Shock Chemistry of Sugars and Implications for Delivery by Meteorites

Abstract

Recent detection of the sugar glycolaldehyde in the interstellar molecular cloud Sagittarius B2(N) (Hollis et al. 2000) and models of its formation (Sorrell, 2001) have helped fuel the idea that biologically-relevant organic compounds can form easily in space and can be delivered to Earth or other planets by comets, meteorites, and asteroids. Glycolaldehyde is a useful bio-ingredient because it can polymerize into higher forms of carbohydrates, such as ribose, the sugar that makes up the backbone for RNA, and glucose, the sugar found in plant saps and fruits (Hollis et al. 2000; see Figure 1). Glycolaldehyde is reactive and can form various kinds of complex organic compounds; therefore, it may be an important ingredient for starting life on the early Earth. Its presence in space, while not ubiquitous, is an important clue for understanding the chemical routes that can lead to the formation of other molecules, both simple and complex. Meteorites contain materials coalesced from dense molecular clouds during or prior to formation of the Solar System. Carbonaceous chondrites are of special interest to studies of the origin of life because they contain carbon-based compounds, such as amino acids (e.g. Pizzarello et al. 1991; Botta and Bada, 2002) and sugarsmore » (Cooper et al. 2001, 2002), essential constituents of terrestrial organisms. Dihydroxyacetone, sugar acids, and sugar alcohols have been identified in the Murchison and Murray meteorites (Cooper et al. 2001, 2002), and laboratory analyses of simple sugar mass spectra have suggested that similar features exist in Comet Halley spectra (Robinson and Wdowiak, 1994). While shock experiments have already been carried out to understand the effects of pressure and temperature on the chemistry of amino acids with relevance to their delivery to Earth by comets (e.g. Blank et al. 2001), to date, no experiments regarding the impact delivery and survivability of sugars have been done. Here we propose studies that will focus on understanding how dimers of glycolaldehyde (C{sub 4}H{sub 8}O{sub 4}) and dihydroxyacetone (C{sub 6}H{sub 12}O{sub 6}), two of the simplest sugars (Table 1), react under the extreme pressures and temperatures of simulated terrestrial impact events. The existing two-stage light-gas gun at LLNL (e.g. Koch et al. 1990) can be used to carry out shock experiments of sugar solutions in a manner similar to that of Blank et al. (2001), and liquid or gas chromatography and mass spectrometry (LCMS, GCMS) can be used to identify the solutions' end products (see Appendix A for a list of the experiments' components). It is likely that these sugars will break down, but they may form more complex molecules, such as ribose (C{sub 5}H{sub 10}O{sub 5}) or glucose (C{sub 6}H{sub 12}O{sub 6}), since sugars provide the carbon skeletons for many molecules. The latter outcome would be significant to understanding the delivery and subsequent shock chemistry of extraterrestrial bio-ingredients because it would show that these molecules could survive impact events to form more complicated molecules, in contrast to other reports (e.g. Chyba et al. 1990) but in support of the findings of Blank et al. (2001).« less