¹Victoria E.Hamilton,²Hannah H.Kaplan,^3,4Harold C.ConnollyJr,⁵Cyrena A.Goodrich,⁶Neyda M.Abreu,²Amy A.Simon
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115054]
¹Southwest Research Institute, Boulder, CO, United States of America
²NASA Goddard SpaceFlight Center, Greenbelt, MD, United States of America
³Rowan University, Glassboro, NJ, United States of America
⁴American Museum of Natural History, New York, NY, United States of America
⁵Lunar and Planetary Institute, USRA, Houston, TX, United States of America
⁶NASA Langley Research Center, Hampton, VA, United States of America
Copyright Elsevier

Orbital spectra collected of asteroid (101955) Bennu by NASA’s Origins, Spectral Interpretation, Resource Identification, Security–Regolith Explorer (OSIRIS–REx) spacecraft have identified ungrouped C, CI, and CM meteorites having petrologic types 1, 1/2, and 2 as the best mineralogical analogues to Bennu to date. Here we present spectral evidence that Grosvenor Mountains (GRO) 95,577, a CR1, is a better analogue for Bennu’s bulk surface mineralogy. CR-like parent bodies are targets of interest because they contain some of the most pristine materials from the solar nebula and can contain substantial amounts of H2O and OH− in addition to exotic organics. Unfortunately, terrestrial weathering makes constraining their indigenous mineralogy and organics challenging. Analysis of samples retrieved directly from an asteroid would help us disentangle the effects of terrestrial weathering and asteroidal aqueous alteration and hence whether some of the exotic organics and large populations of presolar grains were affected by terrestrial processes in meteorites. If Bennu is comprised of CR1(−like) material, in whole or in part, the OSIRIS–REx returned sample represents a tremendous opportunity to explore in depth what is currently a unique material among carbonaceous chondrites.

¹M.Fastelli,¹P.Comodi,²B.Schmitt,²P.Beck,²O.Poch,³P.Sassi,¹A.Zucchini
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115055]
¹Department of Physics and Geology, University of Perugia, I-06123 Perugia, Italy
²Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
³Department of Chemistry, Biology and Biotechnology, University of Perugia, Via Elce di sotto 8, 06123 Perugia, Italy
Copyright Elsevier

It has been proposed that ammonium-bearing minerals are present in a varying amount in icy planetary bodies. Their observation at the surface of large objects was related to the upwelling and cryovolcanism of ammoniated water from possible subsurface oceans forming ammonium-bearing minerals (NH₄⁺) mixed with ice at the surface. We analyzed the temperature evolution of the near-infrared spectra of a selected number of anhydrous and hydrated ammonium-bearing minerals containing different anions and water content. Reflectance spectra were collected in the 1–4.8 μm spectral range at cryogenic temperatures ranging from 293 K to ~65 K and the effect of sample’s grain size between 32 and 150 μm was also investigated at room temperature. Reflectance spectra of anhydrous samples show well-defined absorption bands in the 1–2.5 μm range. The bands located at ~1.06, 1.3, 1.56, 2.02, and 2.2 μm could be useful to discriminate these salts and their characteristics are examined in detail in this work. On the other hand, the reflectance spectra of water-rich samples show H₂O fundamental absorption bands strongly overlapping the NH₄⁺ bands, thus dominating the spectra from 1 to 2.8 μm and fully saturating above 2.8 μm. The position of the absorption bands changes with temperature and grain size, shifting to higher frequencies as temperature decreases. The low-temperature spectra also reveal a fine structure compared to the room temperature ones and display narrower and more defined absorption bands. Granulometry mainly affects the band depth and band area parameters. Moreover, mascagnite, salammoniac, ammonium phosphate, tschermigite, and ammonium nitrate are subjected to a reversible low-temperature phase transition, which is manifested in the spectra by a progressive growth and shift of the bands towards shorter wavelengths with an abrupt change in their depth. This new set of spectra at cryogenic temperatures can be directly compared with remote sensing data to detect the presence of ammonium-bearing minerals on the surface of icy bodies. Their identification can impact our knowledge of the internal composition and dynamics of these bodies as well as their potential habitability.