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(meteorobs) Excerpts from "CCNet, 6 October 1999"
------- Forwarded Message
From: Benny J Peiser <b.j.peiser@livjm.acdot uk>
To: cambridge-conference@livjm.acdot uk
Subject: CCNet, 6 October 1999
Date: Wed, 6 Oct 1999 12:29:26 -0400 (EDT)
CCNet, 6 October 1999
------------------------
[...]
(3) COSMIC DUST AND CLIMATE CHANGE
Doug Keenan <doug.keenan@virgindot net>=20
[...]
(7) COMPANION TO COMET GRIGG-SKJELLERUP
Andrew Yee <ayee@nova.astro.utorontodot ca>
(8) SPACE DEBRIS MEETING
Andrew Yee <ayee@nova.astro.utorontodot ca>
[...]
======================================================
(3) COSMIC DUST AND CLIMATE CHANGE
>From Doug Keenan <doug.keenan@virgindot net>=20
Benny,
B. Napier [British Archaeological Reports 728 (editors--B.J. Peiser=20
et al.), 1998] suggests that the Little Ice Age might have been caused=20
by dust in the Taurid meteoroid stream. S. V. M. Clube [BAR 728]=20
refers to a long-term climate rhythm--first indicated by G. Bond et al. =
[Science, 1997] --and suggests that this rhythm might also be caused by =
Taurid dust.
Bond et al. have just published some important follow-up work:
Bond, G. C. & seven others, "The North Atlantic's 1-2 kyr Climate=20
Rhythm", Mechanisms Of Global Climate Change At Millennial Time Scales=20
(editors-- P. U. Clark, R. S. Webb & L. D. Keigwin), Geophysical=20
Monograph Series 112 (American Geophysical Union, Washington DC, 1999).
They substantially strengthen their 1997 arguments for the climate=20
rhythm and give evidence that the rhythm has endured for at least 50k =20
years. The rhythm is also shown to be related to Heinrich Events=20
(massive discharges of icebergs into the N Atlantic),=20
Dansgaard/Oeschger Cycles (changes in Greenland ice cores that=20
indicate major changes in ocean circulation), and the Little Ice Age.=20
Bond et al. do not propose a mechanism for the rhythm.
The above is only suggestive. But the suggestion seems to be that=20
cosmic dust might have a huge effect on climate.
Cheers,
Doug Keenan
http://freespace.virgindot net/doug.keenan
======================================================
(7) COMPANION TO COMET GRIGG-SKJELLERUP?
>From Andrew Yee <ayee@nova.astro.utorontodot ca>
ESA Science News
http://sci.esa.int
28 Sep 1999
Companion to comet Grigg-Skjellerup discovered using Giotto data?
On 13/14 March 1986, the European Space Agency's Giotto spacecraft=20
obtained the first close-up pictures of a comet nucleus during its=20
close flyby of Halley's Comet. An historic second comet encounter=20
followed on 10 July 1992 when Giotto flew within 200 km of Comet=20
Grigg-Skjellerup.
Seven years later, continuing analysis of data from Giotto's Energetic=20
Particle Detector (EPONA) has led to the conclusion that a second=20
comet, possibly a fragment of the main nucleus, may have been=20
accompanying Grigg-Skjellerup. The new results have been obtained by=20
Professor Susan McKenna-Lawlor, the Irish Principal Scientific=20
Investigator for the EPONA instrument, and Russian scientist Dr.=20
Valeri Afonin. Their discovery is based on fluctuations in the=20
energetic particle data recorded by EPONA.
One of the most important aspects of the Grigg-Skjellerup encounter=20
was that it enabled scientists to use the same instruments to compare=20
the fairly inactive Grigg-Skjellerup with Comet Halley, its much=20
larger, more active cousin. A number of experiments on board Giotto=20
were functioning during both encounters.
One of these was EPONA, which has the capability to record charged=20
particles -- protons and heavier ions -- with energies ranging from=20
several tens of keV to several tens of MeV. (One electron volt or eV=20
is the amount of energy gained by an electron when it is accelerated=20
through a potential difference of one volt.) Characteristic=20
fluctuations in the energetic particle records allowed EPONA to=20
detect the same cometary boundaries at Halley and Grigg-Skjellerup as=20
Giotto's other particles and fields experiments.
Recent, detailed analysis of EPONA data by McKenna-Lawlor and Afonin,=20
(described in the journal Planetary and Space Science Vol. 47, p.=20
557-576 and Circular No. 7243 Central Bureau for Astronomical=20
Telegrams IAU, 1999 August 25), has revealed a complex particle=20
enhancement in the energy range 60-100 keV. This increase was=20
recorded by EPONA some 90,000 km beyond Grigg-Skjellerup.
Several possible explanations for this flux enhancement were=20
considered, but the overall conclusion was that it constituted the=20
signature of a 'companion' comet, three to four times smaller than=20
Grigg-Skjellerup and with a correspondingly lower gas production=20
rate. It is unlikely that these two objects have existed side by side=20
from the beginning of their existence. A more probable explanation is=20
that the smaller object broke away from Grigg-Skjellerup shortly=20
before the Giotto encounter. Splitting of cometary nuclei is a well=20
known phenomenon that can occur even at large distances from the Sun.
This is the first time that the discovery of a comet using energetic=20
particle data has been claimed.
Contacts:
Prof. Susan McKenna-Lawlor
Space Technology Ireland
National University of Ireland
Maynooth, Co. Kildare, Ireland
Phone: +353-1-6286788
E-mail: stil@may.ie
Dr. Valeri Afonin
Institute of Space Research
Moscow
Phone: +7-0953331023
E-mail: vafonin@mx.iki.rssi.ru
Note for the editors:
Splitting of cometary nuclei is a well known phenomenon that can=20
occur even at large distances from the Sun. In the case of=20
Grigg-Skjellerup, evidence for small-scale fragmentation of the=20
nucleus was also identified from Giotto's Optical Probe Experiment=20
(OPE).
The Optical Probe detected a number of striking 'spike' features or=20
'events' during the Grigg-Skjellerup flyby. While scattering of=20
sunlight caused by dust impacts on the spacecraft body may account=20
for some of these, the complex data profiles can also be explained by=20
activity from dust jets in the comet's inner-most coma.
One particular event occurring at least 1000 km from the comet may=20
have been caused by the presence of a small nucleus fragment. The=20
evidence indicates that a chunk, 10-100 m in radius, had broken away=20
from the comet and passed around 50 km from the spacecraft. Despite=20
its small size, it seemed to be producing a small dust coma of its=20
own. Unfortunately, the particular event detected by EPONA was not=20
seen in the OPE data.
(ref. McBride, N., S.F. Green, A.C. Levasseur-Regourd, B.=20
Goidet-Devel and J.-B. Renard, The inner dust coma of comet=20
26P/Grigg-Skjllerup: multiple jets and nucleus fragments? MNRAS 289,=20
535--553, 1997.)
USEFUL LINKS FOR THIS STORY
* Space Technology Ireland
http://www.may.ie/academic/physics/stil.shtml
* Giotto's encounter with Grigg-Skjellerup
http://sci.esa.int/pr-doc/thirty-dis3.html
[IMAGE CAPTION:
http://sci.esa.int/image.cfm?TypeID=3D1&ContentID=3D6991&table=3DContent=
Table&Storytype=3D9]=20
Energetic particle signature recorded by the EPONA instrument on=20
board Giotto in the energy range ~ 60-100 keV. The data are believed=20
to represent the signature of a companion to Comet Grigg-Skjellerup.=20
Particle count rate is shown on the vertical axis. Time and distance=20
from the comet are shown on the bottom scale. (Courtesy Susan=20
McKenna-Lawlor)
============================================
(8) SPACE DEBRIS MEETING
>From Andrew Yee <ayee@nova.astro.utorontodot ca>
European Space Agency
Press Release Nr. 41-99
Paris, France 4 October 1999
World experts on space debris meet in Europe on 11-13 October
Space debris experts from around the globe will gather from 11 until=20
13 October 1999, at the European Space Agency Operations Centre=20
(ESOC) Darmstadt/Germany for the 17-th meeting of the Inter-Agency=20
Space Debris Coordination Committee (IADC). IADC is concerned with=20
all technical issues of the space debris problem. The main objectives=20
of IADC are to exchange results of research in the field of space=20
debris, to cooperate in research activities and to identify debris=20
mitigation options.
The 17-th IADC will discuss ways and methods to control the growing=20
amount of orbiting debris. Radar and optical telescopes regularly=20
track over 10,000 artificial objects in space. The number of=20
untrackable objects in the size range from 1 cm to 10 cm, that could=20
seriously damage an operational spacecraft, is estimated at between=20
100,000 and 150,000. The International Space Station (ISS) will be=20
equipped with about 200 shields in order to defeat impacts of=20
particulates up to about 1 =96 2 cm size.
Some recent and current topics of the IADC include
* guidelines for the disposal of spacecraft in the geostationary orbit; =
* data exchange procedure and communications for reentry of risk
objects;=20
* common database of space objects;=20
* risk assessment for the 1999 Leonids and countermeasures;=20
* measures to reduce the growth of the debris population in Low-Earth
Orbit.
The results from the work of IADC will provide a technical basis for=20
deliberations on space debris at the United Nations Committee on the=20
Peaceful Uses of Outer Space (UNCOPUOS).
Media representatives will have the opportunity to be briefed on the=20
space debris problem and on the main results of the 17-th IADC on 13=20
October at 15:00, at ESOC, Building H, Robert-Bosch Strasse 5,=20
Darmstadt.=20
Those wishing to attend the briefing are kindly requested to fill out=20
the attached form and fax it to ESOC Public Relations, Darmstadt.
Fax: +49 6151 902 961. [NOTE: Form is not attached here. - A.Y.]
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