PLEASE NOTE:
*
CCNet 33/2001, 1 March 2001
---------------------------
"Future historians looking back at the search for
Earth-threatening
asteroids will find a footnote for events that unfolded last
week. [...]
What emerged from the data was a tiny object moving in what
appeared to be
a strikingly Earthlike orbit around the Sun. Calculations
suggested that
it had passed very near the Moon last August and would come
within
360,000 miles (580,000 kilometers) of Earth on February 23rd. The
Minor
Planet Center (MPC) in Cambridge, Massachusetts, assigned it the
preliminary asteroid designation 2001 DO47. [...] from the outset
there were suspicions by the MPC staff that 2001 DO47 might be
artificial
and thus more reflective than a typical asteroid making it
smaller yet.
[...] By February 25th they heard from McDowell, who identified
the
mystery spacecraft as Wind, a NASA probe, and confirmed that an
engine
burn had indeed been scheduled for February 23rd."
--Dennis di Cicco, Sky & Telescope, 28 February 2001
"My idea could solve the missing smaller craters, the sunken
areas
and the angular rocks that may have been eroded out of the
astroid's
surface. Moderate to large impacts could cause an asteroid to
vibrate
like a tuning fork, the loose surface dust would ride along the
surface
seeking low spots in the weak gravity like a fluid bed. Smaller
impact
craters would be filled in while larger craters, or newer smaller
craters, may leave a sunken like look. Rocks could travel along
the
surface a short distance (didn't I read once that a rock left a
short
trail?) loosening more dust for the next impact exposing angular
rock that
may be former impactors or hard accetions within the
asteroid."
--Dave English, 28 February 2001
(1) BIG EARTHQUAKE JOLTS NORTHWEST: DEMAGE ESTIMATED IN BILLIONS
The New York Times, 1 March 2001
(2) ANOTHER "ASTEROID" IDENTIFIED AS SPACECRAFT:
LESSONS LEARNED FROM THE
SG344 DEBACLE
Larry Klaes <lklaes@bbn.com>
(3) NEAR SHOEMAKER PHONES HOME FOR THE LAST TIME
Ron Baalke <baalke@jpl.nasa.gov>
(4) LOUIS FRANK CLAIMS TO HAVE FOUND NEW EVIDENCE FOR SMALL COMET
THEORY
Andrew Yee <ayee@nova.astro.utoronto.ca>
(5) RARE METEORITES REKINDLE CONTROVERSY OVER BIRTH OF THE SOLAR
SYSTEM
Stanford News Service <stanford.report@forsythe.stanford.edu>
(6) NEAR: AWAKENED FROM THE DEAD?
Space.com, 28 February 2001
(7) EROS POINTS WAY TO PHOBOS AND DEIMOS
S. Fred Singer <singer@sepp.org>
(8) DUST MIGRATION ON SMALL BODIES
Dave English <prospector@sd.znet.com>
(9) THE "CHRISTMAS" COMET
Mark Kidger <mrk@ll.iac.es>
(10) IMPACT VOLCANISM CLARIFICATION
Mark Boslough <mbboslo@sandia.gov>
(11) IR, PLUMES & SCIENTIFIC AMERICAN
Hermann Burchard <burchar@mail.math.okstate.edu>
(12) CO2 AS A DINO-KILLER AMPLIFIER?
Jon Richfield <richfield@telkomsa.net>
(13) ABSTRACTS FROM GEOLOGICAL SOCIETY OF AMERICA 2000
Michael Paine <mpaine@tpgi.com.au>
=============
(1) BIG EARTHQUAKE JOLTS NORTHWEST: DEMAGE ESTIMATED IN BILLIONS
From The New York Times, 1 March 2001
http://www.nytimes.com/2001/03/01/national/01QUAK.html
SEATTLE, Feb. 28 - The Pacific Northwest was rocked today by the
most
powerful earthquake to hit the area in 52 years, a 40-second
tremor that
shattered windows, crumbled bricks and buckled pavement across
Seattle and
cracked the Capitol dome in Olympia, Wash., a dozen miles from
the quake's
epicenter.
At least 215 people were injured, at least 8 seriously, and
officials said
property damage would easily run into the billions of
dollars......
http://www.nytimes.com/2001/03/01/national/01QUAK.html
===============
(2) ANOTHER "ASTEROID" IDENTIFIED AS SPACECRAFT:
LESSONS LEARNED FROM THE
SG344 DEBACLE
From Larry Klaes <lklaes@bbn.com>
WAIT, IT'S ONE OF OURS
From Sky & Telescope, 28 February 2001
http://www.skypub.com/news/news.shtml#wind
A puzzling "asteroid" designated 2001 DO47 turned out
to be of terrestrial
origin. The Wind spacecraft was launched in 1994 to study the
interaction
between the solar wind and Earth
magnetosphere. This plot shows the probe's looping trajectory
from May 1999
to April 2000. Courtesy International Solar-Terrestrial Physics
program,
NASA/Goddard Space Flight Center.
http://www.skypub.com/news/images2001/010228news02.gif
Future historians looking back at the search for
Earth-threatening asteroids
will find a footnote for events that unfolded last week.
It began on the evening of February 18th when a fast-moving
object was
spotted in western Cancer by the Arizona-based Spacewatch team -
the
patriarch of contemporary searches, which has been looking for
near-Earth
objects (NEOs) with a 36-inch telescope since the 1980s.
During the next two days amateur and professional observers at
more than a
dozen locations around the world tracked thetracked the
16th-magnitude
object as it raced eastward crossing a Moon's diameter of sky
every 90
minutes.
What emerged from the data was a tiny object moving in what
appeared to be a
strikingly Earthlike orbit around the Sun. Calculations suggested
that it
had passed very near the Moon last August and would come within
360,000
miles (580,000 kilometers) of Earth on February 23rd. The Minor
Planet
Center (MPC) in Cambridge, Massachusetts, assigned it the
preliminary
asteroid designation 2001 DO47.
While certainly an interesting object, 2001 DO47 posed no threat.
Even if it
were headed toward Earth, its estimated diameter of only 10
meters would
have made it too small to survive a passage through our
atmosphere.
Furthermore, from the outset there were suspicions by the MPC
staff that
2001 DO47 might be artificial and thus more reflective than a
typical
asteroid making it smaller yet.
"We would have liked to check out the artificial possibility
before
announcing the object," notes MPC associate director, Gareth
Williams, "but
our resident expert, [Sky & Telescope contributing editor]
Jonathan
McDowell, was observing in Arizona and initially out of
reach."
The story took another twist when observations of the object made
on
February 23rd by John Rogers in California and the undersigned in
Massachusetts - both members of the worldwide network of amateurs
who
measure positions of asteroids and comets - were internally
consistent but
significantly out of step with the earlier sightings.
"2001 DO47 has switched on its engine," is how Williams
described the
situation to MPC director Brian Marsden, who concurred with
Williams that
the object must be artificial.
By February 25th they heard from McDowell, who identified the
mystery
spacecraft as Wind, a NASA probe, and confirmed that an engine
burn had
indeed been scheduled for February 23rd.
Launched on a mission to study the solar wind and Earth's outer
magnetosphere in late 1994, Wind spends most of its time far from
Earth, but
it also makes occasional swings by the Earth and the Moon during
orbital
maneuvers. The spacecraft is 2.4 meters (7.9 feet) in diameter
and 1.8
meters (5.9 feet) high.
Marsden told Sky & Telescope that, inspired by the 2001 DO47
incident, the
MPC has now added the orbital information of about a dozen
spacecraft to its
computers, which should help identify these objects when they
turn up in the
data from NEO surveys.
- Dennis di Cicco
Copyright 2001, Sky & Telescope
=============
(3) NEAR SHOEMAKER PHONES HOME FOR THE LAST TIME
From Ron Baalke <baalke@jpl.nasa.gov>
For Immediate Release
February 28, 2001
Media Contacts:
Helen Worth
(240) 228-5113
helen.worth@jhuapl.edu
Mike Buckley
(240) 228-7534
michael.buckley@jhuapl.edu
The End of an Asteroidal Adventure
NEAR Shoemaker Phones Home for the Last Time
Tonight at 7 p.m. (EST) NASA's Deep Space Network antennas will
pull down
their last Near Earth Asteroid Rendezvous (NEAR) mission data,
bringing to a
close the first mission to extensively study an asteroid. NEAR,
which was
the first mission in NASA's Discovery Program of low-cost,
scientifically
focused space missions, and the first to land on an asteroid, has
delighted
astronomy neophytes and scientists alike.
"NEAR has raised the bar," says Dr. Stamatios Krimigis,
Space Department
head at The Johns Hopkins University Applied Physics Laboratory
in Laurel,
Md., which built the spacecraft and managed the NEAR mission.
"The
Laboratory is very proud to have managed such a successful
mission and
worked with such a strong team of partners from industry,
government and
other universities. The team had no weak links and the result was
an
historic mission that surpassed everyone's expectations."
"This mission has been successful far beyond what was in the
original
mission plan," says NEAR Mission Director Dr. Robert
Farquhar of APL. "We
got the first images of a C-class asteroid when we added a flyby
of asteroid
Mathilde in 1997; we added two low altitude series of passes over
the ends
of Eros this past October and January that gave us spectacular
images from
2.7 kilometers above the surface; and we achieved the first
landing of a
spacecraft on an asteroid on Feb. 12. All this at no extra cost.
When you
talk about ' faster, cheaper, better,' this is what 'better'
means."
On Feb. 12 at 3:01:52 p.m. (EST), NEAR Shoemaker made a gentle,
picture-perfect 3-point landing on the tips of two solar panels
and the
bottom edge of the spacecraft body. But the mission wasn't
finished yet.
Much to the amazement of the mission team and millions of
observers around
the world who were following the descent, the touchdown was so
elegant that
the craft was still operating and sending a signal back to Earth
even after
landing.
Jumping at the chance to get "bonus science" from the
spacecraft, which had
already collected 10 times more data than originally planned, the
mission
team asked for and got a 10-day extension and then four more days
of DSN
antenna time, enabling NEAR Shoemaker to send back data through
Feb. 28. The
extension was granted to allow the gamma-ray spectrometer to
collect data
from an ideal vantage point about four inches from the surface.
The
spectrometer team quickly redesigned software and uploaded it to
the
spacecraft so they could begin collecting elemental composition
readings.
The results were spectacular. "This is the first
gamma-ray experiment that
has ever been done on the surface of a body other than
Earth," says Dr.
Jacob Trombka, of NASA's Goddard Space Flight Center, in
Greenbelt, Md., who
heads the gamma-ray spectrometer team. "In fact, we can say
it's the first
feasibility study of how to design an instrument to be used on a
rover that
could select samples from the surface, look for the presence of
water, or
map the surface for the purpose of future mining."
The gamma-ray spectrometer team was able to retrieve data for a
period of
seven days after the spacecraft landed. "Right now we know
we have good data
with strong signatures," Trombka says. "But it will
take months to
scrutinize what we've collected. What we're looking for is
information that
will help us more precisely classify Eros and determine the
relationship
between the asteroid and meteorites that have fallen to
Earth."
NEAR Shoemaker now rests silently just to the south of the
saddle-shaped
feature Himeros as the asteroid twists more and more away from
the sun with
each rotation, moving the southern hemisphere into its winter
season and
temperatures as low as minus 238 degrees Fahrenheit (minus 150
centigrade).
Project Scientist Dr. Andrew Cheng of APL, says the glamorous
part of the
mission is over but now scientists can get down to studying the
data,
including the more than 160,000 detailed images taken by the
spacecraft. "We
solved mysteries, we unveiled more mysteries. Now we're sharing
the amazing
amount of data that we collected with scientists all over the
world, to sort
through and debate and hopefully to help us discover facts about
Eros and
our solar system that no one knows today."
For more information on the NEAR mission, including a gallery of
images,
visit Web site: http://near.jhuapl.edu.
============
(4) LOUIS FRANK CLAIMS TO HAVE FOUND NEW EVIDENCE FOR SMALL COMET
THEORY
From Andrew Yee <ayee@nova.astro.utoronto.ca>
University Relations
University News Services
University of Iowa
CONTACT:
GARY GALLUZZO
(319) 384-0009; fax (319) 384-0024
e-mail: gary-galluzzo@uiowa.edu
Release: Embargoed 1 a.m. EST, March 1, 2001
UI researcher finds new evidence for small comet theory
IOWA CITY, Iowa -- In a paper published in the March 1, 2001
issue of the
American Geophysical Union's Journal of Geophysical Research,
University of
Iowa physics professor Louis A. Frank says that he has found new
evidence to
support his theory that the water in Earth's oceans arrived by
way of small
snow comets.
Frank reports that he obtained pictures of nine small comets
among 1,500
images made between October 1998 and May 1999 using the Iowa
Robotic
Observatory (IRO) located near Sonoita, Ariz. In addition, he
says that the
possibility of the images being due to "noise," or
electronic interference,
on the telescope's video screens was eliminated by operating the
telescope
in such a manner as to ensure that real objects were recorded in
the images.
This operation of the telescope utilized two simple exposure
modes for the
acquisition of the images. One scheme used the telescope's
shutter to
provide two trails of the same small comet in a single image, and
the second
scheme used the same shutter to yield three trails in an image.
"In the two-trail mode for the telescope's camera, no events
were seen with
three trails, and for the three-trail mode, no events were seen
with two
trails," he says. "This simple shutter operation for
the telescope's camera
provides full assurance that real extraterrestrial objects are
being
detected." Frank notes these images with the IRO confirm
earlier reports of
small comet detection using the ground-based Spacewatch Telescope
during
November 1987, January 1988 and April 1988.
The small comet theory, developed in 1986 with UI research
scientist John
Sigwarth from data gathered using the Dynamics Explorer 1
satellite, holds
that about 20 snow comets weighing 20 to 40 tons each
disintegrate in the
Earth's atmosphere every minute. Over the lifetime of our planet,
the comets
would have accounted for virtually all of the Earth's water. The
small comet
theory has been controversial almost from the beginning, with
some
scientists suggesting that images identified as small snow comets
actually
result from electronic noise on satellite sensors and other
researchers
asserting that the images represent a real phenomenon. In 1997,
Frank
revealed a series of photographs taken by Visible Imaging System
(VIS)
cameras designed by Frank and Sigwarth and carried aboard NASA's
Polar
spacecraft as further proof of the existence of the small snow
comets.
Robert A. Hoffman, senior scientist at NASA's Goddard Space
Flight Center,
Greenbelt, Md. and project scientist for both the Dynamics
Explorer 1 and
the Polar spacecraft missions, says that because satellite-based
imagery
related to the small comet theory has been interpreted in
different ways,
ground-based imagery is a good alternative.
"Due to the controversy surrounding the interpretation of
the images from
space-borne detectors taken primarily in ultraviolet wavelengths,
ground-based visible observations with sufficient signal-to-noise
appear to
be the most practical approach to obtaining clear evidence
regarding the
existence of these objects. I hope more such studies will be
performed,"
Hoffman says.
Frank, a UI faculty member since 1964, has been an experimenter,
co-investigator, or principal investigator for instruments on 42
spacecraft.
His instruments include those used to observe the Earth's
auroras, as well
as those used to measure energetic charged particles and thin,
electrically
charged gases called plasmas. He is a Fellow of the American
Geophysical
Union and the American Physical Society, a member of the American
Astronomical Society, American Association for the Advancement of
Science
and the International Academy of Astronautics, and a recipient of
the
National Space Act Award.
Further information, including images of two small comet trails,
can be
found at the following web site:
http://smallcomets.physics.uiowa.edu/iro/
(Note to editors and reporters: Frank will be traveling out of
the country
from Feb. 26 through March 3 and will be unavailable for
interviews during
that time.)
==========
(5) RARE METEORITES REKINDLE CONTROVERSY OVER BIRTH OF THE SOLAR
SYSTEM
From Stanford News Service <stanford.report@forsythe.stanford.edu>
2/28/01
CONTACT: Mark Shwartz, News Service (650) 723-9296;
mshwartz@stanford.edu
COMMENT: Anders Meibom, Department of Geological and
Environmental
Sciences (650) 725-6536 or
(650) 736-0752; meibom@pangea.stanford.edu
EDITORS: Anders Meibom`s study, ``A new astrophysical setting for
chondrule
formation,`` appears in the March 2 issue of Science
magazine.
EMBARGOED until Thursday, March 1, at 2 p.m. U.S. Eastern Time
Relevant Web URLs:
http://www.psrd.hawaii.edu/Sept00/primitiveFeNi.html
http://www.cwru.edu/affil/ansmet/
http://hubble.esa.int
Rare meteorites rekindle controversy over birth of the solar
system
A new meteorite study is rekindling a scientific debate over the
creation of
our solar system.
The study, published in the March 2 issue of the journal Science,
is based
on the microscopic analysis of two rare meteorites recently
discovered in
Antarctica and Africa.
Most meteorites found on Earth are believed to be fragments of
asteroids -
ancient rocks and that formed during the creation of the solar
system about
4.56 billion years ago. Thousands of asteroids still orbit the
Sun in the
asteroid belt between Mars and Jupiter, about 140 million miles
from Earth.
"Asteroids and meteorites are solids that never got
incorporated into the
planets. These objects have survived, unchanged, for 4.56 billion
years,"
says physicist Anders Meibom, a postdoctoral fellow in the
Stanford
Department of Geological and Environmental Sciences who
co-authored the
Science study.
Chondrites and chondrules
Using electron microscopy and other laboratory techniques, Meibom
and his
colleagues conducted a detailed chemical analysis of two
chondrites -
primitive meteorites made up of thousands of tiny round particles
called
chondrules.
``Chondrules are among the oldest objects in the solar
system, dating back
to the birth of the Sun,`` says Meibom, ``so when we look at
chondrules,
we`re actually looking at the very first steps towards the
creation of our
solar system.``
Meibom points out that most chondrules are made of silicates and
metals that
can only be produced at very high temperatures. Exactly how
chondrules
formed in the early solar system is a hotly debated topic among
scientists.
``The conventional view,`` notes Meibom, ``is that chondrules
started out as
dust balls in the asteroid belt region some 4.56 billion years
ago. Today,
the asteroid belt is ultra-cold, but at that time, the
temperature was just
below 700 degrees Fahrenheit. The dust balls melted after
they were zapped
by quick bursts of lightning or shock waves, which briefly raised
temperatures to about 3000 degrees F.``
According to this theory, as the melted particles cooled, they
turned into
millimeter-size chondrules, which eventually clumped together to
form larger
chondrites.
New theory
But in 1996, astronomer Frank Shu of the University of California
proposed a
different theory based in part on dramatic images from the Hubble
Space
Telescope, which - for the first time - allowed astronomers to
witness the
actual birth of new stars elsewhere in the Milky Way.
The Hubble revealed that most young stars are created from
enormous disks of
whirling gas and dust.
As the disk contracts, it rotates faster and faster, funneling
tons of
interstellar dust toward the center, where temperatures reach
3000 degrees F
or more - hot enough to melt metal and vaporize most solids.
The rotating disk also produces enormous jets of gas capable of
launching
debris far into space at speeds of hundreds of miles per second.
Using the Hubble images as a guide, Shu proposed that chondrules
in our
solar system were created near the hot central disk of the newly
emerging
Sun - not in the relatively cool asteroid belt hundreds of
millions of miles
away.
According to Shu, dust particles were melted by the Sun, then
launched into
space by powerful jets of gas and solar wind. While in flight,
the molten
particles solidified into spherical chondrules, some of which
landed in the
asteroid belt a few days later. Others ended up as the raw
materials that
formed the Earth, Mars and the rest of the planets in our solar
system.
According to Meibom, the March 2 chondrite study in Science
magazine gives
Shu`s version of chondrule creation a tremendous boost.
``Our findings demonstrate that Frank Shu`s ideas are not
just some
fantasy,`` he notes. ``We now have actual rocks that provide hard
numbers,
which fit very nicely into the general framework of Shu`s
theory.``
Rare meteorites
Meibom and his colleagues based their study on two rare meteorite
specimens
- HH 237, a grapefruit-size chondrite recovered from the Hammadah
al Hamra
region of north Africa; and QUE 94411, a walnut-size sample
collected from
the Queen Alexander mountain range in Antarctica.
``Most chondrites are only seven to ten percent metal by volume,
but these
two specimens are about 70 percent iron and nickel,`` says
Meibom.
Microscopic analysis revealed that these iron-nickel compounds
formed by
condensation from hot gas when the temperature was around 2500
degrees F.
``Because HH 237 and QUE 94411 contain pristine samples of
condensed iron
and nickel, we were able to determine that these metal grains
formed on a
time scale of a few days. Furthermore, the newly created metal
grains must
have been transported out of their hot formation region very
quickly.
``Shu`s model provides those kind of temperatures and time
scales, and the
jets certainly provide a way to kick the grains out to much
colder regions
of the solar nebula,`` adds Meibom.
``The scenario we are suggesting is that of a big blobs of
hot gas rising
up through the disk - almost like bubbles in boiling spaghetti
sauce. As the
gas bubbles rose and cooled, silicate and metal grains began to
condense out
of the gas. When these grains got close enough to the surface of
the disk,
they became trapped in the powerful jet streams. Days later, the
particles
arrived in the asteroid belt, where the relatively cold
temperatures
preserved them from destruction.``
These chondrites allow us to look at the very frontier of the
solar system,
concludes Meibom.
``For the first time, we`re really building a bridge between what
we observe
in the meteorites and what astrophysicists like Shu are telling
us.``
Frank Shu agrees.
``In these two very special meteorites we finally have direct
evidence that
certain portions of rock had to move from some place very hot to
some place
very cold in a very short period of time,`` comments Shu. ``This
is a very
important study.``
Meibom`s other collaborators in the Science study are Alexander
N. Krot and
Klaus Keil of the University of Hawaii; Sara S. Russsell and
Timothy E.
Jeffries of the Natural History Museum in London; and Conel M.
O`D.
Alexander of the Carnegie Institution of Washington`s Department
of
Terrestrial Magnetism.
-30-
By Mark Shwartz
-------------------------------------------------------
News Service website:
http://www.stanford.edu/news/
Stanford Report (university newspaper):
http://www.stanford.edu/news/report/
Most recent news releases from Stanford:
http://www-leland.stanford.edu/dept/news/release/curindex.html
To change contact information for these news releases:
email: stanford.report@forsythe.stanford.edu
Phone: (650) 723-2558
=========
(6) NEAR: AWAKENED FROM THE DEAD?
From Space.com, 28 February 2001
http://www.space.com/missionlaunches/missions/near_awakening_010228.html
Is it possible that NEAR Shoemaker could survive its long, deep
sleep? There
is some speculation at APL that awakening the probe after its
long
hibernation might be feasible.
Given full sunlight will fall upon the spacecraft once again in
August 2002,
reactivating solar-powered NEAR Shoemaker might be worth thinking
about,
said Helen Worth, APL spokeswoman.
"As we've learned with NEAR Shoemaker, the impossible always
seems to become
possible. There are no plans at this time to do such a thing. But
it
wouldn't be unreasonable to look into the idea," Worth told
SPACE.com.
"It would give us another opportunity to learn more about
what happens to a
spacecraft. If we can't contact it later, if we tried to, we
would learn
something from that too. Whether they're going to even attempt
that...it
hasn't been decided at this point," Worth said.
In 2002, Eros is much closer to Earth. Reestablishing a radio
link with the
asteroid-sitting spacecraft might be reasonable and feasible.
"This idea has not been thoroughly examined. It's something
that needs to be
looked at to determine if it's even possible. We're not there
yet. I'm sure
there are people who are thinking about it already, but it hasn't
been
pursued at this point, or seriously proposed," Worth said.
Copyright 2001, Space.com
============================
* LETTERS TO THE MODERATOR *
============================
(7) EROS POINTS WAY TO PHOBOS AND DEIMOS
From S. Fred Singer <singer@sepp.org>
Dear Benny
Eros resembles in size and shape (and to some extent in
appearance) the
Martian moons Phobos and Deimos. But are they related? Do they
have similar
bulk density, structure and composition?
Some years ago, I believe in 1968, in the Geophys J of the Royal
Astronomical Society, I wrote a paper testing the
hypothesis that Phobos
and Deimos are captured asteroids. If one calculates their
present
near-circular orbits backward in time, using tidal perturbations,
one finds
similar (initial) parabolic orbits. This is a surprising
result; nothing
else supports capture. One can deal easily with the
time-scale problem by
assuming stronger (than today) tidal dissipation in Mars, perhaps
by
primeval oceans. But how to account for the near-zero
inclinations of the
moons? And small bodies are extremely difficult to capture
(certainly by
tidal dissipation).
There are alternatives: The moons could be the remnants of a much
larger
body (from which they were separated) that has now disappeared by
spiralling into Mars because of tidal perturbations. [See
the "push-pull"
tidal mechanism in my 1968 paper.]
Another possibility: Phobos and Deimos are planetesimals and
remnants of the
formation of Mars.
So---one of the encouraging things about NEAR is the successful
landing on
the surface. For the Martian moons, this is a much easier problem
since they
are locked in rotation facing Mars. Now the Eros gamma-ray
experiment
becomes very important; it needs to be duplicated for Phobos and
Deimos. We
don't even know if the moons have similar compositions! But how
exciting if
we can establish identical compositions for all three bodies.
Another comparative study would involve the migration of dust on
the
surfaces. Perhaps that could account for differences in
appearance. [In the
case of Phobos, the gravity field of Mars may play an important
role.]
ON TO MARS!
Fred
S. Fred Singer, President
Science & Environmental Policy Project
http://www.sepp.org
==========
(8) DUST MIGRATION ON SMALL BODIES
From Dave English <prospector@sd.znet.com>
Dear Benny:
I read with interest the report by Jeffery Bell about the lack of
small
impact craters on Eros, the apparent erosion of angular rocks to
its surface
and J. Fred Singer's well founded idea of electrostatic dust
transport, but
it may be much simpler than that.
My idea could solve the missing smaller craters, the sunken areas
and the
angular rocks that may have been eroded out of the astroid's
surface.
Moderate to large impacts could cause an asteroid to vibrate like
a tuning
fork, the loose surface dust would ride along the surface seeking
low spots
in the weak gravity like a fluid bed. Smaller impact craters
would be filled
in while larger craters, or newer smaller craters, may leave a
sunken like
look. Rocks could travel along the surface a short distance
(didn't I read
once that a rock left a short trail?) loosening more dust for the
next
impact exposing angular rock that may be former impactors or hard
accetions
within the asteroid.
If this idea has merit then the size of the last impactor should
be able to
be calculated by the appearance of the sunken areas which will
reflect the
type of motion and so the energy generated by the impact. I know
that in
panning gold many different motions and taps can cause very
different
results in the gold pan. I'm not a scientist, just an idea person
with
practical knowledge about virbration and fluid bed type motions,
which the
dust in the weak gravity should mimic after larger impacts that
would
vibrate the asteroid like a tunning fork causing the dust to seek
low spots,
exposing new angular rock, and causing further surface erosion by
scraping
and pounding by loose rock.
Dave English
Oceanside,
California
prospector@sd.znet.com
============
(9) THE "CHRISTMAS" COMET
From Mark Kidger <mrk@ll.iac.es>
Benny:
I would strongly recommend that Jonathon Shanklin checks the
source
reference about the propects of Comet C/2000 WM1 (LINEAR) at:
http://www.meteors.com/cometlinear/comet_linear_is.html
as I have already made several of these points and show the whole
range of
*possible* light curves of which a magnitude 2 object is the best
case
headline event. All the projections show that the brightest
magnitude will
be reached around closest approach to the Earth around late
November and not
at perihelion when the comet will be significantly fainter. At
this time it
will still be a northeern hemisphere, evening object although
after closest
approach it will go rapidly south.
Comet Kohoutek is possibly a bad example as it did briefly reach
negative
magnitude in late December 1973 according to groundbased
observers (and
rather brighter for the Skylab astronauts). There is no
possibility at all
that Comet LINEAR will get that bright.
I hope that this clears things up.
Mark
============
(10) IMPACT VOLCANISM CLARIFICATION
From Mark Boslough <mbboslo@sandia.gov>
A few inaccuracies crept into the March Scientific American
article.
1) Our seismic focusing calculations showed that the peak in
seismic energy
dissipation is in the asthenosphere both antipodal and directly
beneath the
point of impact. We suggested that for a sufficiently large
impact the
increased melting in the asthenosphere would be a significant
contributor to
any impact-induced volcanism, but we did not speculate about
effects on
pre-existing plumes or extinctions (although these ideas are
worth
considering). Our idea was that a narrow column of hotter mantle
could
create an instability that *looks* like a plume (as opposed to a
classic
fluid plume that pushes its way up from the CM boundary).
2) I'm not sure where the "may not have been antipodal"
phrase came from.
The impact antipode was clearly something like 30 degrees from
the Deccan
Traps at the time of the K/T boundary. If the Deccan Traps
are
impact-induced it was not the Chicxulub impact (which came too
late and in
the wrong place!) but an earlier impact either into the east
Pacific or into
India.
3) We suggested that an impact might generate the same surface
manifestations normally associated with mantle plumes (i.e. flood
basalts
and long-lived hotspots). We did not connect them to superplumes
which is
what Dallas Abbott proposed. It was Jon Hagstrum of the USGS who
suggested
the connection to sea level, weathering, ocean chemistry,
sediments, etc.
The ideas of Abbott and Hagstrum are also interesting worth
considering--but
they're not mine as the article implies.
Mark Boslough
Sandia National Laboratories
-----------------------
Scientific American, March 2001
http://www.sciam.com/2001/0301issue/0301scicit3.html
...One of those events is Chicxulub--and its relation to the
Deccan Traps.
Mark Boslough of Sandia National Laboratories modeled the
so-called seismic
focusing that would occur from an impact event on the earth's
innards.
A large energy release on one side of the earth would set off
seismic waves,
which would travel through the mantle and converge at the
opposite side, or
antipode, creating another energy peak. That energy would be
converted to
heat, raising temperatures in the mantle and increasing melting
of the rocky
material--thereby heightening the effects of any plume already
there and
further contributing to conditions that lead to extinctions.
Abbott is unsure of the exact mechanisms that would strengthen an
existing
plume, but one possibility is that increasing temperature
differentials
between the core and the mantle would cause fingerlings of hot
core rock to
enter the earth's crust. The subsequent increase in volcanism and
release of
climate-affecting gases would be more than expected for a
superplume or
impact event alone.
Thanks to plate tectonics, however, the Deccan Traps may not have
been
antipodal at the time of the Chicxulub impact. If they weren't,
Boslough
says, "you would have to propose a second impact,"
directly opposite the
Traps, "in the eastern Pacific, on seafloor that's been
subducted." Any
geological evidence would be gone.
"You have to figure out what is in the geological
record" to draw any firm
conclusions, Boslough says. From his models, an impact might
produce the
same kinds of surface manifestations attributed to superplumes:
flood
basalts, large changes in sea level, radically increased
mechanical erosion
that alters ocean water chemistry, and sediment deposits that
indicate a
global change has occurred.
But Abbott and Isley think there is hard evidence for
impact-enhanced
superplumes: certain types of rocks associated only with
superplumes, say,
or some kind of universal, physical characteristic in the earth
consistent
only with major plume events. For now, though, not enough
evidence exists to
indict superplumes as an extinction accomplice....
===========
(11) IR, PLUMES & SCIENTIFIC AMERICAN
From Hermann Burchard <burchar@mail.math.okstate.edu>
Dear Benny,
In his note posted on CCNet Feb 23, Andrew Glikson certainly shot
down my
guesswork concerning abundance of Ir in Hawaii, Sibiria, and the
P/Tr
boundary. Scientific facts are really great, thanks,
Andrew! It's an honor
of sorts to come into the crosshairs of an expert geochemist like
yourself.
Another matter are these globs of rising fluid in the mantle,
referred to in
the Scientific American quote supplied by Michael Paine. This is
based on
the idea of mantle circulation, and has never seemed plausible to
me in the
form in which it has often been stated (I hope to read a few of
the original
articles soon, now that I have references, thanks in part to some
of Andrew
Glikson's papers). Although certain steady state boundary
conditions can
lead to transient plumes this doesn't seem to fit the long-lived
mantle
plumes which we observe.
There are two kinds of locations where mantle melts and rises,
(1) spreading
zones or rifts and (2) plumes or hotspots. The basic mechanism is
the same
in both cases. See my CCNet-notes, Feb 15 and 19, where I tried
to suggest
an alternate, simpler genetic theory of origin: The
pressure is lowered due
to reduced overburden of crustal rocks. Lower pressure forces a
phase
transition leading to equilibrium at a lower Gibbs energy
(melting). The
melting is adiabatic, no extra heat is supplied.
For a plume the inititial event is excavation of crustal rocks in
the impact
explosion. Melting is the next step with mantle upwelling.
Formation of a
long-lived plume is on its way, without any voodoo cooperation of
impact and
with no "accomplice" plume. Why look for
"fingerlings" in an evenly heated
mantle with a simple phase transition theory being
available? There is no
need to have the plume hotter than surrounding mantle. The
original event
left a pore, thus retaining a lower pressure than the surrounding
mantle
rocks, which is surprisingly rigid.
In the other case, of a spreading ridge, once it is started --
e.g., by
erosive removal of overburden -- the familiar pattern evolves
where a kind
of circulation occurs at sinking geosynclines which often run
parallel to
spreading zones. To me, this seems to be due entirely to
surficial isostasy
coupled with phase transition melting at spreading rifts, which
supplies the
driving force. There is no sign that internal instabilities
lead to deep
mantle circulation. Radioactive processes heat the mantle
evenly, I am
guessing, being the ultimate source of energy which needs to be
dissipated.
The mantle is not being heated from below although heat flux is
outward
everywhere.
Naturally, if one accepts causal links between flood basalts and
transient
mantle plumes, then one may be more inclined to reject the
suggestion made
by Robert Dietz to the effect that Norilsk is an impact site like
Sudbury.
This is why I emphasized facts known about the Idaho flood
basalts and the
Yellowstone hotspot as a long-lived "walking plume",
moving about 600 km in
15 Ma from its origin in far Eastern Oregon or Western Idaho
according to
the USGS, or 40 mm/a (the Columbia river plateau further West
appears to
have a separate origin if I read the USGS correctly).
In rejecting the short-lived plume theory of basalt eruptions, I
look for
signs of a traveling plume related to known flood basalts, such
as the
Sibirian traps. Chances are good, I believe, that the latter
chain of
mountain ranges will be found to have progressively younger ages
as one
moves East from Norilsk to the Pacific coastline. Ages for
seamounts, such
as 65 Ma for the western-most mount in the Emperor chain are
doubtful,
reportedly being difficult to establish. I get an average
rate of 40 mm/a
upon taking the kinks out of the Norilsk-Hawaii path. By dead
reckoning, the bend west of Midway Island comes to about 65 Ma,
perhaps
related to the K/T impact(s).
One point to add: The basement rocks under the Northern
Yucatan just might
turn out to be a pluton datable to 65 Ma extruded from a mantle
plume caused
by (as opposed to: co-operating with) the Chicxulub impact, as
predicted by
my model. The plume failed to break through to the surface, but
mantle rock
rose in a plutonic intrusion. Conditions were not favorable for
basalt to be
brought to eruption by an impact plume, as at other places:
(1) Sudbury,
(2) in Western Idaho, where the Yellowstone hotspot started
according to
USGS,
(3) at the Shiva crater giving rise to the plume which
caused the Deccan
flood basalts,
(4) at Norilsk (apparently still controversial despite
Robert Dietz).
The Yucatan plume then migrated East at 40 mm/a (same rate a for
the Norilsk
and Yellowstone plumes), creating the Greater Antilles until
dying out or
merging with the West-Atlantic geosyncline. Here, too, I
predict the island
mountain chain as it tapers to the East will turn out to have
progressively
younger plutonic basements.
Although undoubtedly real, antipodal effects need not be
considered any
longer for the Deccan if my plume formation theory (is this not
really an
ancient theory?) should find acceptance. The Norilsk-Falklands
antipodal
effect could still be true, and I believe it is, except the
impact was in
Sibiria.
Regards,
Hermann G.W. Burchard
=============
(12) CO2 AS A DINO-KILLER AMPLIFIER?
From Jon Richfield <richfield@telkomsa.net>
I have often wondered about the KT extinction event (who
hasn't?). I suspect
that such a global disaster must have been more complex than many
of us tend
to assume when we contemplate hypotheses like asteroidal
disasters or
volcanism. Apart from the whole thing having been a far
longer process than people tend to think of when we speak of an
"event",
large events tend to entail other large events and the larger the
systems
are, the likelier it is that there will be emergent effects.
Also, we are sitting on a time bomb far more alarming to me than
say, global
warming, though the two are not independent. The event at Lake
Nyos has
shown that it is not a purely academic speculation either. In our
deep sea
we have quantities of dissolved free CO2 that boggle the
mind. Let a small seashell sink in the deeps, say a
Foraminiferan, and it
is likely to dissolve in the carbonic acid before it hits the sea
floor. Set
even a large fraction of it free and our atmosphere would become
unbreathable. This would relegate the greenhouse effect to the
status of a
minor detail.
What keeps the stuff down for the moment is the density gradient,
as
stabilised by temperature and solutes, but the situation is at
best
metastable. Once set up a convection current going, and the
evolving gas
could amplify it disastrously, gassing us all to death with a
giant soda
siphon.
Now, suppose a dino killer were to hit a large body of deep sea
containing
about as much CO2 as there is gas in the atmosphere in total.
(This is very
little actually. Remember, condensed to water density, our
atmosphere would
only be some ten metres deep. You could lose it in the
ocean!) Now, apart
from all the putative effects of a large impact, the tidal waves,
fires,
global winter and so on, we could have a soda fountain lasting
maybe days or
weeks, till that body of sea water has too little CO2 left to
drive the
flow. It might gas only say, half the planet; and perhaps
not very well at
that, but why do I get the feeling that giant animals might
suffer worse
than tiny ones?
There is every reason to believe that things were not much
different in the
sea towards the end of the Cretaceous.
I have seen speculations that a rock hitting huge carbonate
deposits might
release huge volumes of CO2 and I accept this, but I think that
the soda
siphon mechanism would more plausibly release really huge volumes
over a
longer period and potentially from a smaller impact.
Also, for all we know, dinosaurs and other large fauna of the day
may have
had a physiology more sensitive to CO2 than their contemporary
mammals did.
And what such a mechanism might have meant to the ecology, I
blanch to
think. It might not have killed all the big beasts, but it might
have killed
a lot of asteroid survivors over tens of millions of square
kilometres, that
otherwise could have re-established the status quo ante
impact.
Just wondering. Any ideas on this?
Cheers,
Jon
=============
* ABSTRACTS *
==============
(13) ABSTRACTS FROM GEOLOGICAL SOCIETY OF AMERICA 2000
From Michael Paine <mpaine@tpgi.com.au>
Dear Benny,
Franco Pirajno (Geological Survey of Western Australa) suggested
I take a
look at the abstracts of the Annual Meeting of the Geological
Society of
America on the subject of impacts and volcanic eruptions. He was
spot on! I
have quickly selected some that cover topics raised on CCnet. You
may wish to post the following as an "essay" since it
is rather large.
regards
Michael Paine
2000 GSA Annual Meeting -- Reno, Nevada
http://www.geosociety.org/cgi-bin/annual-meeting-abstracts-query.pl
Abstract 50935
HYDROCODE SIMULATIONS OF CHICXULUB CRATER COLLAPSE
Presented by Collins, Gareth S.
Authors:
Melosh, H. J.,
Morgan, J. V.,
Warner, M. R..
Key words: Chicxulub, complex, crater, collapse, hydrocode
In Session 73 T6. Impact Crater Excavation, Modification, and
Ejecta
Distribution Mechanisms (GSA Planetary Geology Division) Tuesday,
November
14, 2000 AM in Room: Ballroom D at 09:30 AM for 15 min.
Abstract: The lack of a definitive model for complex crater
collapse has
been due in no small part to the absence of large impact craters
on the
Earth, and to the near impossibility of probing the subsurface on
other
planets. This situation changed following the discovery of the
buried
Chicxulub impact structure in Yucatan, Mexico. The Chicxulub
Seismic
Experiment obtained data that clearly illustrate the third
dimension of a
complex crater and provide new insight into the kinematics of
complex crater
collapse. It is with this motivation that we have embarked upon
an
integrated multi-disciplinary study, coupling numerical hydrocode
modelling
with interpretation of the seismic data. Here we present results
from
simulations of the collapse of a Chicxulub scale impact crater
using the
SALE hydrocode. In simulating the Chicxulub impact event
numerically our
approach has been to model only the collapse stage of the
cratering process.
The collapse begins at approximately the moment of maximum
penetration, when
the transient cavity is assumed to be parabolic in cross section.
The early
stages of the impact event are approximated by the Z-model of
excavation.
The transient over-pressure due to the impact generated shock
wave is
assumed to be entirely dissipated and the target material
stationary.
Consequently, the simulation considers the competition between
the gravity
driven collapse of the unstable cavity and the inherent material
strength
properties of the post-shock target. In order to allow the
relatively low
driving forces associated with the excavated cavity to modify the
transient
craters form, a temporary material weakening mechanism is
employed: Acoustic
fluidization.
Our simulations show that, for appropriate impact parameters,
temporary
fluidization of the target allows the formation of internal peak
and ring
structures analogous to those observed in terrestrial and
extra-terrestrial
craters. Analysis of the dynamic evolution of the crater during
the
simulation suggests a model for the generation of the peak-ring
at
Chicxulub. Observations from the seismic data support this model
in addition
to other aspects of the final simulated crater structure.
Abstract 51639
IMPACT MELT EJECTA SOURCES: COMPARISONS BETWEEN SEVERAL IMPACT
STRUCTURES
AND THEIR EJECTA
Presented by Whitehead, James
Authors:
Spray, John G.,
Grieve, Richard A.F..
Key words: impact, ejecta, tektite, Popigai, provenance
In Session 73 T6. Impact Crater Excavation, Modification,
and Ejecta
Distribution Mechanisms (GSA Planetary Geology Division) Tuesday,
November
14, 2000 AM in Room: Ballroom D at 11:00 AM for 15 min .
Abstract: Ejected, impact-generated glasses have been identified
in several
regions. These include the: 1)North American tektites of the
eastern
seaboard of the U.S.A., the Caribbean Sea and the Atlantic Ocean;
2) Haitian
tektites; 3) moldavites of the Czech Republic; 4) irghizites of
Kazakhstan;
5) Ivory Coast tektites off west Africa, and; 6) the Australasian
tektites
of southeastern Asia and Australia. Although a source impact
structure has not
been identified for the 0.8Ma Australasian tektites, the other
impact ejecta
have been geochemically correlated with their sources. These
impact
structures are, respectively: 1) Chesapeake Bay, Virginia (35.5
Ma); 2)
Chicxulub, Mexico (65 Ma); 3) Ries, Germany (15 Ma); 4)
Zhamanshin,
Khazakhstan (0.9 Ma), and; 5) Bosumtwi, Ghana (1 Ma). In situ
melt rocks in
impact structures commonly have compositions distinct from those
of the
ejected melts, complicating the correlation between melt ejecta
and their
source crater. Compositional analyses of melt ejecta from impacts
into
heterogeneous targets have suggested that only near-surface rocks
are
represented in the ejecta, whereas in situ melts may be derived
from deeper
in the target. However, new isotopic data for some impact ejecta
melts
derived from the 100 km diameter Popigai impact structure,
Siberia are
similar to those of in situ Popigai melt rocks (tagamites). The
ejecta melts
appear to have an Archaean basement source similar to that of the
tagamites,
despite this source having been buried by up to 1 km of
sedimentary and
volcanic rocks. Isotopic variation of other Popigai ejecta may
result from
the melting and ejection of isotopically heterogeneous target
gneisses
and/or the mixing of basement-derived melts with various amounts
of the
fused cover sequence. We review the processes responsible for
target rock
fusion, ejection and final distribution. Taking into
consideration crater
scaling, we also discuss whether ejecta possessing a basement
signature from
Popigai are unusual when compared with ejecta from other impact
structures
which possess an exclusively surficial source.
Abstract 50470
GIANT IMPACT CRATERS LEAD TO FLOOD BASALTS: A VIABLE MODEL
Presented by Elkins Tanton, Linda T.
Authors: Hager, Bradford H.
Key words: crater, flood basalt, mantle convection
In Session 202 Planetary Geology: Impacts, Io,
Asteroids and Ishtar
(Venus) (Posters) Thursday, November 16, 2000 AM in Room: Hall C
at 08:00 AM
for .
Abstract: Previous researchers have suggested that giant impacts
might
trigger flood basalts, but no plausible mechanisms have been
presented.
Impactors striking the Earth at cosmic speeds carry
enough energy to vaporize both themselves and up to 100 times
their mass of
country rock. Though even this cannot provide enough energy to
directly
create a flood basalt province, it does significantly thin the
lithosphere
through vaporization and excavation. The crust under a large
crater will
subsequently rise through isostatic rebound, creating in about
ten thousand
years a dome-shaped elevation of the bottom of the lithosphere.
The lateral
temperature gradient resulting from this lithospheric dome could
trigger
vigorous upper-mantle convection. Mantle material in the upward
flow would
melt adiabatically in sufficient volume to produce a flood basalt
province.
Numerical experiments support this conceptual model for formation
of flood
basalts from giant impact craters. As the lithosphere at the
crater site
cools and returns to a flat thermal gradient, convective flow
would slow and
eruption cease. Any thermal perturbation would be long erased by
65 Ma, as
it has been under Chicxulub. The Deccan and Siberian flood
basalts are both
located on crust of appropriate thickness, and have brief
episodic eruptions
like that produced by our models. A possible impact site for the
Deccan has
been suggested.
Abstract 50288
LARGE OCEANIC IMPACTS AS THE CAUSE OF ANTIPODAL HOTSPOTS AND
GLOBAL MASS
EXTINCTIONS
Presented by Hagstrum, Jonathan T.
Key words: hotspots, flood basalts, impacts, extinctions
In Session 202 Planetary Geology:
Impacts, Io, Asteroids and Ishtar
(Venus) (Posters) Thursday, November 16, 2000 AM in Room: Hall C
at 08:00 AM
for .
Abstract: Hotspots occur as sites of intraplate volcanism or as
sites of
locally intense activity on mid-ocean ridges. It is widely
accepted that
hotspots result from narrow upwellings in the mantle called
'plumes', but
there are major drawbacks with this model. Oddly, hotspots tend
to occur in
near-antipodal pairs. In addition, all sites antipodal to
continental, and
likely oceanic, flood basalts for the last 250 m.y. were in the
deep ocean.
Large deep-ocean impacts differ from continental ones in several
major ways:
they generate mega-tsunamis with >=1 km run-up heights on a
hemispheric
scale, they launch immense quantities of water high into the
atmosphere, and
they likely generate much greater amounts of seismic energy due
to the
'mudcapping' effect of the deep ocean. The impact's seismic
energy is
focused by Earth in the antipodal asthenosphere, and the
resultant heating
and melting, and fracturing of the overlying lithosphere, could
lead to
flood-basalt eruptions, rifting, and hotspot volcanism. Such
bipolar crises
perhaps best explain the regression-transgression (r-t) pulses,
ocean
isotopic anomalies, and flood-basalt volcanism that are
associated with the
major Phanerozic extinctions. The great end-Cretaceous extinction
might have
been initiated by the oceanic 'Socorro' impact at 67-68 Ma, and
the on-land
Chixulub impact at 65 Ma was its coup de grāce. The greatest
end-Permian
extinction was also possibly a double impact event, with r-t
pulses, flood
basalts, and mass extinctions occurring at both the
end-Guadalupian and
end-Tatarian Stages.
Abstract 50659
DO LARGE IMPACTS STRENGTHEN MANTLE PLUMES AND PRODUCE KOMATIITES?
Presented by Abbott, Dallas H.
Key words: komatiite, impact, mantle plume, periodicity
In Session 140 T12. Superplume Events in Earth History: Causes
and Effects I
(GSA International Division) Wednesday, November 15, 2000 AM in
Room:
Ballroom B at 09:15 AM for 15 min.
Abstract: A connection between large impacts and mantle plumes is
suggested
by a spectral analysis of time series of mantle plume rocks and
impacts over
the last 256 Ma. Contrary to previous assertions, the dominant
period
derived from spectral analysis of the impact time series is not
30+/-3 Ma.
The largest spectral peak in the impact spectrum is at 64+/-10Ma,
with
a secondary peak at 30+/-3 Ma. This spectral pattern is
replicated in
spectral analyses of time series of all mantle plume rocks, and
flood
basalts+dikes+layered intrusions. The only spectrum with its
highest peak at
30+/-3Ma is the spectrum for high Mg rocks. The high Mg rocks
include
komatiites, picrites and other extrusives with maximum MgO
contents above
10%. We speculate that the similarity in the dominant spectral
peaks derived
from the impact and plume time series is due to strengthening of
existing
plumes by the seismic energy released during impacts. The exact
mechanism of
plume strengthening is not known. Perhaps the resulting seismic
waves help
to coalesce melt pockets. If impacts do strengthen existing
mantle plumes,
it could explain why komatiites are not always plume tails. It
could also
help to explain why komatiites were more abundant during the
Archean, when
impacts were larger and more frequent.
Abstract 50882
LATE HOLOCENE CLIMATE CHANGE AND ANTHROPOGENIC ENVIRONMENTAL
DESTRUCTION IN
A TROPICAL SETTING: EVIDENCE FROM CAVE CALCITES, ISLA DE MONA,
PUERTO RICO.
Presented by Lundberg, Joyce
Authors:
Brown, M.,
Ford, D. C.,
Troester, J. W..
Key words: Paleoclimate, Speleothem, Isotopes, Holocene, Tropical
In Session 100 Paleoceanography and Paleoclimatology II:
Quaternary Tuesday,
November 14, 2000 PM in Room: B5 at 03:30 PM for 15 min .
Abstract: For tropical regions high resolution paleoenvironmental
records
are rare. Speleothem often contain such information but few
tropical sites
have been studied. We investigated stable
isotopes and petrography of unaltered tropical speleothem from
Isla de Mona,
Puerto Rico. This island has largely been uninhabited, but was
extensively
mined for guano from 1880 to 1927.
A 22 cm long stalagmite was dated by C-14, studied
petrographically, and
sampled every mm for oxygen and carbon isotopes. The record
extends from AD
750 to present, a linear growth rate of 0.18 mm/year. Ice core
records from
Quelccaya Peru give tropical Late Holocene temperature and
precipitation
changes. Oygen isotopes from Mona cave calcites show cyclical
variations
that correlate with temperature, a negative relationship
suggesting that
cave temperature control is dominant. Carbon isotopes also show
cyclical
changes that anti-correlate with temperature, interpreted as an
increase in
biological activity with temperature. Petrographic changes are
not cyclical,
but show a correlation of elongate crystals with warm, wet
periods and short
crystal with drier periods. The most significant climatic change
was the
Little Ice Age, from ~1520 to 1880, marked by a dramatic shift in
ice core
temperature records, and calcite oxygen and carbon isotopes. The
severe
drought of ~1750-1820 shown in the ice core precipitation records
correlates
with a shift in the carbon isotopic values that is consistent
with a shift
to C4 vegetation. This time period is also marked by a band of
very short,
round crystals. The impact of guano mining is marked in all three
calcite
indices. The shift of oxygen and carbon isotopes in response to
higher
temperatures at the end of the Little Ice Age is abruptly
interrupted for
the period of mining. Crystal form also shows an unexpected
shortening at
this time of increasing precipitation and temperature.
Abstract 51002
EVIDENCE FOR A CRETACEOUS-TERTIARY BOUNDARY SLUMP-GENERATED
TSUNAMI ON THE
NEW JERSEY MARGIN.
Presented by Browning, James V.
Authors:
Olsson, Richard K.,
Miller, Kenneth G..
Key words: K/T, boundary, tsumani, Chicxulub
In Session 41 Paleoclimatology and
Paleoceanography (Posters) Monday,
November 13, 2000 PM in Room: Hall C at 01:30 PM for .
Abstract: A Cretaceous-Tertiary boundary (K/T) section with a
6-cm-thick
spherule layer with shocked minerals and elevated iridium values
was
recovered in November 1996 in the Bass River Borehole (New Jersey
Coastal
Plain Drilling Project, ODP Leg 174AX). Above the spherule layer
small clay
clasts, containing calcite-replaced tectites and Cretaceous
foraminifera and
dinoflagellates, occur in the lower 10 cm of the Danian. This
interval of
clay clasts is a marker for the K/T in outcrops and other
boreholes where a
spherule layer is absent. The clasts are interpreted as ripups
that were
transported by tsunami activity shoreward from a deeper part of
the
Maastrichtian sea floor. Evidence from the New Jersey shelf is
consistent
with a major tsunami ath the K/T boundary. Olsson and Wise (1987)
showed
that a long hiatus with missing Maastrichtian and upper Campanian
strata was
encountered in exploration and stratigraphic test wells in the
Baltimore
Canyon Trough beneath the New Jersey continental margin. DSDP
Site 605
located east of the Baltimore Canyon Trough at the foot of the
New Jersey
continental slope terminated in the upper Maastrichtian
(Abathomphalus
mayaroensis Zone) indicating that the hiatus is confined to the
outer
continental shelf and upper slope. The area of the hiatus
encompasses at
least 30,000 square kilometers of the Maastrichtian outer
continental shelf
and upper slope and may represent a giant slump scar. A tsunami
triggered by
seismic shaking from the Chicxulub impact at this area would have
reached
the New Jersey Coastal Plain in less than ½ hour. Surface
seismic waves
generated from the K/T impact at Chicxulub, Yucatan would have
arrived in a
little less than 10 minutes, about the time of the arrival of the
ejecta-vapor cloud. The fact that the Bass River clay clasts
contain
replaced tectites indicates that the tsunami took place after
deposition of
the tectites and that the two events closely followed one
another.
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METEOR(ITE) CRASHES INTO YORKSHIRE FIELD
From Ananova, 1 March 2001
http://www.ananova.co.uk/news/story/sm_224291.html
Police have cordoned off a field after a meteor crashed into the
ground in
North Yorkshire.
A woman walking her dog heard an explosion followed by a rush of
air as she
walked near a field at Hopgrove, near York. She saw a smoking
crater in the
ground, said a North Yorkshire Police spokeswoman.
"A curator has been down from the Yorkshire Museum and has
identified that
we do have a meteor and a suitable crater for it to sit in."
The area was cordoned off by police following the incident.
---------
DOG WALKER TELLS OF 'METEORITE' SHOCK
From Ananova, 1 March 2001
http://www.ananova.co.uk/news/story/sm_224486.html?menu=
A woman who saw what is thought to be a meteorite crashing to
earth has
spoken of her shock.
Silvia Mercer says the rock crashed into the ground near York
just yards
from where she was walking. Mrs Mercer was with dogs when the
crater
appeared on the edge of a field close to her home in Hopgrove.
"It was very frightening. It was a bit of a shock,"
said Mrs Mercer. "I
thought my last moments had come. I was very shaken. It could
have hit me.
"I heard this terrific bang and then a smaller bang and when
I looked around
there was a big cloud of smoke.
"There was a hole in the ground with smoke bellowing out of
it. I had no
idea what it was."
[a photo of the small impact crater has been provided by the
Press
Association at http://www.ananova.co.uk/news/story/sm_224486.html?menu=]
Army bomb disposal experts from Catterick are at the scene.
Police cordoned off the area and stopped traffic from entering
Hopgrove Lane
South, where the crater appeared.
PC Peter McCreedy said the hole was 10 inches in diameter and at
least a
metre deep.
He said it started making popping and cracking noises, believed
to be caused
by background radiation.
Copyright 2001, Press Association
---------
SPACE ROCK FALLS ON YORK
From BBC, 1 March 2001 (16.00 GMT)
http://news.bbc.co.uk/hi/english/sci/tech/newsid_1196000/1196688.stm
A meteoroid has landed in a field in York, UK, narrowly missing a
woman
walking her two dogs.
North Yorkshire police were called to the Hopgrove area of the
city
after Silvia Mercer heard a rush of air and a loud explosion at
0800GMT.
They found a smoking crater, about 15 centimetres (six inches)
wide and
just under a metre (three feet) deep, in a nearby field.
Officials from the Yorkshire Museum have confirmed it was made by
a rock
falling from space. It is almost 10 years since any such similar
event
has been recorded on the UK mainland.
'Last moments'
Mrs Mercer said she was frightened as the rock crashed to the
ground
just metres away from where she was walking. "It was a bit
of a shock,"
she said.
Police set up a cordon while the meteorite was investigated
"I thought my last moments had come. I was very shaken. It
could have
hit me.
"I had no idea what it was. I went to have a look but could
not see to
the bottom of the hole. It was quite deep.
"I don't know anything about meteorites but after this I
will be quite
interested to know what happens to it."
'Popping and crackling'
The area was cordoned off by police after the meteorite - the
name given
to the lump of material that survives the impact - started making
"weird" noises.
Pc Peter McCreedy said: "It started making popping and
cracking noises,
which are not usual.
"Experts from York University have been here with
radioactive detection
equipment. The noises are believed to be caused by background
radiation."
Army bomb disposal experts from Catterick were called to the
scene and
gave the all-clear for the rock to be taken away and examined by
experts.
Some doubt
The last meteorite to be picked up off the ground on the UK
mainland was
found by retired civil servant Arthur Pettifor. A 767-g (27 oz)
meteorite hit a hedge in his garden in Glatton, near
Peterborough, in
the May of 1991.
Golf-ball sized fragments of space rock were recovered after a
fall on
County Carlow in the Republic of Ireland in the November of 1999.
Meteoriticist at the Natural History Museum in London, Dr Matthew
Genge,
said he would like more information before he could be certain
the
Yorkshire rock was a meteorite.
"There are certain factors that identify a meteorite and
from what I've
heard, some things today just aren't consistent with that,"
he said.
"For example, they don't smoke when they hit the ground, but
then they
do make a noise because, as they are travelling faster than the
speed of
sound, they are often accompanied by a sonic boom."
Copyright 2001, BBC
------------
NO OBJECT FOUND ACCORDING TO MUSEUM OFFICIAL
From Kelly Beatty <kbeatty@skypub.com>
Benny...
false alarm. according to Niel (sp?) Sterio, press officer for
the York
Museum, there is no object, meteorite or otherwise. the
electrical cable
that the falling object supposedly struck on impact in fact
itself
exploded, blowing a hole in the ground from below. everyone was
apparently misled by the witness's insistence that something had
whizzed
past her though the air prior to the explosion.
Kelly