^1,2,3Laura E. Jenkins, ^1,2Roberta L. Flemming, ^1,2Sam Nicholson, ⁴Mark Burchell, ⁴Kathryn Harriss, ^5,6Anne H. Peslier, ⁵Roy G. Christoffersen, ^7,8Jörg Fritz, ⁹Cornelia Meyer
Journal of Geophysical Research: Planets, 131, e2026JE010049
Open Access Link to Article [DOI: 10.1029/2026JE010049]
¹Department of Earth Sciences, Western University, London, ON, Canada
²Institute for Earth & Space Exploration, Western University, London, ON, Canada
³Now at: Diamond Light Source, Didcot, UK
⁴Centre for Astrophysics and Planetary Science, School of Engineering, Mathematics and Physics, University of Kent, Canterbury, UK
⁵Jacobs, NASA Johnson Space Center (JSC), Houston, TX, USA
⁶Department of Geological Sciences, New Mexico State University, Las Cruces, NM, USA
⁷Saalbau Weltraum Projekt, Heppenheim, Germany
⁸Zentrum für Rieskrater und Impaktforschung Nördlingen (ZERIN), Nördlingen, Germany
⁹Horizontereignis gUG, Berlin, Germany

Published by arrangement with John Wiley & Sons

Shock metamorphism is a ubiquitous process in our solar system. Shock pressure can be related to the lattice strain (ε) of individual minerals within a shocked sample. The lattice strain can be quantified within intact samples by in situ micro-X-ray diffraction (μXRD) using the Williamson-Hall method. The Williamson-Hall lattice strain (W-H ε) method has so far only been calibrated for olivine. This work extends the W-H ε method to high-Ca clinopyroxene. We obtained three sets of experimentally shocked clinopyroxene samples and calculated ε for each sample using μXRD. We created a calibration curve that relates ε to peak shock pressure experienced. Its trend line has the equation P = 222.85ε−8.60 GPa, with an error of ±9 GPa. The calibration curve was applied to the Martian meteorites Nakhla, Zagami, and Allan Hills A77005 (ALHA 77005) to compare these results with the meteorites’ optically determined shock stages. The peak shock pressures returned by the calibration curve are: 15 ± 9 GPa for Nakhla, 35 ± 9 GPa for Zagami, and 68 ± 9 GPa for ALHA 77005. These results agree with the meteorites’ previously determined shock stages. The development of a W-H ε calibration curve for high-Ca clinopyroxene is preliminary; however, it expands this method for evaluating shock metamorphism of shocked clinopyroxene-bearing samples, such as Martian shergottites.

¹M. C. Deahn et al. (>10)
Journal of Geophysical Research: Planets, 131, e2025JE009471
Open Access Link to Article [DOI: 10.1029/2025JE009471]
¹Purdue University, West Lafayette, IN, USA

Published by arrangement with John Wiley & Sons

The Mars 2020 rover is currently traversing the western rim of Jezero, a Middle to Late Noachian‐aged crater formed by an impactor that struck the northwest edge of Isidis Planitia (hereafter referred to as theIsidis basin) on Mars. Previous studies suggest that pre‐Isidis basin and Noachian outcrops are preservedthroughout this region; however, the nature of these exposures in the Jezero crater rim is unclear. It has beenhypothesized that crater‐forming processes should expose these ancient crustal rocks in the Jezero craterrim—presenting a unique opportunity to explore ancient Mars outcrops that are otherwise typically buried byyounger units. Jezero’s rim has undergone extensive erosion and modification since its formation ∼3.9 billionyears ago. To investigate these ancient lithologies, the Mars 2020 Science Team produced a 1:2500 scalegeologic map and interpreted a bedrock map of the ∼14.5 × 3.5 km area around the western Jezero crater rim.We identified, mapped, and defined nine bedrock units on Jezero crater’s rim to make connections to regionalgeologic units and identify deposits or features unique to Jezero crater. We found that the rim likely preserves arecord of pre‐Isidis bedrock, the Isidis and Jezero impacts, and post‐impact geologic processes. We alsoobserved candidate megabreccia, hydrothermal ridges, and regional volcanics that may be targets for futurerover‐based investigations. Our results show that in situ investigation of pre‐Isidis and Noachian‐agedlithologies preserved on the rim will provide insight into the nature of Mars’ early crustal formation andcratering processes.