Survivability of Amino Acids in Lunar Soil

One of the most stunning findings from the Apollo era was the discovery of organic compounds, including amino acids, in lunar soil samples. This raised the question of how amino acids might manage to survive the harsh environmental conditions of the lunar surface. The surface of the Moon, which lacks a global magnetic field or an atmosphere, is subject to significant space weathering in the form of physical bombardment and radiation. This means that any volatiles or organics deposited on the lunar surface is subject to high temperatures and significant fluxes of ultraviolet (UV) radiation and solar wind plasma. We present a laboratory investigation on the survivability of amino acids in lunar simulant soil under conditions similar to the lunar surface.

In this study, samples are created by depositing amino acids into the lunar simulant JSC-1A. Samples are then exposed to lunar conditions in a custom-built vacuum, gas, and radiation treatment chamber. Survival rates of various amino acids were quantified using ultra high performance liquid chromatography in conjunction with AccQ·Tag derivitization and fluorescence detection.

 Vacuum, Hydrogen Gas, and UV/Plasma.  Samples were separately exposed to different vacuum levels, hydrogen gas, and hydrogen plasma/UV radiation. Results show that vacuum and hydrogen gas exposure have relatively minor effects on amino acid survivability compared to hydrogen plasma and ultraviolet (UV) radiation. Interestingly, in our experiments, exposure to plasma and UV significantly reduces the amount of but does not completely destroy amino acids in lunar soil.

Extended Radiation Dose.  Amino acids in lunar soil systematically exposed to increasing amounts of plasma and UV radiation displayed an exponential decay rate with increasing doses. After the equivalent of 20 years of irradiation at the Moon, a small amount (∼4-7%) of amino acids continue to survive in the soil.

Varied Burial Depths.  To investigate the shielding effects of dust in the survivability of amino acids, we buried 0.1 g of samples of JSC-1A doped with amino acids in 4.5 g columns of undoped JSC-1A. Burial heights were set at 0 mm (surface deposition), 8 mm, 16 mm, and 24 mm. Results highlight the importance of shielding by lunar dust: amino acids buried as little as 8 mm below the surface have a ≳ 95% survival rate under 2.5 years of equivalent radiation.

In summary, amino acids are experimentally shown to survive on human time scales under hydrogen plasma/UV radiation. Lunar dust is found to play an important role in shielding amino acids. These results have important implications for the effects of human exploration of the Moon. Future studies will examine more complex organic molecules, as well as the breakdown and outgassing products of such under hydrogen plasma/UV exposure.