DISTINGUISHING BETWEEN TERRESTRIAL AND EXTRATERRESTRIAL ORGANIC COMPOUNDS IN THE CM2 AGUAS ZARCAS CARBONACEOUS CHONDRITE: IMPLICATIONS FOR INTRINSIC ORGANIC MATTER

All astromaterials that fall to the Earth’s surface are exposed to significant organic contamination, which can challenge what we conclude about their intrinsic organic contents. Distinguishing between intrinsic organics and contamination becomes increasingly important when analyzing astromaterials with a potentially high intrinsic organic content, such as carbonaceous chondrites.

The Aguas Zarcas CM2 carbonaceous chondrite fell on April 23, 2019, in San Carlos county, Alajuela province, Costa Rica. 27 kg of material was recovered, with ~11 kg of the total mass being collected prior to the first rainfall (pre-rain) and the remainder post-rain. In our study, 3 pre-rain and 1 post-rain specimens were powdered, homogenized, and extracted with dichloromethane (DCM) followed by hot ultrapure water. Each extraction was analyzed by gas chromatography-mass spectrometry (GC-MS), with the hot water extractions being derivatized using MTBSTFA. The organic compounds detectable by GC-MS were identified using the NIST database.

The DCM extractions revealed 5 polycyclic aromatic hydrocarbons (PAHs) and two allotropes of sulfur (S6 and S8) that are most likely intrinsic due to their rarity on the Earth’s surface on which Aguas Zarcas fell. The pre- and post-rain DCM extractions did not display any clear trends attributed to the effects of rainfall. Intrinsic compounds detected in the hot water extracts are primarily dicarboxylic acids, such as traumatic acid and succinic acid. The post-rain water extraction had a low total organic compound abundance compared to its pre-rain counterpart, suggesting that the meteorite specimen was “rinsed” during rainfall.

The intrinsic compounds detected in Aguas Zarcas are primarily PAHs and carboxylic acids, both of which are common in other CM chondrites. However, there were minimal compounds detected from other organic compound groupings, like amino acids, contrary to other studies of Aguas Zarcas. This reduced presence could be attributed to the derivatization procedure and instrument method used and/or inter-specimen heterogeneity. Our study demonstrates the importance of taking into consideration the potential contamination history of freshly fallen meteorites in order to more accurately discriminate between intrinsic organics and contamination.