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Isotopic compositions of cometary matter
returned by the STARDUST mission.
McKeegan K. D., Aléon J., Alexander C. M., Bradley
J., Brownlee D., Burnard P., Butterworth A., Chaussidon M.,
Davis A., Floss C., Gilmour J., Gounelle M., Graham G., Guan
Y., Heck P., Hohenberg C., Hoppe P., Hutcheon I., Huth J.,
Ishii H., Ito M., Jacobsen S., Leshin L., Lyon I., Marhas
K., Marty B., Matrajt G., Meibom A., Meshik A., Messenger
S., Mostefaoui S., Nakamura K., Nittler L., Palma R., Pellin
M., Pepin R., Pik R., Tsou P., Robert F., Schlutter D.,
Stadermann F., Stroud R., Westphal A., Young E., Zeigler K.,
Zimmermann L., and Zinner E. (2006)
Eos Trans. AGU, 87(52), Fall Meet. Suppl., Abstract
P52B-03.
ABSTRACT
The STARDUST spacecraft flew through the coma of comet
81P/Wild2 on Jan. 2, 2004, at a distance of ~236km and a
relative velocity of ~6.1 km/s [1]. Dust particles,
which were released from the comet hours before the
encounter, were captured in silica aerogel and successfully
returned to the Earth on Jan. 15, 2006. Cometary debris was
also retained in small impact craters on Al-foil strips
adjacent to the aerogel collector cells. A prelimary
examination team (PET) of ~150 scientists has been engaged
in studying the mineralogy/petrology, chemistry, optical
properties, organic materials, fluence, and isotopic
compositions of a subset of the returned cometary materials
[2,3]. This report summarizes the findings of the
PET isotope subgroup during its 6 month investigation.
Isotopic compositions of hydrogen, carbon, nitrogen, and
oxygen show a range of heterogeneity among individual
particle fragments demonstrating that the comet consists of
unequilibrated samples from a variety of astrophysical
environments. With one exception, extreme isotopic anomalies
indicative of presolar materials are not found, indicating
that the comet does not consist of an unalterered
agglomeration of presolar materials. However, some organic
materials were collected that show isotopic signatures
consistent with molecular cloud chemistry. Neon and nitrogen
isotopic compositions suggest that some volatile materials
were successfully collected and trapped in the aeorgel.
Oxygen isotopic evidence points toward a solar system origin
for almost all crystalline silicate and oxide minerals and
implies large-scale radial transport of dust formed in hot
inner regions of the solar nebula outward to the Kuiper belt
where Wild2 and other Jupiter family comets finally
accreted. References: [1] Brownlee, D.E., et al
(2004). Science 304, 1764-1769. [2] Brownlee D. E.
et al. 2006. Abstract #2286.
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