¹H.Teffeteller,²J.Filiberto,¹M.C.McCanta,²A.H.Treiman,³L.Keller,⁴D.Cherniak,⁵M.Rutherford,⁵R.F.Cooper
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115085]
¹Department of Earth and Planetary Sciences, University of Tennessee at Knoxville, 1621 Cumberland Avenue, 602 Strong Hall, Knoxville, TN 37996, United States of America
²Lunar and Planetary Institute, 3600 Bay Area Blvd, Houston, TX 77058, United States of America
³NASA Johnson Space Center, 2101 E NASA Pkwy, Houston, TX 77058, United States of America
⁴Rensselaer Polytechnic Institute, Troy, NY, United States of America
⁵Dept. Earth, Environmental, & Planetary Sciences, Brown University, Providence, RI 02912, United States of America
Copyright Elsevier

Characterizing the surface of Venus has been complicated by its thick atmosphere and caustic surface conditions (~470 °C, 90 bars). Several approaches, including the collection of spectral data, thermodynamic modelling, lander missions, and surface weathering laboratory experiments have progressed our view of what lies at the surface. However, surface-atmosphere interactions remain somewhat unconstrained and interpretations of the spectral data rely on an understanding of the surface-atmosphere alteration. We used a cold-seal pressure vessel apparatus pressurized with pure CO₂ gas and both synthetic and natural glassy basalts specimens to simulate chemical weathering on the surface of Venus for a duration of two weeks. The extent of alteration was described from the surface of samples to depth using Rutherford Backscatter Spectroscopy (RBS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques. We describe the alteration zones of reacted basalt specimens and report an enrichment of divalent cation species at the near surfaces of basalts; Ca²⁺ was enriched by ~5 wt% and Fe²⁺ was enriched by ~1–2 wt%. The enrichment at the near surface favors the production of iron (Fe) oxide(s) and carbonates on the surfaces, which form discontinuous coatings on all reacted samples in two weeks duration. Our results aid in the interpretation of radar emissivity data by constraining which alteration products should be present on the surface and suggesting timeframes necessary for their detection. Assuming that radar emissivity is able to discern weathered basalt, especially those dominated by carbonates and/or semiconducting minerals Fe oxide(s), our results suggest that basalts at Idunn Mons in Imdr Regio previously thought to be anywhere from 2.5 million to a few years old (Smrekar et al., 2010; D’Incecco et al., 2017; Filiberto et al., 2020; Cutler et al., 2020) could instead be as young as 65,000 years to 110,000 years depending on basalt type.

¹Rachel Y.Sheppard,²Ralph E.Milliken,²Kevin M.Robertson
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115083]
¹Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States of America
²Department of Earth, Environmental, and Planetary Sciences, Brown University, Providence, RI, United States of America
Copyright Elsevier

The martian crust is often viewed through the lens of its dominant secondary minerals, Noachian phyllosilicates and Hesperian sulfates, based on orbital spectral observations. However, the effects of surface exposure on the spectra of these hydrous minerals are not fully understood. We use an environmental chamber to measure changes in near-infrared (NIR) spectral absorptions related to H2O in smectite (montmorillonite) and Mg-sulfate under different temperature, pressure, and relative humidity conditions with relevance to the surface of Mars. Observed spectral differences are attributed to changes in water content (hydration state), mineral phase, and degree of crystallinity. It is observed that even minor changes in hydration state and phase (for Mg sulfate) cause perceptible changes in NIR H2O absorption features when measured in a controlled laboratory setting under dry Mars-like conditions. Based on these results and the known ability of smectite to rehydrate under increased RH, smectites exposed at the surface of Mars are expected to exchange water with the martian atmosphere under specific conditions, making them active participants in the present-day hydrological cycle of Mars, and in theory these hydration-dehydration processes should be detectable using NIR reflectance spectroscopy. However, some of the spectral changes associated with these hydration changes are subtle and may not be detectable with orbital or landed VNIR spectrometers. Furthermore, we find that the presence of clay minerals can spectrally mask the presence of Mg sulfates under a range of hydration states if the clay minerals are above ∼10 wt% abundance. Random noise was added to the laboratory spectral data to simulate orbital-quality reflectance data, and it is observed that expected changes related to hydration state and crystallinity are likely difficult to detect in current orbital VNIR data such as CRISM and OMEGA. This highlights the importance of future in situ NIR reflectance observations to accurately determine the extent to which hydrous minerals exposed as the surface cycle water with the martian atmosphere under present-day environmental conditions and to properly assess the role of hydrous minerals in the martian water budget.

^1,2J.A.Cartwright,²K.V.Hodges,²M.Wadhwa
Earth and Planetary Science Letters 590, 117576 Link to Article [https://doi.org/10.1016/j.epsl.2022.117576]
¹Department of Geological Sciences, University of Alabama, Tuscaloosa, AL 35487-0338, USA
²School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287-6004, USA
Copyright Elsevier

Impact events on planetary surfaces can leave significant volumes of melt, archived in planetary regoliths, which provide important information regarding the timing and nature of these events. For example, an observed ca. 3.9-4.1 Ga age cluster within lunar samples has been interpreted as indicative of a significant Solar System-wide event: the so-called “Late Heavy Bombardment”. Here, we report data from a laser ablation microprobe 40Ar/39Ar study of clasts within two unpaired howardite meteorites (NWA 1929 and Dho 485) to explore the impact history of their asteroid parent body – (4)Vesta. Laser microprobe dates for the howardites varied broadly between 3.5 to 4.5 Ga (NWA 1929) and 2.5 to 4.5 Ga (Dho 485), but show no clear cluster in ages at ca. 3.9-4.1 Ga. Consistent with previously reported U-Pb dates for HED meteorites, our data suggest an extended impact bombardment period on (4)Vesta as compared to the distribution of 40Ar/39Ar impactite dates for available samples from the Apollo and Luna sample archives. The impact history of Vesta revealed here highlights that current models of the impact flux in the inner Solar System based on the Late Heavy Bombardment hypothesis require refinement.