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(meteorobs) Excerpts from "CCNet 88/2001 - 19 July 2001"
A nice, juicy issue this time, with several articles pertaining or related
to a potential evolutionary relationship between comets and some asteroid
groups - of interest in regards the Geminids and other "asteroid" streams.
Re: the first item below, maybe 'meteorobs' founding subscriber Wayne Hally
could offer to speak before AAAP of New Jersey some time soon, to help them
along a bit in their quest to expand their meteor understanding? :)
Clear skies!
Lew Gramer
------- Forwarded Message
From: Peiser Benny <B.J.Peiser@livjm.acdot uk>
To: cambridge-conference <cambridge-conference@livjm.acdot uk>
Subject: CCNet 88/2001 - 19 July 2001
Date: Thu, 19 Jul 2001 10:27:25 +0100
CCNet 88/2001 - 19 July 2001
----------------------------
(1) FIREBALL EXPLODES OVER NEW JERSEY
The Trentonian, 18 July 2001
[...]
(8) TUNGUSKA EXPEDITION
Andrei Ol'khovatov <olkhovatov@mtu-net.ru>
[...]
(10) WOBBLING ASTEROIDS AND COMETS
Michael Efroimsky
(11) DIRECT SIMULATION OF METEOROIDS AND SPACE DEBRIS FLUX
ON LDEF SPACECRAFT SURFACES
Jingqi Miao and J. P. W. Stark
[...]
(13) LOW ALBEDOS AMONG EXTINCT COMET CANDIDATES
Fernandez YR, Jewitt DC, Sheppard SS
[...]
==============================================================================
(1) FIREBALL EXPLODES OVER NEW JERSEY
>From The Trentonian, 18 July 2001
http://www.zwire.com/site/news.cfm?newsid=2099468&BRD=1697&PAG=461&dept_id=4
4551&rfi=6
UFO sightings at dusk, dawn
DAVE SOMMERS, Staff Writer July 18, 2001
Most UFO sightings in the New Jersey-Pennsylvania sky occur either at dawn
or dusk when objects high up in the stratosphere, such as airplanes or
meteorites, are more likely to refract sunlight back to earth, astronomers
say.
That's one of the things that puzzles Kirk Alexander, director of the
Amateur Astronomy Association of Princeton, who notes that Sunday's unusual
sighting occurred in the middle of night.
Alexander said many UFO sightings turn out to be small meteors which split
up, fall back into the stratosphere and burn brightly for several minutes.
"The larger meteorites can explode and the pieces burn in unison as they
fall through the atmosphere," he said.
That's basically the description the 70 or so people gave when they
described the brightly burning lights they observed near Carteret at 12:30
a.m. Sunday.
Alexander also noted that the cool, crisp weather last weekend enabled
people to see for miles, something which can't happen onhazy cloud-filled
nights.
"There have been incidents where aircraft eject small objects out of their
exhaust which can been seen for miles," he said, adding one more explanation
to the long list of possibilities.
The Amateur Astronomy Association group has 150 members. They meet twice a
month, usually at one of the group's two observatories inWashington Crossing
State Park in New Jersey or Jenny Jump, New Jersey.
"As astronomers, we try to look at these weird happenings as a way to learn
something, and we usually do," he said.
)The Trentonian 2001
==============================================================================
* LETTERS TO THE MODERATOR *
==============================================================================
(8) TUNGUSKA EXPEDITION
>From Andrei Ol'khovatov <olkhovatov@mtu-net.ru>
Dear Dr.Peiser,
In CCNet of July 16 there was a post re: "ANOTHER SCIENTIFIC EXPEDITION TO
TUNGUSKA METEORITE FALL SITE," posted by Ron Baalke and citing PRAVDA
newspaper.
Unfortunately, the info about the expedition is a little bit exaggerated. It
is not a big expedition. As far as I know, the expedition consists of about
8 persons in total. Some of them participated in the Krasnoyarsk part of the
TUNGUSKA 2001 International Conference, but failed to buy tickets for the
flight to Vanavara (near the Tunguska epicenter), so they were not able to
join the main group going to Tunguska, and had to go separetely. The main
group of TUNGUSKA 2001 expedition of 10 persons made a short trip to the
epicenter to take samples and making TV-documentaries. More info on the
conference www.geocities.com/olkhov/conf01.htm. As far as I know, at least
one more reader of CCNet took part in the conference and in the trip, so
maybe he will share his impressions with others.
Sincerely,
Andrei Ol'khovatov
Russia, Moscow
==============================================================================
* ABSTRACTS *
==============================================================================
(10) WOBBLING ASTEROIDS AND COMETS
Planetary and Space Science, Volume 49, Issue 9, August 2001, Pages 937-955
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V6T-43GH08G-5&_us
er=777686&_coverDate=08%2F31%2F2001&_rdoc=5&_fmt=summary&_orig=browse&_srch=
%23toc%235823%232001%23999509990%23255461!&_cdi=5823&_sort=d&_acct=C00004303
1&_version=1&_urlVersion=0&_userid=777686&md5=c66ff65d5d32150e5a3594696f3ad1
e6
Relaxation of wobbling asteroids and comets - theoretical problems,
perspectives of experimental observation
Michael Efroimsky [efroimsk@fas.harvarddot edu], Department of Physics, Harvard
University, Cambridge, MA 02138, USA
Received 1 September 2000; revised 5 April 2001; accepted 8 May 2001
Available online 12 July 2001.
Abstract
A body dissipates energy when it freely rotates about any axis different
from principal. This entails relaxation, i.e., decrease of the rotational
energy, with the angular momentum preserved. The spin about the
major-inertia axis corresponds to the minimal kinetic energy, for a fixed
angular momentum. Thence one may expect comets and asteroids (as well as
spacecraft or cosmic-dust granules) to stay in this, so-called principal,
state of rotation, unless they are forced out of this state by a collision,
or a tidal interaction, or cometary jetting, or by whatever other reason. As
is well known, comet P/Halley, asteroid 4179 Toutatis, and some other small
bodies exhibit very complex rotational motions attributed to these objects
being in non-principal states of spin. Most probably, the asteroid and
cometary wobble is quite a generic phenomenon. The theory of wobble with
internal dissipation has not been fully developed as yet. In this article we
demonstrate that in some spin states the effectiveness of the
inelastic-dissipation process is several orders of magnitude higher than
believed previously, and can be measured, by the presently available
observational instruments, within approximately a year span. We also show
that in some other spin states both the precession and precession-relaxation
processes slow down considerably. (We call it near-separatrix lingering
effect.) Such spin states may evolve so slowly that they can mimic the
principal-rotation state.
Copyright ) 2001 Elsevier Science Ltd. All rights reserved.
==============================================================================
(11) DIRECT SIMULATION OF METEOROIDS AND SPACE DEBRIS FLUX ON
LDEF SPACECRAFT SURFACES
Jingqi Miao(a) [j.miao@ukc.acdot uk] and J. P. W. Stark(b)
>From Planetary and Space Science, Volume 49, Issue 9 , August 2001, Pages
927-935
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V6T-43GH08G-4&_us
er=777686&_coverDate=08%2F31%2F2001&_rdoc=4&_fmt=summary&_orig=browse&_srch=
%23toc%235823%232001%23999509990%23255461!&_cdi=5823&_sort=d&_acct=C00004303
1&_version=1&_urlVersion=0&_userid=777686&md5=4ff4ea18b4555b2a797c879028c62d
b4
a The School of Physics Science, University of Kent, Canterbury, CT2 7NR, UK
b Engineering Department, Queen Mary and Westfield College, University of
London, London E1 4NS, UK
Received 20 May 2000; revised 18 December 2000; accepted 3 April 2001
Available online 12 July 2001.
Abstract
The meteoroid flux on all faces of the long duration exposure facility
(LDEF) is predicted by a direct simulation Monte Carlo (DSMC) model, which
for the first time provides a self-consistent method to model the collision
behaviour between both meteoroids and debris with oriented spacecraft
surfaces. This new model includes the modified Divine's meteoroid
population, and Taylor's velocity distribution, to include the effects of
planetary shielding and gravitational enhancement by the Earth. Results
obtained when only meteroid impact is considered show good agreement with
observed data and provide some correlation with previous models. When the
space debris population is also included, the total particle flux on
different faces of LDEF fits well with the observed measurements.
Information concerning Earth shielding, gravity capturing and atmospheric
effects can be obtained by comparing the ratio of the number of meteoroids
moving towards the Earth to the total number of the meteoroids, obtained
from the DSMC model with measured data. Approximately 25% of the meteoroids
flux is predicted as not returning into the interplanetary space due to
these effects.
Copyright ) 2001 Elsevier Science Ltd. All rights reserved.
==============================================================================
(12) THE EUCRITE/VESTA STORY
Drake MJ: The eucrite/Vesta story
METEORITICS & PLANETARY SCIENCE 36 (4): 501-513 APR 2001
Many lines of evidence indicate that meteorites are derived from the
asteroid belt but, in general, identifying any meteorite class with a
particular asteroid has been problematical. One exception is asteroid 4
Vesta, where a strong case can be made that it is the ultimate source of the
howardite-eucrite-diogenite (HED) family of basaltic achondrites. Visible
and near-infrared reflectance spectra first suggested a connection between
Vesta and the basaltic achondrites. Experimental petrology demonstrated that
the eucrites (the relatively unaltered and unmixed basaltic achondrites)
were the product of approximately a 10% melt. Studies of siderophile element
partitioning suggested that this melt was the residue of an asteroidal-scale
magma ocean. Mass balance considerations point to a parent body that had its
surface excavated, but remains intact. Modem telescopic spectroscopy has
identified kilometer-scale "Vestoids" between Vesta and the 3:1 orbit-orbit
resonance with Jupiter. Dynamical simulations of impact into Vesta
demonstrate the plausibility of ejecting relatively unshocked material at
velocities consistent with these astronomical observations. Hubble Space
Telescope images show a 460 km diameter impact basin at the south pole of
Vesta. It seems that nature has provided multiple free sample return
missions to a unique asteroid. Major challenges are to establish the
geologic context of the HED meteorites on the surface of Vesta and to
connect the remaining meteorites to specific asteroids.
Addresses:
Drake MJ, Univ Arizona, Lunar & Planetary Lab, Tucson, AZ 85721 USA
Univ Arizona, Lunar & Planetary Lab, Tucson, AZ 85721 USA
Copyright ) 2001 Institute for Scientific Information
==============================================================================
(13) LOW ALBEDOS AMONG EXTINCT COMET CANDIDATES
Fernandez YR, Jewitt DC, Sheppard SS: LOW ALBEDOS AMONG EXTINCT COMET
CANDIDATES
ASTROPHYSICAL JOURNAL 553 (2): L197-L200, Part 2 JUN 8 2001
We present radiometric effective radii and visual geometric albedos for six
asteroids in comet-like orbits. Our sample has three of the four known
retrograde asteroids (1999 LE31, 2000 DG(8), and 2000 HE46) and three
objects [( 18916) 2000 OG(44), 2000 PG(3), and 2000 SB1] on prograde but
highly elliptical orbits. These measurements more than double the number of
known albedos for asteroids with a Tisserand invariant in the cometary
regime. We find that all six of our objects, and nine of the 10 now known,
have albedos that are as low as those of active cometary nuclei, which is
consistent with their supposed evolutionary connection to that group. This
albedo distribution is distinct from that of the whole near-Earth and
unusual asteroid population, and the strong correlation between Tisserand
invariant and albedo suggests that there is a significant cometary
contribution to this asteroid population.
Addresses:
Fernandez YR, Univ Hawaii, Inst Astron, 2680 Woodlawn Dr, Honolulu, HI 96822
USA
Univ Hawaii, Inst Astron, Honolulu, HI 96822 USA
Copyright ) 2001 Institute for Scientific Information
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