10:45 AM - 11:05 AM
[PPS08-06] Investigation of the potential “nitrogen-cycle” on Mars based on the in-situ nitrogen chemical speciation of Martian samples.
★Invited Papers
Keywords:Martian meteorites, nitrogen, XAFS, Mars analog
Nitrogen (N) is one of the essential elements for terrestrial life. On present Mars, there is no mechanism confirmed that directly fixes the atmospheric N2 (constitute ~2 % of its atmosphere) into N-bearing compounds and deposit onto the topsoil. However, recent explorations reported the presence of nitrate-bearing (NO3-) salts in the ~3.5 Ga sediments from Gale crater on Mars [Stern et al., 2015, 2017], suggesting possible “nitrogen-cycle” on early Martian atmosphere – geosphere – hydrosphere (plus, although not identified, biosphere). On the other hand, abiotic nitrogen fixations associated with geological events such as volcanic eruptions and meteoritical impacts are regarded as important processes to supply N-bearing compounds on early (prebiological) Earth.
Martian meteorites recorded geochemical information concerning past Mars. A unique meteorite, Allan Hills (ALH) 84001, contains trace carbonate minerals which precipitated from Martian near-surface brine at ~4 Ga [e.g., Halevy et al., 2011]. Koike et al. (2020) reported the presence of N-bearing organic matter in these carbonates, while they did not determine its origin. Further studies with various types and ages of Martian samples are required to understand the long-term evolutions of environments and habitability of Mars.
Our research objective is to reveal the possible “Martian nitrogen-cycle” and its long-term history by establishing the in-situ N chemical speciation technique with X-ray absorption fine structure (XAFS). In this presentation, we will introduce our latest results of younger shergottites (Tissint and NWA 13367) and Mars analog sample. All XAFS measurements were conducted at BL27SU, SPring-8.
Tissint is a ~600 Ma olivine-phylic shergottite, fallen in Morocco in 2011. It contains significant amounts of shock-melted glassy phase which is known to trap Martian surface volatiles [e.g., Chennaoui Audjehane et al., 2012]. Northwest Africa (NWA) 13367 is a recently found peridotic shergottite. It also has shock-melted phase, though, its volatile concentrations are not reported. Thick sections of these two meteorites were polished using nitrogen-free Al2O3 powder. Their surfaces were additionally cleaned by Ga-ion beam sputtering with FIB-SEM, before conducting the in-situ XAFS measurement. Our X-ray absorption near edge structure (XANES) spectra of shock-melted glasses in Tissint present nitrate-related peaks, whereas those of NWA 13367 do not show any peak. The difference between the two meteorites may reflect surrounding environments where they resided on Mars. This may be consistent with the local distributions of nitrates in Gale crater sediments [Stern et al., 2017]. It is inferred that the nitrates (and other oxidants as well) existed at the ejection area of Tissint host rock.
In this study, we also analyzed a potential Mars analog sample from Bockfjord Volcanic Complex (BVC), Spitsbergen Island, Norway. The BVC sample is basaltic lava breccia containing secondary carbonate grains that are similar in shapes and compositions to those in ALH 84001 [Treiman et al., 2002; Amundsen et al., 2011]. This rock also contains secondary clay minerals. Our XANES spectra of the BVC carbonates do not show any N-related absorption. In contrast, those of the clay minerals present ammonia-related peaks. The absence of N-absorption in the BVC carbonates is clearly different from ALH 84001 [Koike et al., 2020], indicating the differences in their alteration conditions.
Martian meteorites recorded geochemical information concerning past Mars. A unique meteorite, Allan Hills (ALH) 84001, contains trace carbonate minerals which precipitated from Martian near-surface brine at ~4 Ga [e.g., Halevy et al., 2011]. Koike et al. (2020) reported the presence of N-bearing organic matter in these carbonates, while they did not determine its origin. Further studies with various types and ages of Martian samples are required to understand the long-term evolutions of environments and habitability of Mars.
Our research objective is to reveal the possible “Martian nitrogen-cycle” and its long-term history by establishing the in-situ N chemical speciation technique with X-ray absorption fine structure (XAFS). In this presentation, we will introduce our latest results of younger shergottites (Tissint and NWA 13367) and Mars analog sample. All XAFS measurements were conducted at BL27SU, SPring-8.
Tissint is a ~600 Ma olivine-phylic shergottite, fallen in Morocco in 2011. It contains significant amounts of shock-melted glassy phase which is known to trap Martian surface volatiles [e.g., Chennaoui Audjehane et al., 2012]. Northwest Africa (NWA) 13367 is a recently found peridotic shergottite. It also has shock-melted phase, though, its volatile concentrations are not reported. Thick sections of these two meteorites were polished using nitrogen-free Al2O3 powder. Their surfaces were additionally cleaned by Ga-ion beam sputtering with FIB-SEM, before conducting the in-situ XAFS measurement. Our X-ray absorption near edge structure (XANES) spectra of shock-melted glasses in Tissint present nitrate-related peaks, whereas those of NWA 13367 do not show any peak. The difference between the two meteorites may reflect surrounding environments where they resided on Mars. This may be consistent with the local distributions of nitrates in Gale crater sediments [Stern et al., 2017]. It is inferred that the nitrates (and other oxidants as well) existed at the ejection area of Tissint host rock.
In this study, we also analyzed a potential Mars analog sample from Bockfjord Volcanic Complex (BVC), Spitsbergen Island, Norway. The BVC sample is basaltic lava breccia containing secondary carbonate grains that are similar in shapes and compositions to those in ALH 84001 [Treiman et al., 2002; Amundsen et al., 2011]. This rock also contains secondary clay minerals. Our XANES spectra of the BVC carbonates do not show any N-related absorption. In contrast, those of the clay minerals present ammonia-related peaks. The absence of N-absorption in the BVC carbonates is clearly different from ALH 84001 [Koike et al., 2020], indicating the differences in their alteration conditions.