While scientists have debated for decades about the thickness of Europa's icy shell, Jupiter's icy moon, a new study finally provides a clear answer. This is an important result for estimating whether extraterrestrial organisms could inhabit its subsurface ocean.
To achieve this result, NASA researchers relied on data collected by the Juno space probe. The Microwave Radiometer instrument allowed for analysis of the surface during a close flyby in 2022. The calculations thus reveal a thickness of about 20 miles (30 km) for the rigid, cold part of the ice.
Europa's surface shows signs of geological activity, with salt and carbon dioxide that could come from a subsurface ocean.
Credit: NASA/ESA/K. Retherford/SWRI
This discovery ends a long-standing debate between two opposing theories. Some specialists estimated the crust was very thin, on the order of 1 mile (1.6 km), while others envisioned tens of kilometers. Juno's measurement aligns with the second hypothesis. This information thus allows for a better understanding of the conditions inside the moon.
The team specifies, however, that this thickness could change slightly depending on the exact composition of the ice. If it contains dissolved salt, it could be reduced by about 3 miles (5 km). Furthermore, a warmer, moving internal layer could exist beneath, which would increase the total thickness of the shell.
This thick ice represents a potentially significant barrier to life. Essential elements like oxygen and nutrients, which could come from the surface, would have a longer and more difficult path to reach the liquid ocean hidden below. It is therefore a major parameter to consider when assessing Europa's habitability.
The results of this study come at an opportune time. Two space missions are currently heading towards the Jovian system to study Europa up close. NASA's Europa Clipper probe will arrive around 2030, followed by the European Space Agency's Juice mission. These new data will provide a useful framework for interpreting their future observations.
This advancement was made possible by the meticulous analysis of the radiometer's measurements. The details of the study were published on December 17th in the journal
Nature Astronomy. It marks a notable step in our exploration of the Solar System and in the quest to identify places where life could exist beyond our planet.
What will the Europa Clipper mission look for?
The Europa Clipper mission is a major NASA project currently en route to Jupiter, and its primary objective is to assess, starting in 2030, the habitability of the moon Europa by studying its subsurface ocean, icy crust, and space environment. It will not land but will perform numerous close flybys.
The probe carries a suite of specialized instruments. High-resolution cameras will map the surface to identify future sampling sites. An ice-penetrating radar will probe the internal structure down to several kilometers in depth, notably searching for pockets of liquid water.
Other instruments will analyze the chemical composition of water vapor plumes that might escape through cracks. They will look for organic molecules or chemical signatures that could indicate biological activity. A magnetometer will study the interaction between the ocean and Jupiter's magnetic field.
Juno's data on the ice thickness will help calibrate and interpret the measurements from Clipper's radar. This mission represents a coordinated effort to answer one of the big questions in space exploration: Are there environments suitable for life elsewhere in our Solar System?