PLEASE NOTE:


*

CCNet 109/2002 - 19 September 2002
----------------------------------
 
"An analysis of comets called sungrazers suggests conventional
theories about how comets break up may be wrong, according to a US
astronomer. The idea of comets breaking up in a fairly orderly
pattern is a new one, Dr Sekanina writes, describing how one comet cascades
into large families of smaller comets in a process that could be an
important part of a comet's natural life cycle. This replaces a previous
theory that comets broke up occasionally and only very close to the sun,
as the strong pull of gravity cracked their loosely piled chunks of dust
and ice."
--Danny Kingsley, ABC Science Online, 18 September 2002


"Amateurs play a key role in detecting and tracking the smaller
bodies in the solar system, and have been among the discoverers of
several potentially dangerous objects. If and when a deadly object is
found to be on a collision course with Earth, early detection and tracking
would be crucial to allowing an effective response (such as diverting the
object). It would not be entirely surprising if, somewhere in a
backyard right now, there is a 12-year-old who is about to save the
world."
--Kenneth Silber, Tech Central Station, 18 September 2002


"Asteroids and comets are dangerous in more ways than one. We need
to be aware of them lest an ill-timed and ill-placed natural event
mistakenly provokes a nuclear war."
--Duncan Steel, Rogue Asteroids and Doomsday Comets, 1995


(1) SUNGRAZERS SHED LIGHT ON COMET BREAK-UP
    ABC Space News, 18 September 2002

(2) RUNAWAY FRAGMENTATION OF SUNGRAZING COMETS
    The Astrophysical Journal, 576:1085-1089, 2002 September 10

(3) THE END-PERMIAN 'IMPACT' DEBATE TAKES SHAPE
    Geology , September 2002, pp. 855/56

(4) REPLY
    Geology, September 2002

(5) ASTRONOMERS FIND 100TH 'NEW WORLD' PLANET
    Ananova, 17 September 2002

(6) AMATEUR NIGHT
    Tech Central Station, 18 September 2002

(7) THE NEW SPACE RACE?
    Tech Central Station, 18 September 2002

(8) RE: MULTIPLE COMETARY IMPACTS AT K/T TIME
    Gerta Keller <gkeller@Princeton.EDU>

(9) THINGS THAT GO BANG
    Matthew Genge <M.Genge@nhm.ac.uk>


==============
(1) SUNGRAZERS SHED LIGHT ON COMET BREAK-UP

>From ABC Space News, 18 September 2002
http://abc.net.au/science/news/space/SpaceRepublish_677972.htm
 
An analysis of comets called sungrazers suggests conventional theories about
how comets break up may be wrong, according to a US astronomer.

Dr Zdenek Sekanina, a senior research scientist at NASA's Jet Propulsion
Laboratory has studied images of sungrazers - small comets that pass close
to the sun - and concluded these may break up far away from the sun.

His research is published in this week's issue of The Astrophysical Journal.

Most sungrazing comets are tiny - the smallest could be less than 10 metres
across (compared to other comets with a nucleus of between 1 and 10
kilometres) - and move in a highway-like formation of comets that pass near
the sun and disintegrate.

In contrast, the sungrazer images reveal many sungrazer comets arrive at the
sun in clusters and on parallel paths. Normally, these tiny fragments would
have disintegrated if on an earlier trip they had come so close to the sun.
Therefore the parents of these tiny sungrazers must have broken up after
their previous encounter with the sun and continued to break up far from the
sun on their journey through the solar system, according to Dr Sekanina.

The idea of comets breaking up in a fairly orderly pattern is a new one, Dr
Sekanina writes, describing how one comet cascades into large families of
smaller comets in a process that could be an important part of a comet's
natural life cycle.

This replaces a previous theory that comets broke up occasionally and only
very close to the sun, as the strong pull of gravity cracked their loosely
piled chunks of dust and ice.

In the past seven years of observation by The Solar and Heliospheric
Observatory (SOHO), about 400 sungrazers in the immediate vicinity of the
sun have been observed, although Dr Sekanina estimates there may currently
be as many as 200,000.

The sungrazers move in tight pairs and occasionally SOHO has been able to
capture them simultaneously. By devising a standard model for split comets
using the offsets between the sungrazers, Dr Sekanina is able to work out
when they separated and when their 'parents' did.

It is not just sungrazers that can break up far from the sun, notes Dr
Sekanina. New observations of comet 57P/du Toit-Neujmin-Delporte show
fragmentation has also resulted in a 'highway' of tiny comets. The
separation occurred beyond the orbit of Mars.

Danny Kingsley - ABC Science Online

© 2002 ABC

===========
(2) RUNAWAY FRAGMENTATION OF SUNGRAZING COMETS

>From The Astrophysical Journal, 576:1085-1089, 2002 September 10

Runaway Fragmentation of Sungrazing Comets Observed with the Solar and
Heliospheric Observatory

Zdenek Sekanina
Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak
Grove Drive, Pasadena, CA 91109; zs@sek.jpl.nasa.gov

ABSTRACT

The observed clustering of the Solar and Heliospheric Observatory (SOHO)
sungrazing comets is a product of runaway fragmentation that occurs
throughout their orbits about the Sun. Since the sungrazers in tight pairs
occasionally appear simultaneously in the field of view of the SOHO
coronagraphs, their offsets can be used to determine their separation
parameters, including the time of their parent's breakup, by applying the
author's standard model for split comets. The fragmentation mode of seven
sungrazer pairs is shown to differ fundamentally from that of a SOHO
non-Kreutz double comet. Further support for runaway fragmentation is
provided by a statistically significant argument that employs an orbit-based
search for pairs among the sungrazers.

© 2002. The American Astronomical Society. All rights reserved. Printed in
U.S.A.

==============
(3) THE END-PERMIAN 'IMPACT' DEBATE TAKES SHAPE

>From Geology , September 2002, pp. 855/56

End-Permian catastrophe by bolide impact: Evidence of a gigantic release of
sulfur from the mantle: Comment and Reply

COMMENT

Christian Koeberl (E-mail: christian.koeberl@univie.ac.at)
Institute of Geochemistry, University of Vienna, Althanstrasse 14, A-1090
Vienna, Austria
Iain Gilmour
Planetary and Space Research Institute, The Open University, Milton Keynes
MK7 6AA, United Kingdom
Wolf Uwe Reimold
Impact Cratering Research Group, School of Geosciences, University of the
Witwatersrand, Johannesburg 2050, South Africa
Philippe Claeys
Department of Geology, Vrije Universiteit Brussel, Pleinlaan 2, B-1050
Brussels, Belgium
Boris Ivanov
Institute for Dynamics of Geospheres, Russian Academy of Sciences, Moscow
117334, Russia

Kaiho et al. (2001) report sulfur isotope and chemical data for samples from
the Meishan (China) Permian-Triassic (P-T) boundary section, which they
interpret as evidence for a large-scale impact event that penetrated Earth's
mantle and formed a crater ;1000 km in di-ameter.
We disagree with their interpretation in all major points.

First, Kaiho et al. interpret Fe-Ni-Si-rich grains as ''impact-metamorphosed
grains.'' This interpretation is not supported by their (or other) data. The
data in Table 1 of Kaiho et al. are of insufficient quality. Variations in
the amounts of Ni, Al, Mn, and Cu do not indicate the presence of
extraterrestrial matter. It is not clear which elements occur as oxides and
which as metals. The only publications cited by Kaiho et al. in support of
an impact-related origin of such grains are by Miura et al. (1999). These
two short reports present low-quality data from undocumented sources (impact
structures, volcanic features) as well as cryptic statements, which contrast
with the well-established criteria for the identification of
extraterrestrial components in impact-related materials (e.g., Koeberl,
1998).

The presence or absence of very small grains of badly known com-position
does not constitute evidence for or against an impact event. The statement
of Kaiho et al. that ''the presence of grains of Fe-Si-Ni also represents
evidence for an impact event'' is in conflict with well-documented data from
known impact structures and deposits (Koeberl, 1998).

Second, the stratigraphic horizon analyzed by Kaiho et al. is said to be
characterized by strong Ni enrichment. This statement is sup-ported neither
by analytical data (other than their Fig. 1), nor by ele-mental abundances
that would point toward a definitive extraterrestrial source (e.g., platinum
group element data). Furthermore, the authors do not attempt to ascertain
the carrier phase of Ni, an element that can be enriched by various
terrestrial processes. Does Ni reside in primary meteoritic matter,
impact-generated phases, or minerals that result from biogenic or diagenetic
origins?

Third, the suggestion that the lack of shocked quartz implies an oceanic
impact event is misleading. Shock metamorphic effects are not restricted to
quartz, but occur in all rock-forming and accessory min-erals, which are
abundant in ocean-floor rocks.

Fourth, impact-induced volcanism and/or the excavation of mantle material is
implausible (e.g., Melosh, 2000, 2001; Ivanov and Artem-ieva, 2002). No
known impact on Earth has ever had such consequenc-es. The authors
mistakenly assume complete vaporization of target material
inside the crater cavity. From calculated degassed sulfur volume, the
authors suppose a crater diameter of 600-1200 km. However, this is an
estimate of the zone of vaporization. In fact, the actual size of the crater
should be much larger. For a crater with a diameter of 600-1200 km, the
amount of vaporized material is equal to 2-3 times the mass of a projectile
at 20 km/s impact (O'Keefe and Ahrens, 1977). Hence, for such a large
crater, the volume of vaporized target rock is 10^4 to 10^5 km^3 , a factor
of 1000 less than the 3-10^7 to 3-10^8 km^3 assumed by the authors. A
projectile with a diameter of 750-1500 km would be required to produce these
assumed values. The largest main belt asteroid has a diameter of 1000 km and
the largest crater formed on the terrestrial planets in the past 500 m.y. is
Mead Crater on Venus, with a diameter of ~280 km. This would seem to be an
upper limit for plausible catastrophic impacts during the Phanerozoic on
Earth.

Fifth, Kaiho et al. observe a range in d^34S values for sulfate of between
+28.6? and +2.0?, with more ^34 S-depleted values coincident with the change
from limestones to more organic carbon-rich
marls and claystone. Uncertainty over the evidence for a large impact around
the P-T boundary (Farley and Mukhopadhyay, 2001), Kaiho et al.'s
miscalculation of the amount of material vaporized, and the im-plausibility
of impact-induced volcanism (Melosh, 2000, 2001), all suggest a more
parsimonious interpretation of the data. There is substantive global
evidence for initially dysoxic and ultimately anoxic conditions in many P-T
sections (e.g., Isozaki, 1997; Wignall et al., 1998), and the d^34S values
observed by Kaiho et al. can readily be explained
by fractionation via bacterial sulfate reduction and reoxidation of
isotopically light H>2S, superimposed on a signature of Late Permian
sea-water.

This has been observed in other Permian-Triassic evaporites (e.g., Spoštl
and Pak, 1996). Similarly, the authors have not considered detrital sulfate
as a source for the ^34S-depleted values, despite the evidence of detrital
input from their own Sr isotope data. We conclude that none of the points
raised by Kaiho et al. provides even a vague suggestion of an impact event
at the P-T boundary.

While an impact event is one of several possibilities to explain this mass
extinction, the interpretations presented by Kaiho et al. are poorly
documented, inconclusive, and bypass more obvious explanations of the data.
Attempts to utilize the questionable interpretations by Kaiho et al. to
support the equally controversial (cf. Farley and Mukhopadhyay, 2001) claims
for the presence of extraterrestial 3 He in fullerenes at the P-T boundary
represent circular logic.

ACKNOWLEDGMENTS

Supported by Austrian Science Foundation grant Y58-GEO and the United
Kingdom Particle Physics and Astronomy Research Council. University of the
Witwatersrand Impact Cratering Research Group contribution 31.

REFERENCES CITED

Farley, K.A., and Mukhopadhyay, S., 2001, An extraterrestrial impact at the
Permian-Triassic boundary?: Science, v. 293, p. 2343a.
Isozaki, Y., 1997, Permo-Triassic boundary superanoxia and stratified
super-ocean: Records from lost deep sea: Science, v. 276, p. 235-238.
Ivanov, B.A., and Artemieva, N.A., 2002, Numerical modeling of the formation
of large impact craters, in Koeberl, C., and MacLeod, K.G., eds.,
Cata-strophic events and mass extinctions: Impacts and beyond: Geological
Society of America Special Paper 356, p. 619-630.
Kaiho, K., Kajiwara, Y., Nakano, T., Miura, Y., Kawahata, H., Tazaki, K.,
Ueshima, M., Chen, Z., Shi, G.R., 2001, End-Permian catastrophe by a bolide
impact: Evidence of a gigantic release of sulfur from the mantle: Geology,
v. 29, p. 815-818.
Koeberl, C., 1998, Identification of meteoritical components in impactites,
in Grady, M.M., et al., eds., Meteorites: Flux with time and impact effects:
Geological Society [London] Special Publication, v. 140, p. 133-152.
Melosh, H.J., 2000, Can impacts induce volcanic eruptions? Catastrophic
events and mass extinctions: Impacts and beyond: Houston, Lunar and
Planetary Institute Contribution 1053, p. 141-142.
Melosh, H.J., 2001, Impact-induced volcanism: A geologic myth: Geological
Society of America Abstracts with Programs, v. 33, no. 7, p. A-433.
Miura, Y., Fukuyama, S., and Gucsik, A., 1999, Impact metamorphosed
compositions of the Fe-Si-Ni-S system: Journal of Materials Processing
Technology, v. 85, p. 188-191.
O'Keefe, J.D., and Ahrens, T.J., 1977, Impact induced energy partitioning,
melting, and vaporization on terrestrial planets, in 8th Lunar Science
Conference Proceedings: New York, Pergamon Press, p. 3357-3374.
Spoš tl, C., and Pak, E., 1996, A strontium and sulfur isotopic study of
Permo-Triassic
evaporites in the northern calcareous Alps, Austria: Chemical Geology, v.
131, p. 219-234.
Wignall, P.B., Morante, R., and Newton, R., 1998, The Permo-Triassic
transition in Spitsbergen: d 13 Corg chemostratigraphy, Fe and S
geochemistry, facies, fauna and trace fossils: Geological Magazine, v. 135,
p. 47-62.

© 2002, Geological Society of America

===============
(4) REPLY

>From GEOLOGY, September 2002
http://www.gsajournals.org/gsaonline/?request=get-toc&issn=0091-7613&volume=030&issue=09

Kunio Kaiho
Institute of Geology and Paleontology, Tohoku University, Sendai 980-8578,
Japan
Yoshimichi Kajiwara
Institute of Geoscience, University of Tsukuba, Ibaraki 305, Japan
Yasunori Miura
Department of Earth Sciences, Faculty of Science, Yamaguchi University,
Yamaguchi 753-8512, Japan

Koeberl et al. take issue with our interpretation of geochemical changes at
the end of the Permian in southern China. The main purpose of our paper
(Kaiho et al., 2001) is to show the coincidence of re-markable sulfur and
strontium isotope excursions, concentration of un-usual
Fe-Ni-Si-S grains, increases in kaolinite and significant decreases in
manganese, phosphorous, calcium, and microfossils (foraminifera) at the end
of the Permian in southern China. Our interpretation is that the best
explanation for these changes is the impact of an asteroid or
a comet into the ocean at the end of the Permian, which caused a rapid and
massive release of sulfur from the mantle to the ocean-atmosphere system.
This led to significant oxygen consumption, acid rain, and the most severe
biotic crisis in the history of life on Earth.

Koeberl et al. discuss each feature separately, and claim that the tracers
are not definitive evidence for impact. They did not, however, consider the
coincidence of the changes in several tracers, which is the most important
result of our paper. In our conclusions, we stated that all changes recorded
in the 2-cm-thick Ni-rich layer occurred abruptly, and this evidence implies
a gigantic release of sulfur from the mantle. Our conclusion depends on the
fact that multiple tracers measured by high-resolution analyses changed
coincidentally.

The kinds of impact tracers that typify the end of the Cretaceous may not be
as robust in rocks linked to older mass extinctions (Becker, 2002). New
tracers may therefore be required to define the causes of these mass
extinctions. Grains composed of Fe-Si-Ni system material are a possible new
tracer for bolide impact, because they are thought to form in vapor released
by impact, as the Fe and Ni in the meteoroids would separate and mix with Si
or Al from the crust and mantle (Miura et al., 1999, 2000).

Koeberl et al. propose that there are insufficient data for the
inter-pretation of these grains as ''impact-metamorphosed grains.'' Using
backscattered-electron images of analytical scanning electron microscopy
from the basal part of bed 25 (;1 mm in thickness), we found (1) many
Fe-Si-Ni-S-rich grains distributed irregularly in some untreated fragment
and (2) spherules (;30 mm in diameter) containing such Fe-Si-Ni-S-rich
grains. Similar Fe-Si-Ni-S-rich grains have been reported at the
Cretaceous-Tertiary boundary in some sections (Miura et al., 1999).

Shocked quartz is the best tracer for impacts into continental crust because
it is well preserved in sediments compared with other minerals. Quartz,
however, is rare in the ocean crust. Therefore, the lack of shocked quartz
may indicate a bolide strike in the ocean and oceanic crust at the end of
the Permian.

Koeberl et al. erroneously state that we mistakenly assume complete
vaporization of target material inside the crater cavity. In fact, we think
that the evaporation of sulfur occurs not only from vapor, but also from the
solid ejecta because of the abrupt decrease in pressure and the low boiling
temperature of sulfur (S: 445 8C; SO4 22 : ;317 8C, in 1 atm) relative to
temperatures at the impact site (500-10 000 8C) and the mantle (;1200 8C).
However, such arguments based on the assumption of total evaporation of
sulfur are disputable (Kaiho et al., 2001). The point of our paper was not
to establish the size of the bolide, but to establish the size of the impact
event.

Our model stresses the amount of sulfur required to explain the de-crease in
the sulfate sulfur isotope ratio. Koeberl et al. state that we ob-served a
range in d 34 S values for sulfate between 128.6? and 12.0?, with more 34
S-depleted values coincident with the change from limestone to more organic
carbon-rich marl and claystone. However, there is no relationship between
total organic carbon and sulfate sulfur isotope values (R 2 5 0.1). Although
there may be some relationship between lithology, sulfide values, and
fractionation between sulfide and sulfate, there would be no relationship
between lithology and carbonate structurally substituted sulfate (SSS)
(Kaiho et al., 1999, Fig. 3). We assumed that SSS monitors variation of the
sulfate sulfur isotope ratio in seawater.

Koeberl et al. also state that the d 34 S values we observed can readily be
explained by fractionation via bacterial sulfate reduction and reoxidation
of isotopically light H2 S. The positive shift of the sulfate sulfur isotope
ratio just below the event layer is thought to be due to sulfate reduction.
Previously, one of us argued for the development of a largely anoxic
stratified ocean and its temporary massive mixing at the P-T boundary,
supported by sulfur isotope records from deep-sea facies in Japan (Kajiwara
et al., 1994). In our current paper, we adopted a model of oxidation of
averaged sulfur in the crust with consideration of various sources of the
light sulfur; there is no logical necessity of selective reoxidation of
bacterial sulfide concentrating the light isotope. Koeberl et al. also argue
that we have not considered detrital sulfate as a possible source for the 34
S-depleted values, despite the evidence of detrital input from our own Sr
isotope data. However, the low Sr isotope value derived from clastic
sediments shows an increase in Sr of mantle origin relative to Sr from
continental detritus.

REFERENCES CITED

Becker, R., 2002, Repeated blows: Scientific American, March 2002, p. 62-69.
Kaiho, K., Kajiwara, Y., Tazaki, K., Ueshima, M., Takeda, N., Kawahata, H.,
Arinobu, T., Ishiwatari, R., Hirai, A., and Lamolda, M.A., 1999, Oceanic
primary productivity and dissolved oxygen levels at the Cretaceous/Ter-tiary
boundary: Their decrease, subsequent warming, and recovery:
Pa-leoceanography, v. 14, p. 511-524.
Kaiho, K., Kajiwara, Y., Nakano, T., Miura, Y., Kawahata, H., Tazaki, K.,
Uesh-ima, M., Chen, Z., and Shi, G.R., 2001, End-Permian catastrophe by a
bolide impact: Evidence of a gigantic release of sulfur from the mantle:
Geology, v. 29, p. 815-818.
Kajiwara, Y., Yamakita, S., Ishida, K., Ishiga, H., and Imai, A., 1994,
De-velopment of a largely anoxic stratified ocean and its temporary massive
mixing at the Permian/Triassic boundary supported by the sulfur isotopic
record: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 111, p.
367-379.
Miura, Y., Fukuyama, S., and Gucsik, A., 1999, Impact metamorphosed
com-positions of the Fe-Si-Ni-S system: Materials Processing Technology, v.
85, p. 188-193.
Miura, Y., Fukuyama, S., Kedves, M., Yamori, A., Okamoto, M., and Gucsik,
A., 2000, Chemical separation of Fe-Ni particles after impact: Advances in
Space Research, v. 25, p. 285-288.

© 2002, Geological Society of America

=========
(5) ASTRONOMERS FIND 100TH 'NEW WORLD' PLANET

>From Ananova, 17 September 2002
http://www.ananova.com/news/story/sm_671843.html?menu=news.scienceanddiscovery

Astronomers have announced the discovery of the 100th planet known to
inhabit another solar system.

Dr Hugh Jones of Liverpool John Moores University led the international team
which found the new world orbiting the star Tau 1 Gruis.

The star is 100 light years from Earth in the southern constellation Grus,
"The Crane".

The planet, one and a half times the mass of Jupiter, is about the same
distance from its parent star as the asteroid belt is from the Sun.

Its orbit is roughly circular, like those of the Sun's family of planets.

Scientists believe solar systems whose planets have circular orbits are the
most likely to harbour an Earth-like world containing life.

Astronomers are now beginning to see patterns in planet characteristics.

Chris McCarthy, from the Carnegie Institution of Washington, one of the US
team members, said: "When we first started out, we found planets close in to
their parent stars. But as the planet search programme has matured, we're
finding more planets farther our in nearly circular orbits.

"This means we are getting closer to detecting more systems that are similar
to our own solar system."

Astronomers do not yet have the technology to detect planets orbiting stars
directly. Instead their size and orbits are calculated by measuring the
wobble their gravity imparts on their parent star.

Copyright 2002, Ananova

========
(6) AMATEUR NIGHT

>From Tech Central Station, 18 September 2002
http://www.techcentralstation.com/1051/envirowrapper.jsp?PID=1051-450&CID=1051-091802C

By Kenneth Silber 09/18/2002 
 
Amateur astronomy may be the oldest hobby, in that people have been
observing the night sky for many thousands of years. Amateurs played a
central role in astronomy's development as a science from the 16th through
19th centuries. In much of the 20th century, however, amateurs were eclipsed
by the professionals, whose large and sophisticated telescopes were worlds
apart from the capabilities of backyard stargazers.

But the past few decades have seen an amateur astronomical renaissance, with
non-professionals not only observing the sky in growing numbers but also
making valuable contributions to astronomy's progress as a science. Adeptly
charting this revival, and likely to spur it further, is a notable new book,
Seeing in the Dark: How Backyard Stargazers Are Probing Deep Space and
Guarding Earth from Interplanetary Peril by science writer and amateur
astronomer Timothy Ferris (published by Simon & Schuster).

Amateur astronomy was revivified by three technological innovations, as
Ferris recounts. One was the Dobsonian, an inexpensive type of reflecting
telescope invented by astronomy proselytizer and former monk John Dobson.
Another was the CCD, or charge-coupled device, a light-sensitive chip that
facilitated recording of faint starlight. The third was the Internet, which
gave amateurs new ability to communicate among themselves and with
professionals, and to draw upon computerized databases and other expert
tools.

Amateurs were the first, or among the first, to detect phenomena such as the
vast storm on Saturn in 1991, Comet Shoemaker-Levy (which crashed into
Jupiter in 1994), and the great supernova of 1987 (which is when its light
got to the Earth; the event happened 168,000 years earlier). An amateur
observed "spokes" on Saturn's rings, features doubted by the pros but
subsequently confirmed by images from the Voyager spacecraft. An amateur was
the first to get a naked-eye view of the returning Halley's Comet in 1986.

The capabilities of the amateurs and the pros are, to a large degree,
complementary. Amateurs have sheer numbers and time. There are some 5,000
professional astronomers in North America and perhaps ten times as many
experienced amateurs (plus many more with a casual interest in astronomy).
The big professional telescopes often peer deeply into space but only cover
a small swatch of the sky. The amateurs' telescopes ensure broad coverage
and make it likely that someone will notice transient or unexpected
phenomena. The pros get limited time on expensive instruments to focus on
objects of compelling scientific interest. Amateurs can look for long
periods at whatever they want.

Seeing in the Dark interweaves profiles of amateur astronomers with broader
discussion of the amateur community and vignettes of Ferris's own
experiences as a stargazer. Ferris also provides considerable information of
the celestial objects that are out there to be seen, and in an appendix
offers tips on observational instruments and techniques. The book depicts
the appealing subculture that has arisen around amateur astronomy, which
includes telescopic gatherings called "star parties" and astronomy-oriented
inns.

Moreover, as the book's subtitle suggests, amateur astronomers, besides
having fun and contributing to science, also help protect Earth against the
possibility of a cataclysmic collision with an asteroid or comet. Amateurs
play a key role in detecting and tracking the smaller bodies in the solar
system, and have been among the discoverers of several potentially dangerous
objects. If and when a deadly object is found to be on a collision course
with Earth, early detection and tracking would be crucial to allowing an
effective response (such as diverting the object). It would not be entirely
surprising if, somewhere in a backyard right now, there is a 12-year-old who
is about to save the world.

Copyright 2002, Tech Central Station

============
(7) THE NEW SPACE RACE?

>From Tech Central Station, 18 September 2002
http://www.techcentralstation.com/1051/defensewrapper.jsp?PID=1051-350&CID=1051-091802B

By Glenn Harlan Reynolds 09/18/2002 
 
Last week, I wrote about Orion
( http://www.techcentralstation.com/1051/defensewrapper.jsp?PID=1051-350&CID=1051-091102C ),
the nuclear-pulse-powered spacecraft (well, really, a
nuclear-explosion-powered spacecraft) and suggested that it might be the
favored tool of junior powers looking to leapfrog the United States'
position in outer space. This week I'm going to outline just how that might
happen.

Imagine that you're, say, China. Used to thinking of your nation as the
center of the world for thousands of years, and still, at some level,
regarding China's relative impotence and backwardness over the past two or
three centuries as a mere interlude in history, you'd like to restore things
to what you consider normal.

You could, of course, become a liberal capitalist democracy, free up your
citizens' talents and energy, and let the resulting wealth turn you into a
superpower over a few decades. And there's always the hope that China will
follow this very path, as India (most of the time, at least) appears to be
doing.

But the problem with the liberal-democracy route is that it may make the
nation as a whole richer and more powerful, but it will endanger the
positions and power of a lot of people along the way. That sort of thing
makes the command-economy, big-project, military-industrial approach an
appealing alternative.

At any rate, a China (or, for that matter, perhaps even an India) looking to
make a splash and anxious to get around the United States' supremacy in
military (and civilian) space activity might well consider Orion to be
appealing. China is not a signatory to the Limited Test Ban Treaty, which
bars nuclear explosions in the atmosphere and outer space, so that legal
barrier would be out of the way. China has acceded to the 1967 Outer Space
Treaty, but that treaty bans only the stationing of nuclear "weapons" in
outer space, and there is a plausible argument that nuclear explosives
designed to propel a spacecraft are not "weapons" for the purposes of the
Treaty.

With international law thus neutralized, the only remedy would be for people
to either (1) start a war; or, short of that, (2) to threaten to shoot down
the spacecraft, which probably would amount to starting a war anyway. (Jimmy
Carter, the least bellicose of American presidents, said that an attack on a
U.S. satellite or spacecraft would be treated as an act of war, and it seems
unlikely that the Chinese would take a more pacific approach than Carter.)
And even if shooting down the spacecraft were thought unlikely to lead to
war, it would be unlikely to succeed - the Orion spacecraft would be huge,
fast, and designed to survive in the neighborhood of a nuclear explosion: a
very difficult target indeed.

The chief restraint on China would thus be world opinion, something to which
the Chinese have not shown themselves particularly susceptible. This would
be especially true if the Chinese sprung it as a surprise, which they very
well might.

Much of the physics and engineering behind Orion is already well-known, and
- given that American designers working with puny 1960-vintage computer
technology saw the problems as tractable - it's very likely that the Chinese
could manage to design and build an Orion craft within a few years of
deciding to. Hiding Orion-related work probably wouldn't be very hard,
either. China already has extensive space and nuclear-weapons programs,
which would tend to conceal the existence of Orion-type research. And much
of the necessary research and design work on Orion - involving, as it does,
things like the resonance of huge steel plates and massive hydraulic shock
absorbers - wouldn't look like space-related research even to an American
intelligence agency that discovered it. At least, not unless the
intelligence analysts were familiar with Orion, and had the possibility in
mind. And how likely is that?

Will we wake up one day to find that a 4,000-ton Chinese spacecraft has
climbed to orbit from Inner Mongolia on a pillar of nuclear fireballs and is
now heading to establish a base on the Moon? It wouldn't be the first time
America has had such a surprise, now would it?

Copyright 2002, Tech Central Station

============================
* LETTERS TO THE MODERATOR *
============================

(8) RE: MULTIPLE COMETARY IMPACTS AT K/T TIME

>From Gerta Keller <gkeller@Princeton.EDU>

Dear Benny

I would like to comment on the interesting announcement of the Boltysh
crater as of pre-K/T age and the inference of multiple cometary impacts. We
also found evidence of multiple cometary impacts, but this evidence suggests
that Chicxulub may predate the K/T bondary and that the boundary impact
event has yet to be found.

Recently, Kelley and Gurov determined that the age of a buried 24-km-wide
Ukrainian crater known as Boltysh dates to about 65.2 ± 0.6 million years
and they suggest that multiple cometary impacts occurred at K/T time. The
evidence of the Boltysh crater adds to the increasing evidence for multiple
impacts at K/T time, as recently reported by Keller and co-workers (GSA
Special Paper 356, p. 145-161), who discovered multiple glass spherule
layers of impact origin in late Maastrichtian sediments of northeastern
Mexico. They concluded that at least two impacts occurred, one at K/T time
and one about 300,000 years earlier, with Chicxulub most likely the pre-K/T
impact.

Chicxulub is generally considered the K/T boundary impact that caused the
mass extinction. A K/T age is inferred largely on the basis of the
stratigraphic position  of impact glass spherules reported from K/T boundary
deposits in Haiti and Mexico, the chemical similarity of these spherules
with melt rock in subsurface cores from Chicxulub, and an 40Ar/39Ar age of
about 65 Ma with a large uncertainty factor. The K/T age for the Chicxulub
crater is now in question.

A recent restudy of the Haiti sections and analysis of new and more complete
outcrops revealed that the glass spherule deposit is not at the K/T
boundary, but considerably younger within the early Danian P. eugubina zone
(Keller et al., 2001; Stueben et al., 2002). It was concluded that these
spherule deposits were likely reworked from an older deposit. However, an Ir
anomaly of cosmic origin was indentified in the early Danian above the
spherule deposit (and probably independent from it), suggesting an impact
event in the early Danian. This early Danian Ir anomaly has also been
documented from central Mexico (Stinnesbeck et al., 2002), Guatemala
(Fourcade et al., l998; Keller and Stinnesbeck, l999).

Detailed study and mapping of the spherule deposits over a large area in
northeastern  Mexico discovered the presence of 2 to 4 spherule layers in
late Maastrichtian sediments well below the K/T boundary (Keller et al.,
2002).The oldest glass spherule layer is dated about 65.30 Ma. This spherule
layer contains welded glass spherules that indicate that deposition occurred
while the glass was still hot and ductile, possibly as floating rafts. Two
additional younger spherule layers above this interval - including the
spherule layer originally considered evidence for the Chicxulub impact -
show evidence of reworking, including shallow water benthic foraminifera and
marl clasts, that suggest reworking from the original spherule producing
event. These data indicate a pre-K/T impact event at about 65.3 Ma. Since
the spherules are considered of Chicxulub origin, that impact also must
predate the K/T boundary.

There is currently strong evidence for three impact events at the K/T
transition: one at 65.3 Ma (spherule layers, possibly Chixculub), one at the
K/T boundary (ir anomlay), and one in the early Danian P. eugubina zone
about 100 kyr after the K/T boundary (Ir anomaly).

Gerta Keller

References:
Fourcade et al., l998, Sciences de la Terre et des Planets, 327, 47-53.
Keller et al., 2001, Can. J. Earth Sci., 38, 197-227.
Keller et al., 2002, GSA Special Paper, 356, 145-161.
Keller and Stinnesbeck, l999, Int. J. Earth Sci., 88, 844-852.
Stueben et al., 2002, GSA Special Paper, 356,163-188.

=============
(9) THINGS THAT GO BANG

>From Matthew Genge <M.Genge@nhm.ac.uk>

Hi Benny,

Have I told this story before?

Yesterday's article on a possible meteorite fall in Sri Lanka has parallels
with the discovery of the Bur Abor meteorite in Kenya. This was a large 300
kg iron meteorite found within a few miles of the border which was brought
into the Natural History Museum a few years ago by a relative of the land
owner. The sample was analysed and was indeed a fragment of a new iron
meteorite.

The eye witness accounts suggested that it was a meteorite fall since farm
workers had heard an explosion and saw a pall of smoke rising above a copse
of trees. Investigating they discovered a large mass of metal, which turned
out to be the meteorite, and thin shards embedded in the trees. The only
problem with this very believable scenario was that the iron meteorite was
weathered and had evidently been on Earth for quite some time.

When asked whether there was any other possible explanation the land owner's
representative said that the farm workers had first assumed that a land mine
or shell had exploded. He said this was a relatively common occurrence in
the area.

Perhaps meteorite falls are not the simplest explanation for explosions in
an area where heavy fighting has occurred up until seven month's ago. I do
hope, however, that in this case that the unlikely turns out to be the
correct explanation.

Matthew Genge
Web Manager & Meteoriticist
Near Earth Objects Information Centre
http://www.nearearthobjects.co.uk


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