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(meteorobs) Excerpts from "CCNet, 31 August 1999"
------- Forwarded Message
From: Benny J Peiser <b.j.peiser@livjm.acdot uk>
To: cambridge-conference@livjm.acdot uk
Subject: CCNet, 31 August 1999
Date: Tue, 31 Aug 1999 10:51:55 -0400 (EDT)
CCNet, 31 August 1999
---------------------
(1) FINE LEONID METEOR DISPLAYS PREDICTED THROUGH TO 2002
Jacqueline Mitton <jmitton@dial.pipex.com>
(2) WATER FROM THE DAWN OF THE SOLAR SYSTEM
Andrew Yee <ayee@nova.astro.utorontodot ca>
[...]
(7) DYNAMICAL BEHAVIOUR OF ASTEROIDS NEAR RESONANCE
M. Grau & G. Gonzalez Casado, UNIV POLITECN CATALUNYA
(8) PERIODIC ORBIT FAMILIES NEAR THE 4:1 JOVIAN RESONANCE
M. Grau & M. Noguera, UNIV POLITECN CATALUNYA
[...]
(10) EXPLOSIONS OF METEOROIDS
V.V. Svettsov, RUSSIAN ACAD SCI
[...]
================
(1) FINE LEONID METEOR DISPLAYS PREDICTED THROUGH TO 2002
>From Jacqueline Mitton <jmitton@dial.pipex.com>
ROYAL ASTRONOMICAL SOCIETY
PRESS NOTICE
Date: 30 August 1999
For immediaterelease
Ref. PN 99/27
Issued by: Dr Jacqueline Mitton
RAS Press Officer
Phone: Cambridge ((0)1223) 564914
FAX: Cambridge ((0)1223) 572892
E-mail: jmitton@dial.pipex.com
RAS Web: http://www.ras.orgdot uk/ras/
* * * * * * * * * * * * * * * * * * * * * * * *
CONTACTS FOR THIS RELEASE
Dr David Asher (dja@star.arm.acdot uk)
Professor Mark Bailey (Director: meb@star.arm.acdot uk)
Mr John McFarland (PR Officer: jmf@star.arm.acdot uk)
Armagh Observatory, College Hill, Armagh, BT61 9DG
Tel: 028-3752-2928, Fax: 028-3752-7174
Dr Rob McNaught (rmn@aaocbn.aaodot gov.au)
School of Astronomy and Astrophysics, Australian National University.
* * * * * * * * * * * * * * * * * * * * * * * * *
FINE LEONID METEOR DISPLAYS PREDICTED THROUGH TO 2002
November's Leonid meteor shower will produce good displays this year
and next, and strong storms of meteors in 2001 and 2002, according to
new research by Dr David Asher, of Armagh Observatory, and Dr Rob
McNaught of the Australian National University. Writing in the Monthly
Notices of the Royal Astronomical Society (21 August 1999 issue), they
show how the times when Earth passes through the dense streams of
matter in space that produce meteor showers can now be predicted with
remarkable accuracy.
In the early hours of 17th November last year (1998), meteor watchers
awaiting the Leonid shower were taken by surprise when a spectacular
display of bright meteors occurred 16 hours before the predicted time
for the maximum of the shower. The explanation for this phenomenon was
discovered by Dr Asher and his colleagues Professor Mark Bailey of
Armagh Observatory, and Professor Vacheslav Emel'yanenko of South Ural
University, Chelyabinsk, Russia, and was published in April (see RAS
Press Notice 99/09). They showed that the bright meteors were seen when
Earth passed through a dense arc-shaped cloud of particles shed from
Comet Tempel-Tuttle in the year 1333 and they proved for the first time
that meteoroid streams can have complex braid-like structures within
them. This work pointed the way to more precise predictions of the
timing and intensity of meteor showers, such as those Asher and
McNaught are now making for the Leonids.
The latest analysis, covering Leonid meteor storms over the past two
hundred years, shows that the peak times of the strongest storms and
sharpest outbursts are predictable to within about five minutes. The
technique involves mapping the fine `braided' structure of the dense
dust trails within the Leonid meteoroid stream. Although comet
Tempel-Tuttle, the 'parent' of the Leonid stream, passed close to the
Earth in 1998, Asher and McNaught predict strong meteor storms in both
2001 and 2002. 1999 and 2000 will be less spectacular, but good. In
1999, observers at European longitudes are favoured, and may see up to
20 meteors a minute (in ideal conditions under a clear, dark sky) at
around 2 a.m. on the morning of November 18th.
Meteors, popularly known as 'shooting stars', can be seen on any night,
given a sufficiently clear, dark sky. They are produced by the impact
on the Earth's atmosphere of small dust grains released from comets.
Most meteors arrive in 'showers' at fixed times of the year, when the
Earth passes close to the orbit of the parent comet. But occasionally -
just a few times a century - a phenomenon known as a meteor storm
occurs. During a storm, meteors appear at astonishing rates, sometimes
several per second. The most famous example, the incredible Leonid
display of 1833, is credited with starting the serious scientific study
of meteors.
Good news for meteor observers can be a concern for satellite
operators. A satellite can be disabled by the impact of even a small
dust grain. While the hazard from man-made space debris is well known,
the danger from meteoroids has been more difficult to assess. Prior
knowledge of the detailed structure of the Leonid stream is potentially
of immense value. Satellite operators could use this information to
take appropriate avoiding action and minimise the risk. With this new
work, McNaught and Asher have defined the structure of the Leonid dust
trails more accurately than ever before.
NOTES
What are the Leonid meteoroid stream and the Leonid meteor shower?
The Leonid meteor display is associated with the Earth's passage
through the Leonid stream. This stream consists of the debris of
Tempel-Tuttle, a comet that orbits the Sun about every 33 years.
When do the most intense outbursts occur?
Although the Earth goes through the Leonid stream every November, in
most years the Leonid meteor shower is unspectacular. However, there is
fine structure within the stream, and meteor storms occur when the
Earth runs through the highest density regions. The new technique for
mapping out the structure involves precise calculations of the effect
of the gravity of the planets on the dense dust trails, covering many
revolutions of the dust grains about the Sun over periods of a century
or two.
Why are some longitudes favoured?
The meteors in any given shower come from a particular direction in
space. You need to be on the hemisphere facing that direction to see
the meteors. It also has to be night-time, except for incredibly bright
fireballs. In the case of the Leonids, an approximate rule is to
observe after midnight. Background Leonids (a few meteors per hour)
appear for a few days, and so all parts of the Earth have a chance to
catch them. But some outbursts are of high intensity for less than an
hour, and you have to be at a longitude where the time is between
midnight and dawn. The next few years will provide various excellent
Leonid opportunities, of which 2001 from East Asian longitudes will be
best, especially as the moon will be absent from the sky. Most
immediately, 1999 should produce a good display, although rates will
not match the most spectacular ones: the Zenithal Hourly Rate (defined
for an individual observer in near-ideal observing conditions) is
estimated to peak at 1,200 per hour at 02:08 GMT on November 18th.
Can damage to satellites occur?
Very high speed impacts of tiny dust grains on satellites can cause
plasma to be generated, which can lead to electrical failure. There is
evidence that the Olympus communications satellite was disabled owing
to the impact of a meteoroid from the Perseid stream in 1993.
History of this work
The famous Leonid storms of 1833, 1866 and 1966 were known to relate to
the roughly 33 year period of the comet. But it was only when McNaught
examined the details of those and other Leonid outbursts of the past
two hundred years that the full predictive power of the 'dust trail'
technique became apparent. Whereas theories that considered the comet
alone, rather than the dust trail structure in the stream, would
sometimes match observed timings of storms within hours (but
occasionally fail completely), the dust trail theory allows an accuracy
that many astronomers never suspected possible. Further refinements to
the theory, including a topographic correction, have reduced the
uncertainty to around five minutes.
A few months after developing the technique, McNaught and Asher
extended their work to permit estimates of meteor rates (in addition to
predicting storm timings), and applied it to forthcoming encounters of
the Earth with Leonid dust trails. There is no doubt that 2001 and 2002
will provide opportunities to witness exceptional Leonid meteor storms.
The fact that something out of the ordinary is expected in both 2001
and 2002 had in fact been published more than a decade ago, by two
researchers, Kondrat'eva and Reznikov, in Kazan, Russia. The English
translation of their paper did not come to the notice of many western
researchers.
==============
(2) WATER FROM THE DAWN OF THE SOLAR SYSTEM
>From Andrew Yee <ayee@nova.astro.utorontodot ca>
INSCiGHT
[http://www.academicpress.com/inscight/08271999/grapha.htm]
Friday, 27 August 1999, 5 pm PST
Water From the Dawn of the Solar System
By Govert Schilling
Scientists have found tiny droplets of water, dating from the dawn of
the solar system, in two meteorites that fell to Earth last year. It's
the first time liquid water has been found in extraterrestrial samples.
A study about one of the meteorites is published in today's Science, p.
1377).
Meteorites are fragments of rocky asteroids, and the mineral
composition of some meteorites had convinced scientists that their
"parent bodies" must have contained liquid water in the past.
Consequently, "we have been looking for water in meteorites for a
generation," says mineralogist Michael Zolensky of NASA's Johnson Space
Center in Houston.
In their paper, Zolensky and his colleagues present an analysis of
Monahans, a meteorite that fell near a Texan town on 22 March 1998. The
team also studied a meteorite called Zag, which landed in the Moroccan
part of the Sahara desert 5 months later. Although it hasn't been fully
analyzed yet, Zolensky says Zag's composition closely resembles that of
Monahans. Both contain millimeter-sized, purple salt crystals with
small inclusions of briny water.
Radioactive dating of the crystals -- which contain ordinary table salt
(NaCl) and sylvite (KCl) -- show that they are over 4.5 billion years
old, which means the water must have been trapped around the time the
solar system was formed. But it's unclear if the water was indigenous
to the parent asteroid, or if it was deposited there by a comet or a
rock slamming into it. Determining the brine's isotopic composition
would answer that question, but the inclusions are too small to measure
that composition with current instruments. However, says Zolensky, a
very sensitive mass spectrometer currently being developed at Cambridge
University in the U.K. should be able to do the trick next year.
The discovery, described as "astonishing" in an accompanying
perspective (Science, 27 August, p. 1364) by Robert Clayton of the
University of Chicago, leaves several mysteries unsolved. For one, both
meteorites are ordinary chondrites -- the most common type of meteorite
- -- whose parent bodies were believed to be relatively dry. Also, if
there's water in an asteroid, says Zolensky, you would expect to find
it in the interior, where it's safe from evaporation, erosion, and
cosmic radiation; but Monahans and Zag are both from the asteroid's
surface, as evidenced by contamination with atoms from the solar wind.
The largest riddle, however, is why the salt crystals, which are formed
when water evaporates after reacting with the rock, are so big. "You
need a lot of evaporating water to produce these amounts of [salt],"
says Zolensky.
(c) 1999 The American Association for the Advancement of Science
[Extracted from INSCiGHT, Academic Press.]
==================
(7) DYNAMICAL BEHAVIOUR OF ASTEROIDS NEAR RESONANCE
M. Grau*), G. Gonzalez Casado: Dynamical behavior of asteroids near
resonance: The 4:1 gap and the 7:2 group. CELESTIAL MECHANICS &
DYNAMICAL ASTRONOMY, 1998, Vol.72, No.3, pp.169-186
*) UNIV POLITECN CATALUNYA,FAC MATEMAT & ESTADIST,DEPT MATEMAT
APLICADA 2,PAU GARGALLO 5,E-08028 BARCELONA,SPAIN
A comparative study of the evolution of the Sun-Jupiter-Asteroid system
near the 4:1 and 7:2 resonances is performed by means of two techniques
that proceed differently from the Hamiltonian corresponding to the
planar restricted elliptic three-body problem. One technique is based
on the classical Schubart averaging while the other is based on a
mapping method in which the perturbing part of the Hamiltonian is
expanded and the resulting terms are ordered according to a weight
function that depends on the powers of eccentricities and the
coefficients of the terms. For the mapping method the effect of Saturn
on the asteroidal evolution is introduced and the degree of chaos is
estimated by means of the Lyapunov time. Both methods are shown to lead
to similar results and can be considered a suitable tool for describing
the evolution of asteroids in the Kirkwood gap and the group
corresponding to the 4:1 and 7:2 Jovian resonances, respectively.
Copyright 1999, Institute for Scientific Information Inc.
================
(8) PERIODIC ORBIT FAMILIES NEAR THE 4:1 JOVIAN RESONANCE
M. Grau*), M. Noguera: Periodic orbit families near the 4:1 jovian
resonance. CELESTIAL MECHANICS & DYNAMICAL ASTRONOMY, 1998, Vol.72,
No.3, pp.201-218
*) UNIV POLITECN CATALUNYA,FAC MATEMAT & ESTADIST,DEPT MATEMAT
APLICADA 2,PAU GARGALLO 5,E-08028 BARCELONA,SPAIN
An enlarged averaged Hamiltonian is introduced to compute several
families of periodic orbits of the planar elliptic 3-body problem, in
the Sun-Jupiter-Asteroid system, near the 4:1 resonance. Four resonant
critical point families are found and their stability is studied. The
families of symmetric periodic orbits of the elliptic problem appear
near the corresponding fixed points computed in this model. There is a
good agreement for moderate eccentricity of the asteroid for three of
these families, whereas the remaining family cannot be considered as
a family of periodic orbits of the real model. Copyright 1999,
Institute for Scientific Information Inc.
================
(10) EXPLOSIONS OF METEOROIDS
V.V. Svettsov: Explosions of meteoroids and estimating their parameters
from light emission. COMBUSTION EXPLOSION AND SHOCK WAVES, 1998,
Vol.34, No.4, pp.474-484
*) RUSSIAN ACAD SCI,INST GEOSPHERE DYNAM,MOSCOW 117979,RUSSIA
High-power visible light pulses detected by sensors mounted on
geostationary satellites are analyzed. The distinctive features
of meteoroid explosions which produce these flashes in the atmosphere
are studied. A method is described for determining the parameters of
bodies in space from the known radiation power and altitude of the
explosion. Numerical calculations show that these light pulses were
produced by falling stony and, once, ferrous bodies with dimensions on
the order of a meter. The bursts produced by bodies from outer space in
the atmosphere are compared with the light pulses from spherically
symmetric instantaneous explosions with similar energies. Copyright
1999, Institute for Scientific Information Inc.
----------------------------------------
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