¹Rosa B.Scorzelli,²Edivaldodos Santos
Geochemistry (Chemie der Erde) (in Press) Link to Article [https://doi.org/10.1016/j.chemer.2019.125547]
¹Centro Brasileiro de Pesquisas Físicas – CBPF, Rua Dr. Xavier Sigaud 150, 22290-180, Rio de Janeiro, Brazil
²Instituto de Ciência e Tecnologia – ICT/UFVJM, Rodovia MGT 367 – km 583, n° 5000, 39100-000, Minas Gerais, Brazil
Copyright Elsevier

Discovered by Rudolph L. Mössbauer in 1957, the Mössbauer effect (i.e. gamma-resonance spectroscopy) is the phenomenon of the emission or absorption of a gamma ray without loss of energy due to recoil of the nucleus and without thermal broadening. This technique has been applied to many science fields (e.g., physics, chemistry, geology, biology), since it provides information about the nuclear and electronic properties of materials. In this paper, a review of works focusing on the application of ⁵⁷Fe Mössbauer spectroscopy study of the meteoritic Fe-Ni system will be reported.

^1,5Briony H.N.Horgan,²Ryan B.Anderson,³Gilles Dromart,⁴Elena S.Amador,⁴Melissa S.Rice
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2019.11352]
¹Dept. of Earth, Atmospheric, & Planetary Sciences, Purdue University, West Lafayette, IN, USA
²U.S. Geological Survey, Astrogeology Center, Flagstaff, AZ, USA
³Laboratoire de Géologie de Lyon, Université de Lyon, 69364 Lyon, France
⁴Division of Geological & Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
⁵Dept. of Physics & Dept. of Geology, Western Washington University, Bellingham, WA, USA
Copyright Elsevier

Noachian-aged Jezero crater is the only known location on Mars where clear orbital detections of carbonates are found in close proximity to clear fluvio-lacustrine features indicating the past presence of a paleolake; however, it is unclear whether or not the carbonates in Jezero are related to the lacustrine activity. This distinction is critical for evaluating the astrobiological potential of the site, as lacustrine carbonates on Earth are capable of preserving biosignatures at scales that may be detectable by a landed mission like the Mars 2020 rover, which is planned to land in Jezero in February 2021. In this study, we conduct a detailed investigation of the mineralogical and morphological properties of geological units within Jezero crater in order to better constrain the origin of carbonates in the basin and their timing relative to fluvio-lacustrine activity. Using orbital visible/near-infrared hyperspectral images from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) along with high resolution imagery and digital elevation models, we identify a distinct carbonate-bearing unit, the “Marginal Carbonates,” located along the inner margin of the crater, near the largest inlet valley and the western delta. Based on their strong carbonate signatures, topographic properties, and location in the crater, we propose that this unit may preserve authigenic lacustrine carbonates, precipitated in the near-shore environment of the Jezero paleolake. Comparison to carbonate deposits from terrestrial closed basin lakes suggests that if the Marginal Carbonates are lacustrine in origin, they could preserve macro- and microscopic biosignatures in microbialite rocks like stromatolites, some of which would likely be detectable by Mars 2020. The Marginal Carbonates may represent just one phase of a complex fluvio-lacustrine history in Jezero crater, as we find that the spectral diversity of the fluvio-lacustrine deposits in the crater is consistent with a long-lived lake system cataloging the deposition and erosion of regional geologic units. Thus, Jezero crater may contain a unique record of the evolution of surface environments, climates, and habitability on early Mars.

¹A.Boujibar,²K.Righter,¹E.S.Bullock,¹Z.Du,¹Y.Fei
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.11.014]
¹Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road NW, Washington, DC, United States
²NASA Johnson Space Center, 2101 NASA Pkwy, Houston, TX 77058, United States
Copyright Elsevier

Alkali metals Na, K, Rb and Cs are depleted in planetary mantles and their depletion is commonly attributed to the effect of volatility during the condensation of the first solids in the solar nebula or the high temperatures involved during planetary growth. Most models of planetary differentiation assume that alkalis behave entirely as lithophile elements and do not participate in core segregation. Here, we tested this hypothesis by determining experimentally the partitioning of Na, Cs and Rb between iron sulfide and silicate (D_sulf/sil) and combining it with available data from the literature on K, Na and Cs partitioning. Our experiments were conducted at 1-3.5 GPa, with an additional one at 8 GPa, 1600 to 1900 °C, and varying FeO contents, which lead to a relatively large range of O content in the sulfide phases (up to 13 wt%). We found maximum D_sulf/sil of 0.8, 0.4, and 0.36 for Na, Cs and Rb respectively. In addition, D_sulf/sil for Na, K, Cs and Rb increases with temperature and O content in the sulfide and decreases with FeO content in the silicate. The degree of polymerization of the silicate melt and the S content of the sulfide additionally increase D_sulf/sil for Na, K and Cs. Since the solubility of O in sulfides is correlated with the FeO content of the silicate and both have opposite effects on D_sulf/sil, varying the oxidation state of equilibrating material does not significantly affect D_sulf/sil, which is more controlled by the temperature of equilibration. We modeled core formation for Earth, Mars and asteroid Vesta, assuming that some of the accreted embryos contained immiscible sulfides, that segregated into planetary cores. Our results show that with such a scenario, significant amounts of Na, K, Cs and Rb were sequestered in planetary cores, leading to core/mantle distribution of alkalis between 4.10^-5 and 0.15. The depletion of alkalis in the mantles of Earth, Mars and Vesta could have resulted from combined effects of volatility and core segregation, but are largely due to volatile depletion in the accreting materials.