New Paths for Survivability of Organic Material in the Martian Subsurface

摘要

abstract_textpRecent space missions have identified organics, chlorinated and non-chlorinated, on Mars. Understanding the origin, current state and reactivity of this carbonaceous material is critical to efforts to detect organic signatures of possible past life on Mars. Environmental effects such as ultraviolet radiation, pressure, diagenesis, aqueous activity, and presence of perchlorates have been assessed previously using analog experiments. To this list, Fox, et al. adds and quantifies the effect of galactic cosmic rays and solar winds on organic material on the surface and in the near subsurface of Mars. Their work, using laboratory analog materials and radiation, shows that the same organic acids, formic and oxalic acid, are produced after exposure equivalent to that over Martian history at depths of less than 5 cm, independent of mineral matrix or starting organic materials. These experiments suggest that planned subsurface exploration using the drill on the Rosalind Franklin Rover (ExoMars) will sample organic material which has not been altered by cosmic rays, although it may have been exposed to other environmental factors such as water or salts./ppPlain Language Summary/ppOne of the forthcoming missions to Mars, the Rosalind Franklin Rover (ExoMars), will have the capability to drill and sample the subsurface at depths of up to 2 m. One of the goals of this mission, building on discoveries made by many previous missions, is to further our understanding of the organic material present on Mars and where it came from. As more organic matter is detected, it becomes increasingly important to ask whether it is solely the material delivered by meteorites or if it is evidence of past life on Mars. One issue to overcome when answering this question is the degradation and destruction of organic material by cosmic rays. Using laboratory experiments, Fox et al. show that measurements made at depths deeper than 5 cm, well within the capability of the rover drill, will access organic material which has not been destroyed by cosmic rays. Their research also shows that it is impossible to unambiguously reconstruct the starting material from the products of radiation-mediated decomposition, emphasizing the need to locate unaltered material for study./p/abstract_text