Map depicting radiation on Europa could help direct upcoming missions
Jupiter’s moon Europa, which likely hosts a global subsurface ocean, is one of the most promising locations for finding microbial life beyond Earth in our solar system. However, its parent planet, Jupiter, bombards the moon with radiation that could seriously diminish its habitability.
To guide future missions in the search for biosignatures or signs of life on the large moon, a team of scientists led by Tom Nordheim, a research scientist at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, produced a comprehensive map depicting radiation levels on Europa and beneath its surface.
To create the map, the researchers used data returned by NASA’s Galileo mission, which 20 years ago revealed compelling evidence of a salty ocean beneath the moon’s icy shell, along with electron measurements of Europa taken by NASA’s Voyager 1 spacecraft when it flew by the Jupiter system in 1979.
Among the data collected by Galileo is evidence that water from the underground ocean at times travels to Europa’s surface, carrying ocean materials with it.
Once on the surface, these materials may be significantly altered or even destroyed when blasted with radiation from the giant planet.
If a future probe discovers altered or destroyed materials on the surface, scientists will be hard pressed to determine whether these materials are characteristic of those in the subsurface ocean or whether they were broken down only upon contact with radiation after arriving on the surface.
In their study, Nordheim’s team found that radiation levels on Europa vary by location, with the highest levels found in regions near the equator and the lowest levels found near the poles. More than half the moon is in the high-radiation zones.
On the map, the scientists marked the high-radiation zones with ovals.
“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,” Nordheim emphasized. “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?”
Chris Paranicas of the Johns Hopkins University Applied Physics Laboratory (JHUAPL) in Laurel, Maryland, noted, “This is the first prediction of radiation levels at each point on Europa’s surface and is important for future Europa missions.”
The potentially deleterious effects of radiation on habitability are a similar concern among scientists searching for habitable exoplanets orbiting active red dwarf stars.
In addition to measuring radiation levels on Europa’s surface, Nordheim’s team also created 3D models of Europa showing how deeply the radiation penetrates beneath the surface. Knowing this will be crucial in guiding scientists as to how far they need to drill or dig beneath the surface to find signs of life.
The researchers explored this question in a laboratory by subjecting amino acids, the building blocks for proteins and the simplest biosignatures, to the various radiation levels found on Europa.
They found that in regions with the highest radiation levels, a probe would have to drill between four and eight inches (10 and 20 cm) to find completely preserved biosignatures, the basic building blocks for life. In regions with the lowest radiation levels, a probe would have to drill only 0.4 inches (one cm) to find pristine biosignatures.
“The radiation that bombards Europa leaves a fingerprint,” said study participant Kevin Hand, who serves as project scientist for a proposed NASA project known as the Europa Lander. “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.”
Another spacecraft, NASA’s Europa Clipper, scheduled for launch as early as 2022, is being prepared to conduct around 45 close flybys of Europa. Based on the new radiation map, the mission team plans to fly over the low-radiation areas.
A paper on Nordheim’s team’s study has been published in the journal Nature Astronomy.
Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.