^1,2,3S. Andrejkovičová et al. (>10)
Journal of Geophysical Research: Planets, 131, e2025JE009610
Open Access Link to Article [DOI: 10.1029/2025JE009610]
¹NASA GSFC, Greenbelt, MD, USA
²CRESST, University of Maryland, College Park, MD, USA
³Geosciences Department, GeoBioTec, Aveiro University, Aveiro, Portugal

Published by arrangement with John Wiley & Sons

Ammonium (NH₄⁺) in the interlayer space of phyllosilicates has been proposed as a potential but underexplored nitrogen reservoir on Mars. We synthesized ammonium-exchanged smectites (montmorillonite SWy-2 and nontronite NAu-2) and analyzed them, both as pure phases and in mixtures containing five or 20 wt.% magnesium (Mg) perchlorate, under Sample Analysis at Mars (SAM)–like conditions using evolved gas analysis–mass spectrometry (EGA) and pyrolysis (GC-MS), complemented by FTIR, XRD and EA-IRMS. Ammoniated smectites released N₂ during heating even without perchlorate, whereas mixtures with Mg perchlorate yielded oxidized nitrogen species (NO and N₂O) along with N₂. The temperature ranges and release profiles of NO bear similarities to several Gale crater samples analyzed by SAM, suggesting that part of the martian NO could derive from ammonium-bearing smectites rather than exclusively from nitrate thermal decomposition. Quantitative analysis of EGA data indicates that 4.20%–29.8% of the total nitrogen in the ammoniated smectites was released as NO under SAM-like pyrolysis, depending on smectite type and oxidant abundance. XRD under dry conditions shows partial collapse of basal spacing to d(001) ≈10.8 Å (NH₄SWy-2) and 10.4 Å (NH₄NAu-2), comparable to the broad ∼10 Å peaks observed by the Chemistry and Mineralogy (CheMin) instrument in clay-bearing Gale crater materials. These results indicate that ammonium-bearing smectites are a plausible precursor phase capable of generating NO under SAM-like pyrolysis conditions and could contribute to martian nitrogen cycling in environments where smectite formation and ammonium exchange occurred, although the present martian data do not uniquely distinguish among possible nitrogen precursor phases.