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(meteorobs) Summary: New data on Dust Phase of Hale-Bopp
Apropos our recent thread on the "importance of meteor observing", I thought
the following might be of interest: it's a summary of a research conference
recently convened on all the scientific data obtained from Hale-Bopp... As
already mentioned, we're not likely to see a meteor shower from Hale-Bopp for
many, many years - and probably never a major shower! But what we've learned
from this beautiful comet may help the pros understand the ways in which parent
comets and their meteoroid streams interact, both in composition and spatial
distribution... And also the reverse: observed meteor data combined with this
new data about comets may help us understand both better!
Enjoy!
Lew
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From: Ron Baalke <BAALKE@kelvin.jpl.nasadot gov>
Date: Tue, 24 Feb 1998 20:03:05 GMT
Subject: [ASTRO] Overview Of Comet Hale-Bopp Conference
ESO Education and Public Relations Dept.
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Text with all links is available on the ESO Website at URL:
http://www.eso.org/outreach/info-events/hale-bopp/report-rw-hbitp98.html
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This is a provisional overview of some of the discussions that took place
at the First International Hale-Bopp Conference at Tenerife in February
1998. It was prepared by R. M. West (ESO, email: rwest@eso.org).
[several interesting sections snipped!]
V. Dust Phase
Observations of new minerals
Klaus Jockers reported on extensive observations of the dust in Comet
Hale-Bopp. These concern direct imaging, the distribution of colours
within the coma and the tail and also the polarization. This comet had a
somewhat higher degree of polarization when observed at large phase
angles than other comets, indicating differences in the dust component.
A true breakthrough has occurred in the field of remote observing of
cometary minerals, as discussed by Martha Hanner and others.
Ground-based and space-based observations of the detailed infrared
spectrum of Comet Hale-Bopp have revealed for the first time many new
spectral features which can be assigned to particular minerals with a
great degree of certainty. They include above all cristalline olivines, in
particular the magnesium-rich forsterite, and also pyroxene-rich minerals.
In fact, it seems that the composition of some of the grains observed in
Comet Hale-Bopp are very similar to those of two main types of
interplanetary dust particles which have been collected in the Earth's
atmosphere and subsequently analysed in great detail in terrestrial
laboratories.
Dust production
The dust production of Comet Hale-Bopp was enormous, especially when
compared to other comets, for instance 100 times more than in Comet
Halley. Similarly, the dust-to-gas ratio was very high, from most
measurements estimated as between 2 and 5. The dust production at the
maximum reached about 400 tonnes/sec, but since the nucleus is so large,
the entire mass loss at this passage is probably still less than 0.1 percent
of its total mass.
Similarities with circumstellar dust
It is also very interesting to compare the infrared spectra of Comet
Hale-Bopp obtained with the ISO Observatory with spectra of stars which
are surrounded by circumstellar dust. As Christoffel Waelkens pointed out,
there are great similarities, but also some differences. For instance, the
spectrum of the star HD 100546 also displays the minerals mentioned
above, as well as cristalline water, but contrary to the Comet, it also has
strong spectral features of organic components in the 3.5 micron band.
There may thus be a close relationship between comets like Hale-Bopp
and the material observed in circumstellar disks, e.g. around the southern
star Beta Pictoris. All of this may provide very valuable new information
about the formation of the cometary reservoirs in the solar system (Kuiper
Belt and Oort Cloud).
[followed by much other interesting stuff on cometary comae...]
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