[meteorite-list] Ultracarbonaceous micrometeorites

From: Whitney Riner <majesticmeteorites_at_meteoritecentral.com>
Date: Tue, 11 May 2010 12:39:56 -0400
Message-ID: <AANLkTin9sxU0z8Cy96bhBVpIH_cTpR1SVzlPz7EJgozJ_at_mail.gmail.com>

A new study of (likely) cometary dust is published in Science:

http://tinyurl.com/39w6wyt
http://tinyurl.com/33dcy97


According to the scientists, the ultracarbonaceous micrometeorites,
which are about 0.1 millimetre (mm) in size and contain between 50% to
80% carbonaceous material, are unique because no other laboratory has
meteorites of this kind in its collection. Thanks to the results of
this exciting research, further investigations have been initiated
involving the CSNSM, the University of Lille 1, the Ecole Normale
Sup?rieure, Paris, and the French Natural History Museum.

In their analyses, the CSNSM team used an ion microprobe to show that
the micrometeorites' hydrogen isotopic composition has a very high
deuterium/hydrogen (D/H) ratio.

'Primitive interplanetary dust is expected to contain the earliest
solar system components, including minerals and organic matter,' the
authors write. 'We have recovered, from central Antarctic snow,
ultracarbonaceous micrometeorites whose organic matter contains
extreme deuterium excesses (10 to 30 times terrestrial values),
extending over hundreds of square micrometres.'

The results showed that the particles most likely stem from comets,
which are relatively small bodies in the Solar System. Comets' nuclei
are collections of ice, dust and tiny rocky particles. As comets draw
closer to the Sun, rising temperatures trigger the massive sublimation
of the icy materials. This results in an ejection of a mixture of
gases and cometary grains into interplanetary space.

Some dust grains may cross Earth's orbit as they move towards the Sun,
and the researchers speculate that it may be some of these cometary
grains that they found in central Antarctica.

In their paper, the authors note that so far, only the US Stardust
space mission has provided researchers worldwide with the opportunity
to perform mineralogical and geochemical analyses of cometary grains.
The specks of dust discovered at Concordia are similar to samples
obtained from the Stardust mission.

'The masses of the particles range from a few tenths of a microgram to
a few micrograms, exceeding by more than an order of magnitude those
of the dust fragments from comet 81P/Wild 2 returned by the Stardust
mission,' the authors write.
Received on Tue 11 May 2010 12:39:56 PM PDT