Jupiter’s Europa seems frigid and barren at first glance, but this distant moon may be one of the best places for life to have evolved in the solar system. Beneath its frosty and imposing crust lies a liquid ocean where hydrothermal vents may provide a warm environment for life to thrive. Europa’s thick crust would likely also protect its hypothetical life from Jupiter’s deadly radiation, similar to how our atmosphere shields us from the Sun’s deadly rays. Red material scarring the moon’s surface suggests the presence of potentially life-nourishing salts and also a rough material called chaos terrain suggests the presence of warm subsurface water. Whether that water comes from the deep ocean or shallow pockets within the ice remains a mystery, but either source could be potentially habitable.
Given all these possibilities for discovering extraterrestrial life, NASA is keen on visiting the smallest of the four Galilean moons soon. In the upcoming years, NASA plans to launch its Europa Clipper mission, an orbiter that will make multiple flybys of the moon to map its surface and investigate its oceans. As it does so, the orbiter’s radar will penetrate the icy surface to reveal any pockets of liquid water below. Clipper will also make follow-up observations of the plume-like activity spotted by the Hubble Space Telescope in 2012.
But that’s not all in store for Europa–last year, NASA released the Europa Lander Study, a report outlining the scientific objectives for sending a lander to directly sample Europa’s surface after Clipper’s flybys had determined the best landing spots. Key members of the project met during the 48th Lunar and Planetary Sciences Conference last month to discuss NASA’s February update about the Clipper mission and to gather feedback from the scientific community about sending a follow-up spacecraft. According to the report, the plan is to launch the landing mission by 2024.
Ideally, the Europa Lander would follow soon after Clipper, allowing it to investigate relatively new terrain the satellite spots. But how closely became a subject of debate at the meeting. If Clipper spots a geyser dropping material on the surface that would degrade in less than a decade, a short duration between the two missions would be imperative. If on the other hand, the Europa Lander plans to sample material that is thousands or even millions of years old, then there isn’t such a rush to send it to Europa soon after Clipper.
Ensuring the Europa Lander’s safety also weighed into the debate about the timing between missions. If Europa’s terrain is constantly changing, a selected landing site could be significantly different by the time the Lander arrives. Although current observations don’t suggest the moon’s features move quite so rapidly, multiple scientists at the meeting encouraged the committee to examine the possibility.
During the meeting, Curtis Niebur, program scientist for NASA’s New Frontiers Program, suggested scientists begin pouring over existing images of Europa to identify potential landing sites. Clipper could then prioritize making detailed observations of those regions during its flybys, allowing scientists to determine their suitability. Without having detailed maps of Europa on hand, The Europa Lander Mission scientists may only have a handful of landing sites to choose from. What’s more, it’s possible that Clipper’s flybys may reveal that all of the current preliminary landing sites are unsuitable. Still, there are lots of places to look.
“Even though plumes are the sexiest material, there are plenty of other places,” said Kevin Hand, co-chair of the Europa Lander Mission. These include chaos terrains and salt-rich material. “I’m actually a big fan of us landing on a salt deposit that would be indicative not only of oceanic material but also possibly a concentration of any other materials that might be contained in that ocean material.”
To accomplish the Lander’s mission objective to assess Europa’s habitability, the science team recommended examining at least five samples a minimum of 10 centimeters beneath the surface, where potential life could be shielded from radiation. Three observations would be required to confirm any biosignatures, so five samples would allow the Lander two chances to come up empty. The team invented what they call ‘biosignature bingo,’ a list of complementary measurements that would need to be taken together to determine if life ever thrived on Europa. While NASA’s Viking mission in the 1970s focused on the hunt for activity as a source of life, the Europa Lander hopes to search for actual biosignatures. Hand urged fellow scientists to help nail down a biochemical definition of life, saying such a definition “deserves priority.”
Even if the Europa Lander finds no signs of life on the icy moon, the lack of discovery could yield important results.
“As exciting as a positive result for biosignatures would be, a negative result is also perhaps equally profound,” Hand said. “If we go to Europa and find that it is not just habitable but that it has many of the components we think are essential to the origin of life, and yet it does not have life, that helps inform us with regard to the origin of life here on Earth.”