PLEASE NOTE:


*

CCNet, 049/2000 - 14 April 2000
-------------------------------


     "[The Woodleigh impact] structure is the largest proven impact
     structure discovered to date on the Australian continent and the
     fourth largest in the world after Vredefort in South Africa
     (diameter of 300 km), the Sudbury in Canada (250 km), and the
     Chicxulub in the Gulf of Mexico (diameter of about 170 km). [...]
     The size of the Woodleigh impact structure suggests that it may
     have had a significant role in the tectonic evolution of the
     Southern Carnarvon Basin. Apart from such tectonic implications,
     an impact of this size would have caused catastrophic
     environmental effects that, on the present dating of Woodleigh,
     may correlate with one of three extinction events known in the
     fossil record: the Late Devonian extinction (364 million years),
     the end of the Permian (247 million years), and the end of the
     Triassic (214 million years)."
       --  Arthur Mory, Robert Iasky, Andrew Glikson & Franco Pirajno -
           Australian discoverers of the Woodleigh impact crater


(1) FOURTH LARGEST IMPACT STRUCTURE DISCOVERED IN AUSTRALIA
    Arthur Mory <A.Mory@dme.wa.gov.au>

(2) IMPACT AT HIGH NOON
    Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>

(3) RESEARCHERS REDUCE PLANETARY IMPACT RATES DUE TO
    ECLIPTIC COMETS
    H.F. Levison et al., SW RESEARCH INSTITUTE

(4) 1996 PW & 1997 SE5: EXTINCT COMETS OR D-TYPE ASTEROIDS?
    M.D. Hicks et al., CALTECH,JET PROP LAB

(5) COLLISIONAL EVOLUTION IN THE VULCANOID REGION
    S.A. Stern & D.D. Durda, SW RES INST,DEPT SPACE STUDIES

(6) ESTIMATED ABUNDANCE OF ATENS & IEOS
    P. Michel et al., OSSERV ASTRON TORINO

(7) RADAR MICROMETEORS
    D. Janches et al., PENN STATE UNIVERSITY

(8) SOFT DISASTERS: SCIENCE 'NOT ENOUGH' TO ALLAY FEARS
    BBC News Online, 14 April 2000

(9) AND FINALLY: REDUCED FARTING COULD SAVE WORLD, SCOTTISH
    SCIENTISTS CLAIMS
    YAHOO! News, 12 April 2000

=============
(1) FOURTH LARGEST IMPACT STRUCTURE DISCOVERED IN AUSTRALIA

From Arthur Mory <A.Mory@dme.wa.gov.au>

Dear Benny,

Your readers may be interested in our paper in Earth and Planetary
Science Letters, Vol. 177 (1-2) p. 119-128 on the newly discovered
120-km diameter Woodleigh impact structure in the Carnarvon Basin,
Western Australia.
(http://www.elsevier.nl/gej-ng/10/18/23/80/25/34/article.html).

Regards

Arthur Mory 1) <a.mory@dme.wa.gov.au>
Robert Iasky 1) <r.iasky@dme.wa.gov.au>
Andrew Glikson 2) <geospectral@spirit.com.au>
Franco Pirajno 1) <f.pirajno@dme.wa.gov.au>

1) Geological Survey of Western Australia, 100 Plain St., East Perth,
   W.A. 6004, Australia
2) Research School of Earth Science, Institute of Advanced Studies,
   Australian National University, Canberra, A.C.T. 0200, Australia


We report a newly discovered multi-ring impact structure on the
Gascoyne Platform of the Southern Carnarvon Basin in Western Australia.
The centre of the structure (latitude 2603'25"S, longitude
11439'50"E) lies on Woodleigh Station (after which it is named)
approximately 160 km south-southeast of Carnarvon and directly east of
Hamelin Pool in Shark Bay. The Woodleigh impact structure is not
recognisible from present day topographic features as it is covered by
flat-lying Cretaceous and Lower Jurassic strata, but it has a
multi-ring gravity signature that is characteristic of impact
structures. The structure is the largest proven impact structure
discovered to date on the Australian continent and the fourth largest
in the world after Vredefort in South Africa (diameter of 300 km), the
Sudbury in Canada (250 km), and the Chicxulub in the Gulf of Mexico
(diameter of about 170 km).

An impact origin is indicated by: a central core of uplifted granitoid
basement probably less than 25 km in diameter, which displays
shock-induced planar deformation features in quartz (the single most
diagnostic criterion for an impact origin), pervasive diaplectic
vitrification of feldspar and penetrative pseudotachylite veining, and
an inner ring syncline containing a ~70 m thick thermally modified
diamictite overlain by ~380 m of Lower Jurassic lacustrine deposits. An
outermost diameter of 120 km, defined by gravity, magnetic and surface
drainage, indicates a ring fault that sharply intersects the
NS-striking regional structure. At the centre of the basement uplift
shock metamorphosed granitoid was intersected at a depth of 171 m - at
least 1800 m higher than the gravity-modelled level of regional
basement. Pseudotachylite veins systems within the shocked granitoid
are strongly enriched in Al, Ca, Mg, Ni, Co, Cr, V and S, and depleted
in K and Si, suggesting chemical fractionation attendant on shock
volatilisation, enrichment by an injected and volatilised meteoritic
component, and potentially of sulphide mineralisation.

The impact age is constrained by overlying Lower Jurassic strata,
reworked Early Permian palynomorphs, Late Devonian (Frasnian/ Fammenian
boundary) K/Ar ages derived from the base of the lacustrine section,
and deformed Lower Devonian and older units.

The size of the Woodleigh impact structure suggests that it may have
had a significant role in the tectonic evolution of the Southern
Carnarvon Basin. Apart from such tectonic implications, an impact of
this size would have caused catastrophic environmental effects that, on
the present dating of Woodleigh, may correlate with one of three
extinction events known in the fossil record: the Late Devonian
extinction (364 million years), the end of the Permian (247 million
years), and the end of the Triassic (214 million years).


============
(2) IMPACT AT HIGH NOON

From Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>

NEAR image of the day for 2000 April 13

http://near.jhuapl.edu/iod/20000413/index.html

For people who live in mountain valleys, daylight can be a short-lived
experience. Mountains to the east make the Sun rise later in  the
morning, while mountains to the west make the Sun set  earlier  in 
the evening. The brevity of daytime in a valley is accentuated during
the shortened days of winter.

The floor of the 5.5-kilometer (3.4-mile)  diameter impact  
crater that dominates one face of  Eros experiences the
ultimate in short daylight hours. Three factors  conspire  to  make 
this  true. Firstly,  Eros rotates rapidly, once  every 5.27 hours. 
Secondly, the crater's 0.9-kilometer (0.56-mile)  high walls  tend to
block direct sunlight from the  floor, even  while the outside  of
the crater is illuminated. Thirdly, during the current season on 
Eros, the Sun never makes it high in the sky in this location.

This NEAR Shoemaker image, taken April  1, 2000, from a range of  209
kilometers (130 miles), caught the crater near local noon with the Sun
highest in the sky. On that day,  a hardy  astronaut standing  at the
bottom  of the crater would have experienced 1 hour  and 45 minutes of
daylight.

-----------------
NEAR image of the day for 2000 April 12

http://near.jhuapl.edu/iod/20000412/index.html

The Record of What Came Before

The most common, pervasive, and scientifically informative 
landform on Eros is impact craters. This image from NEAR
Shoemaker, taken March 20, 2000, from a range  of 206  kilometers 
(128 miles), shows a  highly cratered region of the  asteroid. The
whole scene is 7.4 kilometers (4.6 miles) across. Craters are formed
by the explosive impacts  of smaller  asteroid fragments, which
constantly rain  onto  the  surface over  the  eons.  A freshly
exposed surface will have fewer  craters than a surface exposed  to
space for a longer time, because it hasn't experienced the rain of
projectiles for as long a duration.  The great  number  of impact 
craters in the region shown  here shows  that it has  been an
extremely long time since this  region was wiped clean of craters,
or  "resurfaced,"  by a  geologic  process  such as  the chipping 
off of part of the asteroid. Also,  the much greater abundance of
smaller craters than larger craters says  that small  asteroid
fragments have impacted Eros much more frequently than large
asteroid fragments.
--------------------------------------------------------
Built and managed by The Johns Hopkins University Applied Physics
Laboratory, Laurel, Maryland, NEAR-Shoemaker was the first spacecraft
launched in NASA's Discovery Program of low-cost, small-scale
planetary missions. See the NEAR web site for more details
(http://near.jhuapl.edu).

================
(3) RESEARCHERS REDUCE PLANETARY IMPACT RATES DUE TO
    ECLIPTIC COMETS

H.F. Levison, M.J. Duncan, K. Zahnle, M. Holman, L. Dones: Planetary
impact rates from ecliptic comets. ICARUS, 2000, Vol.143, No.2,
pp.415-420

*) SW RESEARCH INSTITUTE,SPACE STUDIES DEPT,BOULDER,CO,80302

We have reevaluated the impact rates for the planets from ecliptic
comets using the integrations in H. Levison and M. Duncan (1997, Icarus
127, 13-32; LD97), We fmd that the current impact rates on the giant
planets are actually about four times smaller than LD97's values due to
differences in methods of calculating the relevant timescales. The
newly calculated impact rates are listed in Table I. However, if the
objects leaving the Kuiper belt were primarily on high inclination
orbits, then the impact rates on the giant planets are larger than
those in Table I by a factor less than or similar to 2. We discuss the
dynamics of objects hitting the giant planets in detail, including
measurements of the impact velocities. We find that 21% of the objects
that hit Jupiter in our simulations were bound to the planet before the
impact. The fraction of bound impactors for Saturn is much lower,
Jupiter, Saturn, and Uranus have a significant apex-antapex asymmetry
for the unbound impactors. (C) 2000 Academic Press.

===========
(4) 1996 PW & 1997 SE5: EXTINCT COMETS OR D-TYPE ASTEROIDS?

M.D. Hicks*), B.J. Buratti, R.L. Newburn, D.L. Rabinowitz: Physical
observations of 1996 PW and 1997 SE5: Extinct comets or D-type
asteroids?.ICARUS, 2000, Vol.143, No.2, pp.354-359

*) CALTECH,JET PROP LAB,4800 OAK GROVE DR,MS 183-501,PASADENA,CA,91109

The minor planets 1996 PW and 1997 SE5 are two of the few known
asteroids with orbital elements typical of long-period and
Jupiter-family comets and as such represent strong candidates
for extinct cometary nuclei. We obtained filter photometry of 1996 PW
and filter photometry and medium-resolution CCD spectroscopy of 1997
SE5 during their discovery apparitions. We also observed a suite of
D-type asteroids as possible spectral analogs of cometary nuclei. Both
1996 PW and 1997 SE5 have moderately red, featureless spectra typical
of the D-type asteroids, cometary nuclei, and other extinct cometary
candidates. The photometry for 1997 SE5 was fit by a triple-peaked
lightcurve with a period of 9.050 +/- 0.005 h and an amplitude of 0.4
magnitude, suggesting a relatively complex and elongated shape. With
this work, 1997 SE5 and 1996 PW join the ranks of 3552 Don Quixote and
944 Hildago as established candidates for extinct comet nuclei. (C)
2000 Academic Press.

===========
(5) COLLISIONAL EVOLUTION IN THE VULCANOID REGION

S.A. Stern*), D.D. Durda: Collisional evolution in the Vulcanoid
region: Implications for present-day population constraints. ICARUS,
2000, Vol.143, No.2, pp.360-370

*) SW RES INST,DEPT SPACE STUDIES,BOULDER,CO,80302

We explore the effects of collisional evolution on putative Vulcanoid
ensembles in the region between 0.06 and 0.21 AU from the Sun in order
to constrain the probable population density and population structure
of this region today. Dynamical studies have shown that the Vulcanoid
Zone (VZ) could be populated. However, we find that the frequency and
energetics of collisional evolution this close to the Sun, coupled with
the efficient radiation transport of small debris out of this region,
together conspire to create an active and highly intensive collisional
environment that depletes any very significant population of rocky
bodies placed in it, unless the bodies exhibit orbits that are circular
to similar to 10(-3) or less or highly lossy mechanical properties that
correspond to a fraction of impact energy significantly less than 10%
being imparted to ejecta. The most favorable locale for residual bodies
to survive in this region is in highly circular orbits near the outer
edge of the dynamically stable Vulcanoid Zone (i.e., near 0.2 AU),
where collisional evolution and radiation transport of small bodies and
debris proceed most slowly. If the mean random orbital eccentricity in
this region exceeds similar to 10(-3), then our work suggests it is
unlikely that more than a few hundred objects with radii larger than 1
km will be found in the entire VZ; assuming the largest objects have a
radius of 30 km, then the total mass of bodies in the VZ down to 0.1 km
radii is likely to be no more than similar to 10(-6) M+, <10(-3) the
mass of the asteroid belt. A 0.01-AU-wide ring near the outer stability
boundary of the VZ at 0.2 AU would likely not contain over a few tens
of objects with radii larger than 1 km. Despite the dynamical stability
of large objects in this region (Evans, N. W., and S. Tabachnik, 1999,
Nature 399, 41-43), it is plausible that the entire region is
virtually empty of kilometer-scale and larger objects. (C) 2000
Academic Press.

==========
(6) ESTIMATED ABUNDANCE OF ATENS & IEOS

P. Michel*), V. Zappala, A. Cellino, P. Tanga: Estimated abundance of
Atens and asteroids evolving on orbits between Earth and Sun. ICARUS,
2000, Vol.143, No.2, pp.421-424

*) OSSERV ASTRON TORINO,I-10025 PINO TORINESE,ITALY

The so-called Aten asteroids, evolving on orbits with semimajor axis a
< 1 AU and aphelion distance Q > 0.983 AU, spend most of their time
inside Earth's orbit. Currently, they account for about 7% of the
observed near-Earth asteroid population and 13% of the Earth-crossing
one. However, observational biases play against their discovery; thus
the present number of Atens is probably severely underestimated.
Another still unobserved population of asteroids, which we call IEO
(inner-Earth objects), could also exist and evolve entirely inside
Earth's orbit. Orbital numerical integrations of known source
populations of Earth-crossers indicate that the real fraction of Atens
and IEOs in the Earth-crossing population depends on the considered
objects' diameters and could be close to 20% considering only the
multikilometer bodies. Moreover, the fraction of IEOs could be as large
as half that of Atens. Since these asteroids can also impact Earth,
their threat should seriously be taken into account. (C) 2000 Academic
Press.

==========
(7) RADAR MICROMETEORS

D. Janches*), J.D. Mathews, D.D. Meisel, V.S. Getman, Q.H. Zhou:
Doppler studies of near-antapex UHF radar micrometeors. ICARUS, 2000,
Vol.143, No.2, pp.347-353

*) PENN STATE UNIVERSITY,COMMUN & SPACE SCI LAB,316 EE
   EAST,UNIVERSITY PK,PA,16802

A 'radar micrometeor' is the radar-scattering signature from the free
electrons in the plasma generated by entry of a dust-sized meteoroid
into the atmosphere. We report the first direct Doppler measurements,
made using the Arecibo Observatory 430-MHz radar, of the so-called
meteor head echo. Our observations demonstrate that this region is
moving with the speed of the meteoroid as determined from the meteor
head-echo altitude-time trajectory and that this radar return is
distinct spatially and in velocity from the much more commonly observed
trail echo. We also report the first observations of near-antapex
micrometeors which are characterized by the very slow atmospheric
speeds expected from low-ecliptic-inclination objects entering the
atmosphere from behind Earth's orbital path. Of the 32 meteors observed
during four early evening hours of observations on 10 January 1997,
velocities were determined for 18 of the meteors of which 7 were at or
just below Earth escape velocity (11.2 km/s), We give heliocentric
orbits for the 11 meteor events with speeds greater than the escape
velocity and present a detailed analysis of these orbital parameters
and their possible origins. One particle was determined to be
interstellar: a preliminary analysis indicates that the ecliptic
coordinates of the radiant relative to the local standard of rest (LSR)
(with the solar motion relative to the nearby stars removed) are lambda
= 43.02 degrees, beta = -43.28 degrees, V = -25.11 km/s or, in system
II galactic coordinates l(II) = 219.8 degrees, b(II) = -52.4 degrees, V
= -25.1 km/s. (C) 2000 Academic Press.

===============
(8) SOFT DISASTERS: SCIENCE 'NOT ENOUGH' TO ALLAY FEARS

From The BBC News Online, 14 April 2000
http://news.bbc.co.uk/hi/english/sci/tech/newsid_711000/711753.stm

By environment correspondent Alex Kirby

In highly technological societies, governments can no longer rely on
science alone to win consent for potentially risky new developments,
according to social scientists.

The scientists say more crises of public trust, like those over mad cow
disease (BSE) and genetically-modified (GM) food, are almost
inevitable.

They think likely candidates for new concern are the safety of mobile
telephones, and the effects of chemicals which disrupt human hormones.

And British Nuclear Fuels, now embroiled in a dispute over the
falsification of data at its Sellafield plant in north-west England,
could be another.

The scientists, from the Global Environmental Change Programme (GECP)
at the University of Sussex, are speaking at a conference on
sustainability.

Destroying trust

They classify the BSE and GM crises as examples of "soft disasters",
which kill few people or even none, but destroy public trust in
politicians.

A GECP report last year said the current approach to such risk issues
"would inevitably lead to political and environmental crises that
emerge only slowly but at great cost to society".

The GECP team, which is funded by the Economic and Social Research
Council, says soft disasters require new public policy approaches.

"While enhanced scientific information is important to inform debates,
it is not enough on its own to determine the best way forward.

"Research shows that values and subjective factors are central to
decisions on such issues, so a new, more transparent and participative
style of decision-making is required.

"Scientific institutions need to develop their ability to respond
rapidly to emerging risk issues.

Endemic disasters

"There is also an urgent need to develop more sophisticated science
that is capable of monitoring and establishing cause and effect around
highly complex environmental risk factors."

The GECP scientists say soft disasters "are endemic in highly
technologically advanced risk societies. Governments therefore need to
develop much better capabilities to handle these issues."

They say ordinary people are not as ignorant about the issues involved
in debates like the one over GM foods as politicians are inclined to
believe.

This is partly because science cannot provide definitive answers about
the safety of such new technologies, something which people know from
their experience.

Yet public trust is central to effective decisions on risk issues,
although it is both difficult to establish and fragile to maintain.

The director of the GECP, Dr Frans Berkhout, told BBC News Online: "The
central, co-ordinating parts of government such as the Cabinet Office
seem to have grasped the issue.

Few practical changes

"They understand both the importance of soft disasters and the changes
needed in how they make decisions.

"Other parts of government are not doing so well. They often
acknowledge the value of our analysis, but have made few attempts to
tackle the issues in practical ways.

"This is not surprising, as soft disasters are extraordinarily
difficult to handle. There are no magic bullets."

The GECP is calling for "a new style of governance in which scientific
evidence plays an important but not dominant role. Public values should
inform the questions asked of the science rather than being addressed
as a token 'add-on'."

Copyright 2000, BBC

========
(9) AND FINALLY: REDUCED FARTING COULD SAVE WORLD, SCOTTISH
    SCIENTISTS CLAIMS

From YAHOO! News, 12 April 2000
http://dailynews.yahoo.com/h/nm/20000412/sc/science_warming_2.html

Scientists: New Animal Feed Can Cut Global Warming

LONDON (Reuters) - Scientists in Scotland said on Wednesday they have
come up with a novel method of reducing global warming.

By adding a bacteria supplement to feed for farm animals such as sheep
and cattle, they said it was possible to cut the amount of methane, a
major greenhouse gas, the animals produce when they break wind.

Preliminary tests of the method, which will be presented at a
conference in France next month, have been promising. "We discovered
that we could cut the amount of methane produced by almost 50 percent
by adding the bacteria Brevibacillus parabrevis," Dr. Jamie Newbold,
of the Rowett Research Institute in Aberdeen, said in a statement.

When Newbold tested the feed in sheep the amount of methane each animal
produced per day fell by an average of about four liters.

If the method is incorporated on a worldwide scale, Newbold estimates
it could reduce methane output by about six percent.

MORE HOT AIR at
http://dailynews.yahoo.com/h/nm/20000412/sc/science_warming_2.html

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*

CCNet-ESSAY, 14 April 2000
--------------------------

DISCOVERY OF THE WORLD'S FOURTH LARGEST IMPACT, AND THE TALE
OF TWO CRATERS


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

Research School of Earth Science,
Australian National University
Canberra, ACT 0200


As Eugene and Carolyn Shoemaker knew so well during their 13 years-long
(1984-1997) exploration in the Australian outback, for every
eventually-proven extraterrestrial impact crater there are numerous
false alarms. The question is often raised whether any particular
circular feature, be it a lake, a geological dome, or a geophysical
anomaly, may be of impact origin, even though positive identification
depends on the occurrence of diagnostic criteria for shock
metamorphism, i.e. planar deformation features (in quartz, feldspar or
zircon), shatter cones, impact melt, contribution by meteoritic
components including siderophile elements (Ni, Co, Cr, V) and platinum
group elements (PGE) anomalies, and other criteria. Compounding the
enthusiasm of crater hunters is the geo-centric philosophy which
lingers among many geologists, denying the reality and the essential
role of asteroid and comet impacts in Earth history.

. . .[continued]

 



CCCMENU CCC for 2000

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