¹Honglei Lin,²Rui Xu,¹Wei Yang,¹Yangting Lin,¹Yong Wei,¹Sen Hu,²Zhiping He,³Le Qiao,¹Weixing Wan
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2019JE006076]
¹Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China
²Key Laboratory of Space Active Opto‐Electronics Technology, Shanghai
Institute of Technical Physics, Chinese Academy of Sciences, Shanghai, China
³Shandong Provincial Key Laboratory of Optical Astronomy and Solar‐Terrestrial Environment, Institute of Space Sciences, Shandong University, Weihai, China
Published by arrangement with John Wiley & Sons

China’s Chang’E‐4 (CE‐4) mission successfully landed in Von Kármán crater within South Pole‐Aitken basin of the Moon. The Visible and Near‐Infrared Imaging Spectrometer (VNIS) on board Yutu‐2 rover investigated the photometric properties of lunar regolith. Seven VNIS measurements were conducted on a small lunar surface with a diameter <5 m by the rover rotating at the center, with the phase angles from 39.6 to 97.1° obtained in the similar observational geometry of solar altitude and observation angle. The phase function, which varies in different wavelength, is derived using a third‐order polynomial fitting, in combination with the calibration and comparison of orbital/in situ VNIS data at the Chang’E‐4 landing site and the same regions. After the photometrical correction of the spectra with the phase function, the derived FeO contents and optical maturity parameters of the regolith reduce much of their deviations, which is consistent with the homogeneity of the regolith and hence demonstrates the significance of the photometric correction on the VNIS spectra.

¹S. A. Singerling,¹A. J. Brearley
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13450]
¹Department of Earth & Planetary Sciences, University of New Mexico, MSC‐03 2040, Albuquerque, New Mexico, 87131 USA
Published by arrangement with John Wiley & Sons

The presence of primary iron sulfides that appear to be aqueously altered in CM and CR carbonaceous chondrites provides the potential to study the effects and, by extension, the conditions of aqueous alteration. In this work, we have used SEM, TEM, and EPMA techniques to characterize primary sulfides that show evidence of secondary alteration. The alteration styles consist of primary pyrrhotite altering to secondary pentlandite (CMs only), magnetite (CMs and CRs), and phyllosilicates (CMs only) in grains that initially formed by crystallization from immiscible sulfide melts in chondrules (pyrrhotite‐pentlandite intergrowth [PPI] grains). Textural, microstructural, and compositional data from altered sulfides in a suite of CM and CR chondrites have been used to constrain the conditions of alteration of these grains and determine their alteration mechanisms. This work shows that the PPI grains exhibit two styles of alteration—one to form porous pyrrhotite‐pentlandite (3P) grains by dissolution of precursor PPI grain pyrrhotite and subsequent secondary pentlandite precipitation (CMs only), and the other to form the altered PPI grains by pseudomorphic replacement of primary pyrrhotite by magnetite (CMs and CRs) or phyllosilicates (CMs only). The range of alteration textures and products is the result of differences in conditions of alteration due to the role of microchemical environments and/or brecciation. Our observations show that primary sulfides are sensitive indicators of aqueous alteration processes in CM and CR chondrites.

¹T.J.Bowling,² B.C.Johnson,³ S.E.Wiggins,⁴E.L.Walton,²H.J.Melosh,⁵T.G.Sharp
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.113689]
¹Department of Geophysical Sciences, University of Chicago, United States of America
²Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, United States of America
³Department of Earth, Environmental, and Planetary Sciences, Brown University, United States of America
⁴Department of Physical Sciences, MacEwan University, Canada
⁵School of Earth and Space Exploration, Arizona State University, United States of America
Copyright Elsevier

Martian meteorites are currently the only rock samples from Mars available for direct study in terrestrial laboratories. Linking individual specimens back to their source terrains is a major scientific priority, and constraining the size of the impact craters from which each sample was ejected is a critical step in achieving this goal. During ejection from the surface of Mars by hypervelocity impacts, these meteorites were briefly compressed to high temperatures and pressures. The period of time that these meteorites spent at high pressure during ejection, or the ‘dwell time’, has been used to infer the size of the crater from which they were ejected. This inference requires assumptions that relate shock duration to impactor size, and the relation used by many authors is neither physically motivated nor accurate. Using the iSALE2D shock physics code we simulate vertical impacts at high resolution to investigate the dwell time that basaltic rocks from Mars (shergottites) spend at high pressure and temperature during ejection. Future simulation of oblique impacts will lead to more accurate dwell time estimates. Ultimately, we find that dwell time is insensitive to changes in impact velocity but for a given impact, dwell times are longer for material originating from greater depth and material that experiences higher shock pressures. Using our results, we provide scaling laws for estimating impactor size. During the formation of craters 1.9, 14, and 104 km in diameter, material capable of escaping Mars will have mean dwell times of 1, 10, and 100 ms, respectively.