Amino Acids Unlikely to Survive on Mars
UV radiation quickly degrades amino acids on most Martian minerals, a new study shows.
Using the “Open University Mars Chamber” in the UK, four British scientists watched to see what happened when amino acids were subjected to ultraviolet (UV) light. They spiked 11 different minerals known to exist on Mars with different concentrations of amino acids, then irradiated the rocks with UV ray levels expected at local noon for a total of 28 hours of exposure, the equivalent of about 6.5 Martian days’ worth of UV dosage. They published their results in an open-access paper on Icarus. Here are the highlights:
- D- and L-amino acids were degraded equally under simulated Mars conditions.
- Smectites and sulfates preserved the highest amino acid proportions from degration [sic].
- Sulfates protect amino acids likely due to their opacity to UV radiation.
- Minerals containing ferrous iron promote the destruction of amino acids.
Finding #1 reinforces the idea that L-amino acids (left-handed) are thermodynamically equal to D-amino acids (right-handed); i.e., nothing in the environment would favor their survival. Life on Earth uses only L-amino acids. Without a mechanism to favor one over the other (produce an “enantiomeric excess”), there is no known cause other than chance to incorporate all one-handed amino acids in a protein (see online book).
Although some of the minerals preserved amino acids, Finding #4 shows that ferrous iron (II), which is common in basaltic lava, promotes their destruction. Of those minerals that did preserve them, the initial “spiking” abundances were higher than considered plausible. This sentence in the paper could be easily missed: “The abundances used in this manuscript are higher than what it is expected to be present on Mars, placing a limit of detection for the preservation of amino acids under Mars conditions.” If they had started with the most optimistic but realistic abundances, would any amino acids have remained?
Mars, not having a global magnetic field, has no natural shielding from solar UV rays. Even if one could hope for some amino acids to survive the daily barrage of UV radiation, there are other discouragements for astrobiologists. The authors lay this one out in the final paragraph of the Discussion section:
As a final note, UV irradiation on Mars is limited to the first millimeters, but energetic particles (solar energetic particles (SEP) and galactic cosmic rays (GCR)) can go deeper in the subsurface, reach organic molecules and contribute to their degradation. A SEP dose of 600–700 mGy/yr can reach the surface of Mars and penetrate to around 10 cm, while GCR are typically capable of penetrating up to 3 m into the subsurface (Parnell et al., 2007) and over geological time, deactivate spores and degrade organic species (Dartnell et al., 2007). Therefore, future work should study the influence of the minerals on the preservation of organic molecules under simulated Mars conditions using SEP and GCR.
Since SEP and GCR penetrate far deeper than the UV studied in the Mars Chamber, they would clearly predominate. The experiments in the Mars Chamber excluded the very radiation that would likely overpower any protection from UV afforded by the minerals tested. Armor that can deflect BBs may be ineffective against machine guns. In the Introduction, the authors had said,
Two of the factors contributing to the harsh current martian environmental conditions are the thin atmosphere and the absence of a significant magnetosphere (Fairén et al., 2010), resulting in the inability to attenuate the intensity of the multiple forms of solar radiation that reach the planet, such as UV radiation, galactic cosmic rays and solar energetic particles (Cockell et al., 2000 and Hassler et al., 2014). As a result, the martian regolith is exposed to intense levels of radiation, contributing to the reactivity of the soil which may destroy potential martian life and degrade organic molecules ( Dartnell et al., 2007 and Quinn et al., 2013).
The paper, therefore, has little bearing on the actual preservation of “building blocks of life” on the red planet. Unless astrobiologists seriously want to consider life evolving deep under the surface, Mars appears to have a 10-foot-deep dead zone where the combined radiation from solar and cosmic would easily destroy amino acids, nucleotides and other biological ingredients over years, decades and centuries of exposure. How, then, would any deep-down emergent life ever survive a rise up to the surface where it could be detected? Even its basic molecules would be burned to a crisp in due time.
Remember that Mars is the most likely place where astrobiologists think life could survive beyond the Earth. “The detection of organic molecules associated with extra-terrestrial life has been primarily focused on Mars due to its proximity to Earth, evidences of a congenial past environment and potential to support microbial life,” the paper begins. Anybody see potential there now that the results are in? Get real. Our moon is in the sun’s habitable zone, and look at it. Without planetary protection from the right atmosphere and a global magnetic shield, it’s not going to be habitable except for intelligent humans for short periods in intelligently-designed spacesuits that carry a simulated Earth environment with them.