PLEASE NOTE:


*

CCNet DIGEST, 27 April 1999
---------------------------

(1) ARE ARGENTINE IMPACT CRATERS RUSSIAN SATELLITE SCARS?
    CNN Interactive

(2) CLIMATE CHANGE AND MASS MIGRATION
    Michelle Edwards <medwards@nsf.gov>

(3) MASSIVE VOLCANISM AND THE TRIASSIC/JURASSIC MASS EXTINCTION
    Andrew Yee <ayee@nova.astro.utoronto.ca> wrote:

(4) TUNING IN TO APRIL METEOR SHOWERS
    NASA Science News <expressnews@sslab.msfc.nasa.gov>

(5) THE RATE OF NAKED-EYE COMETS FROM 101 BC TO 1970 AD
    A.L. Licht, UNIVERSITY OF ILLINOIS

(6) COMET HYAKUTAKE: DYNAMICS OF FRAGMENTS OF ITS COMETARY NUCLEI
    E. Desvoivres et al., UNIVERSITY OF GRENOBLE

(7) POLARIMETRIC OBSERVATIONS OF COMET HALE-BOPP
    Y.N. Gnedin et al., RUSSIAN ACADEMY OF SCIENCE

(8) DUST FLOW IN A POROUS COMET NUCLEUS
    Y. Shoshany et al., TEL AVIV UNIVERSITY

(9) RADAR OBSERVATIONS OF THE GIACOBINID METEOR STREAM
    M. Simek et al., ACADEMY OF SCIENCE OF THE CZECH REPUBLIC


==================
(1) ARE ARGENTINE IMPACT CRATERS RUSSIAN SATELLITE SCARS?

From CNN Interactive
http://www.cnn.com/TECH/space/9904/22/argentina.spaceprobe.reut/index.html

Argentine craters could be Russian satellite scars

April 22, 1999

BUENOS AIRES (Reuters) -- Argentine border guards have found craters
they believe were punched into a remote Andean plateau by a
plutonium-powered Russian space probe, officials said on Wednesday.

The guards dispatched a team to the northwestern province of Jujuy near
the Bolivian border following reports from locals that a ball of fire
had fallen to Earth in November 1996, one officer told Reuters.

At that time, a Russian space probe bound for Mars had crashed in South
America after lifting off from Central Asia. Carrying six ounces (200
grams) of highly radioactive plutonium as fuel, it was thought to have
hit Bolivia.

Guards failed to spot remains of the satellite in the three large
craters measuring up to 13 feet (four meters) wide by five feet (1.5
meters) on the Andean plateau 13,000 feet (4,000 meters) above sea
level.

Wary of the possible presence of plutonium, they called for help from
the Argentine government's Nuclear Regulatory Authority.

But a team sent from the capital Buenos Aires did not detect unusual
radioactivity at the site.

The plutonium fuel canisters could have become separated and would not
necessarily have fallen in the same place as the rest of the probe,
scientists involved in the project have said.

The Nuclear Regulatory Authority said it wants to return to the site
with digging tools to look for remains of the satellite.

A Russian embassy spokesman said he had no information on the discovery
of the craters.

Copyright 1999 Reuters.

============
(2) CLIMATE CHANGE AND MASS MIGRATION

From Michelle Edwards <medwards@nsf.gov>

Media contact:
April 26, 1999
Peter West
NSF PR 99-30
(703) 306-1070/pwest@nsf.gov

Program contact:
Fae Korsmo
(703) 306-1029/fkorsmo@nsf.gov

ARCHEOLOGISTS FIND MILDER ARCTIC CLIMATE MAY HAVE AIDED ALEUTIAN
SETTLEMENT

A milder Arctic climate more than 3,000 years ago may have aided humans
to cross the Bering Sea from Alaska and migrate into the remote
Aleutian Island chain, according to preliminary findings by a
three-woman research team funded by the National Science Foundation.

Dixie L. West, a professor of anthropology at the University of Kansas,
said radiocarbon dating of bones found in an ancient midden, or refuse
pit, on Shemya Island indicates that the westernmost Aleutians were
settled roughly 3,500 years ago, or 1,000 years earlier than previously
thought.  Island soil and plant matter dated by Russian scientists
indicates that the prevailing climate may have calmed the usually
turbulent Bering Sea during that period, she added.

"This new environmental evidence indicates that the Northwest Pacific
was becoming warmer and drier at that time.  That may have allowed the
Aleuts to take those first long, dangerous sea voyages," she said.

The team will return to the Aleutians in late May to further
investigate evidence uncovered during the past three years that may
help science to better undertand how and when the most remote and
isolated areas of North America were colonized.

"West and her team have uncovered many 'firsts' that will become vital
pieces in the history and pre-history of the western Aleutian Islands,"
said Fae Korsmo, who oversees Arctic social science research in NSF's
Office of Polar Programs.

The team was the first to identify a bone from a Stellar's sea cow, a
large walrus-like animal, ever be found in the Aleutians east of the
Commander Islands, adjacent to the Russian coast.  The presence of the
bone on Buldir Island may indicate that the animals lived in the
Aleutians as well as the Commanders, and that humans moving westward
from Alaska may have exterminated them from the eastern islands.

Buldir also is the site of the only whalebone house ever scientifically
excavated in the Aleutians.  Christine LeFevre, a team member with
French Museum of Natural History, made the find while excavating a pit
near the beach.  Because of the position of the bones, "we could tell
immediately that this wasn't a whale that had stranded on the beach and
died there," West said.  "In one side of the house, someone had
excavated a pit and lined it with the shoulderblades of sea lions and
they had placed a whale skull nose-down in the pit."

The whalebone house dates from the 15th century and it is almost
certain that the island was occupied much earlier than that, though
evidence of that occupation has yet to be found.  But West noted that
Buldir is difficult to land on even today and that perhaps Aleuts
temporarily by-passed it and then returned later.

West also has obtained permission from the Aleut Corporation to remove
bones that may be the remains of ancient Aleuts from a cave on Attu
island.  If the remains prove to be the bones of Aleuts, DNA sampling
will allow for comparison with contemporary Aleuts and perhaps shed
light on changes in nutrition and health as well as additional clues to
the puzzle of migration patterns.

The team also will take a first look this field season at what it
believes are the first petroglyphs -- or stone carvings - discovered in
the Aleutians.  Debra Corbett, an archeologist with the U.S. Fish &
Wildlife Service and a member of the NSF-funded team, said the carvings,
which were found on automobile-sized rocks on a beach on Agattu Island,
are the first evidence of such artwork on the Aleutian chain.  Although
some evidence of cave painting has been documented in the Aleutians, she
said, "petroglyphs are pretty rare generally in Alaska, and there have
never been any reported in the Aleutians.  It's a major puzzle."

=======
(3) MASSIVE VOLCANISM AND THE TRIASSIC/JURASSIC MASS EXTINCTION

From Andrew Yee <ayee@nova.astro.utoronto.ca> wrote:

Public Information Office
University of California-Berkeley

Contact:
Robert Sanders, Public Affairs
(510) 643-6998, rls@pa.urel.berkeley.edu

NEWS RELEASE: 4/22/99

New evidence links mass extinction with massive eruptions that split
Pangea supercontinent and created the Atlantic 200 million years ago

BERKELEY -- Hundreds of basalt outcroppings rimming the Atlantic Ocean
are actually the remnants of a single huge volcanic eruption some 200
million years ago that may have triggered a large extinction of life at
the end of the Triassic period, according to a report in this week's
issue of Science.

A team of researchers led by Paul R. Renne, director of the Berkeley
Geochronology Center and an adjunct associate professor of geology and
geophysics at the University of California, Berkeley, concluded that
these basalt dikes, sills and lavas, dispersed from the New Jersey
Palisades and the Brazilian Amazon to Spain and West Africa, resulted
from the most extensive pulse of magma eruptions known to date.

At the time these areas were near one another in the center of a
supercontinent known as Pangea. The eruptions began a process that
drove the land mass apart to create the Atlantic Ocean, at the same
time dispersing evidence of the eruption widely on the margins of four
continents.

The large flows of magma, which the researchers dubbed the Central
Atlantic Magmatic Province (CAMP), came from the Earth's upper mantle
and covered about seven million square kilometers over a geologically
short period of a few million years.

The beginning of the event matches within 20,000 years a global
extinction at the end of the Triassic period and the beginning of the
Jurassic. During this mass extinction, about half of all marine
species, mostly the ammonoid and bivalve mollusks, died out, while on
land several families of reptiles disappeared. Paleontologists regard
the extinction as one of the most deadly in the 600-million-year
history of multi-celled life. Many believe these changes set the stage
for the rise of dinosaurs in the Jurassic.

The close correspondence between the beginning of the CAMP eruptions
and the mass extinction suggests that the global disruption caused by a
long series of volcanic eruptions could have set off or at least
exacerbated the die-off.

"This is the best example of flood basalts associated with an
extinction," Renne said. "Some of the best stratigraphic evidence of
the mass extinction occurs in exactly the same site in which you find
the flood basalts -- they sit right smack on top of one another."

The likely scenario is that, as the magma surfaced in the form of
volcanoes over a large area of Pangea, noxious aerosols and greenhouse
gases disrupted the global climate and caused the extinction of a large
number of species. The basalts would have taken more than a million
years to cover the area and, thus, would overlay sedimentary evidence
of the extinction.

In 1995, a group led by Renne attributed another mass extinction, the
one that occurred at the end of the Permian and beginning of the
Triassic, to a similar magma flood in Siberia 250 million years ago. A
third mass extinction, the well-known event associated with the demise
of the dinosaurs at the boundary between the Cretaceous and Tertiary
periods, has been linked to a large volcanic flood that produced the
Deccan Traps in India.

"This is still one of the most intriguing issues in geology, the
relationship between extinctions and cataclysms such as magma floods or
asteroid impacts," he said. "What we now have is another piece of
evidence that shows there was a relationship between flood basalts and
biologic crises."

The article detailing the extent of the CAMP basalts appears in the
April 23 issue of Science. Renne's coauthors include postdoctoral
fellow Andrea Marzoli, formerly of the Berkeley Geochronology Center
and now a research scientist at the University of Geneva, Switzerland;
Marcia Ernesto, a paleomagnetist at the University of São Paulo; and
geochemist Enzo M. Piccirillo of the University of Trieste, Italy.

Though many of these basalt outcrops, such as the well-studied
Palisades sill, had been dated to this general time period, until now
no one had realized the extent of the eruptions.

One reason the extent of the magma flow had not been recognized before
is that much of the evidence for the event is in temperate or tropical
forests, where outcroppings are obscured by vegetation and are heavily
eroded. However, recent field studies by French geologists in West
Africa and American geologists in the southeastern U.S. have provided
new information on the extent of basalt dikes and sills around the
Atlantic margins.

Sills are what remain after magma intrudes into horizontal underground
fissures, then cools and is subsequently exposed. Dikes are the
remnants of magma that flowed into vertical fractures. Lava is magma
that broke through the Earth's crust and flowed on the surface before
cooling.

The researchers in this study used the argon-argon (40Ar/39Ar) method
to date basalt lava flows, dikes and sills in Brazil, many of them
2,000 kilometers (1,300 miles) inland from the coast, and correlated
them with the ages of known formations up and down the East Coast of
the United States, in southwestern Spain, throughout West Africa, and
on the northern coast of South America. All proved to be from the same
era 200 million years ago, suggesting they have a common origin.
Paleomagnetic data from the Brazilian rocks confirmed the date.

While other episodes of flood basalts that have been correlated with
mass extinctions -- the Siberian Traps and the Deccan Traps, for
example -- are often several thousand feet thick, the preserved CAMP
lava flow piles are only about 1,000 feet thick. The researchers
estimate that in all the CAMP magmatism extended over 7 million square
kilometers in a period of a few million years, peaking about 200
million years ago. The total volume of magma is estimated at 2 million
cubic kilometers (500,000 cubic miles).

"While the volume is comparable to other flood basalt events, this one
spread over an area far larger than the others," Renne said. "This
system could have had many more volcanoes than the others."

As for the cause, Renne favors a theory put forward 10 years ago by UC
Berkeley geophysics professor and chair Mark Richards. Richards
ascribes flood basalts to a buoyant magma plume rising through the
viscous mantle from a spot near the boundary between the mantle and the
molten iron core, eventually cracking the surface in the middle of the
continent. The resultant rift zone pushes the land masses apart to
create an ocean, with an island chain forming over the hot spot and
recording the continual movement of the sea floor away from the rift
zone.

Though numerous hot spot island chains have been identified -- the
Hawaiian Islands in the Pacific, Iceland in the north Atlantic -- no
such chain has been associated with the break up of Pangea 200 million
years ago, Renne noted.

Two other coauthors of the paper are geochemist Giuliano Bellieni of
the University of Padova, Italy, and geochemical technician Angelo De
Min of the University of Trieste.

The research is supported by the National Science Foundation, several
Brazilian and Italian funding agencies and the Ann and Gordon Getty
Foundation.

Paul Renne can be reached at (510) 644-9200 or (510) 644-1350, or via
email at prenne@bgc.org.

==============
(4) TUNING IN TO APRIL METEOR SHOWERS

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

NASA Space Science News for April 27, 1999

Tuning in to April meteor showers:  Last week's Lyrid meteor shower was
a bit of a disappointment visually, but it put on quite a show for
radio observers. In this story you can learn about the basics of radio
meteors and listen to radar echoes from a bright shooting star.
FULL STORY at http://science.nasa.gov/newhome/headlines/ast27apr99_1.htm

=============
(5) THE RATE OF NAKED-EYE COMETS FROM 101 BC TO 1970 AD

A.L. Licht: The rate of naked-eye comets from 101 BC to 1970 AD.
ICARUS, 1999, Vol.137, No.2, pp.355-356

UNIVERSITY OF ILLINOIS,DEPT PHYS MC 273,845 W TAYLOR ST,
ROOM 2236,CHICAGO,IL,60607

The number of comets that are bright enough and that come close enough
to Earth to be seen with the unaided eye fluctuates randomly from
century to century. The mean number seen per century, R, is a parameter
determined by the distribution of short-period comets and by the escape
of new, near parabolic comets into the inner Solar System from the Oort
Cloud (J. H. Oort, 1963, The Solar System, Univ, of Chicago Press,
Chicago, London) and the Kuiper Belt (H. F. Levison and M. J. Duncan,
1997, Icarus 127, 13-32). A measurement of R provides a constraint on
possible escape mechanisms. In the following it is shown that R can be
determined by a comparison of the number of comets reported from the
east and west with those reported from both regions, An analysis of the
reports compiled by I. Hasegawa (1980, Vistas in Astronomy, Pergamon,
Great Britain) shows that R = 86.0 +/- 6.7 comets/century and moreover
R has been remarkably constant over the past two millennia. One could
conclude from this that the mean rate at which all comets, visible and
invisible, enter the inner Solar System has also been constant over
this period. (C) 1999 Academic Press.

==============
(6) COMET HYAKUTAKE: DYNAMICS OF FRAGMENTS OF ITS COMETARY NUCLEI

E. Desvoivres*), J. Klinger, A.C. LevasseurRegourd, J. Lecacheux, L.
Jorda, A. Enzian, F. Colas, E. Frappa, P. Laques: Comet C/1996 B2
Hyakutake: observations, interpretation and modelling of the dynamics
of fragments of cometary nuclei. MONTHLY NOTICES OF THE ROYAL
ASTRONOMICAL SOCIETY, 1999, Vol.303, No.4, pp.826-834

*) UNIVERSITY OF GRENOBLE 1,CNRS,LGGE,54 RUE MOLIERE,BP 96,F-38402 ST
   MARTIN DHER,FRANCE

Comet C/1996 B2 Hyakutake was extensively observed at the Pic du Midi
observatory during late March of 1996, Bright condensations were
observed in the near-nucleus coma. We have performed a detailed data
analysis in order to derive the position of these features with respect
to the nucleus. We make the hypothesis that they are induced by
fragments of the nucleus. Despite the frequency of fragmentation of
cometary nuclei, the dynamics of the fragments is not yet well
understood. We propose a general approach in order to study the motion
of the fragments in the orbital plane of the comet. An estimate of the
non-gravitational forces is used to describe the motion of the fragment
and of the nucleus with respect to their centre of mass. Then the
equations of the theory of perturbed Keplerian motion are solved in
order to study the motion of the centre of mass, This approach is
applied to Comet C/1996 B2 Hyakutake, The results are in good agreement
with the observations, An excellent fit is obtained for a fragment size
of 20 m, assuming a density of 300 kg m(-3). Copyright 1999, Institute
for Scientific Information Inc.

================
(7) POLARIMETRIC OBSERVATIONS OF COMET HALE-BOPP

Y.N. Gnedin*), T.M. Natsvlishvili, V.D. Bychkov, V.P. Romanenko:
Polarimetric observations of comet Hale-Bopp. ASTRONOMY LETTERS-A
JOURNAL OF ASTRONOMY AND SPACE ASTROPHYSICS, 1999, Vol.25, No.3,
pp.191-197

*) RUSSIAN ACADEMY OF SCIENCE,MAIN ASTRON OBSERV,ST PETERSBURG
   196140,RUSSIA

We report the results of polarimetric observations of comet Hale-Bopp
made at the I-m telescope of the Special Astrophysical Observatory in
October 1996 and in March/April 1997 using MINIPOL polarimeter. We
present the wavelength dependences of the degree and position angle of
polarization, which differ from those of other comets and characterize
the unusual activity of comet Hale-Bopp. We estimate the contribution
of molecular scattering. Strong variability in the degree and position
angle of polarization and in the wavelength dependences of these
parameters indicate both very high inhomogeneity of the dust component
and a presence of dust grain alignment mechanism. Copyright 1999,
Institute for Scientific Information Inc.

==========
(8) DUST FLOW IN A POROUS COMET NUCLEUS

Y. Shoshany, M. Podolak, D. Prialnik, B. Berkowitz: A Monte Carlo model
for the flow of dust in a porous comet nucleus. ICARUS, 1999, Vol.137,
No.2, pp.348-354

*) TEL AVIV UNIVERSITY,DEPT GEOPHYS & PLANETARY SCI,IL-69978
   RAMAT AVIV,ISRAEL

We describe a Monte Carlo model that simulates dust migration in a
porous cometary nucleus. We present computations for media in which the
pore-size distributions are either random or normal; additional
computations indicate that media with power-law size distributions
behave very similarly to random distributions. We show how the average
time to cross the medium varies as a function of porosity and how the
structure of the medium varies with time. Implications for the
structure of the cometary nucleus are discussed. (C) 1999 Academic
Press.

================
(9) RADAR OBSERVATIONS OF THE GIACOBINID METEOR STREAM

M. Simek*), P. Pecina: The Giacobinid meteor stream observed by radar
in 1998. ASTRONOMY AND ASTROPHYSICS, 1999, Vol.343, No.3, pp.L94-L96

*) ACADEMY OF SCIENCE OF THE CZECH REPUBLIC,INST ASTRON,CZ-25165
   ONDREJOV,CZECH REPUBLIC

The return of the 1998 Giacobinid meteor shower associated with the
comet 21P/Giacobini-Zinner was observed by meteor radar at Ondrejov,
Czech Republic. The duration of the intense part of the shower was
approximately 3 hours. Though the Limiting magnitude of the radar is +8
M-r, only overdense echoes down to +4.2 M-r were analyzed. A maximum
number of 82 such shower meteors was recorded in the ten minute
interval 13h 00m-13h 10m UT corresponding to solar longitude L. =
194.degrees 8200 +/- 0.degrees 0034 (J2000.0). The mass-distribution
index s; = 1.38 +/- 0.04 indicates a lack of faint meteors in the most
dense part of the stream. Copyright 1999, Institute for Scientific
Information Inc.


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