Illustration of a potential NASA lander on the surface of Jupiter's icy, ocean-bearing moon Europa
Credit: NASA / JPL
When life sign On Jupiter's ice moon Europe, they may not be as hard to find as scientists have assumed, reports a new study.
Researchers see Europe as one of the solar system's best ways to host extraterrestrial life. Europe is also a geologically active world, so that samples of the buried ocean can routinely reach the surface – for example, through localized expansion of the ocean itself and / or geyser-like outgassing, whose evidence has been discovered multiple times using NASA's Hubble Space Telescope. [Photos: Europa, Mysterious Icy Moon of Jupiter]
NASA wants to look for such samples in the not too distant future. The agency is developing a flyby mission called Europa Clipper, which is scheduled to launch in the early 2020s. Clipper will examine Europe closely at dozens of fly-bys, some of which may whiz through the moon's supposed plumes of water vapor. And NASA is also working on a potential Post Clipper Lander mission that would look for traces of life on or near the Europan surface.
However, it is unclear how deep a European Lander would have to dig in order to have a chance to find something. This is because Europe is orbiting Jupiter's radiation belt and being bombarded by fast-moving charged particles that can turn amino acids and other possible biosignatures into pulps.
This is where the new study comes in.
NASA scientist Tom Nordheim and his colleagues have faithfully reproduced Europe's radiation environment in terms of how bad things go from place to place. They then combined these results with data from laboratory experiments that documented how quickly different doses of radiation absorbed amino acids (a replacement for complex biomolecules in general).
The researchers found significant differences, with some European areas (equatorial regions) reaching about 10 times the radiance of others (medium and high latitudes).
In the most harmless places, the team found, a lander would probably have to dig only 0.4 inches (1 centimeter) or so into the ice to find recognizable amino acids. In the high-explosive zones, the target depth would be on the order of 4 to 8 inches (10 to 20 cm). (This is not to imply that potential European organisms would still live at such depths; the doses are high enough to cook even the world's toughest microbes, study members said.)
The latter range is still fairly manageable said Nordheim, who is based at the California Institute of Technology and NASA's Jet Propulsion Laboratory, both of which are based in Pasadena.
"Even in the harshest radiation zones in Europe, you really do not have to scratch anything under the surface to find material that has not changed much or been damaged by radiation," he told Space.com.
This is good news for the potential lander mission, Nordheim added: Since radiation exposure does not appear to be a limiting factor, planners can feel free to choose the areas of Europe most likely to harbor oceanic debris – the Fallout Zone under a cloud example – wherever they may lie.
Scientists have still not identified such promising touchdown areas; The Europe images that have been shot so far were simply not sharp enough. But Europe Clippers work should change things, Nordheim said.
"If we get the Clipper Enlightenment, the high-resolution images, it will be a very different picture," he said. "This Clipper Enlightenment is really important."
The new study was published online today (July 23) in the journal Nature Astronomy.