In the coming decade, NASA and the ESA will be sending two dedicated missions that will explore Jupiter’s moon Europa. These missions are known as the Europa Clipper and the JUpiter ICy moons Explorer (JUICE) missions, which will fulfill a dream that has been decades in the making – searching for possible evidence of life inside Europa. Since the 1970s, astronomers have theorized that this satellite contains a warm-water ocean that could support life.

The case for life in Europa has only been bolstered thanks to multiple flybys and observation campaigns that have been mounted since. According to new research led by the University of Hawaii at Manoa, the best way to look for potential signs of life (aka. biosignatures) would be to analyze small impact craters on Europa’s surface. These patches of exposed subsurface ice could point the way towards life that might exist deeper in the moon’s interior.

Speculation about the possible existence of an interior ocean in Europa began in 1979 after the Voyager 1 and 2 missions flew past Jupiter and its moons on their way to the outer Solar System. With data obtained by the Galileo and New Horizons spacecraft and the Hubble Space Telescope have provided additional indications, which included how it interacted with Jupiter’s magnetic field, tidal models, surface features, and plume activity.

Radiation from Jupiter can destroy molecules on Europa’s surface. Material from Europa’s ocean that ends up on the surface will be bombarded by radiation, possibly destroying any biosignatures, or chemical signs that could imply the presence of life. Credit: NASA/JPL-Caltech

Between resurfacing events and surface plumes that originate from the interior, scientists have speculated that biosignatures – chemicals produced by living organisms – that are the result of life in Europa’s interior ocean may have made it to the surface as well. However, since Europa orbits within Jupiter’s powerful magnetic field, its surface is subject to intense amounts of radiation that would destroy any traces of biological material.

This means that any biomolecules that are periodically ejected by plume activity or resurfacing events would only be likely to survive beneath the surface. Luckily, Europa’s surface is covered with small impacts that have taken place over the course of millions of years, which measure about 30 cm (12 inches) deep. These impacts would have also resulted in what is known as “impact gardening,” where impacts cause material from above and below the surface to be mixed.

Led by Emily S. Costello, a postdoctoral researcher at the Hawaii Institute of Geophysics and Planetology (HIGP), part of the UH Manoa’s School of Ocean and Earth Science and Technology (SOEST), the researchers sought to create the first comprehensive estimate of the effects of impact gardening on Europa. Their results are described in a study that recently appeared on July 12th in the scientific journal Nature Astronomy.

As Costello indicated in a recent SOEST press release, searching for potential signs of life on airless bodies like Europa presents a significant challenge. “If we hope to find pristine, chemical biosignatures, we will have to look below the zone where impacts have been gardening,” she said. “Chemical biosignatures in areas shallower than that zone may have been exposed to destructive radiation.”

Artist’s concept of a Europa Clipper mission. Credit: