Background
Impact gardening is a major geologic process that influences both water and organics in lunar permanently shadowed regions. The past LCROSS impact experiment on the moon demonstrated the presence of simple organics including CH4, C2H4, and CH3OH in lunar permanently shadowed regions, which likely represent fragmentation products formed during the impact. Thus, impacts may be a key driver of organic cycling (e.g., degradation of primordial organics and synthesis of new organics). If this is the case, then impact gardening likely influences the types of organics present and their deuterium to hydrogen ratios, which would complicate interpretation of the origin of both the Earth and moon’s water. The purpose of this research effort was to determine the potential for micrometeorite impacts to induce organic cycling, i.e., the production of new organic compounds along with the destruction of initial organics in the sample, in the lunar permanently shadowed regions. This study provides important constraints on how impact gardening influences the cycling of organics in lunar permanently shadowed regions. This effort establishes SwRI’s expertise in organic cycling on the moon and enable future Artemis and PRISM mission participation.
Approach
The Targeted IR&D project supported the design and fabrication of a new experimental apparatus, including a sample holder, cooling system, and sample capture after the impact for analysis. We conducted triplicate shots using the two-stage light gas gun at average speeds of 4.6-7 km/s to determine the destruction of naphthalene in 1-10 ppm naphthalene-doped lunar analogs, which contained 10 wt.% water.
Accomplishments
We determined the breakdown of naphthalene and the production of secondary organics using GC-MS. These data demonstrated our experimental apparatus avoids contamination from gases generated by the two-stage light gas gun. Moreover, two-dimensional GCxGC analysis of our post-impacted PSR analog materials demonstrates that both organic synthesis and degradation occurs during hypervelocity impact experiments. The energy available for reaction is greatest closest to the impact, which would enable the synthesis of additional organics (Figure 1). Our data show that impact gardening, an important ongoing geologic process on the moon, will induce cycling of organics in these environments, resulting in the production of complex organic molecules. This suggests that where samples are collected on the moon will influence our interpretation of the organic inventory present on the moon. Lunar samples collected distally from impact craters will likely have lower concentrations of organics. Our team provided the science case for Dr. Ryan Blase’s DALI proposal focused on MEMS GC applications on the Moon. Dr. Phillips-Lander submitted a Space Biology Proposal that looks at plant growth in the naphthalene-doped simulants created for this project effort and she subsequently participated as a science team member of a NASA Artemis Tools proposal that will attempt to grow plants on the moon.
Figure 1: Two-dimensional GCxGC plot of the organic chemistry pre- and post- impact for the hydrogen impact experiments at 6.5 km/s. The organics in the starting material (A) is similar to those detected in the mold sample, however, clear differences between the samples are evident and demonstrate both the preservation of some of the initial organics present in the sample and synthesis of additional organics close to the impact (B). Some peaks, including the prominent peak between 1-2 sec on the right axis (A) decrease post-impact, demonstrating the breakdown of some organics during impact. The concentration and type of organics progressively decreases with distance from the mold to the sphere (B-D). This suggests that impact material moved the greatest distance during a micrometeorite impact will also contain the least organic materials.