In the 1970s, NASA’s Voyager probes passed through Jupiter’s system and snapped pictures of its largest moons, also known as the Galilean Moons.
These pictures and the data they gathered offered the first hints that a global ocean may be beneath Europa’s icy crust.
Moreover, planetary models indicated that Europa’s interactions with Jupiter’s powerful gravity could lead to tidal flexing in the moon’s interior.
In short, scientists learned that Europa could have all the necessary ingredients for life in its interior.
Since then, Europa has been considered a prime target in the search for life beyond Earth (astrobiology). A major focal point in this search is Europa’s surface plumes, which are the result of cryovolcanism.
By positioning a lander near an active cryovolcano or sending a probe to fly through one, scientists could examine these plumes for potential biosignatures.
In a new study led by NASA’s Jet Propulsion Laboratory (JPL), a team of scientists propose a framework for future missions to identify plumes emanating from Europa’s deep interior.
Elodie Lesage, a Postdoctoral Researcher in the Planetary Interiors and Geophysics Group at JPL, led the study. She was joined by multiple JPL colleagues, researchers from the University of Maryland, Brown University, the Laboratoire de Planétologie et Géosciences at Nantes Université, and the Planetary Environments Laboratory at the NASA Goddard Space Flight Center.
The paper describing their findings recently appeared in Nature Communications.
Currently, two astrobiology missions are headed for Europa: NASA’s Europa Clipper mission and the ESA’s JUpiter Icy Moon Explorer (JUICE). The former will arrive by 2030 and will begin observing Europa’s surface, probing its interior structure, and characterizing the surrounding space environment. The latter will reach Jupiter the following year, performing similar studies of Callisto, Ganymede, and Europa. Since Ganymede and Callisto are farther from Jupiter, they experience less tidal heating, resulting in less cryovolcanism.
Several notable surface features on Europa, including vapor plumes, domes, dark deposits, and flow-like features, are attributed to cryovolcanism. Similarly, lenticular features, double ridges, pits in impact craters, and chaos terrain are attributed to liquid brine reservoirs in Europa’s ice shell.
As the authors indicate, subsurface reservoirs are also likely to experience eruptions due to pressure exerted by plumes that have frozen back onto the surface.
Future missions could observe these features, providing new insights into Europa’s icy shell, habitability, and evolution.
Studying and characterizing erupted materials and subsurface liquid reservoirs could also pave the way for detailed astrobiology studies of Europa’s interior ocean. However, the team notes that:
“[E]ruptions from subsurface reservoirs may not represent their composition at the time of their formation because melting and freezing of trapped brines are expected to affect their chemical composition through salt rejection, entrapment, precipitation, and dissolution.”
What is needed, they add, is an improved understanding of the physicochemical properties and evolution of subsurface features. This includes how they are affected by ambient ice temperature and depth within the ~20–40 km (~12.5- 25 mi) ice shell. Building on previous research, the team presents CRYOLAVASAURUS, a publically available simulation model that studies the thermal, mechanical, compositional, and temporal evolution of ice shells and cryo-magma reservoirs, helping to identify signatures of past and present cryovolcanism.
Using this program, the team conducted simulations of briny water reservoirs in Europa’s ice shell, which allowed them to identify spectral, thermal, radar, and gravimetric data from cryovolcanism and reservoir eruptions. Their results indicate that it is possible to discriminate between eruptions caused by cryovolcanism and those from shallow liquid reservoirs based on combined measurements of the plume’s salinity and the surface temperature and ice shell thickness at the plume site.
This framework could inform future missions to Europa, including NASA’s Europa Clipper mission and the ESA’s JUpiter Icy Moon Explorer (JUICE). These missions are currently en route to Jupiter and will arrive by 2030 and 2031, respectively.
These missions will pave the way for additional astrobiology missions, which include a Europa Lander to study plume activity directly on the moon’s surface. The data returned by these missions could provide the first evidence that life does exist beyond Earth.
Written by Matthew Williams/Universe Today.
