Meteoritic abundances of fatty acids and potential reaction pathways in planetesimals

Abstract

The origin of fatty acids on the prebiotic Earth is important as they likely formed the encapsulating membranes of the first protocells. Carbon-rich meteorites (i.e., carbonaceous chondrites) such as Murchison and Tagish Lake are well known to contain these molecules, and their delivery to the early planet by intense early meteorite bombardments constitutes a key prebiotic source. We collect the fatty acid abundances measured in various carbonaceous chondrites from the literature and analyze them for patterns and correlations. Fatty acids in meteorites include straight-chain and branchedchain monocarboxylic and dicarboxylic acids up to 12 carbons in length-fatty acids with at least 8 carbons are required to form vesicles, and modern cell membranes employ lipids with ∼12-20 carbons. To understand the origin of meteoritic fatty acids, we search the literature for abiotic fatty acid reaction pathways and create a candidate list of 11 reactions that could potentially produce these fatty acids in meteorite parent bodies. Straight-chain monocarboxylic acids (SCMA) are the dominant fatty acids in meteorites, followed by branched-chain monocarboxylic acids (BCMA). SCMA are most abundant in CM2 and Tagish Lake (ungrouped) meteorites, ranging on average from 10 2 ppb to 4×10 5 ppb, and 10 4 ppb to 5×10 6 ppb, respectively. In CM, CV, and Tagish Lake meteorites, SCMA abundances generally decrease with increasing carbon chain length. Conversely, SCMA abundances in CR meteorites peak at 5 and 6 carbons in length, and decrease on either side of this peak. This unique CR fatty acid distribution may hint at terrestrial contamination, or that certain fatty acid reactions mechanisms are active in different meteorite parent bodies (planetesimals). We identify Fischer-Tropsch-type synthesis as the most promising pathway for further analysis in the production of fatty acids in planetesimals.

Possible Ribose Synthesis in Carbonaceous Planetesimals

“…The frozen ribose might have been preserved until it was distributed in the solar system as fragments of the parent body, and some of the fragments fell to the Earth as meteorites. Extraterrestrial organic and prebiotic molecules were found in meteorites on the Earth’s surface today, see, e.g., [ 1 , 40 , 110 , 111 , 112 , 113 , 114 ], although the possibility of at least partial terrestrial contamination has to be considered. Theoretical studies coupled with experimental data [ 2 , 3 , 115 , 116 ] suggested that a significant portion of organics might survive the heating due to friction in the atmosphere and the energy of the impact [ 117 ] and arrive intact on the Earth’s surface even in comets and interplanetary dust particles.…”

Macrobiont: Cradle for the Origin of Life and Creation of a Biosphere

“…Another hypothesis is that over time, many individual carbonaceous chondrites landed in natural ponds rather than on bare land [ 40 ]. These provided the starting constituents, including a variety of amino acids [ 28 , 149 ] and membrane-forming amphiphiles [ 15 , 150 ]. An advantage of this proposal is that it is amenable to laboratory analysis because of the availability of the meteoritic starting material.…”

False biosignatures on Mars: anticipating ambiguity

“…McCollom 2013;Milesi et al 2015;Dalai et al 2016;Steele et al 2018;Franz et al 2020). Taken together, these various sources would have provided, inter alia, polyaromatic hydrocarbons, alkanes, amines, fatty acids/lipids, carboxylic acids, amino acids, nucleobases, aldehydes, ketones and carbohydrates, all of which are presentalong with marked enantiomeric excessesin carbonaceous chondrites (Botta and Bada 2002;Simoneit 2004;Myrgorodska et al 2015;Dalai et al 2016;Furukawa et al 2019;Lai et al 2019).…”