The ongoing search for alien life doesn’t necessarily mean finding extraterrestrial organisms that are alive right now. While that would be great, finding solid evidence of extinct life on Mars or Europa would be almost as amazing. However, a pair of new studies call into question whether we’d even be able to detect the remains of biological creatures on the surface of either planet. The harsh radiation in the solar system could scour a planet’s surface clean of biological remnants in as little as a few thousand years.
Space is filled with harsh cosmic radiation from far away sources like supernovas. Here on Earth, we are protected from the worst of it thanks to our thick atmosphere and magnetic field. Mars and Europa don’t have any such protections. Even in the past, Mars had only a thin atmosphere. According to Alexander Pavlov at NASA’s Goddard Space Flight Center, biological remains like fossils and amino acids may not survive as long as we thought.
The team at Goddard were skeptical about previous studies on amino acids that showed they could survive high radiation levels for as long as 1 billion years. Pavlov and the other planetary scientists at Goddard mixed amino acid samples with simulated Martian regolith. They found that amino acids under Martian conditions would probably only last about 50 million years. More than 80% of the samples were destroyed after absorbing just 1 megaray of radiation, equivalent to 20 million years. Scientists believe that would have been long after Mars lost its atmosphere and dried up. It gets even worse when water is figured in. Areas that were wet in the past would have accelerated the degradation of biological samples, rendering them undetectable in as little as 500,000 years.
The news is similarly bad on Europa, based on a study from NASA’s Ames Research Center headed by planetary scientist Luis Teodoro. Simulations of radiation levels on Europa (which are similar to Mars) show that organic material on the surface or in the first meter of ice would be destroyed by radiation in about 1 to 2 million years. When the radiation from Jupiter is figured in, that timeline might shrink even further.
So, what can space agencies do? In the case of Mars, we may have to dig deeper. While the surface will be quickly washed clean of biological material, molecules and fossils should be protected about 2 meters down. Rovers like Curiosity aren’t designed to drill that deep, but maybe future missions will take this into account. On Europa, the ice sheet over the sub-surface ocean is many miles deep, but scientists believe that the brownish material visible in surface fissures indicates water leaks out on occasion. If a probe can sample this material before it’s been on the surface too long, we could get a good idea whether or not there is biological activity inside the planet. The key is making sure the surface was breached recently in the area sampled.
It may still be feasible to find evidence of ancient alien life in the solar system, but NASA and other space agencies will have to account for this new data.