^1,2Gustavo P. Maia, ²Laurent Remusat, ^2,3Kana Amano, ²Jean-Christophe Viennet, ^4,5,6Jason P. Dworkin, ^4,5,6Hannah L. McLain, ¹José A.L. da Silva
Earth and Planetary Science Letters, 692, 120237 Open Source Link to Article [DOI: 10.1016/j.epsl.2026.120237]
¹Centro de Química Estrutural, Institute of Molecular Sciences, Instituto Superior Técnico, University of Lisbon, Lisbon, Portugal
²Institut de Minéralogie, Physique des Matériaux et Cosmochimie, UMR CNRS 7590, Sorbonne Université, Muséum National d’Histoire Naturelle, Paris, France
³Institut d’Astrophysique Spatiale (IAS), Université Paris-Saclay, Orsay Cedex, 91405, France
⁴Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, USA
⁵Center for Space Science and Technology, University of Maryland Baltimore County, Baltimore, Maryland, USA
⁶Center for Research and Exploration in Space Science and Technology, NASA/GSFC, Greenbelt, MD, 20771, USA
Copyright Elsevier

Carbonaceous chondrites contain up to 4 wt% organic matter, likely inherited from precursors synthesised during preaccretion events. This organic inventory was later altered by hydrothermal and radiative processes, though the role of shock-induced impacts remains unclear. In this study, we examine the solid-state mechanochemical reactivity of hexamethylenetetramine (HMT) with sodium-rich montmorillonite (MMT) as an analogue to investigate the influence of shock- or impact-induced processes on organic matter evolution. HMT is reactive under mechanical stress, particularly when the clay mineral structure is disrupted, resulting in a wide range of molecules, including HMT-related compounds (as HMT-CH₃, HMT-OH, among others), pyrazine and triazinane/triazine derivatives. Notably, the incorporation of oxygen in N-rich species was also observed, despite the absence of liquid water. Conversely, when the clay mineral remains intact, mechanical input promotes the solid-state insertion of HMT-like molecules (as HMT, HMT-CH₃ and triazinane derivative) within its interlayer space, thereby protecting it from further reaction. The “cyclic mechanical input” delivered by laboratory milling (i.e., MM 200) and grinding (i.e., McCrone) is relevant to shock processes at an asteroid surface through repeated micrometeorite and IDPs impacts (i.e., space gardening). This work highlights shock/impact as a key factor driving both transformation and protection of extraterrestrial organics, offering new insights on how impact processes might have shaped extraterrestrial organic matter and consequent exogenous delivery of possibly prebiotic compounds to planetary surfaces.