Investigation of Ammoniated Clays and Altered Materials for Understanding the Nitrogen Cycle on Asteroids and Perhaps Mars

Session: Advancing Mineral Science and Exploring Planetary Surfaces: In Honor of MSA Dana Medalist, Elizabeth B. Rampe, Part I

Presenting Author:

Dr. Janice L. Bishop

Authors:

Bishop, Janice L¹, Andrejkovičová, Slavka², Elwood Madden, Megan³, Fakhrshafaei, Kyle⁴, Rebelo, Rafael⁵, Pálková, Helena⁶

(1) SETI Institute, Mountain View, CA, USA, (2) Geosciences Department, Geobiotec Unit, University of Aveiro, Aveiro, Portugal, (3) Earth and Environmental Sciences, Michigan State University, East Lansing, Michigan, USA, (4) University of Oklahoma, Norman, Oklahoma, USA, (5) Geosciences Department, Geobiotec Unit, University of Aveiro, Aveiro, Portugal, (6) Institute of Inorganic Chemistry, SAS, Bratislava, Slovak Republic,

Abstract:

Nitrogen is an essential element for life and ammonia-bearing clays on Ceres, Ryugu and Bennu represent intriguing geochemical conditions on these bodies. Nitrogen is also present on Mars although its form is not yet known. We are investigating the spectral properties of a suite of ammoniated smectite clays and a collection of NH₄⁺-treated clay mixtures and alteration products in order to advance our understanding of how ammonia-bearing clays form on asteroids and potentially on Mars as well. Smectites require an interlayer cation to balance the charge in the mineral structure and NH₄⁺ can be readily exchanged for the normally present Na⁺ and Ca²⁺ cations. For this study we have characterized the spectral properties of several NH₄⁺-treated Al-smectites (montmorillonite), Fe-smectites (nontronite, ferruginous smectite), and Mg-smectites (saponite, hectorite). NH₄⁺ bands are observed in reflectance spectra of our samples near 1.55, 2.01, 2.12, 3.06, 3.29, and 3.53 µm, although the band centers vary slightly in some cases depending on the octahedral cation. The NH₄⁺ bands near 2.12 and 3.06 µm are the strongest and would be easiest to detect in spectra acquired of planetary bodies. The band near 3.06 µm currently has had the best coverage in spectral data of asteroids and is similar to features observed at Ceres. Serpentines, carbonates, and hydrocarbons are also observed on Ceres, but the NH₄⁺ bands appear to be connected to smectites there.

Additional experiments are analyzing the presence of NH₄⁺ incorporated in smectites, other clay minerals, clay mixtures, carbonates, and altered volcanic materials through NH₄Cl brine experiments. Asteroids including Ceres, Bennu, and Ryugu include serpentine as the primary clay mineral, with smaller amounts of smectite. NH₄⁺ spectral bands consistent with NH₄⁺ bands in smectites are observed for these planetary bodies although the smectite abundances appear to be lower. Further, NH₄⁺ is not readily incorporated into serpentines in the lab because it lacks the charged interlayer region present in smectites. For these reasons we are investigating the possibility of more aggressive brine treatments to produce ammoniated materials as well as ammoniated smectite-serpentine mixtures and other altered materials.

Identifying ammonia supports understanding the N cycle and will improve our knowledge of planetary processes (e.g., impacts and reduction) that could have fixed N into a bioavailable form such as ammonia.