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(meteorobs) Excerpts from "CCNet, 034/2000 - 17 March 2000"
Note in particular the item regarding meteor showers potentially observable at
Mars: Amazing the synchonicity here, as this very thread came up not too long
ago here on the 'meteorobs' forum...
Clear skies!
Lew Gramer <owner-meteorobs@jovian.com>
------- Forwarded Message
From: Benny J Peiser <b.j.peiser@livjm.acdot uk>
To: cambridge-conference@livjm.acdot uk
Subject: CCNet, 17 March 2000
Date: Fri, 17 Mar 2000 12:51:19 -0500 (EST)
CCNet, 034/2000 - 17 March 2000
-------------------------------
(1) YUKON METEORITE MAY PROVIDE "NEW WINDOW INTO
THE UNIVERSE"
NASANews@hq.nasadot gov
[...]
(4) WOBBLY ASTEROIDS AND COMETS
M. Efroimsky*) & A. Lazarian, HARVARD UNIVERSITY
(5) METEOROID STREAMS AT MARS
A.A. Christou*) & K. Beurle, UNIVERSITY OF LONDON
[...]
(8) ASTEROID SPIN PARAMETER
Jeremy Tatum <UNIVERSE@uvvm.UVicdot ca>
(9) FAST RESPONSE TO FAST-SPINNING ASTEROIDS
Charles F. Peterson <cfp@mcn.org>
[...]
========================================================
(1) YUKON METEORITE MAY PROVIDE "NEW WINDOW INTO
THE UNIVERSE"
>From NASANews@hq.nasadot gov
Donald Savage
Headquarters, Washington, DC March 16, 2000
(Phone: 202/358-1547)
Ann Hutchison
Johnson Space Center, Houston, TX
(Phone: 281/483-5111)
Jean-Claude Paradis
Natural Resources Canada, Ottawa, ON
(Phone: 613/992-9426)
RELEASE: 00-41
YUKON METEORITE MAY PROVIDE "NEW WINDOW INTO THE UNIVERSE"
A meteorite that exploded over a remote area of northwest
Canada in January may offer "a new window into the universe before
the solar system was created," said a NASA scientist who has begun
analyzing some of the meteorite fragments.
The very primitive composition and pristine condition of the
4.5-billion-year-old meteorite "offers us a snapshot of the
original composition of the entire solar system before the planets
formed," said Dr. Michael Zolensky, a cosmic mineralogist at
NASA's Johnson Space Center (JSC) in Houston. "It tells us what
the initial materials were like that went into making up the
Earth, the Moon and the Sun." The age of the solar system is
about 4.5 billion years.
"These meteorite fragments are of immense scientific value
and interest," said Dr. Richard Herd, Curator of National
Collections for the Geological Survey of Canada. "This rare find
potentially will contribute to a better understanding of the
nature of the universe." He added that finding previously
undetected compounds in the fragments will have implications for
both planetary and biological sciences worldwide.
The scientists described the fragments -- lumps of crumbly
rock with scorched, pitted surfaces -- as resembling partly used
charcoal briquettes: black, porous, fairly light and still
smelling of sulfur.
Several factors combined to make this meteorite a cosmic
bonanza for scientists. First, it is a carbonaceous chondrite, a
rare type of meteorite that contains many forms of carbon and
organics, basic building blocks of life. Carbonaceous chondrites,
which comprise only about 2 percent of meteorites known to have
fallen to Earth, are typically difficult to recover because they
easily break down during entry into Earth's atmosphere and during
weathering on the ground.
Zolensky said the last time a carbonaceous chondrite like
this fell to Earth and was recovered was 31 years ago. "This is
probably the only time in my career this will happen," he said.
The location and timing of the fireball also contributed to
the scientific value of the samples. The fragments are part of a
meteor that blew apart over a remote area of the Yukon Territory
the morning of Jan. 18, 2000. The resulting sonic booms startled
residents as far away as British Columbia and Alaska. The frozen,
snow-covered ground of the remote Yukon provided near-ideal
conditions for preservation, Herd said.
The finder, a local resident who has requested anonymity,
collected the fragments in clean plastic bags and kept them
continuously frozen. These are the only freshly fallen meteorite
fragments recovered and transferred to a laboratory without
thawing. Keeping the fragments continuously frozen minimized the
potential loss of organics and other volatile compounds in the
fragments.
About 2 pounds of meteorite fragments have been recovered so
far. Of those, Zolensky has about a pound of fragments provided
by the Canadian government and the University of Calgary. The
finder loaned them to the university and to the National Meteorite
Collection of the Geological Survey of Canada, Natural Resources
Canada (NRCan) in Ottawa, which provided the still-frozen samples
to JSC for study and analysis. NASA is working closely with NRCan
scientists and is providing results of the analysis to them. "We
are very sensitive to the fact that these are Canadian
meteorites," Zolensky said. Any future studies will be done in
cooperation with scientists worldwide.
Scientific analysis of the fragments has just begun. Tests
have been limited to two non-destructive activities: making a thin
section to analyze the mineralogy of the fragments, and measuring
induced radioactivity. Tests for induced radioactivity, which are
being carried out by Dr. David Lindstrom of JSC, measure the
object's exposure to space radiation. This can be used to
determine the size of the original meteoroid in space, estimates
of which range up to 50 feet in diameter, with a mass of more than
55 tons.
The next step in the study of the fragments will be baseline
analyses of the organics in the meteorite. This would require the
destruction of some samples, and negotiations are under way with
the finder for permission to do such tests.
"The nice thing about having a sample like this is that you
don't really know what you're going to find or where it's going to
lead," Zolensky said. "You can tuck samples away for the future
when new questions come along that people can't even think up
now."
========================================================
(4) WOBBLY ASTEROIDS AND COMETS
M. Efroimsky*) & A. Lazarian: Inelastic dissipation in wobbling
asteroids and comets. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL
SOCIETY, 2000, Vol.311, No.2, pp.269-278
*) HARVARD UNIVERSITY,DEPT PHYS,17 A OXFORD ST,CAMBRIDGE,MA,02138
Asteroids and comets dissipate energy when they rotate about any axis
different from the axis of the maximal moment of inertia. We show that
the most efficient internal relaxation happens at twice the frequency
of the precession of the body. Therefore earlier estimates that ignore
the double frequency input underestimate the internal relaxation in
asteroids and comets. We suggest that seismological data of the Earth
may poorly represent the acoustic properties of asteroids and comets as
internal relaxation increases in the presence of moisture. At the same
time, owing to the non-linearity of inelastic relaxation, small angle
nutations can persist for very long time spans, but our ability to
detect such precessions is limited by the resolution of the
radar-generated images. Wobbling may provide valuable information on
the composition and structure of asteroids and on their recent history
of external impacts. Copyright 2000, Institute for Scientific
Information Inc.
========================================================
(5) METEOROID STREAMS AT MARS
A.A. Christou*) & K. Beurle: Meteoroid streams at Mars: possibilities
and implications. PLANETARY AND SPACE SCIENCE, 1999, Vol.47, No.12,
pp.1475-1485
*) UNIVERSITY OF LONDON QUEEN MARY & WESTFIELD COLL,ASTRON UNIT,SCH
MATH SCI,MILE END RD,LONDON E1 4NS,ENGLAND
In order to assess the possibility of meteoroid streams detectable from
the surface of Mars as meteor showers we have derived minimum distances
and associated velocities for a large sample of small body orbits
relative to the orbits of Mars and the Earth. The population ratio for
objects approaching to within 0.2 AU of these two planets is found to
be approximately 2:1. The smaller relative velocities in the case of
Mars appears to be the main impediment to the detection of meteors in
the upper atmosphere of that planet. We identify five bodies, including
the unusual object (5335) Damocles and periodic comet 1P/Halley, with
relative orbital parameters most suitable to produce prominent meteor
showers. We identify specific epochs at which showers related to these
bodies are expected to occur. An overview of possible detection methods
taking into account the unique characteristics of the Martian
environment is presented. We pay particular attention on the effects of
such streams on the dust rings believed to be present around Mars. (C)
1999 Elsevier Science Ltd. All rights reserved.
============================
* LETTERS TO THE MODERATOR *
============================
(8) ASTEROID SPIN PARAMETER
>From Jeremy Tatum <UNIVERSE@uvvm.UVicdot ca>
Concerning the recent correspondence concerning what spin parameter
is most significant about an asteroid, I was encouraged that Petr
Pravec suggested the ratio between centrifugal and gravitational
force, because just last week I made my students calculate exactly
that quantity (also including oblateness effects) for the major
planets Mercury to Neptune. Not surprisingly, the effeect is very
pronounced for rapidly-rotating oblate Jupiter and negligible for
slowly-rotating spherical Venus. Perhaps I should not get them to
repeat the same calculation for all 100,000 asteroids, or however
many there are.
I suppose it might also be argued that what causes an asteroid to
spin rapidly might be an oblique collision by an impactor. In that
case, I think the asteroid experiences an impulsive torque, and the
time integral of that torque results in (indeed is equal to) a change
in the angular momentum of the asteroid. From that point of view, I
suppose one could argue that the significant spin parameter would be
the asteroid's angular momentum - which is proportional to the
product of the linear speed at the equator, and the radius and the
mass.
In any case, rather than make my students calculate any of these
quantities for 100,000 asteroids, I shall torture them with another
one this morning: A spherical asteroid is struck obliquely. Show
that the centre of the asteroid will move forwards if the impact
parameter is less than 40% of the radius; otherwise it moves
backwards.
Enjoy.
Jeremy Tatum
========================================================
(9) FAST RESPONSE TO FAST-SPINNING ASTEROIDS
>From Charles F. Peterson <cfp@mcn.org>
Many thanks for Petr Pravec's prompt response. There is so much to
keep in mind, and there are so many exciting, new programs and
discoveries. Thank goddess for the internet and CCnet! Access to ask
questions... access to answers...
Charles F. Peterson
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