Europa is one of the most fascinating places in the Solar System, and is considered to be at or near the top of the list of worlds to search for possible evidence of life. Beneath its outer ice crust lies a deep and dark salty ocean, thought to be quite to Earth's own oceans. Could that ocean be inhabited, even if just by microbes? Scientists want to know, and now a new proposal calls for a joint orbiter/lander mission between NASA and ESA (European Space Agency), to try to answer that question.
The proposal was presented on April 24 by Michel Blanc from France’s Research Institute in Astrophysics and Planetology in Toulouse, at the annual European Geosciences Union meeting in Vienna, Austria. Called the Joint Europa Mission, it could launch in the mid-2020s and would be designed specifically to look for signs of life.
“The whole idea is that if we think exploring Europa for life is important, it should be an international adventure,” Blanc said. “The ultimate goal is to get to the surface and look for biosignatures of life.”
The mission would have three major parts to it. First, the lander would be on the surface for at least 35 days and sample the surface material of ice and rock for potential biosignatures such as biomolecules and metabolites. The orbiter, meanwhile, would take laser, magnetic and seismic measurements of Europa for three months, to learn more about the interior of the moon, notably the composition and depth of the ocean. After it has finished its mission, the orbiter would crash into Europa's surface, gathering data on the composition of Europa’s very thin atmosphere as it descends; it would be able to identify any life-related gases such as carbon dioxide and oxygen. The lander would need to be thoroughly sterilized to avoid contaminating Europa's surface with any microbes from Earth. It would also need to be able to withstand the intense radiation in that region around Jupiter.
Altogether, the mission would be designed to last about six and a half years. Since Europa is so far away, it would take about five years just to get there. Since it is a joint mission, the lander would be designed by NASA and both NASA and ESA would build the orbiter and other components.
Another NASA mission to Europa has already been committed to, called Europa Clipper, but that probe will not land. Instead, it will make repeated close flybys of Europa and use a wide variety of instruments to study the moon's surface and interior. It would also launch sometime around the mid-2020s. Another possible lander mission has also been proposed to follow that one, but it would be separate from Europa Clipper.
The last time Europa was studied up close was by the Galileo mission in the late 1990s/early 2000s. Galileo provided incredible views of Europa's surface and was able to analyze the surface and interior to some extent, but was not equipped to look for life itself. It did, however, show that Europa's subsurface ocean is likely quite habitable by earthly standards.
The Hubble Space Telescope has also detected what appear to be water vapour plumes coming from Europa's surface, similar to those on Saturn's moon Enceladus, which also has a subsurface ocean. Although not 100% confirmed, the evidence is now very strong, and such plumes would present another way to search for life. An orbiter could analyze them directly to see what they contain, just as the Cassini spacecraft has done at Enceladus. Cassini is also not able to detect life directly, but it has shown that Enceladus' plumes contain water vapour, ice particles, salts, ammonia and organics. These plumes are now known to originate from the ocean below, so this gives scientists a good idea of what conditions are like in the ocean itself. More advanced orbiters could examine the plumes for biosignatures at both Enceladus and Europa. Otherwise, it might be necessary to drill through the ice, which would have to wait for an even more advanced future mission.
A new mission to Europa would be technologically challenging and expensive. This joint US/European proposal might be just the way to do it, to finally return to this intriguing world and, just perhaps, help to answer the long-standing question of whether life exists elsewhere in the Solar System.
“There’s great enthusiasm for this on both sides,” Jakob van Zyl, director for solar system exploration at NASA JPL, told New Scientist. “The budget request is now with the president.”