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Institut de minéralogie, de physique des matériaux et de cosmochimie

Volatile elements in small bodies and protoplanetary dust

According to dynamical models, significant transport of small bodies from the outer solar system towards both more external and internal regions of the protoplanetary system occurred during accretion. The Earth may have gained significant amounts of volatiles, in particular H, C and N during these processes. Understanding the processes of fixation of volatile elements in the first solids formed in the solar system and their transfer during the early processes of formation of rocky bodies sheds light on the origin and inventory of volatiles in terrestrial planets. Several projects aim at studying the origin, speciation and stability of water- N- or C-bearing phases in early solids of the solar systems. These questions are addressed through various approaches, from isotopic and mineralogical studies of chondrites to experimental studies.


Element and isotopic fractionation of volatiles

Experimental studies focus on the elemental and isotopic fractionations of volatiles during interactions between the first fine-grained materials present in the protoplanetary disk and in the parent bodies of meteorites, liquids and the surrounding gases. The fractionation of the isotopes of light elements caused by ionizing irradiations of organic and silicate precursors is also an important topic of research (COSMO, ROCKS). Another key issue addressed through elemental and isotopic fractionation studies, mostly of H and O, is related to the distribution and origin of volatile elements in chondrites, which host various hydrated phases and organic molecules (COSMO, ROCKS). The H-isotope signature of these phases is a powerful tool for determining their origin in chondrites and assessing their influence on the Earth composition.

Much less is known about the H and C content in chondrules, expected to have formed at high temperature from precursors condensed in the solar nebula. Thanks to micron-scale investigation by NanoSIMS, the water content and its H-isotope signature can be used to determine the origin of water in chondrules, and refine scenarios for water delivery on Earth (ROCKS). Meteoritic refractory inclusions, which are among the most ancient rocks of the solar system, may also contain trace amounts of water, whose O- and H-isotopes can be studied by NanoSIMS (COSMO, ROCKS). These studies shed new light on the processes that influenced the formation of solids in the solar system.


Mineralogical processes of hydration and dehydration

The processes of hydration of small bodies are studied within the PALM group by means of mineralogical investigations down to the nano-scale and crystal-chemistry of hydrous phases.The main products of asteroidal water-rock interactions are phyllosilicates (frequently serpentines) with high amounts of Fe, which conditions of formation and stability are still poorly understood. A better understanding of them would bring clues to the conditions of hydration of their parent bodies, at early stages of the solar system. Two approaches are combined, the fine mineralogy of carbonaceous chondrites (crystal chemistry by STXM-XANES and TEM, XRD-computed tomography of altered assemblages) and experiments (alteration of primary chondritic phases, crystal growth of chondritic serpentines, Fe oxidation processes under anoxic conditions) through collaborations (Biominerals, XRD experimental platform).

In order to understand how the asteroidal vectors of water would deliver H upon impacts between a planetesimal and a planet, it is essential to evaluate the volatility of H under temperature, pressure and dynamical conditions relevant to planetary accretion. We develop shock dehydration experiments on materials in which the speciation of H is analogous to its speciation in potential impactors. We study both in situ and ex situ the shock dehydration processes of serpentines of chondritic composition and other hydrous phases using x-ray absorption spectroscopy, XRD as well as IR and Raman spectroscopy and TEM (PALM, MP3, TQM).



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