¹Gene Schmidt, ²Frank Fueten, ³Robert Stesky, ⁴Jessica Flahaut, ⁵Ernst Hauber
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2018JE005658]
¹IRSPS, Universita “G.D’Annunzio”, Pescara, Italy
²Department of Earth Sciences, Brock University, St. Catharines, Ontario, Canada
³Pangaea Scientific, Brockville, Ontario, Canada
⁴CNRS (institute)/CRPG Nancy (department), France
⁵Institute of Planetary Research, German Aerospace Center (DLR), Berlin, Germany
Published by arrangement with John Wiley & Sons

Hebes Chasma is an 8 km deep, 126 by 314 km, isolated basin that is partially filled with massive deposits of water‐altered strata called interior layered deposits (ILD). By analyzing the ILD’s structure, stratigraphy and mineralogy, a depositional history of Hebes Chasma is interpreted. Three distinct ILD units were found and are informally referred to as the Lower, Upper and Late ILD. These units are distinguished by their layer thicknesses, layer attitudes, mineralogies and erosional landforms. The Lower and Upper ILDs comprise the chasma’s 7.5 km tall, 120 by 43 km, central mound and the Late ILD is located in the valley between the central mound and the chasma’s northern wall. A horizontal unconformity separates the Lower and Upper ILDs and layer attitudes revealed large‐scale shallow folding within the Lower ILD. All ILDs are characterized by both monohydrated and polyhydrated sulfates (MHS and PHS) signatures. Erosional landforms such as hummocks, polygons, and debris flows suggest past glacial activity within the chasma. A scenario involving several ash fall events during various stages of chasma formation is proposed as the dominant setting throughout Hebes’ geologic history.

¹J. V. Hogancamp, ²B. Sutter, ³R. V. Morris, ²P. D. Archer, ³¹D. W. Ming, ³E. B. Rampe, ⁴P. Mahaffy, ⁵R. Navarro‐Gonzalez
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2018JE005691]
¹Geocontrols Systems–Jacobs JETS Contract, NASA Johnson Space Center, Houston, TX, USA
²Jacobs, NASA Johnson Space Center, Houston, TX, USA
³NASA Johnson Space Center, Houston, TX, USA
⁴NASA Goddard Space Flight Center, Greenbelt, MD, USA
⁵Universidad Nacional Autonoma de Mexico, Mexico
Published by arrangement with John Wiley & Sons

Oxygen and HCl gas releases detected by the Sample Analysis at Mars (SAM) instrument on board the Mars Science Laboratory Curiosity rover in several Gale Crater samples have been attributed to the thermal decomposition of perchlorates and/or chlorates. Previous experimental studies of perchlorates mixed with Fe‐bearing phases explained some but not all of the evolved oxygen releases, and cannot explain the HCl releases. The objective of this paper was to evaluate the oxygen and HCl releases of chlorates and chlorate/Fe‐phase mixtures in experimental studies and SAM evolved gas analysis (EGA) datasets. Potassium, magnesium, and sodium chlorate were independently mixed with hematite, magnetite, ferrihydrite, and palagonite and analyzed in a thermal evolved gas analyzer configured to operate similarly to the SAM instrument. Fe‐phases depressed the chlorate decomposition temperature 3‐214 °C and consumed up to 75% of the evolved oxygen from chlorate decomposition. Chlorate/Fe‐phase mixtures have oxygen and HCl releases consistent with some samples analyzed by SAM. Reported oxychlorine abundances based on calculations using oxygen detected by SAM could be minimum values because Fe‐phases consume evolved oxygen. The results of this work demonstrate that chlorates could be present in the Martian soil and that oxygen and HCl release temperatures could be used to constrain which chlorate cation species are present in samples analyzed by SAM. Knowledge of which chlorates may be present in Gale Crater creates a better understanding of the detectability of organics by evolved gas analysis, habitability potential, and the chlorine cycle on Mars.

¹Steven A.Binnie, ¹Kunihiko Nishiizumi, ¹Kees C.Welten, ^2,3Marc W.Caffee, ⁴Dirk Hoffmeister
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2018.09.036]
¹Space Sciences Laboratory, University of California, Berkeley, 7 Gauss Way, Berkeley, CA 94720-7450, USA
²Department of Physics and Astronomy, Purdue University, West Lafayette, IN 47907-1306, USA
³Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN 47907-1306, USA
⁴Institute for Geography, University of Cologne, Otto-Fischer-Str. 4, 50674, Cologne, Germany
Copyright Elsevier

Measurements of cosmogenic ¹⁰Be, ²⁶Al and ³⁶Cl in Apollo 16 double drive core 68002/68001 are combined with a high resolution digital surface model of the sampling site to investigate the surface processes on the Moon. We find both a significant deficit of solar cosmic ray (SCR)-produced ²⁶Al and a lack of SCR-produced ³⁶Cl in the top 3-5 g/cm² of the lunar regolith. The topographic model shows the core was taken from just inside a crater with a rim diameter of 25-30 cm. These observations are consistent with regolith removal and displacement by a shallow impact that occurred on the order of 100 kyr ago, or less. Our findings are also compatible with shallow mixing, or gardening, of the lunar regolith to depths of a few cm, a value often found in other lunar cores over the ∼10⁶ yr averaging times of ²⁶Al and ⁵³Mn measurements. More definitive regolith mixing depth estimates are not possible due to the likelihood of disturbance in the top of the core as a result of sampling and/or handling. Our results support the hypothesis that the lunar surface experiences more frequent disturbances by small primary and secondary impacts than has previously been assumed. Additionally, we find no evidence that fine-grained ejecta from the 2.0 Myr old South Ray Crater impact reached this site. If the layer of fine-grained ejecta that reached the sampling site from the South Ray Crater was no more than a few cm thick, this absence can be explained by the erosion that formed the small, relatively recent crater at the coring location.