations evaluated this idea with an ice shell about 18.6 miles (30 kilometers) thick. In different scenarios, the surface ice, slightly weakened, can descend in a few tens of thousands to a few million years. In the most favorable cases, it reaches the ocean in 30,000 years.
These results open up new perspectives for Europa's habitability. If this mechanism works, it would regularly bring oxidants and other essential compounds to the subsurface ocean, potentially supporting microbial life forms. This phenomenon thus makes this moon even more interesting for the search for extraterrestrial life in our Solar System.
To learn more, NASA's Europa Clipper mission, launched in 2024, will arrive around Jupiter in 2030. It will perform close flybys to study the depth of the ocean and assess the conditions inside. This mission could confirm if this transport process is effective.
Salty ice and its properties
On Europa, the ice is not pure; it contains salts and other impurities from the underlying ocean or surface interactions. These inclusions significantly modify its physical characteristics.
The presence of salt lowers the melting point of the ice, generating softer and more mobile areas. This facilitates deformation and displacement under the effect of Jupiter's gravitational forces, which continuously stretch and compress the moon.
These properties allow salty ice to play an active role in material transport. By becoming heavier, it can initiate downward movements through the icy shell, acting as a natural conveyor toward the depths.
Understanding the composition of the ice is therefore fundamental for modeling geological processes on Europa. Future space missions will seek to analyze these impurities to better predict internal dynamics and the chances of finding environments conducive to life.