¹Ajay Dev Asokan,¹Yogita Kadlag,²Yash Srivastava,³Khirod Kumar Das,³Rumanshu Hazarika,²James M. D. Day
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.70099]
¹Geosciences Division, Physical Research Laboratory, Ahmedabad, Gujarat, India
²Scripps Institution of Oceanography, San Diego, California, USA
³Department of Geology, Babasaheb Bhimrao Ambedkar University, Lucknow, India
Published by arrangement with John Wiley & Sons

The Holocene Luna Structure in western India has been claimed to be the fourthand youngest impact crater on the Indian subcontinent. The circular shape; the unusualmineralogy including high-temperature mineral phases such as kirschsteinite and w€ustite;and the elevated abundance of highly siderophile elements (HSE: Os, Ir, Ru, Rh, Pt, andPd) have been provided as evidence in favor of an impact origin. Here, we present newmineralogical, bulk rock geochemical data including isotope-dilution HSE abundances and187 Re- 187 Os compositions of the suspected Luna impactites. The samples are dense irregularnodules with undulated surface and flow-like structures and are glassy to extremely finegrained, with or without vesicles. The new HSE data show no Ir enrichment compared toupper continental crust. The radiogenic measured 187 Os/ 188 Os compositions (0.2289–0.7253)further rule out any extraterrestrial contribution in the suspected impactites. The observedhigh-temperature mineral assemblage shows similarity to that of iron-rich archaeologicalslags. We reinterpret the Luna Structure materials as slags that are likely associated with theBronze Age in the Harappan Civilization and may have formed as a byproduct of coppersmelting. Considering the new evidence, the Luna Structure of western India is not ameteorite impact crater.

^1,2,3,4Anthony M. Gargano,²Justin I. Simon,⁴Erick Cano,^4,5Karen Ziegler,⁵Charles K. Shearer,³James M. D. Day,⁴Zachary Sharp
Proceedings of the National Academy of Sciences of the USA (PNAS) 123, e2531796123 Open Access Link to Article [https://doi.org/10.1073/pnas.2531796123]
¹Lunar and Planetary Institute, Houston, TX 77058
²Astromaterials Research and Exploration Science Division, NASA Johnson Space Center, Houston, TX 77058
³Scripps Institution of Oceanography, Geosciences Research Division, University of California San Diego, La Jolla, CA 92093
⁴Center for Stable Isotopes, University of New Mexico, Albuquerque, NM 87131-0001
⁵Institute of Meteoritics, University of New Mexico, Albuquerque, NM 87131

The impactor flux record to Earth has largely been erased by active tectonics, weathering, and continual reworking of the crust. Instead, a record of highly siderophile elements (HSE: Re, Os, Ir, Ru, Rh, Pt, Pd, and Au) in lunar impactites has been used as a proxy for the type of impactor material added to the Earth–Moon system. Quantifying impactor mass and flux with the HSE can potentially be complicated by numerous secondary processes, however, including silicate–metal segregation and multiple impact heritage. In contrast, because oxygen has an invariant geochemical affinity, triple oxygen isotope compositions have the potential to offer a robust long-term record of impactor fluxes in complex mixtures such as regolith. Here, we use high-precision triple oxygen isotopes to deconvolve the influences of meteorite addition and silicate vaporization and identify a ubiquitous impactor contaminant comprised of partially evaporated CM or ureilite-like material representing at least 1 wt% of the lunar regolith. Water delivered to Earth by meteorite material over 4 billion years therefore is only a fraction of an ocean’s worth of water but is a significant contributor to the ice reservoir of the lunar cold traps.