The researchers report that the chances of finding organic molecules roughly 0.8 inches (2 centimeters) below the surface are close to zero. The top layer of the Martian surface has absorbed so much cosmic radiation over the past billion years that all organic material is likely to have been destroyed, the scientists said. Past rovers on Mars collected and analyzed only loose soil from the topmost layer of the Martian surface. [7 Biggest Mars Mysteries]
Yet only inches deeper — within reach of Curiosity — simple organic molecules could still exist, the researchers said.
Even if Curiosity detected these molecules, the discovery wouldn't necessarily mean ancient life existed on Mars. Simple organic molecules could have originated from other sources, such as meteors and interplanetary dust particles, the researchers said.
Complex organic molecules, such as those made up of 10 or more carbon atoms, would be more reliable indicators of past life on the planet, since they could closely resemble building blocks of life as we know it. These structures, however, would be much harder to find, and they would have been more vulnerable to the radiation that mercilessly bombards the Red Planet.
The new study offers suggestions for where Curiosity could begin its search.
Previous studies focused on the maximum depth that cosmic radiation can reach, Pavlov said, since organic molecules below that point – approximately 5 feet (1.5 meters) – conceivably could survive unharmed for billions of years. But drilling to that depth using existing rover technology would be impractical.
In the new research, the scientists examined a range of more-attainable depths and modeled the accumulation of cosmic ray radiation and its effects on organic molecules. To reach their results, researchers looked at soil and rock composition on Mars, changes in the planet's atmospheric density over time, and the various energy levels of cosmic rays.