Research Topics

Evolution of organic molecules under hydrothermal conditions typical of carbonaceous chondrites

Organic matter occurs in carbonaceous chondrites shows an impressive molecular diversity: more than 14,000 different soluble organic molecules were identified in a methanol extract of the Murchison meteorite. The organic content of CC can be divided into insoluble and soluble organic material, the former one being the most abundant (more than 50 wt%). The soluble fraction comprises various classes of molecules; among them were reported: carboxylic acids, amino acids, hydrocarbons, sugar derivatives, alcohol, ketones and nucleobases. It must be noted that significant variations can be observed from one meteorite to another, in both abundance and distribution.

The question of the origin of these molecules remains debated: were they formed on the parent body? Were they accreted as constituents of dust or ice? Are they solar or interstellar products?

Building of organic matter / mineral associations during hydrothermal alteration on the carbonaceous asteroids

Although carbonaceous chondrites still contain primordial solar system constituents, like chondrules and CAIs, in addition to presolar grains, they exhibit signs of secondary processes. Due to the decay of short-lived radionucleides, including ⁶⁰Fe and ²⁶Al, temperature of the parent body increased and induced reprocessing of the accreted components. If ice was present, a local fluid circulation has altered the matrix, resulting into a fine scale association of hydrated silicates, oxides, hydrated sulfides and OM. This aqueous alteration occurred a few million years after the formation of the solar system, but the exact duration of the hydrothermal events remains undisclosed.

Interestingly, the most hydrated CC (petrologic types 1 and 2, type 3.0 being the least modified by secondary parent body processes) are also the richest in OM. Matrix texture and petrology are related to the hydrothermal process intensity. The organo-mineral association points to a co-evolution of organic matter and minerals in the matrix of CC. These observations are consistent with the accretion of OM associated with water ice and inorganic dust to form the first solids in the protoplanetary disk, which evolved due to hydrothermal events. But how did the mineral influence the evolution of organic molecules? How the presence of organic molecule could influence the stability of minerals in the matrix?

Preservation and evolution of isotope signatures of organic molecules on carbonaceous asteroids

Stable isotope compositions constitute valuable tools to investigate the origin and evolution of organic molecules in geological systems; in particular, H and N isotopes are relevant to determine the origin of OM in carbonaceous chondrites and in comets. Organic matter is heterogeneous in isotope composition distribution. This heterogeneity is visible at all scales: between chondrites, within chondrites and the molecular scale. Is this heterogeneity a heritage of pre-accretion processes (in the protoplanetary disk or the parent molecular cloud)? How is this heterogeneity affected by hydrothermal events on the parent body? Can this heterogeneity constitute a new proxy to understand the formation of the solar system and the first small bodies?

Global hydrogen budget of carbonaceous chondrites

Two main reservoirs of hydrogen occur in carbonaceous chondrites hydrated minerals and organic matter, which are intimately mixed at the nm scale. Besides, hydrated CC have experienced fluid circulation that may have redistributed H-isotopes, hence blurring the original isotopic signature of both components. The origin of hydrogen and water in CC hence remains questioned: are they inherited from nebula molecular gas? Are they related to ice that condensed in the solar system, beyond the snow line? How was water reprocessed in the gaz phase?

Answering this question requires to assess the extent of H-isotope redistribution that occurred during hydrothermal events between organic matter and water, in addition to the determination of the content and isotope signature of H contained in chondrules, the largest mineral component of chondrules.