Kees C. WELTEN¹, Marc W. CAFFEE², Kevin RIGHTER^3,4, Ralph P. HARVEY^5,6, John SCHUTT⁵, and James M. KARNER⁷
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14376]
¹Space Sciences Laboratory, University of California, Berkeley, California, USA
²Department of Physics and Astronomy, Purdue University, West Lafayette, Indiana, USA
³ARES, Mail Code XI2, NASA Johnson Space Center, Houston, Texas, USA
⁴Department of Earth and Environmental Sciences, University of Rochester, Rochester, New York, USA
⁵Department of Earth, Environmental and Planetary Science, Case Western Reserve University, Cleveland, Ohio, USA
⁶Antarctic Search for Meteorites (ANSMET), Case Western University, Cleveland, Ohio, USA
⁷Geology & Geophysics, University of Utah, Salt Lake City, Utah, USA
Published by arrangement with John Wiley & Sons

We reevaluated pairing relationships among 56 Antarctic howardites, eucrites, and diogenites (HED) from the Miller Range ice fields (MIL) based on new measurements of cosmogenic radionuclides and bulk composition of 28 HED samples and one HED-related dunite. These measurements were combined with petrographic examinations and find locations of the majority of the HED samples at MIL. During these studies, we reclassified 1 howardite, MIL 07665, as a brecciated diogenite and eight howardites as brecciated eucrites. We conclude that 18 of the 23 diogenites belong to a single large pairing group of brecciated diogenites. This pairing group includes at least seven samples with bulk compositions that indicate they contain 10%–25% of eucritic material, so technically the meteorites of this pairing group cross the boundary between diogenites and howardites. We also identified several smaller pairing groups (of 2–5 members each) among the eucrites and two paired samples among the howardites. The pairing relationships among the Miller Range eucrites are not fully resolved yet, as the collection contains many small specimens (<10 g) that were not included in this study. Altogether, we conclude that the 56 HED meteorites at Miller Range represent between 19 and 26 individual falls.

L. C. CHAVES^1,2*, M. S. THOMPSON², C. A. DUKES³, M. J. LOEFFLER⁴, M. F. MARTINEZ-MOTTA⁵, H. VANNIER², B. H. N. HORGAN², N. SMITH⁶, and K. ARDREY⁶
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14371]
¹Lunar and Planetary Laboratory, The University of Arizona, Tucson, Arizona, USA
²Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, Indiana, USA
³Laboratory for Astrophysics and Surface Physics, University of Virginia, Charlottesville, Virginia, USA
⁴Department of Astronomy and Planetary Science, Northern Arizona University, Flagstaff, Arizona, USA
⁵Departamento de Geociencias, Facultad de Ciencias, Universidad de los Andes, Bogota, Colombia
⁶Materials Science and Engineering, University of Virginia, Charlottesville, Virginia, USA
Published by arrangement with John Wiley & Sons

Pentlandite (Fe, Ni)₉S₈ is an important accessory mineral on asteroidal surfaces. It has been identified in returned regolith samples from asteroids Itokawa, Ryugu, and Bennu. Currently, systematic studies to understand the response of this mineral phase under space weathering conditions are lacking. In this work, we performed pulsed laser irradiation to simulate micrometeoroid impacts, and ion irradiation with 1 keV H⁺ and 4 keV He⁺ to simulate solar wind exposure for pentlandite. To understand the chemical, microstructural, and spectral alterations resulting from simulated space weathering, we conducted X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, and reflectance spectroscopy across the visible to near-infrared wavelengths. Our results reveal S depletion and a change in the Fe:Ni ratio at the sample surface with continuing ion irradiation. Ion irradiation also created compositionally distinct rims in the pentlandite samples, while laser irradiation produced a surface melt. Additionally, we identified hillocks protruding from the pentlandite rim after He⁺ irradiation. Our findings also show that laser and H⁺-irradiation cause the sample to brighten, while He⁺ ion irradiation causes darkening. The change in spectral slope for samples irradiated with the laser and He⁺ is minimal, while H⁺ causes the sample to redden slightly. This work will enable the identification of space weathering signatures on pentlandite grains present in the recently returned samples from asteroids Ryugu and Bennu.