PLEASE NOTE:
*
CCNet 67/2002 - 11 June 2002
----------------------------
"Scientists have long suspected that an extraterrestrial
impact
played a major role in the mass extinction of creatures recorded
in
rocks at the end of the Cretaceous Period. They have even
identified
what they think is the 100-kilometre-wide crater left by the
space
object, at Chicxulub on the Yucatan Peninsula. But suspicions
still remain
that a vast "flood" of lava and gas in India at about
the same time may
have been the more decisive factor in "poisoning" the
planet's
biology.... Their calculations suggest the change in CO2 levels
would
have led to catastrophic global warming, making it impossible for
the
ancient reptiles and countless other lifeforms to continue."
(1) GLOBAL WARMING, NOT COSMIC WINTER, KILLED DINOSAURS,
SCIENTISTS CLAIM
BBC News Oneline, 11 June 2002
(2) DEAD CLADE WALKING: SURVIVAL DOESN'T EQUAL SUCCESS
Julie Smith <jasmith@nsf.gov>
(3) STRENGTH, TIMING, SETTING AND CUASE OF MID-PALAEOZOIC
EXTINCTIONS
Michael Paine <mpaine@tpgi.com.au>
(4) NORTH CASPIAN RING STRUCTURES POSSIBLY IMPACT CRATERS
Steve Zoraster <Szoraster@lgc.com>
(5) ASTEROID TSUNAMIS COULD BE HUGE
Discovery News, 11 June 2002
(6) BACKYARD SEARCH FOR ASTEROIDS AND EXTRASOLAR PLANETS
Sky & Telescope, 7 June 2002
(7) CZECH ASTRONOMERS DISCOVER NEW ASTEROID
Radio Praha, 10 June 2002
(8) ODIN SATELLITE DETECTS H2-180 IN COMET C/2002 C1
(IKEYA-ZHANG)
Ron Baalke <baalke@jpl.nasa.gov>
(9) ODDS OF AN IMPACT OVER A NUCLEAR NATION
Michael Paine <mpaine@tpgi.com.au>
(10) BASALTS OF THE WSB - DATES
Hermann Burchard <burchar@mail.math.okstate.edu>
==============
(1) GLOBAL WARMING, NOT COSMIC WINTER< KILLED DINOSAURS,
SCIENTISTS CLAIM
>From BBC News Oneline, 11 June 2002
http://news.bbc.co.uk/hi/english/sci/tech/newsid_2038000/2038599.stm
Dino heatwave recorded in leaves
Fresh evidence to show an impact from space lay behind the demise
of the
dinosaurs has been published by scientists.
The researchers say analysis of fossil leaves from 65 million
years ago
shows there was a sudden and dramatic rise in carbon dioxide in
the Earth's
atmosphere.
Only the impact of a large asteroid, vaporising billions of
tonnes of
limestone rocks, could have released so much gas so quickly into
the
environment, they believe.
Their calculations suggest the change in CO2 levels would have
led to
catastrophic global warming, making it impossible for the ancient
reptiles
and countless other lifeforms to continue.
Competing theories
Scientists have long suspected that an extraterrestrial impact
played a
major role in the mass extinction of creatures recorded in rocks
at the end
of the Cretaceous Period.
They have even identified what they think is the
100-kilometre-wide crater
left by the space object, at Chicxulub on the Yucatan Peninsula.
But suspicions still remain that a vast "flood" of lava
and gas in India at
about the same time may have been the more decisive factor in
"poisoning"
the planet's biology.
Now, researchers from the University of Sheffield, UK and
Southwest Texas
State University and Pennsylvania State University, US, have
estimated
atmospheric carbon dioxide levels for the period.
They studied leaf fossils of gingkoes and ferns that grew around
the time of
the dinosaurs' demise.
Shallow sea
The number of carbon dioxide-absorbing pores in the fossils
reflects the
amount of carbon dioxide in the air: the fewer the pores, the
more carbon
dioxide.
By using computer simulations and doing real experiments on
plants, the
scientists can show there was a sudden, five-fold increase in CO2
at the end
of the Cretaceous.
This can only be explained, they believe by the sudden
vaporisation of
between 6,400 and 13,000 billion tonnes of carbon - the
substantial
component of the limestone rocks that lined the shallow sea that
existed at
Chicxulub 65 million years ago.
Such an injection of CO2 into the atmosphere could have created
blistering
heatwave, raising global temperatures by as much as 7.5 Celsius.
Time dependent
"We estimate that the CO2 levels were four to five higher
for 10,000 years
after the impact," Sheffield's Professor David Beerling told
BBC News
Online.
"The trouble with the [volcanism in India] is that it is
spread over two
million years. If you release that much CO2 into the atmosphere
at that
rate, the oceans will just suck it straight back out.
"So, the only thing that can explain such a large and sudden
jump in CO2
would be this idea of a space impact."
Professor Beerling said other research teams had found evidence
of rapid
warming at the time.
"A Dutch team has shown that salt-water organisms,
dinoflagellates, migrated
at this time to polar regions; there was this rapid spreading of
warm-water
organisms to the poles, which is indicative of a biological
response to a
strong warming.
"You see it also in the isotopic records from ocean
cores."
The fossil leaf research is published in the journal Proceedings
of the
National Academy of Sciences (PNAS).
Copyright 2002, BBC
===============
(2) DEAD CLADE WALKING: SURVIVAL DOESN'T EQUAL SUCCESS
>From Julie Smith <jasmith@nsf.gov>
NSF PR 02-52
Media Contact:
Cheryl Dybas
(703) 292-8070, cdybas@nsf.gov
Program Contact:
Richard Lane
(703) 292-8551, hlane@nsf.gov
IN EVOLUTION GAME, SURVIVAL DOESN'T EQUAL SUCCESS
Finding has implications for future of biodiversity
A significant number of organisms that survived the five greatest
mass
extinctions in Earth's history subsequently failed to achieve
evolutionary
success, according to a new study funded by the National Science
Foundation
(NSF) and conducted by University of Chicago scientist David
Jablonski.
"It's clear that there is a lot of evolutionary action in
the aftermath of
mass extinctions," said Jablonski. "During the rebound
from mass
extinctions, it's not an all-or-nothing thing. The shape of the
post-extinction world comes not only from who goes extinct, but
from which
survivors are successful - or, instead, become extinct or
marginalized in
the aftermath." Jablonski lays out his evidence in the June
11 issue of the
journal, Proceedings of the National Academy of Sciences. The
research was
also supported by the Guggenheim Foundation.
"Because most extinction event survivor organisms rebound so
robustly,
paleontological studies are generally focused on these
evolutionary
winners," explains Richard Lane, director of NSF's
paleontology program. "Jablonski's research examines why
other groups of
organisms weakly struggle through these major catastrophic events
only to
meet their demise somewhat later, geologically speaking."
To test the idea that many survivors go on to lose the
evolutionary game,
Jablonski turned to the paleontological literature and to his own
work on
the aftermath of mass extinction at the end of the Mesozoic Era.
In a global
analysis of marine genera, he determined how many lineages
survived each of
the largest mass extinctions in Earth's history only to die off
within the
first five or 10 million years thereafter.
Patterns at higher levels of biological organization - for
example, orders
that include a large number of genera - often play out
differently. However,
Jablonski also found a 17 percent extinction rate for orders
following three of
the five big mass extinctions.
This result surprised Jablonski, who had assumed that survival of
a mass
extinction would be good news for most major groups. "It
wasn't good news
for everybody, even at this level," he said.
These sets of doomed survivors are the last representatives of
their clades,
a technical term for an evolutionary group of organisms that
includes an
ancestor and all of its descendants.
Jablonski creates a special category for them in his article,
calling them
"Dead Clade Walking," in homage to the 1995 film
"Dead Man Walking," about a
death-row inmate.
Paleontologists still poorly understand the process that sorts
the winners
from the losers after a major extinction, Jablonski said. His
statistical
analysis ruled out one of the most straightforward of possible
causes - that
lineages that have suffered a major blow to their numbers during
a mass
extinction might be especially extinction-prone in the aftermath
because
they contain fewer species to buffer against the hard times.
Instead,
Jablonski found that many of the biggest post-extinction winners
had passed
through a diversity bottleneck as narrow as the Dead Clade
Walking groups.
Other possible causes include environmental change and increased
competition
between species. Both issues need further study, Jablonksi said,
and there
are probably examples of each in
the fossil record.
================
(3) STRENGTH, TIMING, SETTING AND CUASE OF MID-PALAEOZOIC
EXTINCTIONS
>From Michael Paine <mpaine@tpgi.com.au>
Strength, timing, setting and cause of mid-Palaeozoic extinctions
Michael R. House
Palaeogeography, Palaeoclimatology, Palaeoecology
Volume 181, Issues 1-3, 20 June 2002, Pages 5-25
Abstract
Much has been written over the last 20 yr on the Upper Kellwasser
Event
(Frasnian/Famennian or F/F boundary) as the major extinction
event of the
Middle Palaeozoic (Devonian) and as the fifth largest extinction
event in
the Phanerozoic; this opinion was based on analysis of family
range data.
These views are misleading. A current analysis of family
extinction data,
largely based on The Fossil Record 2, but updated in some
respects,
supersedes the data base of Raup and Sepkoski (1982) and shows
that the
Famennian has the highest total family extinction of marine taxa,
with the
Givetian in second and Frasnian in third place. If these new data
are
related to current (unreliable) estimated length of stages, then
the
severest extinction rates are: first, the Givetian at 14.2 family
extinctions per Ma, secondly the Frasnian at 11.2 and thirdly the
Eifelian
at 6.8. Many short-term `events' have been named for the Devonian
based on
short-term distinctive sedimentary and/or faunal perturbations. A
review of
these shows how they are often transgression/regression couplets,
many with
an association of anoxia and poor in benthos, or spreads of
pelagic faunas,
and some are phased and complex. Evidence is presented to suggest
that the
transgressive pulses correspond to warm temperatures which are
terminated by
cooling. Possible links with orbitally forced patterns are
considered. A
common explanation seems required, not just for the Kellwasser
Event, but
for all these events. The relation of the family stage
extinctions,
especially the Kaák, Taghanic, Kellwasser and Hangenberg Events,
which are
of much more limited duration, is discussed particularly in
relation to new
and more precise data of the extinction events known within these
stages. In
the absence of detailed studies for many groups, those that have
been well
documented may serve as a temporary proxy for others. Copyright
© 2002
Elsevier Science B.V. All rights reserved.
===============
(4) NORTH CASPIAN RING STRUCTURES POSSIBLY IMPACT CRATERS
>From Steve Zoraster <Szoraster@lgc.com>
Ring Structures of North Caspian - Possible Hydrocarbon
Reservoirs
Internet Geology News Letter No. 145, April 15, 2002
Seismic surveys in the Shortanbay area in the south of the North
Caspian
depression have disclosed several ring structures, which are
interpreted as
buried craters of possible meteorite impact origin. Many oil and
gas fields
in the southeast part of Ural-Volga province are associated with
ring
systems. The South Emba ring structure with diameter of 200 km is
recognized
in the southeast of the North Caspian depression. Study of
satellite images
along with geological and geophysical data has disclosed the
gigantic Aral
ring, which has a diameter on the order of 700 km.
The ring structures of Shortanbay area show up in the pre-
Kungurian section
of the Lower Permian at depths of 4.0-4.5 km beneath reflector
P-1, the
first reflector below the Kungurian salt. One of these structures
is west of
Kotlevskiy-Severnyy salt dome and has a diameter of about 3.5 km.
Another
such structure is east of this dome; it is not as well expressed.
Then to
the west of these is yet another possible structure. The
morphology of these
structures is attributed to meteorite impact.
The structures described here are synchronous, occurring in the
Lower
Permian section. Continental conditions were maximum in tne
Permian for the
entire Paleozoic. Platforms almost everywhere became land areas.
Salt was
deposited in broad internal seas (North Germany and Poland,
Near-Urals,
North America, North Caspian). The largest catastrophic
extinction of life
was at the boundary between the Permian and Triassic about 240
million years
ago. Only at the end of the Permian did life forms develop that
extended
into the Mesozoic. The cause of this extreme situation remains
unclear.
The traces of cosmic activity on the pre-Kungurian surface
suggest that the
cause of this profound global change at the end of the Paleozoic
may have
been intense meteorite bombardment during the first half of the
Permian.
Geologic and climate changes following this bombardment led to
deposition of
thick salt beds that covered the impact structures. This created
ideal traps
for accumulation of hydrocarbons. The volume of the fracture pore
space in
only one of the structures of Shortanbay area could hold about
250 million
tons of oil or 120 billion cubic meters of gas. Similar
structures are known
in the Williston Basin, where three of the five known buried
craters yield
commercial oil. It is quite possible that the proposed impact
craters of the
south of the North Caspian depression are synchronous with those
of the
Williston Basin.
The possibility for finding zones of impact crushing with good
reservoir
properties in thde sub-salt section of the North Caspian
depression along
with a reliable salt seal offers new prospects for this region.
Taken from Zeylik and Zozulin, 1995; digested in Petroleum
Geology, vol. 31,
no. 4, 1997, two seismic sections.
Copyright 2002 James Clarke. You are encouraged to print out this
News
Letter and to forward it to others. Earlier News Letters are
available at:
http://geocities.com/internetgeology
===========
(5) ASTEROID TSUNAMIS COULD BE HUGE
>From Discovery News, 11 June 2002
http://dsc.discovery.com/news/briefs/20020603/tsunami.html
By Larry O'Hanlon, Discovery News
June 7 - Just when you thought it was safe to go in the water, a
new
supercomputer model predicts that meteors and asteroids splashing
down in
the oceans can create waves twice as big, but slower moving, than
previous
estimates.
In other words, if Earth gets walloped by a sizable chunk of
cosmic debris,
there's more time to run from the wave, but a much wider
potential
destruction zone, say researchers at Los Alamos National
Laboratory, where
the simulations were created.
The results of the study were presented June 5 at the American
Astronomical
Society meeting in Albuquerque, N.M.
"The previous models were wrong," said Jim Danneskiold,
a Los Alamos
spokesperson for the team that worked out what is, to date, the
most
meticulous look at how air, water and the asteroids themselves
behave when
they smash into the oceans at 45,0000 miles per hour.
Computer scientists Galen Gisler and Bob Weaver used Los Alamos'
Blue
Mountain supercomputer and Lawrence Livermore National
Laboratory's ASCI
White supercomputer to run the simulations.
After three weeks of computing - the equivalent of more than
million hours
of individual processor time - they were able to work out the
fine details
of ocean impacts ranging from a quarter kilometer to a full
kilometer in
diameter. Their imaginary asteroids also ranged in density from
heavy iron
to lighter-weight rocks.
"One kilometer is about the threshold for global
effects," said asteroid
researcher Daniel Durda of the Southwest Research Institute in
Boulder,
Colo.
The model showed that a one kilometer iron asteroid strikes with
the power
of 1.5 trillion tons of TNT and produces a spout of water more
than twelve
miles high, said Gisler.
The simulation also confirmed what was shown in the movie Deep
Impact: a big
asteroid can produce tsunamis large enough to inundate huge
areas. There's
even evidence in the Yucatan that the dino killer asteroid that
struck there
65 million years ago caused tsunamis that washed over large areas
of land,
Durda said.
But the real concern isn't just the big impacts, said Durda. Even
a moderate
to small chunk of rock from space could cause a lot of trouble
when it hits
the oceans, he pointed out.
For instance, on land, a relatively small, 30 to 50-meter-wide
asteroid
would create quite a crater and a blast what would cause local
damage. The
same event in the sea, however, would cause weaves that would
scour a much
larger area, Durda said.
"We know that the timescale of impacts (makes them) common
enough that it
warrants our attention," said Durda.
Copyright © 2002 Discovery Communications Inc.
=============
(6) BACKYARD SEARCH FOR ASTEROIDS AND EXTRASOLAR PLANETS
>From Sky & Telescope, 7 June 2002
http://skyandtelescope.com/news/current/article_627_1.asp
By David L. Chandler
June 7, 2002 | An ingenious arrangement of three homebuilt
14-inch
telescopes on fixed mountings is enabling Tucson-based amateur
astronomer
Roy Tucker to conduct a backyard hunt for asteroids whose quality
is on par
with the best professional searches in the world.
Tucker, an instrumentation engineer at the National Optical
Astronomy
Observatory (NOAO), completed his new telescope setup in April.
The fixed
mountings made the whole construction far less expensive than any
telescope
set up on a normal, steerable mount. Tucker's fixed telescopes,
equipped
with big CCDs, scan a strip of sky 0.8° wide as the Earth turns.
Their
images reach a limiting magnitude of 20.5 - fainter than most
professional
asteroid searches. And thanks to a cleverly designed bimetallic
(steel and
aluminum) framework that automatically compensates for
temperature changes,
the telescopes can run unattended all night with no need for
focus
adjustments.
The three telescopes take three images of the same sky area a
short time
apart. The three images can be compared to reveal any objects
that moved
between exposures. Tucker's system scans an impressive 12 square
degrees of
sky per hour and produces roughly 1 gigabyte of imagery per
night.
Since his earlier searches began in 1998 (Sky & Telescope:
March 1999, page
76), Tucker has detected 4,812 asteroids, several hundred of
which were new
discoveries. He presented his latest results in a poster at the
Albuquerque
meeting of the American Astronomical Society. Now, with the help
of a
nonprofit organization of amateur and professional astronomers
called GNAT
(Global Network of Astronomical Telescopes), he hopes to expand
the system,
which initially cost him just $12,000, into a globe-spanning
network of 48
telescopes to provide 24-hour-a-day time coverage. GNAT is
seeking
involvement by universities, small colleges, schools, and serious
amateurs.
Such a network could make it possible not only to discover many
more
asteroids, but also to do precise photometric searches for
supernovae,
variable stars, and even extrasolar planet transits, says Tucker.
Roger Culver, an astronomer at Colorado State University and one
of GNAT's
organizers, says this is "a chance to really bring small
telescopes back to
the fore and really do some interesting things."
Copyright 2002, Sky & Telescope
============
(7) CZECH ASTRONOMERS DISCOVER NEW ASTEROID
>From Radio Praha, 10 June 2002
http://www.radio.cz/en/article/28869
Czech astronomers discover new asteroid
[10-06-2002] By Pavla Horakova Listen
Czech astronomers have made a number of important discoveries
recently.
Earlier this year they discovered a Nova, which is a star
temporarily
emitting a great amount of energy and light, and solved a
question which was
puzzling astronomers around the world, that is whether one very
bright
object was or was not actually two stars. Several days ago, an
unknown
asteroid was observed from the Klet observatory in South Bohemia.
More from
Pavla Horakova.
Astronomers Milos Tichy and his wife Jana who work at the Klet
observatory
discovered an unknown asteroid moving close to the earth last
week. The
object, about 70 metres in diameter, passed our planet at a
distance of 3.5
million kilometres, which is relatively close by astronomical
standards. We
know of around 900 such objects, known as near-earth asteroids.
They present
a potential threat to the earth because they interfere with the
earth's
orbit. The one discovered last week has a similar size to the
object which
caused the Tunguz catastrophe in Siberia in 1908. Czech
observatories
participate in a joint programme of monitoring these near-earth
asteroids.
Petr Harmanec is the director of the Astronomical Institute of
Charles
University.
"This programme has immediate consequences for people. In
case there is
indeed some large asteroid which could one day fall into the
earth's
atmosphere, this would be a catastrophe of global proportions. If
this
monitoring allowed us to know the exact orbit of such a body well
in
advance, the present rocket technology would allow us probably to
do
something against it. It means to change the trajectory of such a
body when
it is still far away from the earth. You know that one satellite
was sent to
the Eros asteroid and which then became an artificial satellite
of this
asteroid, therefore the technology is indeed there."
The discovery made by the Tichys was confirmed on the same night
by
astronomers from New Zealand and Canada. The asteroid was given
the
international designation 2002 LK and is now moving safely away
from the
earth. Czech astronomers are celebrating their new success and
they hope the
new law reducing light pollution in the country will help to
improve
conditions for observing and thus enable more such discoveries.
============
(8) ODIN SATELLITE DETECTS H2-180 IN COMET C/2002 C1
(IKEYA-ZHANG)
>From Ron Baalke <baalke@jpl.nasa.gov>
Observatoire de Paris
Paris, France
6 June 2002
The Odin satellite detects H2-18O in comet C/2002 C1
(Ikeya-Zhang)
Comet C/2002 C1 (Ikeya-Zhang) displayed its beautiful coma and
tails in the
spring sky. Discovered on February 1st, 2002 by Kaoru Ikeya and
Daqing
Zhang, the comet could be seen with naked eye in March and April
2002.
Reaching its maximum brightness (visual magnitude of 3) on the
end of March,
it was the brightest comet since comet Hale-Bopp in 1997.
Ikeya-Zhang closest approach to the Sun occurred on March 19, at
a distance
of 0.507 AU (1 AU = 150 million kilometres). It came near the
Earth, on
April 29, at a distance of 0.405 AU. These close approaches, as
well as
abundant productions of dust and gas from its nucleus, were the
reasons for
its unusual brightness. With a revolution period of about 360
years, comet
Ikeya-Zhang certainly visited our environment many times. Comet
Ikeya-Zhang
is possibly the great comet that appeared in 1661 and was
observed by J. Hevelius.
Why observe water vapour in comets?
Immediately after its discovery, astronomers carried out a number
of
experiments in order to study dust and gases released by comet
Ikeya-Zhang's
nucleus. Comets indeed provide valuable information about the
origin and the
formation of the Solar System. Mainly made of water (for 80%),
cometary ices
contain various other molecules that are relics of the primitive
nebula at
the epoch of formation of planetesimals. Our present knowledge of
comets
suggests that many of these molecules were produced in the
primordial interstellar cloud,
before its collapse gave birth to the Solar System.
Since comets are variable objects, measurements of the chemical
composition,
based on observation of species in the comet atmosphere, must be
referred to
the water production rate from the nucleus. Water in the Universe
cannot be
easily observed from the ground, because of the water in the
terrestrial
atmosphere, which absorbs radiation from space. Most often, the
water
production rate in comets is deduced from observation of the OH
radical. The
OH radical is produced by the dissociation of the water molecule
by solar UV
radiation. The observation of OH lines at 18 cm in comets is one
of the key
programmes of the Nançay radio telescope.
Observations by the Odin spacecraft
The Odin satellite is a small spacecraft, orbiting the Earth,
designed and
built by Sweden, in collaboration with Canada, Finland and
France. It was
launched in February 2002. Aimed for studying both the Universe
(astronomy)
and the terrestrial atmosphere (aeronomy), it allows for the
observation of
a number of molecular lines, at radio (submillimetre range)
wavelengths,
otherwise not accessible from the ground: in particular the
fundamental
water line at 556.9 GHz. The Odin radiometer includes a 1.1m
diameter
antenna, several receivers covering the 480-580 GHz frequency
rangeand
corresponding spectrometers (one acousto-optical and two
auto-correlation
spectrometers). The acousto-optical spectrometer was developed
under the
CNES responsibility by three CNRS laboratories: the LAS in
Marseille, the
CESR in Toulouse and the radio astronomy department (ARPEGES) of
the Paris
Observatory.
The study of water vapour in comets is one of the main topics of
the Odin
observing programme. The sensitivity of the ODIN radiometer
allows us to
detect water in weakly active comets, and its high spectral
resolution
capability (80 m/s by using the auto-correlators) provides
accurate
measurement of line profiles. The first comet detected by Odin
was C/2001 A2
(LINEAR), observed from end of April until July 2001.
Comet Ikeya-Zhang was observed from April 21 to 29, 2002. First,
a detailed
mapping of the water vapour brightness distribution in the sky
was done at
557 GHz. The line intensity at the centre of the map reached 27 K
km/s on
April 21 (integrated signal over the line profile), then
decreased slowly as
the comet moved further away from the Sun. The observations
provide a first
estimate of the water production rate at about 2 x 10**29
molecules/s (i.e.
about six tons per second). The line profile, very accurately
measured,
gives information on the velocity of the water molecules and on
their
radiation mechanism. For example, one could observe
that the line is shifted towards positive speed, due to
self-absorption
effects in the cometary atmosphere.
The H218O detection
The strong activity of comet Ikeya Zhang and its close approach
to Earth,
allowed to carry out more challenging observations. Thus, the
isotopic
variety H2-18O [H(subscript)2 (superscript)18 O] was searched for
and
finally successfully detected.
Oxygen exists under three isotopic, stable varieties: 16O, the
most abundant
isotope, 17O and 18O. In terrestrial water (oceans), the ratios
H216O/H218O
and H216O/H217O are 499 and 2681, respectively. The H216O/H218O
ratio could
only be measured by the ESA Giotto spacecraft in comet Halley
using mass
spectrometers. For the first time, with Odin, was obtained a
spectroscopic
measurement of this ratio.
The H218O line spectrum, at 547.7 GHz, was detected in comet
Ikeya-Zhang
after 45 hours of Odin observations and an effective integration
time, on
the comet, of 28 hours. The line was observed
in parallel by using two of the four sub-millimetre receivers,
centred at
549 and 555 GHz and tuned at the line frequency. The receiver
outputs were
connected to the high resolution spectrometers and to the
acousto-optical
spectrometer. The integrated signal was, as expected, very weak
(0.24 K
km/s). The successful detection demonstrates the excellent
capability of the
Odin instrumentation, regarding the receiver sensitivity and
stability, as
well as the spacecraft pointing accuracy.
The preliminary measurement of the H216O/H218O ratio in comet
Ikeya-Zhang is
in agreement with that measured in terrestrial oceans (500), and
confirms
measurements done in comet Halley. This result is not surprising.
With only
a very few exceptions, all bodies in the Solar System show a
H216O/H218O
ratio similar to the terrestrial one. Differences by an amount of
5% at
maximum can be observed in some meteorites. Such variations can
be explained
by slight differences in nucleo-synthesis sources producing 16O
(mainly
supernovae), nearby the Solar System formation region.
Involved French scientists
Alain Lecacheux, LESIA, Observatoire de Paris
alain.lecacheux@obspm.fr
Nicolas Biver, ESA ESTEC
nicolas.biver@obspm.fr
Jacques Crovisier, LESIA, Observatoire de Paris
Dominique Bockelée-Morvan, LESIA, Observatoire de Paris
References:
A. Lecacheux, "Comet C/2001 A2 (LINEAR)" IAU Circ 7706,
2001
A. Lecacheux, N. Biver, "Comet C/2002 C1 (Ikeya-Zhang)"
IAU Circ 7910, 2002
[NOTE: Images supporting this release are available at
http://www.obspm.fr/actual/nouvelle/jun02/comete-odin.en.shtml
]
============================
* LETTERS TO THE MODERATOR *
============================
(9) ODDS OF AN IMPACT OVER A NUCLEAR NATION
>From Michael Paine <mpaine@tpgi.com.au>
Dear Benny
Inspired by Leonard David's item (CCNet 7 Jun 02) I have done a
rough
calculation of the odds of a Tunguska-size airburst occuring over
a
"sensitive" region of the Earth. Assuming annual
probability of this type of
event somewhere over the globe of 1 in 100 (p=0.01) , then the
probability
of it happening over a given area of land is simply 0.01 x area
of interest
/ surface area of Earth I used this simplified technique for my
estimates of
tsunami risk at
http://www4.tpg.com.au/users/tps-seti/spacegd7.html
This assumes the area of devastation is small compared with the
size of the
area of interest. The results are set out below. There is about a
1 in 1200
chance of an asteroid airburst over a nuclear nation. I hope that
all the
generals are aware of this possibility!
regards
Michael Paine
Surface area of Earth 510,000 Kkm (1000s of square kilometres)
Nuclear Countries Area Kkm
USA 9500
Russia 17000
France 547
UK 240
Ukraine 603
China 9600
India 3200
Pakistan 880
TOTAL 41570 = 8.2% of Earth gives P(annual) = 1 in 1227
India 3200
Pakistan 880
4080 0.8% P(annual)= 1 in 12500
Mid-East
Israel 21
Egypt 1000
Gaza/West Bank 10
Jordan 91
Syria 185
Lebanon 10
Saudi Arabia 2240
Iraq 440
Iran 1600
Afganistan 650
TOTAL 6247 1.2% P(annual) = 1 in 8164
===========
(10) BASALTS OF THE WSB - DATES
>From Hermann Burchard <burchar@mail.math.okstate.edu>
Dear Benny,
the new dates for the basalts underlying the West Sibirian Basin
(WSB)
published Fri, 2002/6/7, in Science Magazine by Marc Reichow,
Andrew
Saunders, Rosalind White, Malcolm Pringle, Alexander
Al'Mukhamedov,
Alexander I. Medvedev, Nikolay Kirda [Science 296, 1846 (2002)],
are most
welcome as they confirm deposition was simultaneous with the
eruption of the
Sibirian traps East of Noril'sk, principally the Putorana
Mountains.
Contrary to some of the headlines, impact causation is left open
as a
possibility, and not at all excluded both in the article by
Reichow,
Saunders et. al., as well as in Renne's analysis [Paul R. Renne
Science 2002
296: 1812-1813, (in Perspectives), posted on CCNet]. If the
original theory
of mantle plumes still has much support, it seems to be fighting
a
rear-guard battle. See Renne's article, where he cites the
original paper by
W. J. Morgan, Princeton University, Hotspot tracks and the
opening of the
Atlantic and Indian Oceans, 1981. Louis and Walter Alvarez had
just proposed
the asteroid impact theory, 1980, for the Cretaceous/ Tertiary
event.
The paper by Reichow, Saunders, et al. has several observations
of great
interest to round out the picture of a hot spot-track coming into
existence.
As expected, rifting of the Asian continent was widespread.
Similar rifting
occured in the NW United States in five States along the Snake
River
hot-spot track in Idaho. This is readily apparent on topographic
maps
especially in Nevada from numerous N-S trending basin-and-
ranges. In Asia,
too, the rifts appear to be N-S trending, orthogonal to an
overall E-W track
direction. Explosive eruptions are conjectured, as are known from
the Snake
River track (period ~600-800 Ka). This would be in line with
Steve Sparks'
frothing magma model which seems to be applicable whenever a
significant
mantle involvement has occurred, as it does in major cosmogenic
impacts.
Chicxulub would have been small compared with the Sibirian
end-Permian
impacts. There, the mantle rose by about 20 miles, about a tenth
of the
crater diameter. According to Jay Melosh {recent abstract posted
on CCNet),
about 1/10 of crater diameter is typical. Hence for the 2,000 km
WSB crater,
the mantle would have risen by 200 km. That's a whole lot of hot
magma!
Inspite of the great progress achieved by Reichow, Saunders, et
al., several
other, closely related questions were not considered by them:
1. How did the events (whatever their cause) lead to the
exhumation of the
Urals? These had become peneplained already by Permian Times, see
papers by
Mary Leech, Stanford University. Evidence for exhumation is from
her
detailed analysis of reheating and from the eclogite band running
for 2,000
km along the entire mountain belt and formed under ultra-high
pressure at
depths>10 km.
2. The Sibirian traps, the way I have understood this formation,
is a
continuing hot-spot track running from the Putorana to the Far
East all the
way to Magadan toward, and probably under, the Sea of Okhotsk. If
drill
cores are available, detailed timing probably could be obtained
quickly
through methods similar to those used in the new paper by
Reichow, Saunders,
et al. based on AR40/AR39 radioactive decay.
3. The Sibirian platform is quoted [in the full paper] as stable.
However,
it appears that during the Permian there was only ocean here,
with
micro-continents [Mary Leech, loc. cit.]. In fact it seems plain
that the
Sibirian continent came into existence from the massive
outpouring of magma
in the WSB and and the Putorana, and further East. Only in the
Jurassic was
it sutured to the main Asian continent, as shown by recent work.
4. The odd E-W cross-section of the Urals suggests a crater wall.
The major
bend of the mountain chain runs around the Western edge of the
WSB. On the
W-flank of the mountains the city of Perm sits on Permian
sedimentary rocks,
hence the name. The volcanic E-slope drops abruptly to
the featureless terrestrial mare of the WSB, as expected for a
crater wall.
5. A secondary crater seems to be located in the S Kara Sea,
adjacent to the
WSB. It is surrounded on the W by the second bend in the Urals,
here the
islands of Novaya Semel'ya.
None of these questions are considered in the new work, neither
is a third
(likely) impact area, the Meishan in China, where evidence for
impact
causation has been found recently by Luann Becker [posted on
CCNet].
Regards,
Hermann
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