Preservation of Organic Materials during Hypervelocity Impact Experiments

Introduction: The survivability of carbonaceous compounds during hypervelocity impacts has particular importance in exobiology, astrobiology, and origin of life studies. The delivery of biotic organics such as amino acids, which are found in meteorites [1], during impact is an important hypothesis for the source of life's early organics [2]. Furthermore, trapping or preservation of target organics can provide clues to a tar-get's original organic content, including that of extra-terrestrial targets such as Mars. Historically, it was believed that no organic material could survive the intense temperatures and pressures involved in major hypervelocity impacts, but more recently this assumption has been challenged. First, impact glasses from Argentina have been shown to entrain fragile grasses and water [3, 4]. Second, hypervelocity impact experiments [4] reproduced this process using hyperve-locity impact experiments. The survivability of organic amino acids [5] and polycyclic aromatic hydrocarbons (PAHs) [6] during high shock using flat plate experiments have set constraints on limiting conditions for suvival. Here, however, we used the light-gas gun facility at the NASA Ames Vertical Gun Range (AVGR) to conduct three-dimensional experiments to assess the mechanism and potential for survival of amino acids and PAHs in organic-rich targets under open conditions. Experimental Methods: Impact experiments were conducted at the NASA AVGR. Organic analyses were conducted at organic geochemical laboratories at Brown University. PAHs were chosen for study due to their known stability under high temperatures relative to other small organics, whereas amino acids represent a more extreme case of survival during impact. AVGR Experiments. Two target types were used. The first consisted of the dry amino acid L-norvaline or a mixture of PAHs with varying stabilities mixed with sieved 100-200 sand. In the second case, L-norvaline was frozen into 5 cm-diameter wafer of ice embedded in the 100-200 sieved sand target. Blank tests were also conducted, i.e., targed sand contained no organics. L-norvaline was chosen as a model amino acid for several reasons: a) it is non-racemizable through normal means due to the presence of an α-methyl group, allowing the potential for an analysis of chiral changes during impact; b) it is non-proteneic, which avoids an otherwise difficult to avoid dilemma of biogenic contamination; and c) it has been found in carbonaceous chondrites [7]. Inert Pyrex projectiles were launched at two different speeds (4.5 and 5.5