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Re: Great Siberian Explosion
Dona Ebert schrieb:
> ..., what are comets made of which cause mutations of the elements? It
> has been reported that they are dirty snowballs of water, amonium,
> dirt, etc. What else is there? - dona
Hello Dona, hello List,
Here is an abstract from MAPS 32-4, Suppl., 1997 July, A044 that might
also be of interest (at least to some of you):
Carbonaceous components of organic/inorganic assemblages in comet Halley
dust.
M. Fomenkova(l) and S. Chang(2)
(1) Center for Astrophysics and Space Sciences, University of
California-San Diego, La Jolla CA 92093-0424, USA
(2) Mail Stop 239-4, NASA Ames Research Center, Moffett Field CA
92035-1000, USA.
Mass spectra of about 5000 individual submicrometer cometary grains were
obtained during flyby missions to Comet P/Halley in 1986 [1]. It has
been established that both organic and inorganic materials are present
in cometary dust particles in variable proportions [1,2]. The spectra
were classified [3] into three major types based on the ratio of the
number of C ions in a spectrum to the number of ions of each of the
major rock-forming elements (Mg, Si, Fe, and Ca): CHON particles
(dominated by C alone or in combination with H, O, and N), rock
particles (containing <1% of C in their spectra), and mixed particles
(all the rest). Cluster analysis was applied to CHON grains [4] and
revealed more than 30 distinguishable types of grains, including
elemental C grains, aliphatic, and aromatic hydrocarbons, polymers of C
suboxide and of cyanopolyynes.
In order to complete the inventory of carbonaceous compounds in the
Comet Halley dust particles, we applied the same procedures of cluster
analysis to study the composition of the organic component of mixed
particles. Percentages of H, C, N, and O were calculated (normalized to
the sum of these elements in a spectrum) after subtracting from the
total O abundance the number of ions attributed to bonding in minerals
with rock-forming elements. Then the matrix of pair-wise distances
between the data points was calculated and the hierarchical cluster
analysis was carried out.
In most cases, the organic component of mixed particles appears to be a
multicomponent mixture of C phases and organic analysis and are the same
as previously found in CHON grains. For example, about 20% of mixed
grains contain elemental C (C-group), about 10% contain hydrocarbons (H,
C-group). Polymers of C suboxide and of cyanopolyynes are also present.
The proportions of all these species are similar in CHON and in mixed
grains.
We hypothesize that these simple compounds are essential "building
blocks" that give rise to all other compositional types present in the
cometary dust. For example, some H-containing species may be formed from
C suboxide and/or cyanopolyynes polymers by hydrogenation on grains in
the interstellar medium.
Other compositional groups revealed by the cluster analysis of the
organic component of mixed particles will also be discussed. The main
difference between these groups and the groups found in CHON grains is
the abundance of N, which appears to be higher in mixed particles.
References:
[1] Kissel J. et al. (1986) Nature 321, 280-282.
[2] Lawler M. and Brownlee D., Nature 359, 180-182.
[3] Fomenkova et al. (1992) Science 258, 266-269.
[4] Fomenkova et al. (1994) GCA 58, 4503-4512.
Regards,
Bernd
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