Organic Matter Evolution on Asteroids: New Clues from Paris

Remusat L, Vinogradoff V, Le Guillou C & Bernard S

Goldschmidt 2015, Prague, 16-21 August 2015

PDF (abstract)

The Paris meteorite is the least altered CM carbonaceous
chondrite, as witnessed by the presence of unaltered metal
grains and amorphous silicate, usually absent in CM
chondrites [1]. Its O-isotopes are intermediate between
altered CM and the thermally metamorphosed CO chondrites.
Chondritic organics have most likely a multi-stage history
that remains complex to disentangle, but Paris provides a
unique opportunity to assess the specific role of parent body
processes on their evolution. Therefore, we have studied the
insoluble organic matter (IOM) of Paris and compared it to
IOM from Murchison and other CMs. By focusing on a single
chondrite group, we can rule out possible precursor influence
that we encountered in a previous study of IOM in
carbonaceous chondrites from different groups [2].
We obtained a “bulk” IOM of Paris by HF/HCl digestion
of a large sample (>10g) of matrix isolated by the freeze-thaw
method [1]. The bulk C, H and N-isotope compositions of
Paris IOM fall among the heaviest CM chondrites.
NanoSIMS images of H and N-isotopes reveal numerous hot
spots. D-rich hot spots in Paris span the same range as in
Murchison, however 15 N-rich hot spots are significantly
heavier (mean value at 550‰, max at 1000‰), albeit lighter
than in Bells [3]. The Raman signature points to a disordered
material, similar to type 1 and 2 chondrites [4]. FTIR,
XANES and NMR reveal that Paris is intermediate between
CR2 and CM2 IOMs. In particular, they show that the
aliphatic/aromatic carbon ratio is larger in Paris than in
Overall, it appears that during aqueous alteration on the
CM parent body, IOM underwent some degree of
aromatization in addition to slight D/H decrease and a more
significant 15 N-rich hot spot depletion. Coupled hydrous and
thermal effects could explain this evolution. Paris IOM
appears primitive with respects to other CM and could
resemble to the organic matter that accreted on the CM parent