PLEASE NOTE:


*

CCNet, 20 October 1999
------------------------

(1) POTENTIAL 'SURPRISE' METEOR SHOWER ON NOVEMBER 11?
    Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>

(2) CLARK CHAPMAN RECEIVES SAGAN MEDAL
    Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>

(3) ROCKS  NAMED AFTER ROCKERS
    Michael Paine <mpaine@tpgi.com.au>

(4) POSSIBLE FALKLANDS IMPACT STRUCTURE
    Michael Paine <mpaine@tpgi.com.au>

(5) PROJECT SPACEGUARD: SAVING HUMANKIND FROM GOING
    THE WAY OF THE DINOSAURS
    JMU, Astrophysics Research Institute

(6) ORBITAL EVOLUTION OF INTERPLANETARY DUST PARTICLES
    J.C. Liou et al., GB TECH LOCKHEED MARTIN

(7) SIZE DISTRIBUTION OF ASTEROID FAMILIES
    P. Tanga et al., OSSERV ASTRON TORINO

(8) VELOCITY-SIZE RELATIONSHIP OF ASTEROIDS
    A. Cellino et al., OSSERV ASTRON TORINO

(9) SIZES AND MASSES OF CHONDRULES
    K.E. Kuebler et al., UNIVERSITY OF TENNESSEE

===========
(1) POTENTIAL 'SURPRISE' METEOR SHOWER ON NOVEMBER 11?

From Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>
Forwarded from Joe Rao (Skywayinc@aol.com)

The recently discovered Comet LINEAR (C/1999J3) may serve to give rise
to a new meteor shower on November 11.

The circumstances concerning a prospective "Linearid" display on the 
evening of November 11th is most intriguing.  The moment when Earth
passes closest to the ascending node of C/1999J3 at 2:41 p.m. EST/11:41
a.m. PST. Unfortunately -- daylight for North America, although well
into evening darkness over Europe.

The radiant for this prospective display very near to the star Phecda, 
the lower left star in the bowl of the Big Dipper.  From my own
calculations, I come up with an RA of 11h 40m, Dec. +53 deg.  So even
for Europeans, the radiant stands only about a mere 5-degrees above the
northern horizon (at latitude 40N) at the time that the shower may
reach its peak!

Nonetheless . . . the separation between the Earth's orbit and that of 
the parent comet is just over 0.011 a.u.  As to what type of activity
might be expected, it should be noted that the 1985 Giacobinids briefly
produced an outburst of ZHR's of 600 to 800 from Japan, with the Earth
following 21P/Giacobini-Zinner to its node by just 26.5 days.  The
separation between the orbit of the comet and Earth was 0.033 -- or
three times the separation between the upcoming case of Earth and
C/1999J3. 

In 1933, when a major Giacobinid storm (ZHR = 3000 - 29000) occurred,
these values were 80 days and 0.005 a.u.  Earth is following LINEAR to
its ascending node by ~39.9 days.  Hence, the situation regarding the
prospective LINEARIDS is roughly midway between the two above cases.

Among the chief differences between Giacobini-Zinner and LINEAR is that
Earth intersected comet debris on the inside of Comet G-Z's orbit,
whereas we would intersect debris on the outside of comet LINEAR.  In
addition, the dust-distribution surrounding LINEAR is completely
unknown. Also, Giacobini-Zinner is a well-known short-period comet of
6.5 years and has been observed to circle the Sun on many other
occasions, whereas LINEAR is a newly discovered long-period object of
~63,000 years.

Nonetheless . . . I would strongly urge all observers to carefully
monitor the skies for possible meteors from this shower, especially
during the pre-dawn hours of November 11 (when the radiant is high up
in the northeast sky), as well as later that evening.  It appears that
should any significant outburst occur, those in western and central
Asia would have the best chance of viewing it (for them, in the
after-midnight/pre-dawn hours of November 12 local time). 

Although we know that the Earth will be closest to the comet's
ascending node at ~19.6 UT on November 11, this doesn't mean that the
actual peak of a prospective LINEAR display could not occur many hours
earlier or later. An example of this occurred one year ago with the
1998 Giacobinids: the time when Earth was predicted to cross the node
of 21P/Giaconini-Zinner was 20:53 UT on October 8; but the shower
actually reached its peak at 13:15 UT -- more than 7.5 hours earlier.

Thus, I would strongly suggest that all interested observers should be
on high-alert for a 24-hour interval on either side of the predicted
nodal crossing time of 19.6 UT/November 11. 

Who knows? It might prove to be an interesting warm-up for the Leonids,
which are due to peak just a week later!

-- joe rao     

==============
(2) CLARK CHAPMAN RECEIVES SAGAN MEDAL

From Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>

Southwest Research Institute scientist receives Sagan Medal
http://www.swri.edu/9what/releases/chapman.htm

Boulder, Colorado -- October 11, 1999 -- The Division for Planetary
Sciences (DPS) of the American Astronomical Society has awarded the
Carl Sagan Medal to Dr. Clark R. Chapman, an Institute scientist at
the Southwest Research Institute (SwRI) Department of Space Studies
in Boulder, Colorado. Chapman is the second recipient of the award,
named in honor of the late astronomer Carl Sagan, who was known for
exploring the grandeur of the universe in lectures, books, and on
television.

The Sagan Medal recognizes outstanding scientific communication to
the general public by an active planetary scientist. Chapman was
chosen in honor of his many promotional activities, such as writing
articles, books, and a regular column for The Planetary Report,
giving frequent commentaries on television and the popular science
journals, and for other projects involving education and public
outreach. Chapman recently testified before Congress about the
potential hazards of an asteroid or comet impacting the Earth.

"We live in a society that is increasingly dominated by science and
technology, yet the gap continues to widen between public understanding
of science and reality," he says. "That is why it is so important for
scientists and engineers to bridge that gulf or to help journalists and
educators do it.

"The general public is always quite fascinated by astronomy, so
planetary science is an especially fertile subject to use for engaging
them about scientific issues," he says. "And it is forward-looking, as
we move to the next century when humankind will strive to explore - and
perhaps populate - the solar system."

The DPS will present the Sagan Medal and a cash award at a meeting in
Padua, Italy, in October 1999.

For more information about Dr. Chapman's Sagan Medal, contact Maria
Martinez, Communications Department, Southwest Research Institute,
P.O. Drawer 28510, San Antonio, Texas, 78228-0510, Phone (210)
522-3305, Fax (210) 522-3547.

================
(3) ROCKS  NAMED AFTER ROCKERS

From Michael Paine <mpaine@tpgi.com.au>

Dear Benny

Scientific American brought this website to my attention
http://cfa-www.harvard.edu/cfa/ps/special/RockAndRoll.html
"A number of minor planets have been named in honor of contemporary
musicians..." Yes - the Minor Planet Centre. Nice to see a sense of
humour in this field!

Michael Paine

=================
(4) POSSIBLE FALKLANDS IMPACT STRUCTURE

From Michael Paine <mpaine@tpgi.com.au>

Dear Benny,

In response to several inquiries about my "Crater and exinction events"
graph I have tried, without success, to find out more about the
possible Late Permian impact structure on the Falklands undersea
plateau off Argentina. In his book "Rogue asteroids and doomsday
comets" Duncan Steel refers to investigations by Michael Rampino (then
at the Goddard Institute of Space Studies): "The appropriate antipodal
point to Siberia (Siberian Traps 250Ma) is the Falkland plateau off
Tierra del Fuego... on that plateau Rampino has identified two
sub-oceanic circular basins with diameters of about 300km and 200km
respectively. Dating the rocks indicates the same age as the Late
Permian Extinction." He cites a Rampino paper in the book "Hazards due
to Comets and Asteroids" called "Extraterrestrial impacts and mass
extinctions" - this may contain more information.

I cannot find any recent references to this subject. It seems that the
same issues that delayed discovery of Chicxulub are occurring in the
case of the Falklands Plateau - commercial and political sensitivities.
The area has potential oil reserves and, as Brits would know, it is
also very sensitive politically. Apparently several scientists are
working on possible Late Permian impact structures (not necessarily on
the Falkland Plateau) so we will just have to wait to see if huge
impacts played a role in the greatest extinction event on record.

On another matter, in my "Riches from the rubble of the solar system"
Explorezone article I wrote about the potential for steam powered
rockets and mining the propellant (ice) from Near Earth Asteroids.
UniSci has a news item about a new satellite propulsion system that
uses components similar to those in a microwave oven: "In recent
tests, Micci operated the system using nitrogen, helium and ammonia
as propellant gases. The thruster can also potentially be operated
with water as propellant." http://unisci.com/stories/19994/1018995.htm

Michael Paine

===============
(5) PROJECT SPACEGUARD: SAVING HUMANKIND FROM GOING
    THE WAY OF THE DINOSAURS

From JMU, Astrophysics Research Institute

Dr Duncan Steel (University of Salford)

Public Lecture
LIVERPOOL JOHN MOORES UNIVERSITY
Byrom Street
Wednesday 20th October
7-8pm

It is common knowledge that many scientists believe that the dinosaurs
were extinguished 65 million years ago as the result of an asteroid or
comet impact on Earth.  Many people fondly believe that this was the
last such impact, but that is not the case: our planetary home orbits
the Sun amongst a cosmic swarm of potentially-lethal projectiles, any
one of which could end civilisation as we know it. It is an
uncomfortable fact that the average person has a greater chance of
dying due to an asteroid strike than he or she does of being killed in
a jetliner crash, and so this celestial hazard is one which we must
take seriously, else we will inevitably go the way of the dinosaurs.
The movies ARMAGEDDON and DEEP IMPACT were not entirely fiction! In
this talk the nature of the threat and what is being done to counter it
will be discussed at the layperson's level.

For further information please contact

Astrophysics Research Institute           enquiry@astro.livjm.ac.uk
Liverpool John Moores University          http://www.livjm.ac.uk/astro
Twelve Quays House, Egerton Wharf         Tel - + 44 151 231 2900
Birkenhead CH41 1LD, UK                   Fax - + 44 151 231 2921

============
(6) ORBITAL EVOLUTION OF INTERPLANETARY DUST PARTICLES

J.C. Liou*), H.A. Zook, A.A. Jackson: Orbital evolution of retrograde
interplanetary dust particles and their distribution in the solar
system. ICARUS, 1999, Vol.141, No.1, pp.13-28

*) GB TECH LOCKHEED MARTIN,MAIL CODE C104,2400 NASA RD 1,
   HOUSTON,TX,77058

The orbital evolution of interplanetary dust particles (IDPs) from
both retrograde and prograde Halley-type comets is numerically
simulated. It is found that dust particles nearly always get trapped
into one or more mean motion resonances (MMRs) with giant planets
while in retrograde orbits. Of the 1000 retrograde particles
simulated 116 are trapped in MMRs that last longer than 100,000
years, and the MMRs are typically exterior MMRs of the type p:1 with
Jupiter where p ranges from 1 to 12. We present a simple analysis of
the physical processes involved when an IDP is in a resonance. A
quasistable resonance is maintained by the combined effect of the
direct perturbation from the planet as well as the indirect
perturbation that arises because the Sun is moving around the
Sun-planet barycenter. The direct and indirect perturbations are
often of comparable magnitudes, although one or the other can be
dominant. Of the 1000 retrograde particles simulated, 45 of them
evolved to prograde orbits while in MMRs with a giant planet.
Although the overall distribution in eccentricity and inclination of
10(-7) g dust particles from Halley-type comets is consistent with D.
H. Humes' (1980, J. Geophys. Res. 85, 5841-5852) interpretation of
the Pioneer 10 and 11 data, the spatial density variation is not.
Instead of the constant spatial density derived by Humes, the spatial
density of Halley-type comet dust varies as r(-gamma) with
heliocentric distance r, where gamma ranges from 1.5 to 1.8.
Additional sources of interplanetary dust particles are needed to
account for the discrepancy. (C) 1999 Academic Press.

=============
(7) SIZE DISTRIBUTION OF ASTEROID FAMILIES

P. Tanga*), A. Cellino, P. Michel, V. Zappala, P. Paolicchi, D.
DellOro: On the size distribution of asteroid families: The role of
geometry. ICARUS, 1999, Vol.141, No.1, pp.65-78

*) OSSERV ASTRON TORINO,I-10025 PINO TORINESE,TO,ITALY

The steep slopes of the size distributions of the presently known
asteroid families have long represented a debated problem. The reason
is that it is not easy to reproduce them by the usual modeling
techniques based on the application of standard power-laws as
suggested by laboratory experiments. In this paper, we suggest that
the failures of the previous models were due to the fact that
geometric effects were not taken into account. In other words, the
finite sizes of the parent bodies and the fact that fragments tend to
have convex shapes cannot be disregarded. Following this approach, we
find that steep size distributions are necessarily produced by
fragmentations of the parent bodies. Moreover, we have been able to
reproduce fairly well the observed size distributions of the major
families, and we have also obtained some reasonable constraints on
the original sizes of the parent bodies. Some anomalous mass
depletions, probably due to injection of fragments in nearby
resonances have also been found, not unexpectedly, in a few cases
(Maria, Themis). (C) 1999 Academic Press.

============
(8) VELOCITY-SIZE RELATIONSHIP OF ASTEROIDS

A. Cellino*), P. Michel, P. Tanga, V. Zappala, P. Paolicchi, A.
DellOro: The velocity-size relationship for members of asteroid
families and implications for the physics of catastrophic collisions.
ICARUS, 1999, Vol.141, No.1, pp.79-95

*) OSSERV ASTRON TORINO,I-10025 PINO TORINESE,TO,ITALY

An extensive analysis of the size-ejection velocity relationship for
members of several of the most important asteroid families identified
in the Main Belt is presented. We have found a well defined behavior,
with smaller fragments having on the average higher ejection
velocities. The results provide useful constraints to current models
of catastrophic breakup processes and lead also to a new estimate of
the transition limit in largest remnant/parent body mass ratio,
distinguishing cratering, and shattering regimes. Moreover, we have
now available a practical method for estimating fragment ejection
velocities in interasteroid collisional events. This can be easily
implemented in numerical models of the collisional evolution of the
asteroid belt. In particular, it should be possible to undertake a
more quantitative assessment of the efficiency of collisional events
in the Main Belt as the sources of near Earth asteroids of different
sizes. (C) 1999 Academic Press.

============
(9) SIZES AND MASSES OF CHONDRULES

K.E. Kuebler*), H.Y. McSween, W.D. Carlson, D. Hirsch: Sizes and
masses of chondrules and metal-troilite grains in ordinary
chondrites: Possible implications for nebular sorting. ICARUS, 1999,
Vol.141, No.1, pp.96-106

*) UNIVERSITY OF TENNESSEE,DEPT GEOL SCI,KNOXVILLE,TN,37996

Intergroup variation in chondrule sizes is commonly attributed to
mass or aerodynamic sorting in the solar nebula, a concept that has
recently been extended to other chondrite constituents (metal
chondrules, metal-troilite grains). Both sorting mechanisms are
dependent on grain density and size. Because metal chondrules and
metal-troilite grains have smaller average sizes than their
coexisting chondrule populations, the assumption of mass equivalence
has been made and invoked in support of nebular sorting. We present
the results of a quantitative comparison of the sizes, masses, and
aerodynamic stopping times of chondrules and metal-troilite grains
from three ordinary chondrites: Kelly (LL4), Bjurbole (L/LL4), and
Hammond Downs (H4). Chondrule volumes were determined from corrected
thin-section measurements, and metal-troilite grain volumes were
estimated from X-ray tomographic images. Chondrule and metal-troilite
grain populations have similar masses in Hammond Downs but are
dissimilar in Bjurbole and Kelly. The difference in the average
particle aerodynamic stopping times of the chondrules and
metal-troilite grains (15% for Hammond Downs, 16% for Bjurbole, 32%
for Kelly) are much smaller than differences in their average masses
(28% for Hammond Downs, 73% for Bjurbole, 82% for Kelly). The
observed ranges in mass of the two populations are relatively narrow
in Hammond Downs and are wider in Bjurbole and Kelly. Furthermore, in
all three meteorites the observed range in mass of the chondrules is
narrower than that of the corresponding metal-troilite grain
populations. It appears that the chondrules were sorted more
efficiently than the metal-troilite grains. Our results agree
with the idea that aerodynamic stopping times vary with particle size
and density and disagree with sorting only by mass. While the average
stopping times (expressed as r(p) p(s)) of the two populations
correlate better than their average masses, the percent difference in
(r(p) p(s)) between the two populations (Hammond Downs, 15%;
Bjurbole, 16%; and Kelly, 32%) is greater than that between the
chondrules and metal chondrules previously reported for the Acfer 059
carbonaceous chondrite (W. R. Skinner and J. M. Leenhouts 1993, Proc.
Lunar Planet. Sci. Conf. 24th, 1315-1316). We attribute this to the
small and irregular shapes of the metal-troilite grains, although
thermal metamorphism may have also affected the metal-troilite grain
data. For these reasons, our results are at variance with the concept
of nebular mass sorting but may be in agreement with aerodynamic
sorting models. Our results are consistent with the hypothesis that
chondrule sorting is related to the phenomena of metal-silicate
fractionation. However, these data are only preliminary. Final
interpretation should be reserved until more meteorites can be
analyzed, the effects of thermal metamorphism on metal grain sizes
quantified, and software capable of true three-dimensional analysis
developed. (C) 1999 Academic Press.


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