Objectives for Europa Clipper

Planned future missions will be able to hunt for these ionic species via instruments in orbit or in-situ. The Europa Clipper mission, which is set to launch in 2023, will study Europa’s surface and interior through a series of fly-bys. Some of the onboard scientific instruments will be able to identify these components on the surface.

NASA is also considering a Europa lander mission, with the goal of sending a science platform to the surface of that moon to search for past and present life, and whether Europa could be habitable.

“A Europa lander mission is in formulation, but there is no current plan to drill [into the surface] all the way to the ocean,” says Choukroun. “Thus, until a future mission, whether it is a lander, rover, or submarine, is able to reach the ocean directly, our understanding of the ocean composition will only be through indirect physical measurements.”

As the authors write in their paper, “as exciting as these missions will be, they will only be able to access and interrogate the near surface … Our near-term ability to characterize the sub-surface ocean fluids will rely on their expression on the surface.”

Mixing salts

Jeffrey Kargel, who is a senior associate research scientist at the University of Arizona in the United States, says that the paper could direct aspects of future research on Europa’s oceans, and “serves to keep attention focused on the fact that the composition of the surface and the ocean are likely linked.” However, he says that a major weak-ness in the research is that the authors did not include mixed salts, such as bloedite, which is a hydrated sodium magnesium sulfate mineral.

“We don’t know the temperature of the ocean, so we cannot conclude that the temperature rules out such salts,” Kargel says. Such salts provide a close match to the near-infrared spectra recorded during the Galileo mission, according to research published in 1999.

In the paper, the authors acknowledge that their research only examines a few possible ions. Choukroun says that, “Depending on future results of geochemical models applied to Europa, we will refine this list of species that are predicted to be both somewhat abundant and important for biology.”

The study, “Insights into Europa’s ocean composition derived from its surface expression,” was published in the journal Icarus. The work was supported in part through the NASA Astrobiology Institute (NAI) element of the NASA Astrobiology Program.