^1,2Xiaohui Fu,¹Liangchen Jia,³Alian Wang,¹Haijun Cao,^1,2 Zongcheng Ling,¹Changqing Liu,¹Erbin Shi,¹Zhongchen Wu,¹Bo Li,¹Jiang Zhang
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2019.113435]
¹Shandong Provincial Key Laboratory of Optical Astronomy & Solar-Terrestrial Environment, Institute of Space Sciences, Shandong University, Weihai, China
²CAS Center for Excellence in Comparative Planetology, Hefei, China
³Department of Earth and Planetary Sciences, McDonnell Center for Space Sciences, Washington University, St. Louis, MO, USA
Copyright Elsevier

Akaganeite has been found in Yellowknife Bay mudstones of the Gale crater by the Chemistry and Mineralogy X-ray diffraction instrument (CheMin) aboard the Curiosity rover. This phase has also been discovered in limited locations on Mars by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) aboard the Mars Reconnaissance Orbiter. Akaganeite has also been proposed as a precursor candidate of hematite on Mars. To better constrain the stability and occurrence of akaganeite on Martian surfaces, structural and spectral modifications of akaganeite introduced by heating and desiccation were systematically investigated. We found that the phase transformation from akaganeite to hematite starts at 245 °C, which is accompanied by the removal of chloride in tunnels. We propose that geological activities (e.g., impact and volcanism on Mars) could heat the surrounding area and cause the transformation of akaganeite into hematite in Martian rocks and surface materials. Relative humidity (RH) variations result in water combination and overtone absorptions band strength changes. The CRISM spectrum of akaganeite detected in the Robert Sharp crater shows relatively weak 1.39 μm band compared to that of desiccated akaganeite under simulated Martian environments, indicating that akaganeite found on Mars could be highly desiccated. The water adsorption of akaganeite occurred when exposed to ambient laboratory conditions (RH ~65%). This suggests the water adsorption and desorption of akaganeite on Mars correspond to RH changes in a diurnal cycle.

¹S.T.Port,¹V.F.Chevrier,²E.Kohler
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2019.113432]
¹University of Arkansas, Center for Space and Planetary Sciences, Fayetteville, AR 72701, United States
²NASA Goddard Space Flight Center, Greenbelt, MD 20771, United States
Copyright Elsevier

The source of the unusually high radar reflectivity signal found on the highlands of Venus is hypothesized to be caused by a mineral with a high dielectric constant. We propose that this source is a combination of tellurium, sulfur, and bismuth. All three elements are commonly outgassed in terrestrial eruption plumes and thus are likely to be found on Venus. To test our hypothesis, we used a Venus simulation chamber and studied the stability of various tellurium, bismuth, and sulfur mixtures at Venus temperatures and pressures and in atmospheres of CO2, 100 ppm SO2 in CO2, or 100 ppm COS in CO2. When mixed together bismuth, tellurium, and sulfur phases preferentially formed tetradymite (Bi2Te2S). The remaining minerals that formed in each experiment strongly depended on the initial mixture. For instance the Bi2S3/Bi2Te3 mixture experiments resulted in the original minerals as well as BiTe at hotter temperatures, meanwhile the Bi/Te/S mixture produced Bi2S3 and occasionally Bi2Te3, Bi(S,Te), and Bi4(S,Te)3 depending on the temperature/pressure. There is evidence that COS, but not SO2, affected the stability of some minerals. Due to the presence of these elements in volcanic gases we propose that they can be present in the highlands and can, at least in part, account for the high radar reflectivity signal on the highlands.

^1,2Keyron Hickman-Lewis,¹Frédéric Foucher,³Steven Pelletier,⁴Fabio Messori,¹Frances Westall
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2019.104743]
¹CNRS Centre de Biophysique Moléculaire, Rue Charles Sadron, 45071, Orléans, France
²Dipartimento di Scienze Biologiche, Geologiche e Ambientali (BiGeA), Università di Bologna, Via Zamboni, 67, I 40126, Bologna, Italy
³Université François Rabelais de Tours, Tours, France
⁴Università Degli Studi di Modena e Reggio Emilia, Modena, Italy

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