PLEASE NOTE:
*
CCNet DIGEST, 11 March 1999
---------------------------
ON THIS DAY A YEAR AGO: HOW THE
1997 XF11 STORY BROKE
ONE-MILE-WIDE ASTEROID TO PASS
CLOSER THAN THE MOON IN 2028
See CCNet ARCHIVE http://abob.libs.uga.edu/bobk/ccc/cc031298.html
(1) AWESOME ASTEROIDS
Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>
(2) A ROCK IN A HARD PLACE
THE ECONOMIST, 6-12 March 1999
(3) NEW MARTIAN METEORITE FOUND
BBC News Online
(4) ANCIENT CLIMATE MAY MAP FUTURE
ABC NEWS Online
(5) HOLOCENE GLACIAL RECORD
E.M. Leonard & M.A. Reasoner, COLORADO
COLLEGE
(6) A 5000-YEAR RECORD OF CLIMATE CHANGE
U. von Rad et al., BUNDESANSTALT FUER
GEOWISSENSCHAFTEN
(7) A 28,000-YEAR MARINE RECORD OF CLIMATE CHANGE
F. Lamy et al., UNIVERSITY OF BREMEN
(8) REMINDER: AN EVENING OF EXTRATERRESTRIAL ACTIVITY
The Society of Chemical Industry <kellyq@chemind.demon.co.uk>
(9) SATURN'S MYSTERIOUS MOON TITAN
NASA Science News <expressnews@sslab.msfc.nasa.gov>
================
(1) AWESOME ASTEROIDS
From Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>
A NASA TV Simulcast: NASA...On the Cutting Edge
http://quest.arc.nasa.gov/ltc/special/small-bodies/awasteroids.html
"Awesome Asteroids"
Simulcast: March 11, 11:00 - 11:30 am Pacific (2:00 - 2:30 pm
Eastern)
Asteroids get a lot of attention. It's no wonder - small ones
continually
pelt the Earth and a large one may have caused the extinction of
the
dinosaurs. But that's just part of their story. Space missions to
orbit
and map a near-Earth asteroid for the first time will help us
discover
more about these "minor planets," and could reveal
clues about the
formation of our solar system...Get answers to your questions
about
asteroids directly from the scientists keeping tabs on them. And,
see a
sneak preview of NASA's exciting plans to put a rover on an
asteroid!
To learn more about these programs and to register, visit the
program
web site:
http://www.okstate.edu/aesp/VC.html
*Technologies Available During the Live Events:
(Caution: These links may not be active until the time of the
event.)
* RealAudio (Audio only)
* RealVideo (Audio and Video)
* Chat Room
Visit
http://quest.arc.nasa.gov/ltc/special/small-bodies/awasteroids.html
for
more details.
Program also broadcast on NASA TV: GE-2, transponder 9C, C-Band,
located at 85 degrees West longitude, frequency 3880.0 MHz,
polarization is vertical, audio is monauraul at 6.8 MHz.
It will also be broadcast on this satellite: Telstar C4,
Transponder 1,
Downlink 3720 MHz.
=================
(2) A ROCK IN A HARD PLACE
From THE ECONOMIST, 6-12 March 1999
On February 23rd an asteroid called 1999BJ8 sailed past the Earth
at a
distance of 5m kilometres (3m miles)—a pretty close shave by
astronomical standards. This is just one of several hundred
rocks,
varying in size from a few metres to a few kilometres across,
whose
orbits around the sun cross the Earth’s. A few dozen are
potentially
extremely hazardous, because they could one day do to humanity
what one
of their number did to the dinosaurs 65m years ago. So
understanding
their behaviour is important. But astronomers have been unable to
figure out how they get from the main asteroid belt between Mars
and
Jupiter to the vicinity of the Earth.
It was once thought that asteroids in the main belt occasionally
collided with one another, sending fragments into orbital
resonance
bands where they could be affected by the gravity of Jupiter or
Saturn.
After a million years or so the influence of these large planets,
it
was thought, caused the fragments to be ejected from the asteroid
belt
altogether—potentially ending up in an Earth-crossing orbit.
But
computer modelling revealed that most of the asteroids ejected by
Jupiter and Saturn quickly dive into the sun, and thus cannot
account
for the large number of known Earth-crossers.
In this week’s Science, two astronomers—Paolo Farinella
of the
University of Trieste and David Vokrouhlicky of Charles
University in
Prague—have proposed an alternative mechanism. It relies on
a subtle
phenomenon called the Yarkovsky effect (named after the Russian
engineer who discovered it a century ago). This describes how
sunlight
falling on a rotating asteroid and subsequently re-emitted as
heat can
give it an amazingly gentle push.
Depending on the direction in which the heat radiation is
emitted—something that depends on the asteroid’s
thermal properties,
its axis of rotation and its rotational speed—the asteroid
is nudged
either towards or away from the sun. The effect is, however,
extremely
subtle, and is detectable only over millions of years.
Yet it is enough, suggest the researchers, to make a difference.
New
computer models have recently shown that, as well as Jupiter and
Saturn, Mars is also capable of influencing the trajectories of
asteroids in 100 or so much weaker resonance bands in the
asteroid
belt. Combine the hitherto overlooked influence of Mars with the
Yarkovsky effect, and you have what Dr Farinella calls a “slow
track”
on which asteroids can be sent towards Earth.
All that has to happen, he says, is for the Yarkovsky effect to
nudge
an asteroid into one of the many resonance bands where Mars can
influence it. Then, over the course of tens of millions of years,
its
orbit will be modified so that it is eventually ejected from the
asteroid belt and can, at least potentially, switch into an
Earth-crossing orbit.
Computer modelling shows that although the influence of Mars is
weaker
than that of Jupiter or Saturn, the fact that there are more
orbits in
which that planet’s influence makes itself felt enables it
to eject
three or four times as many asteroids. And that, say Dr Farinella
and
Dr Vokrouhlicky, explains why there are so many potentially
lethal
asteroids floating around in Earth-crossing orbits.
Copyright 1999, The Economist Newspapers Ltd.
===================
(3) NEW MARTIAN METEORITE FOUND
From the BBC News Online
http://news.bbc.co.uk/hi/english/sci/tech/newsid_294000/294187.stm
By BBC News Online Science Editor Dr David Whitehouse
A brown stone the size of a coconut has been identified as only
the
14th known meteorite from Mars.
It was picked up in the Dar al Gani region of the Libyan Sahara
desert
last year by an anonymous meteorite hunter.
A 10-gramme section of the rock was supplied by the finder to Dr
Luigi
Folco, meteorite curator of the Museo Nazionale dell'Antartide of
the
University of Siena in Italy.
The meteorite was also investigated by Dr Ian Franchi of the UK's
Open
University, who, through an analysis of oxygen isotopes,
identified a
unique "Martian signature" in the rock.
FULL STORY at:
http://news.bbc.co.uk/hi/english/sci/tech/newsid_294000/294187.stm
Copyright 1999, BBC
===================
(4) ANCIENT CLIMATE MAY MAP FUTURE
From ABC NEWS Online
http://abcnews.go.com/sections/science/DailyNews/climate990310.html
By Joseph B. Verrengia
March 10 — Carbon dioxide levels in the atmosphere
fluctuated after the
Ice Age, helping to heat up Earth’s climate and trigger the
spread
of deserts thousands of years ago, a study suggests....
They also found that the fluctuations correlate with droughts and
the
spread of deserts in Africa and Asia during the prehistoric
period
known as Holocene...
FULL STORY at:
http://abcnews.go.com/sections/science/DailyNews/climate990310.html
Copyright 1999 The Associated Press.
==================
(5) HOLOCENE GLACIAL RECORD
E.M. Leonard*) & M.A. Reasoner: A continuous Holocene glacial
record
inferred from proglacial lake sediments in Banff National Park,
Alberta, Canada. QUATERNARY RESEARCH, 1999, Vol.51, No.1, pp.1-13
*) COLORADO COLLEGE,DEPT GEOL,COLORADO SPRINGS,CO,80903
Sediment cores from three proglacial lakes in northern Banff
National
Park, Alberta, preserve a record of Holocene glacial activity
upvalley
which is more continuous and better dated than available
surficial
records. Dating of the cores is based on tephrochronology and 16
AMS
C-14 ages of terrestrial macrofossils. All cores contain a
threefold
sequence of lacustrine sediments overlying a late Pleistocene
diamicton, Basal lacustrine sediments >10,100 C-14 Yr Old
contain
little organic matter. Sediment composition indicates a large
glacigenic contribution. A sharp increase in organic content
marks the
beginning of the Altithermal interval at all three lakes. This
transition occurred abruptly at about 10,100 C-14 yr B.P. at
Crowfoot
Lake and possibly more gradually at the other lakes. Altithermal
sediments contain relatively little glacigenic material, and
during
most of the Altithermal, glaciers may have been absent above
Crowfoot
and Bow Lakes, Glaciers draining into Hector Lake appear to have
persisted through the Altithermal. A subsequent decrease in
organic
content in each lake, reflecting increased elastic sedimentation,
marks
the end of the Altithermal and the onset of Neoglacial ice
advances.
The transition took place between about 5800 and 4000 C-14 yr
B.P, and
may be time-transgressive, beginning earlier in Hector Lake than
in
Crowfoot Lake. Changing Neoglacial elastic sedimentation rates
through
the Neoglacial interval indicate two main periods of increased
glacier
extent, between ca, 3000 and 1800 varve yr ago (ca, 2900-1900
C-14 yr
B.P.) and during the last several hundred years. During the
intervening
period glaciers were less extensive, but much more extensive than
during the recessions of the Altithermal interval, (C) 1999
University
of Washington.
====================
(6) A 5000-YEAR RECORD OF CLIMATE CHANGE
U. von Rad, M. Schaaf, K.H. Michels, H. Schulz, W.H. Berger, F.
Sirocko: A 5000-yr record of climate change in varved sediments
from
the oxygen minimum zone off Pakistan, northeastern Arabian sea.
QUATERNARY RESEARCH, 1999, Vol.51, No.1, pp.39-53
*) BUNDESANSTALT FUER GEOWISSENSCHAFTEN & ROHSTOFFE,STILLEWEG
2,D-30655
HANNOVER,GERMANY
The upper Holocene marine section from a kasten core taken from
the
oxygen minimum zone off Karachi (Pakistan) at water depth 700 m
contains continuously laminated sediments with a sedimentation
rate of
1.2 mm/yr and a unique record of monsoonal climatic variability
covering the past 5000 years. Our chronostratigraphy is based on
varve
counts verified by conventional and AMS C-14 dating. Individual
hemipelagic varve couplets are about 0.8-1.5 mm thick, with
light-colored terrigenous laminae (A) deposited mainly during the
winter monsoon alternating with dark-colored laminae (B) rich in
marine organic matter, coccoliths, and fish debris that reflect
deposition during the high-productivity season of the late
summer monsoon (August-October). Precipitation and river runoff
appear to control varve thickness and turbidite frequency. We
infer that precipitation decreased in the river watershed
(indicated by
thinning varves) after 3500-4000 yr B.P. This is about the time
of
increasing aridification in the Near East and Middle East, as
documented by decreasing Nile River runoff data and lake-level
lowstands between Turkey and northwestern India. This
precipitation
pattern continued until today with precipitation minima about
2200-1900
yr B.P., 1000 yr B.P., and in the late Middle Ages (700-400 yr
B.P.),
and precipitation maxima in the intervening periods. As
documented by
spectral analysis, the thickness of varve couplets responds to
the
average length of a 250-yr cycle, a 125-yr cycle, the Gleissberg
cycle
of solar activity (95 yr), and a 56-yr cycle of unknown origin,
Higher
frequency cycles are also present at 45, 39, 29-31, and 14 yr.
The
sedimentary gray-value also shows strong variability in the 55-yr
band
plus a 31-yr cycle. Because high-frequency cyclicity in the ENSO
band
(ca. 3.5 and 5 yr) is only weakly expressed, our data do not
support a
straightforward interaction of the Pacific ENSO with the
monsoon-driven
climate system of the Arabian Sea. (C) 1999 University of
Washington.
===============
(7) A 28,000-YEAR MARINE RECORD OF CLIMATE CHANGE
F. Lamy*), D. Hebbeln, G. Wefer: High-resolution marine record of
climatic change in mid-latitude Chile during the last 28,000
years
based on terrigenous sediment parameters. QUATERNARY RESEARCH,
1999, Vol.51, No..1, pp.83-93
() UNIVERSITY OF BREMEN,FACHBEREICH GEOWISSENSCH,POSTFACH 33 04
40,D-28334 BREMEN,GERMANY
Marine sediment cores from the continental slope off midlatitude
Chile
(33 degrees S) were studied with regard to grain-size
distributions and
clay mineral composition. The data provide a 28,000-yr C-14
accelerator
mass spectrometry-dated record of variations in the terrigenous
sediment supply reflecting modifications of weathering conditions
and
sediment source areas in the continental hinterland. These
variations
can be interpreted in terms of the paleoclimatic evolution of
mid-latitude Chile and are compared to existing terrestrial
records.
Glacial climates (28,000-18,000 cal yr B.P.) were generally
cold-humid
with a cold-semiarid interval between 26,000 and 22,000 cal yr
B.P. The
deglaciation was characterized by a trend toward more arid
conditions.
During the middle Holocene (8000-4000 cal yr B.P.), comparatively
stable climatic conditions prevailed with increased aridity in
the
Coastal Range. The late Holocene (4000-0 cal yr B.P.) was marked
by
more variable paleoclimates with generally more humid conditions.
Variations of rainfall in mid-latitude Chile are most likely
controlled
by shifts of the latitudinal position of the Southern Westerlies.
Compared to the Holocene, the southern westerly wind belt was
located
significantly farther north during the last glacial maximum. Less
important variations of the latitudinal position of the Southern
Westerlies also occurred on shorter time scales, (C) 1999
University of
Washington.
===================
(8) REMINDER: AN EVENING OF EXTRATERRESTRIAL ACTIVITY
From the Society of Chemical Industry <kellyq@chemind.demon.co.uk>
Liverpool 11 March 1999. Exactly one year after the world's press
announced that the asteroid known as 1997 XF11 might be on a
collision
course with Earth, the Liverpool Section of the Society of
Chemical
Industry (SCI) will hold an Evening of Extraterrestrial Activity
at the
Peter Jost Centre at Liverpool John Moores University.
Thursday 11 March, 7.00 pm
Peter Jost Enterprise Centre, JMU
All are welcome and there is no charge for this meeting.
Refreshments
will be available from 6.30 pm.
COMETS AND ASTEROIDS: AN ASTRONOMICAL PERSPECTIVE
Mike Bode
Astrophysics Research Institute, Liverpool John Moores University
ENVIRONMENTAL AND EVOLUTIONARY EFFECTS OF COSMIC IMPACT
CATASTROPHES
Benny J Peiser
School of Human Sciences, Liverpool John Moores University
========================
(9) SATURN'S MYSTERIOUS MOON TITAN
From NASA Science News <expressnews@sslab.msfc.nasa.gov>
NASA Space Science News for Mar. 10, 1999
Saturn's Mysterious Moon: Saturn's giant moon Titan is one of the
strangest places in the solar system. Its cloudy smog-like
atmosphere
hides a surface that may include continents the size of Australia
and
oceans of gasoline-like liquids. Amateur astronomers can see
Titan this
week through a small telescope just after sunset. FULL STORY at
http://science.nasa.gov/current/event/ast10mar99_1.htm
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