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(meteorobs) RASC Annual Convention...
Hi guys!
Got back Tuesday night from our annual RASC (Royal Astronomical Society of
Canada) convention, held this year in Kingston, Ontario. There were several
meteor/comet related events, which I thought I'd try to give you some info
on....
1. Tour of Miller Museum of Geology at Queen's University:
This was a neat place! They have an extensive collection of minerals and
fossils, the best I've seen - not a lot of large specimens, but very
extensive. The curator, Mark Badham, gave us a slide talk on the geology of
the Kingston area, and the Holleford meteor crater in particular. It was
formed between 500 and 550 million years ago, by an impacting body about 100
metres in diameter. This was when the continent was much further south in
latitude, and the site of present day Kingston about minus 20 in latitude.
He talked about meteorites in general as well, and passed around a
palm-sized piece of Canyon Diablo, which I had to hold for most of the slide
show, as they turned the lights out just as it reached me ;) He talked
about impact indicators - coesite, shock metamorphism, shatter cones. The
meteorite samples at the museum were:
Gao, Upper Volta
Baca County, New Mexico
Chaves County, New Mexico
Xiquipilca, Mexico
Pultusk, Poland
Henbury, Australia
Canyon Diablo, Arizona
Saint Robert, Quebec
The Saint Robert fall was on June 14, 1994, east of Montreal, Canada. It
exploded 10-20 km. above the earth, and pieces fell in an area 4 km. by 7
km.. The estimated size on entering the atmosphere was 10-100 tonnes, mass
at explosion 100-150 kg.. The largest fragment found was 6.5 kg., and the
smallest 55 g..
2. Talk by Dr. Martin Duncan of Queen's University, Kingston: "The Kuiper
Belt: Its Structure & Possible Origins"
The program book listed his talk as:
"Since the discovery of its first member in 1992, the trans-Neptunian
Kuiper belt has been transformed from a theoretical construct invoked to
explain the origin of short-period comets to a bona fide constituent of the
solar system. In this talk I will summarize the interplay between theory
and observations over the last 5 years that has shaped our current thinking
about the current structure of the belt and the implications of these
studies for our understanding of solar system formation."
Notes I took (in writing I am trying to decipher!) include:
He mentioned that experiments to be carried out by Hubble from August 15-20
would be looking for comet sized objects, both in the classical Kuiper belt
and the Kuiper scattered disk. Most of the smaller objects are believed to
be in the scattered disk of planetesimals.
The Kuiper scattered disk has an estimated 6 x 10^8 comets. 1996 RQ20 and
TL66 are probably the 1st discovered disk members. The estimated amount of
material in the scattered disk is the equivalent of an earth mass. Objects
in the scattered disk have a higher inclination, about 30-40 degrees.
He talked about how objects can become trapped in the Kuiper belt, but then
slowly leak away - and that this is where short-period comets come from.
Objects encounter Neptune, then migrate both inward - and outward. The
objects migrating inward towards the sun are passed down in successive
orbits from planet to planet. Some objects, on encountering Neptune, remain
closeby instead of migrating, about 1 % still left after about 4 billion
years. The objects migrating outward are a source for the Oort cloud.
He has been working with computer simulations, up to 1 billion year
simulations - and has offered to send me copies of several of his papers....
3. Talk by Dr. Gene Shoemaker: "Impact Cratering Through Geologic Time"
The abstract that he provided was as follows:
"New data on lunar craters and recent discoveries about craters on Earth
permit a reassessment of the bombardment history of Earth over the last 3.2
billion years. The combined lunar and terrestrial crater records suggest
that the long-term average rate of production of craters larger than 20 km.
in diameter has increased, perhaps by as much as 60 percent, in the last 100
to 200 million years. Production of craters larger than 70 km. diameter may
have increased, in the same time interval, by a factor of 5 or more over the
average for the preceding 3 billion years.
A large increase in the flux of long-period comets appears to be the most
likely explanation for this long-term increase in the cratering rate. Two
large craters, in particular, appear to be associated with a comet shower
centered at about 35.5 million years ago. The infall of cosmic dust, as
traced by ^3 He in deep sea sediments, and the ages of large craters, impact
glass horizons, and other stratigraphic markers of large impacts seem to be
approximately correlated with estimated times of passage of the Sun through
the galactic plane, at least for the last 65 million years. These are
predicted times for increased near-Earth flux of comets from the Oort Cloud
induced by the combined effects of galactic tidal perturbations and
encounter of the Sun with passing stars. Long term changes in average comet
flux may be related to changes in the amplitude of the z-motion of the Sun
or stripping of the outer Oort cloud by encounter with GMC's, followed by
restoration from the inner Oort Cloud reservoir."
I was unable to take notes during his talk.... but was fascinated! He
talked a lot about Australian craters, and showed some incredible slides of
them! He talked about comet showers, and the various impact 'markers'.
This ^3 He is a new one, accidently discovered <very> recently, and ties in
remarkably well with the other indicators, with peaks about 35 and 65
million years ago... (I am trying to remember numbers here)... and an
unusual peak <right now> in the ^3 He, which is interesting... Apparently
the ^3 He is very easily destroyed, and is found only in minute amounts,
where the velocity of the particles in their fall to the earth is
<extremely> slow. It is believed to be asteroidal in origin (if I remember
correctly).
It was a fascinating talk... although I got lost several times... I think
one of our RASC members videotaped the talk....
4. Tour of the Holleford Meteor Crater, near Kingston, Ontario:
This was neat! It's in an area of rolling hillside, but when you're
standing down in the center, you can see a gentle rolling rim around you.
It was identified in 1955 by a study of aerial photographs. Studies were
done - magnetic, seismic, gravity, and diamond drilling - between 1955 and
1957.
Estimated velocity of impact was 20 km./sec., and the energy of impact
supposedly about 6 times that of the Barringer crater.
It is now in the middle of a dairy farm, aptly named "Crater Farm" ;))
You can see fossils in some of the sedimentary rock laid down after the
crater was formed!
5. Other things....
After David Levy's talk on SL-9, while everyone was busy getting him to
autograph copies of his latest book... on astronomical poetry... I managed
to get a bit time alone with Gene Shoemaker to ask some questions ;)). I
asked about his opinion on the 'mini-comet' theory. He said that he felt
the numbers were out by a very large factor, by about 10,000 or so, and that
the equations used had fundamental flaws! Talked a bit about Australia -
they were taking off down under again...
Met an ALPO member from Barnesville, Georgia, Dr. Richard Schmude, who has
joined the RASC Kingston Centre ;). He came up to give a talk on photometry
of Mars, and then was headed off to the Astronomical League convention in
Denver, to give a talk on sporadic meteors.
Met a lady from the eastern townships of Quebec, Ank Mascle, who is
interested in meteorite craters, and who has visited some of the Quebec
craters...
Convention attendees included comet discoverers Gene and Carolyn Shoemaker,
David Levy, Rolf Meier, and Doug George - and (another) impact discoverer ;)
Alan Hildebrand.
Canadian radio pioneer Dr. Arthur Covington was also able to attend..
*****
And... that's sort of a summary of the meteor/comet related convention
stuff... I am going to try to get a copy of the papers... ;)
- Cathy
Great White North