PLEASE NOTE:


*

CCNet DIGEST, 5 May 1999
------------------------

(1) LATE TRIASSIC IMPACTS, FLOOD BASALTS AND ATLANTIC RIFTING -
    POSSIBLE GENETIC CONNECTIONS?
    Andrew Glikson <andrew.glikson@anu.edu.au>

(2) NINTH IMPACT CRATER IDENTIFIED IN FINLAND: BUT WHERE HAVE ALL THE
    OTHERS GONE?
    Timo Niroma <timo.niroma@tilmari.pp.fi>

(3) CHAMPOLLION'S COST-SAVING KEEPS COMET MISSION ALIVE
    Ron Baalke <baalke@ssd.jpl.nasa.gov>

(4) METEOR MYSTERY MAY BE SOLVED
    Boston Globe, 2 May 1999

(5) METEORS DOWN UNDER
    NASA Science News <expressnews@sslab.msfc.nasa.gov>

(6) PROJECT SPACEGUARD: SAVING HUMANKIND FROM EXTINCTION

(7) LECTURE ON THE IMPACT OF COMETS AND ASTEROIDS UPON THE EARTH

==============
(1) LATE TRIASSIC IMPACTS, FLOOD BASALTS AND ATLANTIC RIFTING -
    POSSIBLE GENETIC CONNECTIONS?

From Andrew Glikson <andrew.glikson@anu.edu.au>

Dear Benny,

I was interested to read the item "Massive volcanism and the
Triassic/Jurassic mass extinction" (CCNet Digest 27.4.99), as much
for what it reports as for the neglect of the potential impact factor
in triggering rifting and volcanism along the Triassic-Jurassic,
Permian-Triassic and Cretaceous-Tertiary boundaries. The following
points need to be made:

(1)  The late Triassic is marked by an impact cluster, including
Manicouagan, Quebec (100 km diameter; U-Pb zircon age - 214+/-1 Myr),
Saint Martin, Manitoba (40 km diameter; Rb-Sr age 219+/-32 Myr),
Rochechouart, France (~25 km diameter; Ar-Ar age 214+/-8 Myr), and
the geochronologically less well defined Obolon, Ukraine (~15 km
diameter; stratigraphic age - 215+/-25 Myr), Red Wing, western US (9
km diameter; stratigraphic age - 200+/-25 Myr) [reference 1] - within
isotopic age dating error from the Triassic-Jurassic boundary defined
in Australia at 205 Myr.

(2) Potential connections between impacts and flood basalts occur (A)
at the Cretaceous-Tertiary boundary, where the ages of the Chicxulub
mega-impact (170 km diameter; 64.98+/-0.05 Myr), the Deccan Plateau
Basalts and the onset of the Emperor volcanic chain in the Pacific
(65 Myr) closely coincide; (B) at the Permian-Triassic boundary,
where occurrences of shocked quartz with PDF (planar deformation
lamella) [reference 2] and the Araguinha impact structure, Brazil (40
km diameter; 247+/-5.5 Myr) are within isotopic age dating error from
the age of the Siberian Norilsk flood basalts (Ar-Ar age -
248.3+/-0.3 Myr and Zircon age - 251.1+/-3.6 Myr)[reference 3].

(3) Potential connections between impacts, flood basalts and
extinctions were suggested, although not proven, by Rampino and
Stothers [reference 4] and Stothers [reference 5]. Some of these
events coincide with impacts within isotopic age dating errors,
including: (A) Ethiopean Plateau basalts (35+/-2 Myr, but a wider age
range reported in reference 3] and the late Eocene bombardment,
including Chesapeake Bay, Virginia (90 km diameter; 35.2+/-0.3 Myr),
Popigai, Siberia (100 km diameter; 35.7+/-0.8 Myr), several other
craters, the North American strewn tektite field, Iridium anomalies,
and nickel spinel-bearing impact spherules. Another potential
correlation exists between the Morokweng impact structure, south
Kalahari (340 km; 145+/-3 Myr) and Jurassic-Cretaceous boundary age
volcanics in the Sudan - possibly constituting precursors of the East
African rift system.

(4) Clearly there is not enough evidence to prove genetic connections
between large impacts and flood basalts, nor is there independent
evidence for the hypothetical core-mantle generated plume model
invoked by Mark Richards. It must be stressed that, due to
destruction of craters by erosion, burial and subduction - to date
only a small fraction of the impact history of the Earth has been
unraveled, including impacts along critical Phanerozoic boundaries. 
New impact craters are being found at a rate of 3-4 each year. 
Seismic modelling of the effects of very large impacts predicts deep
lithospheric faulting and crustal rifting capable of triggering
adiabatic melting in the underlying mantle [reference 6]. A
fundamental question is raised by D.L. Anderson [reference 7] -
whether mantle melting is related exclusively to deep seated
upwelling from lower mantle sources and/or can also arise by
structural disruption of the lithosphere and consequent melting in
the underlying asthenosphere? One factor for the latter may well be
provided by very large impacts, not least where they impinge on
tectonically unstable crustal regions. 

(5) Finally, a comment on the still dominant "Geocentric" philosophy
among many Earth scientists - sharing a pre-Galileo sentiment. It is
a fact of life that, despite overwhelming evidence for the
Cretaceous-Tertiary impact, many still treat the impact scenario with
suspicion. This is not surprising. Traditionally, Earth scientists
think in terms exclusively inherent to the Earth - as if this planet
is not a part of the solar system. Extraterrestrial impacts are
regarded as an irrelevant interference on the parts of astronomers
...  Many palaeontologists much prefer to see the demise of the
dinosaurs as inherent in their biological evolution, while many
volcanologists prefer to search the factors which trigger volcanic
activity along the core-mantle boundary.

"Look up to the skies" - said dinosaur A  ... "don't bother me with
irrelevant nonsense", said dinosaur B and returned to chew the green 
grass.

References

1.  Spray et al., 1998. Nature, 392:171-173.
2.  Rettalack et al., Geology, 1998.
3.  Courtillot et al., 1999. Earth Planet. Sci. Lett., 166:177-195.
4.  Rampino and Stothers, 1990. Geol. Soc. Am. Sp. paper 247:9-18.
5.  Stothers, 1993. Geophys. Res. Lett., 13:1399-1402.
6.  Boslough et al., 1995, LPI Contrib., Huston, p.16-17.
7.  Anderson, D.L., in: James Hutton Memorial Volume, 1998, The
    Geological Society of London.

Andrew Glikson
Research School of Earth Science,
Australian National University
Canberra, ACT 0200
(andrew.glikson@anu.edu.au)

====================
(2) NINTH IMPACT CRATER IDENTIFIED IN FINLAND: BUT WHERE HAVE ALL THE
    OTHERS GONE?

From Timo Niroma <timo.niroma@tilmari.pp.fi>

Dear Benny,
 
The ninth impact crater in Finland has been identified recently. It
is situated 29 degrees E and 62 degrees N. Named Paasselka
(Paasselkä). It's connected in the southern part of Orivesi
through a strait. It is the second largest of the impact craters thus
far recognized in Finland, second only to Lappajarvi (Lappajärvi).
The crater is about 10 km in diameter and fairly round. Its age has
not been determined yet but its wear out makes it look older than
Lappajarvi (77 million years).
 
Because there are 172 confirmed impact craters on Earth thus far
found, the Finnish craters are about 5% of all known craters on Earth.
Given that the area of Finland is only 0.07% of the Earth's surface,
Finland is highly overrepresented when it comes to crater counts.

In all fairness, however, one must remember that of the 172 craters
only 4 have been found in oceans. Now Finland occupies 0.2% of the
continental area, and our 5% (of impact craters) must be compared to
this figure. Thus, the frequency of the identified crater density in
Finland, i.e. one per 37,000 km2, is 27-fold of the world's continental
area.
 
If we were to make a projection, we sould expect about 4,600 impact
craters, instead of the 168 continental impact craters. Of course this
is a little bit exaggerated given that the Finnish rock is billions of
years old. Still, if we look on a world map, we can see that large
areas such as South America, Africa, East Asia (China, for example) are
still rather blank in this sense. The best represented areas for impact
craters are North America, North and East Europe and Australia.
 
To get some idea of the supposed density on Earth, take a transparent
paper, put it on a map of Moon, select one area and copy all
impact craters. Then select one part of Earth (remember the scale
should be about the same), and put the paper on that map. You'll see
what you should see, yet don't see. This is how I, as a schoolboy in
the 1960s, asked myself: where have all the craters gone? Erosion and
the Wegener movement (later named plate tectonics) had of course
damaged part of the scenery, but something should have left marks
there nevertheless. This led me to study Lappajarvi (theoretically,
not empirically) and a claim way back in 1965-66 that it was an
impact crater. Many scientists, of course, laughed at me 30 years
ago - except, perhaps, Martti Lehtinen, who later had the same idea
and who proved the theory right.
 
A systematic search for impact craters is worthwhile. Only 8 years
ago, in 1991, there was only three impact craters known in Finland:
Lappajarvi (Lappajärvi), 17 km in diameter, Saaksjarvi (Sääksjärvi)
and Soderfjarden (Söderfjärden). Now our intensive search has brought
to light 6 more craters between 1992-1999, in other words, 0.75
craters per year (and the search is going on): Naakkima (1992),
Lumparn (1994), Suvasvesi (1994), Karikkoselka (Karikkoselkä, 1995),
Saarijarvi (Saarijärvi, 1997) and now Paasselka (Paasselkä, 1999).
 
In light of these recent findings, I believe we have two big
questions to which we need answers: is the frequency of cosmic
impacts constant, is it increasing, or decreasing or oscillating? And
is there, perhaps, some periodicity in the frequency? The correlating
questions about crater sizes are of course as much interesting: are
the 'recent' impactors (meaning during the last hundred of millions
of years) of the same or of a different size than the older ones?
 
Timo Niroma
Helsinki
Finland       

====================
(3) CHAMPOLLION'S COST-SAVING KEEPS COMET MISSION ALIVE

From Ron Baalke <baalke@ssd.jpl.nasa.gov>

Fast Response Keeps Champollion On Track
By JOHN G. WATSON
JPL Universe
April 30, 1999

Engineering ingenuity and dawn-to-dusk efforts over the past few
weeks have resulted in a successful and lifesaving redesign of Space
Technology 4/Champollion, a proposed mission to land on a comet
nucleus.

The mission will feature a single spacecraft instead of a mother ship
and lander as part of newly announced, reconfigured mission
architecture. Some of JPL's most creative solutions come out of the
crucible of rigid budget and engineering constraints, and Space
Technology 4/Champollion has emerged from the fire a leaner and
meaner mission.

Changes in the mission plan will allow Space Technology 4/Champollion
to accomplish all of its technology validation and science goals
while working within budget limits of approximately $158 million,
excluding launch costs and operations.

Earlier plans had assumed that industry and/or government agencies
would partner with the project in some key areas of technology. When
such partners failed to materialize, the mission was faced with a
significant funding shortfall.

On March 19, NASA headquarters formally requested a plan on how the
ambitious comet rendezvous mission could be kept at its roughly $158
million cap.

Project Manager Brian Muirhead and his team rolled up their sleeves
and got to work. "Within one week, the team had brainstormed,
developed 18 pages of options, narrowed them down, arrived at what we
thought was the most likely option to succeed and fleshed that option
out," Muirhead said. "We then took two more weeks to detail the
concept, estimate its mass and cost it."

A successful pair of presentations to NASA's Office of Space Science
on April 8 and 14 led to reauthorization for JPL to proceed with
formulating the mission based on the concept as presented.

"The ST4/Champollion team developed a revised mission plan that was
capable of meeting the budget constraints," Muirhead said. "We went
from a two-spacecraft paradigm to a single spacecraft, which gives us
a simpler set of hardware that's easier to test on the ground. The
new design is more robust, and our chances of a successful landing
are as good or better than they were before.

"We received offers of support from all over the Lab, especially the
technical divisions," he added. "JPL is really at its best when it's
focused on supporting a project during a crisis."

The lifesaving transformation of the mission recalls similar
resurrections of past JPL missions that had been threatened with
cancellation. The Galileo mission, for example, was completely
replanned several times due to changes made in launch configurations
and upper stages, most dramatically after the Space Shuttle
Challenger accident in 1986. The Cassini mission, too, was completely
restructured in 1992 in response to a new budget squeeze and the
cancellation of its sister mission, Comet Rendezvous Asteroid Flyby.

Attempting a feat never done before, Space Technology 4/Champollion
will land on a comet's nucleus after surveying and mapping it for
several months. The key to the success of this mission is a suite of
10 technologies that must work together as a system to deliver a
payload safely to the surface of an active comet. These
technologies-including multi-engine ion propulsion (building from
Deep Space 1), a large, 10-kilowatt, high-efficiency solar array
using inflatables and precision guidance and landing using a
miniature scanning laser altimeter-have wide application to other
future space science missions.

Once on the surface, the spacecraft will take images of its
surroundings, drill for material below the surface of the nucleus and
perform scientific experiments to determine the composition of this
untouched material from the original solar nebula.

For further details about Space Technology 4/Champollion, visit

http://nmp.jpl.nasa.gov/st4

=========
(4) METEOR MYSTERY MAY BE SOLVED

From The Boston Globe, 2 May 1999
http://www.boston.com:80/dailyglobe2/122/metro/Meteor_mystery_may_be_solved+.shtml

By David L. Chandler, Globe Staff, 05/02/99

When astronomers at the Cambridge-based international clearinghouse for
astronomical observations began last November to get reports from
around the world of sightings of the annual Leonid meteor shower, it
was clear that something was off.

While the Leonids can sometimes produce a spectacular storm of shooting
stars at 33-year intervals, the storms are not reliable, and nobody was
sure if there would be one last year (or possibly this year).

It soon became clear from the sightings that the '98 display was far
short of a true meteor storm, but that there had been a totally
unexpected peak of spectacular bright meteors called fireballs - about
16 hours before the peak activity was supposed to occur.

Now, some British astronomers think they have solved the puzzle of the
ahead-of-schedule activity. Knowing that the Leonids are junk left
behind by comet Tempel-Tuttle, they carefully analyzed the comet's path
for the last several centuries to see where fragments shed in the past
would have ended up.

It turns out, they wrote this month, that the unexpected fireballs seen
last fall were composed of bits shed by the comet when it passed the
Earth way back in 1333.

The astronomers, David Asher and Mark Bailey of the Armagh Observatory
in Northern Ireland, say their work for the first time proves that
meteors are associated with complex braid-like streams of debris in a
comet's orbit, and they have been able to create computerized maps of
these braids from comet Tempel-Tuttle. This should help in forecasting
future meteor showers.

The bad news is that their mapping shows that, contrary to many
astronomers' hopes, there will be no spectacular meteor storm this
coming November, just a slightly-stronger than usual Leonid shower.

© Copyright 1999 Globe Newspaper Company.

==============
(5) METEORS DOWN UNDER

From NASA Science News <expressnews@sslab.msfc.nasa.gov>

NASA Space Science News for May 3, 1999
 
Meteors Down Under:  On May 5th, debris from Halley's comet will strike
Earth's atmosphere and put on a sky show for southern observers. The
eta Aquarid meteor display is the first of two upcoming annual showers
caused by the famous comet. FULL STORY:
 
http://science.nasa.gov/newhome/headlines/ast03may99_1.htm

=============
(6) PROJECT SPACEGUARD: SAVING HUMANKIND FROM EXTINCTION

Talk by Duncan Steel 

on Wednesday, 5 May

at Cardiff University

Law Building, Lecture Hall 2.27. at 18.00 pm (all are welcome)

PROJECT SPACEGUARD: SAVING HUMANKIND FROM EXTINCTION
 
Sixty-five million years ago the dinosaurs seem to have been wiped
out in the aftermath of an impact by a large asteroid or comet. Since
then, and earlier, other mass extinction events have occurred through
similar catastrophes. Smaller impacts by projectiles up to a mile in
diameter are capable of causing devastation on a global scale, and
occur much more frequently. A one-mile asteroid striking the Earth
would kill about half of all humankind, and it is easy to show that
your chance of dying this way is higher than that of being killed in
a jetliner crash. After the evolution of life on Earth has been
subject for 3.8 billion years to dislocations through huge impact
calamities, at last a species has evolved which has the science and
technology to intervene: homo sapiens. In this talk I will summariz
the planned Spaceguard project, aimed at searching out all
Earth-threatening asteroids and comets, and determining whether there
is one due to hit us within the next century.

=============
(7) LECTURE ON THE IMPACT OF COMETS AND ASTEROIDS UPON THE EARTH

By Donald K. Yeomans
Supervisor, Solar System Dynamics Group
Jet Propulsion Laboratory
Monday, May 17, 1999
7:30 p.m. at
GRIFFITH OBSERVATORY

Comets and asteroids have been receiving bad press of late. In two
recent movies, they have been portrayed as Earth threatening
villains. While comets and asteroids do smack into the Earth from
time to time, it is also likely that they helped deliver the water
and carbon-based molecules to the early Earth, thus providing the 
building blocks for the formation of life. Subsequent collisions may
have punctuated life's evolutionary cycles allowing only the most
adaptable species to evolve further. We mammals may owe our
preeminent position atop the Earth's food chain to a collision some
65 million years ago that wiped out most of our competition -
including the dinosaurs.

Ironically, the same comets and asteroids that can most closely
approach the Earth are also the most accessible in terms of
exploiting their vast supplies of water and metals. Comets and
asteroids could easily supply the raw materials necessary for
colonizing the inner solar system in the next century. In addition to
the utility of assessing their potential as future threats and
resources, there are compelling scientific reasons for studying these
primitive leftovers from the solar system formation process.
Knowledge of their compositions and structures will provide important
clues to the conditions and chemical mix from which the planets
formed some 4.6 billion years ago. The nature and chemical 
composition of these enigmatic objects should soon become clear as
spacecraft missions closely study a dozen comets and asteroids in the
next 13 years.

At the Jet Propulsion Laboratory, Don Yeomans is a Senior Research
Scientist and Supervisor for the Solar System Dynamics Group. Dr.
Yeomans is the Project Scientist for the MUSES-CN mission to explore
the surface of a near-Earth asteroid and Radio Science Team Chief for
the Near-Earth Asteroid Rendezvous (NEAR) mission. He is the current
Chairman for the Division of Planetary Sciences and has recently been
appointed manager of NASA's Near-Earth Object Program Office. His
research work is focused upon the physical and dynamical modeling of
comets and asteroids. He has been active in providing the observing
community and flight projects with position predictions for hundreds
of comets and asteroids including those that have been, or will be,
mission targets. In refining the motions of comets and asteroids, he
has used data types as diverse as recent radar measurements,
Hipparcos-based astrometry, and ancient Chinese observations. Don has
received 10 NASA Achievement awards including an Exceptional Service
Medal in 1986. He has published three books and over 100 technical
papers. Asteroid 2956 was renamed 2956 YEOMANS to honor his
professional achievements.

Friends Of The Observatory (FOTO) is the non-profit support group for
Griffith Observatory. Currently, one of FOTO's primary goals is to
support the renovation and expansion of the Observatory, so that it
continues to provide the nearly 2 million visitors and 50,000 school
children annually with accurate astronomical and scientific
information and programs and remains the internationally recognizable
icon of Los Angeles.

Admission: $2 for FOTO members, $5 for non-members; tickets are
available at the door. (Children under 5 are not admitted.)

Griffith Observatory                   Griffith phone: (323) 664-1181
2800 East Observatory Road               Griffith fax: (323) 663-4323
Los Angeles, California 90027 USA          http://www.GriffithObs.org
                       mailto:list@GriffithObs.org


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