[meteorite-list] Unique Observations of Comet McNaught Reveal Sprinkling Nucleus

From: E.P. Grondine <epgrondine_at_meteoritecentral.com>
Date: Sun, 25 Feb 2007 08:25:08 -0800 (PST)
Message-ID: <631408.54563.qm_at_web36912.mail.mud.yahoo.com>

Hi all,

Sorry for all the mail; but there are days when I post
nothing...

Bernd, do we have any carbonaceous chondrites with
high sodium?

congratulations Rob,
E.P. Grondine
Man and Impact in the Americas
 

 Their images show
> spectacular jets of gas from
> the comet spiralling several thousands of kilometres
> into space, while the
> spectra reveal the presence of sodium in its
> atmosphere, something seen very
> rarely.
>
> As well as taking images, the astronomers were able
> to investigate which
> gases were present in the comet's atmosphere [2]
> using spectroscopy. The
> usual gaseous species have been detected, such as
> cyanide, carbon, and
> ammonia, whose analysis will help the astronomers to
> determine the activity
> level of the comet and its chemical type.
>
> But already in the first high resolution spectrum
> obtained on 29 January,
> the astronomers noted something quite unusual.
>
> "We detected two very bright lines -- the brightest
> of the whole spectrum
> taken on this day as a matter of fact -- close to
> 589 nm and quickly
> identified them as belonging to neutral sodium
> atoms," said Emmanu Jehin
> (ESO). "Further measurements showed this sodium
> emission to be extending
> over more than 100,000 km in the tail direction and
> fading rapidly with
> time."
>
> Such lines have only been detected in the greatest
> comets of the past
> century like C/Ikeya-Seki in 1965, C/West in 1976
> and C/Hale-Bopp in 1997,
> for which a very narrow sodium tail was even
> photographed. This straight
> neutral tail appears in addition to the dust and
> ionised gas tails when the
> comet is close to the Sun.
>
> "Its origin lies most probably in the dissociation
> of the cometary dust
> grains," said Jehin. "In very active comets, which
> are also usually the ones
> which pass closer to the Sun, the dust grains are
> vaporised under the
> intense heat and start releasing sodium atoms which
> then react to the solar
> radiation and emit light -- at the very same
> yellow-orange wavelength of the
> lamps on our streets."
>
> Sodium has also been observed around Mercury and the
> Moon forming a very
> tenuous atmosphere. But closer to us, at 90 km
> altitude in our atmosphere,
> there is the so-called 'sodium layer'. The origin of
> that layer is not well
> known but might be coming from the ablation of
> meteoroids that are burning
> (due to their high entry speed in the atmosphere) at
> the same altitude. As
> most shooting stars (or meteors) originate from
> comets (annual showers like
> the Eta Aquarids and Orionids originate from comet
> P/Halley, the Leonids
> come from comet P/Tempel-Tuttle, and the Perseids
> from comet
> P/Swift-Tuttle), the sodium in those dust particles
> might just be the same.
> As a kind of gift to the astronomers that layer is
> used by observatories
> like Paranal to produce with a laser an artificial
> star that allows for the
> correction of atmospheric turbulence!
>
> Notes
>
> [1] The team is composed of Colin Snodgrass, Emmanu
> Jehin, and Olivier
> Hainaut (ESO), Alan Fitzsimmons (Queen's University,
> Belfast, UK), and Jean
> Manfroid and Damien Hutsemers (Universitde Lie,
> Belgium). These results were
> presented in a Circular Telegram to the
> International Astronomical Union
> (IAU CBET 832).
>
> [2] When a comet is approaching the Sun, the ices
> trapped in the small
> nucleus sublimate, sometimes in the form of very
> strong gaseous jets,
> dragging in the process a lot of dust particles into
> space and forming a
> dusty atmosphere -- called the coma -- of several
> thousands of kilometers
> around the nucleus. All those molecules and dust
> particles are then pushed
> in the direction opposite to the Sun (by the solar
> radiation pressure),
> creating the gaseous and dust tails of the comet.
>
> ______________________________________________
> Meteorite-list mailing list
> Meteorite-list at meteoritecentral.com
>
http://six.pairlist.net/mailman/listinfo/meteorite-list
>



 
____________________________________________________________________________________
The fish are biting.
Get more visitors on your site using Yahoo! Search Marketing.
http://searchmarketing.yahoo.com/arp/sponsoredsearch_v2.php
Received on Sun 25 Feb 2007 11:25:08 AM PST