title: Abiotic nitrogen fixation on terrestrial planets: reduction of NO to ammonia by FeS.
abstract: Understanding the abiotic fixation of nitrogen and how such fixation can be a supply of prebiotic nitrogen is critical for understanding both the planetary evolution of, and the potential origin of life on, terrestrial planets. As nitrogen is a biochemically essential element, sources of biochemically accessible nitrogen, especially reduced nitrogen, are critical to prebiotic chemistry and the origin of life. Loss of atmospheric nitrogen can result in loss of the ability to sustain liquid water on a planetary surface, which would impact planetary habitability and hydrological processes that shape the surface. It is known that NO can be photochemically converted through a chain of reactions to form nitrate and nitrite, which can be subsequently reduced to ammonia. Here, we show that NO can also be directly reduced, by FeS, to ammonia. In addition to removing nitrogen from the atmosphere, this reaction is particularly important as a source of reduced nitrogen on an early terrestrial planet. By converting NO directly to ammonia in a single step, ammonia is formed with a higher product yield (~50%) than would be possible through the formation of nitrate/nitrite and subsequent conversion to ammonia. In conjunction with the reduction of NO, there is also a catalytic disproportionation at the mineral surface that converts NO to NO₂ and N₂O. The NO₂ is then converted to ammonia, while the N₂O is released back in the gas phase, which provides an abiotic source of nitrous oxide.
authors.affiliation: Carl Sagan Center, SETI Institute, c/o NASA Ames Research Center, Moffett Field, CA 94035-1000, USA. David.P.Summers@nasa.gov
authors.forename: David P
authors.initials: DP
authors.lastname: Summers
authors.forename: Ranor C B
authors.initials: RC
authors.lastname: Basa
authors.forename: Bishun
authors.initials: B
authors.lastname: Khare
authors.forename: David
authors.initials: D
authors.lastname: Rodoni
mesh_terms: D000641:Ammonia / Q000138:chemical synthesis*; D005296:Ferrous Compounds / Q000737:chemistry*; D009569:Nitric Oxide / Q000737:chemistry*; D009586:Nitrogen Fixation; D010084:Oxidation-Reduction; D010103:Oxygen Isotopes; D016083:Planets
chemical_list: D005296:Ferrous Compounds; D010103:Oxygen Isotopes; D009569:Nitric Oxide; D000641:Ammonia; C022597:ferrous sulfide