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(meteorobs) Excerpts from "CCNet 18/2001 - 1 February 2001"
Among the items deleted from this issue were two very long, very erudite
essays on the history, etymology (and entomology!), and cultural aspects
of naming of various solar system bodies. Of interest to meteor observers
were references by University of Georgia (USA) Head Librarian Bob Kobres
(bkobres@ugadot edu) to ancient Babylonian texts possibly describing meteor
storms, fireballs or comets - along with Bob's analysis of the possible
meanings of these words in the context of their texts.
Of additional interest to meteoroids, in another deleted item, Dr. Duncan
Steel pens the following intriguing lines about comets-cum-asteroids that
were new to this writer:
>Now let's apply that concept to the smaller bodies in the solar system, at
>least those in heliocentric orbits (i.e. leave aside all moons/natural
>satellites, and ring systems). It would appear that one population of small
>bodies are made of rock and metal. We call these asteroids, or minor
>planets. There are some cross-over examples: asteroids produced from dead or
>dormant comets (e.g. 4015 Wilson-Harrington).
>
>I am entirely happy to have all these minor planets/asteroids numbered in
>that big sequence, so long as they are not comets. That means that I think
>that 2060 Chiron should really have been a comet Kowal, but mistakes get
>made as we progress and we really didn't know in 1977 (when it was
>discovered) that it would make the cross-over in the opposite direction:
>becoming active (producing a coma/atmosphere) as it neared perihelion.
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 18/2001 - 1 February 2001
Date: Thu, 1 Feb 2001 13:27:22 -0000
CCNet 18/2001 - 1 February 2001
-------------------------------
(1) NEAR MISSION COMPLETES MAIN TASK, NOW WILL GO WHERE NO
SPACECRAFT HAS GONE BEF0RE
NASANews@hq.nasadot gov
(2) MASS OF OORT CLOUD 10 TIMES SMALLER THAN THOUGHT?
Ron Baalke <baalke@zagami.jpl.nasadot gov>
(3) COMETS IN DISTANT CLOUD MAY BE SMALLER THAN THOUGHT
Space.com, 1 February 2001
(4) CHIXULUB CRATER RESEARCH
Michael Paine <mpaine@tpgi.com.au>
[...]
=========================================================================
(1) NEAR MISSION COMPLETES MAIN TASK, NOW WILL GO
WHERE NO SPACECRAFT HAS GONE BEF0RE
>From NASANews@hq.nasadot gov
Donald Savage
Headquarters, Washington, DC January 31, 2001
(Phone: 202/358-1727)
Michael Buckley
Johns Hopkins University Applied Physics Laboratory, Laurel,
MD
(Phone: 240/228-7536)
RELEASE: 01-13
NEAR MISSION COMPLETES MAIN TASK, NOW WILL GO WHERE NO SPACECRAFT HAS GONE
BEF0RE
NASA's Near Earth Asteroid Rendezvous (NEAR) Shoemaker spacecraft, the first
to orbit an asteroid, has met all its scientific goals in its year of
orbiting the asteroid Eros,
and will now attempt another first: a controlled descent to the surface of
the asteroid on Feb. 12.
The chief goal of the controlled descent to the surface is to gather
close-up pictures of the boulder-strewn surface of 433 Eros, more than 196
million miles from Earth.
"NEAR Shoemaker has set a high standard for low-cost planetary exploration,"
said Dr. Edward Weiler, Associate Administrator for Space Science, NASA
Headquarters, Washington, DC. "This mission has provided answers to a range
of fundamental science questions, and it has excited the public with its
exploration and great images. The team at Johns Hopkins University Applied
Physics Laboratory and its many partner institutions are to be congratulated
for achieving this historic first in space exploration."
During its 5-year, 2-billion-mile journey, the NEAR Shoemaker mission, which
was built and is managed by The Applied Physics Laboratory (APL) in Laurel,
MD, provided the most detailed profile yet of a small celestial body. It
began a yearlong orbit of Eros on Feb. 14, 2000, and has collected 10 times
more data than originally planned.
The data include a detailed shape-model culled from more than 11 million
laser pulses; radar and laser data on Eros' weak gravity and solid but
cracked interior; X-ray, gamma-ray and infrared readings on its composition
and spectral properties; and about 160,000 images covering all of the
21-mile-long asteroid's bouldered, cratered, dusty terrain.
"We have answered the questions we had when the orbit began. We now know
that Eros is a solid body of uniform composition, made of material probably
older than the Earth," said Dr. Andrew Cheng of APL, Project Scientist for
NEAR. "But we also found many other things we didn't expect to see and have
questions we didn't know to ask at the start of the mission. Scientists will
be looking at these data for years."
"On the tiny fraction of the surface we've seen at high resolution, we
noticed strange processes we haven't seen on the moon or anywhere else,"
added Dr. Joseph Veverka, NEAR imaging team leader from Cornell University
in Ithaca, NY. "For example, some boulders seem to have just disintegrated
on the surface. We've also seen that some of the fine surface material moves
downhill, filling low areas and creating flat surfaces in craters, even with
Eros' low gravity. These are big puzzles and we need to get a better look."
That look should come Feb. 12. The primary goal of the controlled descent is
to get the closest images yet of Eros, particularly its "saddle" area, a
6-mile wide depression that has intrigued scientists with its boulder
patches, relatively craterless surface and patterns of grooves and ridges.
The secondary aim is to practice the maneuvers that would lead to a landing,
creating a flight plan for future missions to land on a small body.
"With the spacecraft just about out of fuel and our science objectives met,
this is a great way to end a successful mission," said NEAR Mission Director
Dr. Robert Farquhar of APL. "It's all bonus science. It's never been tried
before and it certainly is a complicated set of maneuvers, but at this point
the only real risk is not taking one."
NEAR Shoemaker's 4-hour descent is scheduled to start at 10:31 a.m. EST with
a maneuver moving it out of its current orbit 22 miles from the center of
Eros. On the way down it will take images that will help determine its exact
location and altitude, and set the timing for the final thruster firings.
This series of thruster firings are designed to decelerate the spacecraft
from about 20 mph to 5 mph.
NEAR Shoemaker will approach the surface on its side, its outward-facing
camera pointed down, snapping a photo every minute. The last clear pictures
from the telescopic camera, taken from approximately 1,650 feet could show
surface features as small as four inches across. After that, NEAR mission
operators will use the blurring photos, altitude data from NEAR Shoemaker's
laser range-finder, Doppler tracking and the eventual loss of signal to
learn when the spacecraft touches down, predicted for just after 3 p.m. EST.
"The whole sequence of engine burns has to go right, or it might not be a
very soft touchdown," Farquhar said. " The unknown nature of the surface
makes it hard to predict what will happen to the spacecraft, especially
since it wasn't designed to land. The most we can hope for is a beacon from
NEAR Shoemaker that says it's still operating."
Images and information on end-of-mission media activities can be found at:
http://near.jhuapldot edu/media/index.html
=========================================================================
(2) MASS OF OORT CLOUD 10 TIMES SMALLER THAN THOUGHT?
>From Ron Baalke <baalke@zagami.jpl.nasadot gov>
MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109 TELEPHONE (818) 354-5011
http://www.jpl.nasadot gov
Contact: Martha J. Heil, (818) 354-0850
FOR IMMEDIATE RELEASE January 31, 2001
COMET COLLISIONS: ONLY THE STRONG SURVIVED?
Recurring collisions between comets during the solar system's formation may
have ground smaller comets to bits, leaving only big comets larger than 20
kilometers (12 miles) to survive, according to a new model developed by
researchers at NASA's Jet Propulsion Laboratory, Pasadena,
Calif., and the Southwest Research Institute, Boulder, Colo.
The finding, by Dr. Paul Weissman of JPL and Dr. Alan Stern of Southwest
Research Institute, published in the February 1 issue of the journal Nature,
demonstrates that previous models may have significantly overestimated the
mass of the Oort cloud -- a region far beyond the planets populated by
comets flung outward in the solar system's youth.
"We're introducing a new wrinkle in the process of how the Oort cloud
formed," said Weissman. One result of the new finding, he said, is that "the
cloud may be 10 times less massive than previously thought."
By studying comets of different sizes, the scientists predicted how the
comets would collide with each other, and how the collisions would erode the
comet's cores, dirty snowballs of dust and ice. Their model showed that
comets with nucleus diameters smaller than 20 kilometers (12 miles) would
have been destroyed in the early solar system's demolition derby. Previous
Oort cloud formation models neglected the effects of these collisions.
Another apparent implication of this violent collisional environment is that
the comets in the Oort cloud could be smaller than previously thought, said
the scientists. If comets were so eroded that they would never have left the
region of the giant planets, then few of them would have survived to be
ejected to the Oort cloud. Taking into account their new findings, Weissman
estimates that typical comets in the Oort cloud may be about half as large
across as compared with current best estimates.
JPL is a division of the California Institute of Technology in Pasadena.
=========================================================================
(3) COMETS IN DISTANT CLOUD MAY BE SMALLER THAN THOUGHT
>From Space.com, 1 February 2001
http://www.space.com/scienceastronomy/solarsystem/comet_collisions_010131.ht
ml
By Robert Roy Britt
Senior Science Writer
Beyond what's normally considered to be the outskirts of our solar system,
well beyond even Pluto's distant orbit, is a vast orbiting reservoir of icy
comets known as the Oort Cloud.
We're talking way out there: up to a fifth of the way to the nearest star.
Despite their incredible distance, the comets of the Oort Cloud still manage
to orbit the Sun. The only time we spot one, in fact, is when it zooms into
the inner solar system. For some, this might occur once in a million years.
For others, it can take 30 times that long to make a single orbit.
Sometimes, on its way around the Sun, an Oort Cloud comet passes close to
Earth. Now and then, one slams into our planet. So researchers would like to
know how many comets are in the Oort Cloud, how big they are, and how they
got there.
The leading theory of Oort Cloud formation holds that the giant planets --
Jupiter, Saturn, Uranus and Neptune -- were the bullies of early solar
system, using their immense gravity to push comets off the main playground
and then right on out of the neighborhood. The Sun and passing stars weighed
in on the side of the bullies.
Scientists have used this theory, along with estimates of how much material
was available to be bullied, to predict the total mass of all comets in the
Oort Cloud.
Nifty idea. Problem is, it might be totally wrong.
FULL STORY at
http://www.space.com/scienceastronomy/solarsystem/comet_collisions_010131.ht
ml
===========
(4) CHIXULUB CRATER RESEARCH
>From Michael Paine <mpaine@tpgi.com.au>
Dear Benny,
There is a news story at
http://www.kcstar.com/item/pages/printer.pat,fyi/37751701.129,.html
"Prehistoric meteorite punched hole in crust"
While checking this out I came across the following.
UT Austin scientist reports results from study of Yucatan crater linked to
mass extinctions of dinosaurs
http://www.ig.utexasdot edu/outreach/Media/Chicxulub/crater.htm
UT Press Release (15 December 2000)
UTIG Scientist Gail Christeson presented a report on December 17, to the
Fall Meeting of the American Geophysical Union in San Francisco offering new
geophysical clues to a cataclysmic event that may have killed off the
dinosaurs. The Chicxulub structure was formed 65 million years ago
when a large celestial body -- a comet or an asteroid -- slammed into the
Yucatan Peninsula with a force that makes a nuclear blast seem like a
firecracker. The impact produced fires, acid rain and tsunami-like
destructive waves. The collision gouged a crater nearly eight miles deep
and sent 12,000 cubic miles of rock, dirt and debris spinning into the
earth's atmosphere. The material blocked the sun, causing extreme changes in
the Earth's climate, which many scientists believe resulted in mass
extinctions.
regards,
Michael Paine
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