Europa's ocean may be harder to reach than thought

New research suggests that Jupiter's moon Europa, long considered one of the best candidates for hosting extraterrestrial life, may have a subsurface ocean that is far more isolated than previously believed. A study published in the journal Nature indicates that Europa's thick icy shell likely prevents significant exchange between the deep ocean and the moon's surface, complicating efforts to detect signs of life.

The findings affect scientists planning future missions to Europa, particularly NASA's Europa Clipper, which aims to study the moon's ice shell and ocean. If the ocean is sealed off from the surface, it would be harder to sample ocean material without drilling deep into the ice, making it more challenging to search for biosignatures.

This matters because Europa's subsurface ocean is considered one of the most promising places in the solar system to find life beyond Earth. The ocean, kept liquid by tidal heating, contains more water than all of Earth's oceans combined. If it is isolated from the surface, any life there would have evolved independently, but sampling it would require penetrating tens of kilometers of ice.

The study, published in Nature, used computer models to simulate fluid flow within Europa's ice shell. The researchers found that the ice shell is likely too thick and cold to allow significant vertical mixing between the ocean and the surface. The study did not provide specific numbers for the ice thickness, but previous estimates range from 15 to 25 kilometers.

Earlier research had suggested that Europa's ice shell might be dynamic, with plumes of water vapor erupting from the surface, as observed by the Hubble Space Telescope in 2012 and 2016. However, the new study argues that such plumes are likely rare and may not originate from the deep ocean, but rather from shallow pockets of liquid water within the ice.

Looking ahead, the Europa Clipper mission, scheduled to launch in 2024, will conduct detailed reconnaissance of Europa's ice shell and ocean. The new findings suggest that the mission may need to focus on areas where the ice is thinnest or where surface features indicate recent geological activity, to maximize the chances of detecting ocean material. If the ocean is truly isolated, future lander missions would require advanced drilling technology to access it.