^1,2O.Ruesch et al (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2018.01.022]
¹NASA Goddard Space Flight Center/USRA, Greenbelt, MD 20771, USA
²ESTEC, European Space Agency, Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
Copyright Elsevier

Vinalia and Cerealia Faculae are bright and salt-rich localized areas in Occator crater on Ceres. The predominance of the near-infrared signature of sodium carbonate on these surfaces suggests their original material was a brine. Here we analyze Dawn Framing Camera’s images and characterize the surfaces as composed of a central structure, either a possible depression (Vinalia) or a central dome (Cerealia), and a discontinuous mantling. We consider three materials enabling the ascent and formation of the faculae: ice ascent with sublimation and carbonate particle lofting, pure gas emission entraining carbonate particles, and brine extrusion. We find that a mechanism explaining the entire range of morphologies, topographies, as well as the common composition of the deposits is brine fountaining. This process consists of briny liquid extrusion, followed by flash freezing of carbonate and ice particles, particle fallback, and sublimation. Subsequent increase in briny liquid viscosity leads to doming. Dawn observations did not detect currently active water plumes, indicating the frequency of such extrusions is longer than years.

¹J.T. Poitras, ¹E.A. Cloutis, ², M.R. Salvatore, ³S.A. Mertzman, ¹D.M. Applin, ¹P. Mann
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2018.01.023]
¹Department of Geography, University of Winnipeg, Winnipeg MB R3B 2E9 Canada
²Department of Physics & Astronomy, Northern Arizona University, Flagstaff, Arizona, USA 86011
³Department of Earth and Environment, Franklin and Marshall College, Lancaster, Pennsylvania, USA
Copyright Elsevier

We investigated the spectral reflectance properties of minerals under a simulated Martian environment. Twenty-Eight different hydrated or hydroxylated phases of carbonates, sulfates, and silica minerals were selected based on past detection on Mars through spectral remote sensing data. Samples were ground and dry sieved to <45 µm grain size and characterized by XRD before and after 133 days inside a simulated Martian surface environment (pressure 5 torr and CO2 fed). Reflectance spectra from 0.35 to 4 µm were taken periodically through a sapphire (0.35 to 2.5 µm) and zinc selenide (2.5 to 4 µm) window Over a 133-day period. Mineral stability on the Martian surface was assessed through changes in spectral characteristics. Results indicate that the hydrated carbonates studied would be stable on the surface of Mars, only losing adsorbed H2O while maintaining their diagnostic spectral features. Sulfates were less stable, often with shifts in the band position of the SO, Fe, and OH absorption features. Silicas displayed spectral shifts related to SiOH and hydration state of the mineral surface, while diagnostic bands for quartz were stable. Previous detection of carbonate minerals based on 2.3-2.5 µm and 3.4-3.9 µm features appear to be consistent with our results. Sulfate mineral detection is more questionable since there can be shifts in band position related to SO4. The loss of the 0.43 µm Fe3+ band in many of the sulfates indicate that there are fewer potential candidates for Fe3+ sulfates to permanently exist on the Martian surface based on this band. The gypsum sample changed phase to basanite during desiccation as demonstrated by both reflectance and XRD.Silica on Mars has been detected using band depth ratio at 1.91 and 1.96 µm and band minimum position of the 1.4 µm feature, and the properties are also used to determine their age. This technique continues to be useful for positive silica identifications, however, silica age appears to be less consistent with our laboratory data. These results will be useful in spectral libraries for characterizing Martian remote sensed data.

^1,2,3Gunther Kletetschka
Earth and Planetary Science Letters 487, 1-8 Link to Article [https://doi.org/10.1016/j.epsl.2018.01.020]
¹Institute of Geology, Academy of Sciences of the Czech Republic, Czech Republic
²Faculty of Science, Charles University, Czech Republic
³Department of Geology and Geophysics, University of Alaska Fairbanks, USA
Copyright Elsevier

The origin of magnetization in Allende may have significant implications for our understanding of core formation/differentiation/dynamo processes in chondrite parent bodies. The magnetic Allende data may contain information that could constrain the magnetic history of Allende. The measurements on Allende chondrules reveal an existence of magnetization component that was likely acquired during the meteorite transit to terrestrial conditions. Both the pyrrhotite carrying magnetic remanence intensity and direction of the chondrules change erratically when subjecting the Allende meteorite’s chondrules to temperatures near 77 K and back to room temperature. Chondrules with more intense original magnetization are denser and contain larger inverse thermoremanent magnetization (ITRM). Temperature dependent monitoring of ITRM revealed that magnetization was acquired at temperature near 270 K. Such temperature is consistent with the condition when, in addition to temperature increase, the atmospheric uniaxial pressure applied during the meteorite entry on the porous material was responsible for meteorite break up in the atmosphere. During this process, collapse of the pore space in the matrix and some chondrules would generate crystalline anisotropy energy accumulation within pyrrhotite grains in form of parasitic magnetic transition.