Chemistry Reference
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2. Meter- and centimeter-sized pebbles of compacted, massive dust-ice
mixtures with variable degrees of hydration of the embedded dust.
3. Dust in the ''glue'' matrix.
So far, no carbynes were reported in the completely hydrated CI carbo-
naceous meteorites. It is likely that pervasive hydration had destroyed
metastable carbons originally present. If so, they should still be present in
the anhydrous proto-CI materials, which are not yet recognized among the
collected meteorites.
The generally carbon-rich aggregate IDPs (10-15
m
m) and cluster IDPs
(
100
m
m) are in all of their mineralogical, textural, chemical and spectral
properties completely different from any of the collected meteorites [86].
These IDPs are solid debris of the very primitive, IR-spectroscopic P- and
D-class bodies. The matrix of IDPs is an aggregate of
100 nm to
1000 nm
sized principal components (PCs):
1. Carbonaceous PCs of refractory hydrocarbons, amorphous organic
carbons [61], pure amorphous carbon, poorly graphitized and pre-
graphitic turbostratic carbons.
2. Carbon-bearing ferromagnesiosilica PCs of ultrafine (2 to
50 nm)
Fe,Mg-silicate, Fe,Ni-sulfide and Fe-oxide grains in a refractory
hydrocarbon and amorphous carbon matrix.
3. Pure ferromagnesiosilica PCs with either a Mg-rich smectite-dehy-
droxylate [(Mg,Fe)
6
Si
8
O
22
] or a Fe-rich serpentine-dehydroxylate
[(Mg,Fe)
3
Si
2
O
7
], metastable eutectic composition.
The chemical analyses and mass measurements of dust released from the
nucleus of comet Halley showed a mixture of these PCs [82] although it was
proposed [87] that silicates and organic materials were mostly interspersed
in dust resembling C-bearing ferromagnesiosilica PCs. There is no minera-
logical evidence for carbynes in the matrix of aggregate IDPs, wherein most
of the carbon resides, or in cluster IDPs. The lack of evidence cannot be
accepted as proof that carbynes do not exist in these very primitive particles.
All collected IDPs have experienced flash-heating (5-15 s) that raised the
temperature of the entire particle to between
1200K [82].
Indigenous metastable carbons would probably not survive this thermal
event but perhaps vestiges might survive ''shielded'' inside another carbon
phase.
Evidence for carbynes in comets might come from remote-sensing ana-
lyses of the volatile species in the coma of active comets, in particular from
the study of carbon-chain molecules abundances [88]. Using narrowband
filter photometry, C
3
and C
2
were detected in amounts that are classified as
being ''typical'' in comets Hale-Bopp and Halley [89] and as ''being depleted
in carbon-chain molecules'' in comet 67P/Churyumov-Gerasimenko, the
new target of the ESA ROSETTA mission, and comet LINEAR 1999
600K and
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