Isotopic evidence for extraterrestrial organic material in the Martian meteorite, Nakhla

In this paper, we report on new ¹⁴C and ¹³C isotopic analyses of organic and carbonate phases in pristine samples of the martian meteorite, Nakhla (fell 1911AD). We undertook water and acid extractions of soluble phases as well as a study of insoluble material. We used ¹⁴C to differentiate between extraterrestrial organic material and recent terrestrial contamination. Results indicate that most of the organic matter in Nakhla is released by 6N HCl and there appear to be two isotopically distinct sources of extraterrestrial organics with δ¹³C of -33‰ and -15‰ and low ¹⁴C. We estimate that at least 75% of the organic material released by 6N HCl acid etching is extraterrestrial. We conclude that this acid-labile component is likely similar to polymeric organics observed in CM2 chondrites (Gilmour and Pillinger, 1994) and could have accumulated on the Martian surface from the accumulation of meteoritic material and cometary debris and cosmic dust. We also determined that the terrestrial organic contamination is characterized by approximately modern ¹⁴C values and δ¹³C of -25‰. Copyright (C) 2000 Elsevier Science Ltd.