Jupiter’s moon Europa and its global ocean may currently have conditions suitable for life. Scientists are studying processes on the icy surface as they prepare to explore.“The radiation that bombards Europa’s surface leaves a fingerprint,” said Kevin Hand, project scientist for the Europa Lander mission in a 2018 study. “If we know what that fingerprint looks like, we can better understand the nature of any organics and possible biosignatures that might be detected with future missions, be they spacecraft that fly by or land on Europa.”
What Lies Beneath?
“If we want to understand what’s going on at the surface of Europa and how that links to the ocean underneath, we need to understand the radiation,” said Tom Nordheim, research scientist at NASA’s Jet Propulsion Laboratory (JPL), in 2018. “When we examine materials that have come up from the subsurface, what are we looking at? Does this tell us what is in the ocean, or is this what happened to the materials after they have been radiated?”
It’s easy to see the impact of space debris on our Moon, where the ancient, battered surface is covered with craters and scars, reports NASA’s Jet Propulsion Laboratory (JPL). Jupiter’s icy moon Europa withstands a similar trouncing – along with a zap of hyper-intense radiation. As the uppermost surface of the icy moon churns, material brought to the surface is zapped by high-energy electron radiation accelerated by Jupiter’s magnetic field.
NASA-funded scientists are studying the cumulative effects of small impacts on Europa’s surface as they prepare to explore the distant moon with the Europa Clipper mission and study the possibilities for a future lander mission. Europa is of particular scientific interest because its salty ocean, which lies beneath a thick layer of ice, may currently have conditions suitable for existing life. That water may even make its way into the icy crust and onto the moon’s surface.
In this zoomed-in image of Europa’s surface, captured by NASA’s Galileo mission, the thin, bright layer, visible atop a cliff in the center shows the kind of areas churned by impact gardening. NASA/JPL-Caltech
Impact Gardens Tens of Million Years Old
New research and modeling estimate how far down that surface is disturbed by the process called “impact gardening.” The work, published July 12 in Nature Astronomy, estimates that the surface of Europa has been churned by small impacts to an average depth of about 12 inches (30 centimeters) over tens of millions of years. And any molecules that might qualify as potential biosignatures, which include chemical signs of life, could be affected at that depth.
That’s because the impacts would churn some material to the surface, where radiation would likely break the bonds of any potential large, delicate molecules generated by biology. Meanwhile, some material on the surface would be pushed downward, where it could mix with the subsurface.
“If we hope to find pristine, chemical biosignatures, we will have to look below the zone where impacts have been gardening,” said lead author Emily Costello, a planetary research scientist at the University of Hawaii at Manoa. “Chemical biosignatures in areas shallower than that zone may have been exposed to destructive radiation.”
“Over time,” Costello told The Daily Galaxy, “impact gardening on Europa exposes a column of material to the uppermost surface, where radiation can have chemically altering effects.
“This new paper helps tell us where to look for material that will have been less altered by surface radiation processing, but our model does not provide any more information about what a chemical biosignature processed by radiation would look like,” Dr. Cynthia B. Phillips, Europa Project Staff Scientist at JPL told The Daily Galaxy.
While impact gardening has long been understood to be likely taking place on Europa and other airless bodies in the solar system, the new modeling provides the most comprehensive picture yet of the process. In fact, it is the first to take into account secondary impacts caused by debris raining back down onto Europa’s surface after being kicked up by an initial impact. The research makes the case that Europa’s mid- to high-latitudes would be less affected by the double whammy of impact gardening and radiation.
“This work broadens our understanding of the fundamental processes on surfaces across the solar system,” said Phillips, a co-author of the study. “If we want to understand the physical characteristics and how planets in general evolve, we need to understand the role impact gardening has in reshaping them.”
While Europa Clipper is not a life-detection mission, says the JPL scientist, it will conduct detailed reconnaissance of Europa and investigate whether the icy moon, with its subsurface ocean, has the capability to support life. Understanding Europa’s habitability will help scientists better understand how life developed on Earth and the potential for finding life beyond our planet.
Image credit: NASA/JPL-Caltech and Goddard Space Flight Center