Jupiter's moon Europa is regarded as one of the most likely places in the solar system to find extraterrestrial life, but where to look for evidence of it? To aid future space missions, a team of scientists led by Tom Nordheim, research scientist at NASA's Jet Propulsion Laboratory, has drawn up comprehensive maps of the radiation bombarding the moon to determine where and how deep explorers must look to find signs of life.
Ever since the NASA Voyager flyby missions of the 1970s, scientists have speculated that life of some sort might exist on Europa. After the unmanned Galileo probe went into orbit around Jupiter in 1995 to begin an eight-year mission of exploration, evidence mounted that the interior of Europa contained a vast global ocean of salty, mineral-rich water 100 km (62 mi) deep. If this is indeed the case, such an ocean might be home to at least some form of microbial life.
The trouble is, if this ocean does exist, it's sealed by an outer crust of ice 10 to 30 km (6 to 19 mi) thick. Drilling through that much ice with equipment sent from Earth would be a daunting task to say the least, but there may be an easier source of samples from the subterranean ocean via the great water vapor plumes that blast 200 km (120 mi into space from great geysers at the south polar region.
Such plumes could carry microbes or organic molecules that could collect on the surface, where they'd provide a treasure trove of information for exobiologists. However, Europa has an atmosphere that is almost non-existent, hardly any magnetic field, and is continually bombarded by Jupiter's intense radiation belts.
This means that any organic molecules on the surface of Europa would be quickly broken down or altered until they are useless for study. According to Nordheim, the good news is that the radiation isn't uniformly distributed on Europa, and it only penetrates the surface to a very limited extent.
Through data from Voyager 1 and Galileo, Nordheim's team found that the radiation dosage on Europa is very uneven, with intense radiation in oval-shaped zones around the equator connected at the tips, while the poles get less exposure. NASA says that this fact will be of great importances to NASA's Europa Clipper mission that is scheduled to launch sometime around 2022. This will go into orbit around Jupiter and make about 45 close flybys of Europa to carry out a detailed survey. Another mission that would benefit from the new maps is a proposed Europa lander.
The team's findings based on studying the effects of radiation on amino acids indicate that, although it is widespread, the radiation might only penetrate in damaging doses 10 to 20 cm (4 to 8 in) beneath the surface in the high radiation areas, and under 1 cm (0.4 in) in the low radiation zones. This means that a lander would need only a modest capability to dig or drill to find intact samples in the right areas.
"The radiation that bombards Europa's surface leaves a fingerprint," says Kevin Hand, project scientist for the potential Europa Lander mission. "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. That's good news for looking at potentially fresh ocean material that has not been heavily modified by the fingerprint of radiation."
The research was published in Nature Astronomy.
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