PLEASE NOTE:


*

Date sent: Fri, 20 Mar 1998 13:12:05 -0500 (EST)
From: Benny J Peiser B.J.PEISER@livjm.ac.uk
Subject: CCD II/20 March 1998
To: cambridge-conference@livjm.ac.uk
Priority: NORMAL

CC DIGEST, 20 March 1998 - late edition before the weekend
----------------------------------------------------------

(1) NINE REASONS WHY ASTEROID 1997 XF11 CHANGED ITS MIND
Darryl Pitt dpitt@interport.net

(2) GENE SHOEMAKER MIS-QUOTED?
Duncan Steel dis@a011.aone.net.au

(3) APOCALYPSE POSTPONED
NEW SCIENTIST, 20 March 1998

==================================
(1) NINE REASONS WHY ASTEROID 1997 XF11 CHANGED ITS MIND

From: Darryl Pitt dpitt@interport.net

in the op-ed section of this past wednesday's new york times, jesse
gordon enumerated--with illustrations of a comet zig-zagging every
different way--the "9 reasons that asteroid 1997 xf11 changed its
mind" as follows:

--human race will destroy the planet anyway
--dinosaurs were more fun to make extinct
--healthier to collide with a nonsmoking planet
--six points on asteroid driver's license
--worried about being subpoenaed by the independent counsel
--doesn't know...can't commit to anything lately...is considering
therapy
--felt humans had a negative attitude toward visit
--jury duty
--no desire to spend the rest of its days in the lobby of the museum of
natural history

======================
(2) GENE SHOEMAKER MIS-QUOTED?

From: Duncan Steel dis@a011.aone.net.au

Dear Benny,

In that interesting article from the NY Times, Gene Shoemaker is quoted
as saying:

>If you do the maneuver 10 to 20 years before the predicted collision,
>then the impulse that must be delivered to the asteroid -- the change
>in velocity -- is only of the order of one or two centimeters a year,
>to deviate a center hit on Earth to a clean miss.

In fact the required speed change required to get a potential impactor to
miss, given a lead time of decades, is one or two centimeters PER SECOND.
This is easy to see. Let the lead time be 20 years and the impulse be
such that the change in speed is 1 cm/sec. Then the difference in
distance moved between the unperturbed (by our intervention) and the
perturbed (we kicked it) orbit is 20 x 365.25 x 24 x 60 x 60 x 0.01
metres which equals 6312 kilometres, near as dammit. The Earth's radius
is 6371 km. Thus an induced speed change of just over 1 cm/sec would be
sufficient to get an asteroid whose path w a s due to pass through
the centre of the Earth to miss our planet: just.

I don't know, of course, whether Gene was mis-quoted, or perhaps he
mis-spoke himself. Easily done. Gene undoubtedly knew the impulse
required (which is still small!) but may have slipped (although I'd
need to hear the tape to be convinced of that!).

Another part of the article states:

>As a result of the Shoemakers' search and a handful of others', about
>1,500 Earth-crossing asteroids five-eighths of a mile or more in
>diameter are known and their orbits are plotted. Dr. Shoemaker believed
>there could be three times as many. Each is capable of taking out a city,
>a country, or much more.

That is nonsense. The known population of Earth-crossers larger than 1
km (which is what that 'five-eighths of a mile' derives from) is ten
times less, only about 150, especially at the time of the interview in
1996. This is undoubtedly an error on the part of the journalist, not
Gene. And Gene knew that we had so far found only a b o u t 5 to 10%
of the Earth-crossers above that canonical 1 km size. On the other
hand, there c o u l d be three times 1,500 at sizes >1 km needing
discovery, although most estimates are lower (1500-3500, say; depends
on what sorts of albedos you think they've got). And the damage
potential of 1 km asteroid is rather understated in the final sentence
quoted above, and again I must ascribe the error to the journalist.
Gene knew better.

Regarding:

>He discussed other ways of accomplishing
>this, such as using conventional explosives.

Again, I'd like to hear the tape. Gene knew damn well that there's no
point in using 'conventional explosives'. You would do as well using
just lead in a hypervelocity impact, with less chance of an accident
along the way! At a speed of 3 km/sec a kg of lead (or
a n y t h i n g) has the same kinetic energy as the chemical energy of
a kg of TNT. So there's no point in using conventional explosives. One
needs things with high specific energies, and that implies nuclear.

Duncan Steel

=========================================
(3) APOCALYPSE POSTPONED

From: NEW SCIENTIST, 20 March 1998

After a day-long drama in which it seemed there was an outside
chance that civilisation might end 30 years from now with a
catastrophic asteroid impact, astronomers declared the all clear
last Thursday. Revised calculations based on data from 1990 show that
on 26 October 2028 asteroid 1997 XF11 should miss the Earth by 960 000
kilometres--25 times farther away than the Moon.

1997 XF11 was discovered by Jim Scotti of the University of Arizona in
Tucson on 6 December last year. Gareth Williams and Brian Marsden of
the Harvard-Smithsonian Center for Astrophysics in Cambridge,
Massachusetts, soon added it to their list of "potentially hazardous
objects" which might hit the Earth.

Initial calculations indicated that 1997 XF11 would miss the Earth by
about 800 000 kilometres in 2028. But the inclusion of observations
made on 3 and 4 March showed 1997 XF11 skimming just 42 000 kilometres
above the Earth's surface--with a small chance that it would hit us.

Marsden announced the bad news in an electronic circular sent out on 11
March, trying to encourage more observations. He also asked astronomers
to check their archives for any sightings from the previous occasions
1997 XF11 came within viewing distance: in 1990, 1983, 1976, 1971 and
1957. "But we didn't think the chances were that large of finding
something," says Dan Green, who works with Williams and Marsden.

So the team was surprised when Eleanor Helin of the Jet Propulsion
Laboratory (JPL) in Pasadena promptly unearthed images of the 1990
encounter on photographic plates. While Marsden talked with reporters
who had arrived to cover the story on 12 March, Williams recalculated
the orbit, and found the asteroid would miss the Earth by 960 000
kilometres. Don Yeomans of JPL has confirmed that result.

The impact of an asteroid the size of 1997 XF11, which is 2 kilometres
across, would release about half a million megatons of explosive
energy. That could devastate global agriculture, warns Scotti.

With sufficient warning, it could be possible to nudge an asteroid
away by exploding nuclear weapons a kilometre or so above its surface.
Identifying all the potential threats from outer space will require a
ten-year, $50-million programme, says David Morrison of the NASA Ames
Research Center in California. That's less than the budgets of the two
asteroid disaster movies scheduled to reach the screen this summer--but
the money has not yet been forthcoming.

Jeff Hecht, Boston

(c) 1998 New Scientist

--------------------------------
THE CAMBRIDGE-CONFERENCE NETWORK
--------------------------------
The Cambridge-Conference List is a scholarly electronic network
moderated by Benny J Peiser at Liverpool John Moores University,
United Kingdom. It is the aim of this network to disseminate
information and research findings related to i) geological and
historical neo-catastrophism, ii) NEO research and the hazards to
civilisation due to comets, asteroids and meteor streams, and iii) the
development of a planetary civilisation capable of protecting itself
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not be copied or reproduced for any other purposes without prior
permission of the copyright holders.



*

Date sent: Fri, 20 Mar 1998 09:08:13 -0500 (EST)
From: Benny J Peiser B.J.PEISER@livjm.ac.uk
Subject: CC DIGEST 20/03/98
To: cambridge-conference@livjm.ac.uk
Priority: NORMAL

CC DIGEST 20 March 1998
-----------------------

A man said to the universe:
"Sir, I exist!"
"However," replied the universe,
"The fact has not created in me
A sense of obligation."

(Stephen Crane, Collected Works VI)


(1) GENE SHOEMAKER'S VOICE IS MISSING, BUT HIS LEGACY IS FELT
Henry S.F. Cooper, The New York Times

(2) NASA'S TRANSITION REGION AND CORONAL EXPLORER MISSION SET TO STUDY
THE SUN'S TURBULENT UPPER ATMOSPHERE
NASANews@hq.nasa.gov

(3) NATIONAL SPACE SOCIETY TEAMS WITH TIME MAGAZINE AND PARAMOUNT
PICTURES FOR IN-DEPTH EXPLORATION OF COMET THREAT
meteorobs@latrade.com

(4) WORKNOTES ON THE JOSHUA IMPACT EVENT
Ed Grondine epgrondine@hotmail.com

(5) MAKING A COMET NUCLEUS
J.M. Greenberg, LEIDEN UNIVERSITY

(6) THE RELEVANCE OF LABORATORY IMPACTS FOR THE STUDY OF COMETS
D. Koschny, MAX PLANCK INSTITUTE

===============================
(1) GENE SHOEMAKER'S VOICE IS MISSING, BUT HIS LEGACY IS FELT

From: Clark Whelton cwhelton@mindspring.com

Excerpted from the New York Times Science Section, Tuesday, March 17,
1998 page F4

Asteroid Expert's Voice is Missing, but His Legacy is Felt

by Henry S.F. Cooper

In all the discussion about Asteroid 1997 XF11 and its chances of
hitting Earth, and what to do about it, one voice badly missing was Dr.
Eugene M. Shoemaker's. He was the geologist who first brought the study
of rocks into space and whose work, first with impact craters and then
with the asteroids and comets that blasted them, has made most people
accept the notion -- revolutionary in the 1950s and 1960s -- that big
rocks from space can make big holes in planets, with catastrophic
results.

The Palomar Asteroid Search, which he initiated in 1973, was the first
systematic search for asteroids (and later, comets) whose trajectories
crossed Earth's and might hit the planet.

Dr. Shoemaker was killed in an automobile accident in July near Alice
Springs, Australia, where he and his wife, Carolyn Shoemaker, his
partner in the asteroid and comet search, were studying impact craters.

In the spring of 1996, I spent a couple of weeks with the Shoemakers
at their house in Flagstaff, Arizona, interviewing them for a book I am
writing...

By good fortune, I happened to ask Dr. Shoemaker to unfold for me
the scenario of how we could deal with an asteroid one-kilometer wide --
about five-eighths of a mile -- if we learned early enough that it was going
to hit Earth. I taped his answer, so that in fact we are not without
Dr. Shoemaker's voice on this subject after all. It is a soothing and
gently persuasive voice, making whatever he said sound reasonable,
however outlandish or devastating.

"If you could manage to get the nations of the world organized, or
at least the lead nations, then you could think in terms of sending up a
nuclear device," he said. "In fact you would send several devices on
several separate spacecraft, with which you have stand-off explosions that
would result in gentle pushes on the asteroid.

"We want to do the maneuver when it is near the Sun, near the
asteroid's perihelion, to get the maximum effect. If you can do it, you
can change the the semi-major axis of the orbit, you can change its
period, so that the Earth is somewhere else when the object goes by.
It turns out you don't have to push very hard. If you do the maneuver
10 to 20 years before the predicted collision, then the impulse that
must be delivered to the asteroid -- the change in velocity -- is only
of the order of one or two centimeters a year, to deviate a center hit
on Earth to a clean miss. Clearly you don't do just one big shot; you
give it a series of smaller shots; you very carefully herd it into the
new orbit that you want." He discussed other ways of accomplishing
this, such as using conventional explosives.

"Whatever you do, you don't want to break it," he said. "You push on it
gently -- that is why you do a stand-off explosion. If you break it
up, then it becomes an uncontrolled problem. You wouldn't be able to
herd it if you suddenly got pieces going off in various directions --
it's out of control. You have multiple objects hitting the Earth, and
they could actually cause more damage rather than less."

Although Dr. Gene Shoemaker is no longer on this planet, he, along with
Carolyn Shoemaker and another observer, Dr. Eleanor Helin, may have had
the last word on Asteroid 1997 XF11. Photographic plates that the
Shoemakers took in April 1990 as well as plates that Dr. Helin took in
March 1990, which were re-examined last week, revealed extremely faint
images of the asteroid on an earlier orbit. The pictures provided a
longer arc of information on the asteroid's trajectory that had been
available before, enabling astronomers at the Jet Propulsion Laboratory
in Pasadena to determine with authority that in 2028 the comet would
miss Earth by a distance very likely greater than that of Earth from
the Moon.

As a result of the Shoemakers' search and a handful of others', about
1,500 Earth-crossing asteroids five-eighths of a mile or more in
diameter are known and their orbits are plotted. Dr. Shoemaker believed
there could be three times as many. Each is capable of taking out a city, a
country, or much more. Following the Shoemaker-Levy impacts, an
obviously impressed Congress asked NASA to study what would be needed
for a full survey, and a NASA committee led by Dr. Shoemaker
recommended a program called Spaceguard, requiring an initial five-year
effort that would cost $24 million, followed by an additional $3
million a year to continue the search. The proposal was shelved.

Mrs. Shoemaker hopes the recent scare will revive Spaceguard. At the
very least, expanding the library of plates might prevent future false
alarms. And as surely as the Moon follows the Sun across the sky, the
alarm some day will be real. (c) 1998 The New York Times.

========================
(2) NASA'S TRANSITION REGION AND CORONAL EXPLORER MISSION SET TO STUDY
THE SUN'S TURBULENT UPPER ATMOSPHERE

From: NASANews@hq.nasa.gov

Donald Savage
Headquarters, Washington, DC March 19, 1998
(Phone: 202/358-1547)

Donna Drelick/Jim Sahli
Goddard Space Flight Center, Greenbelt, MD
(Phone: 301/286-8955)

RELEASE: 98-48

NASA'S TRANSITION REGION AND CORONAL EXPLORER MISSION SET TO
STUDY THE SUN'S TURBULENT UPPER ATMOSPHERE

NASA's Transition Region and Coronal Explorer (TRACE) mission,
scheduled for launch at 9:40 p.m. EST (6:40 p.m. PST) March 30, 1998,
will greatly improve understanding of events in the Sun's atmosphere,
including intense storms and flares, which can have an impact on power
and communications systems on Earth.

The TRACE mission will join a fleet of spacecraft studying the Sun
during a critical period when solar activity is beginning its rise to a
peak early in the new millennium. The Sun goes through an 11-year cycle
from a period of numerous intense storms and sunspots to a period of
relative calm and then back again. The coming months in the Sun's cycle
will provide solar scientists with periods of strong solar activity
interspersed with periods when the Sun is relatively passive and quiet.
This will give TRACE the chance to study the full range of solar
conditions, even in its relatively short planned lifetime.

TRACE will train its powerful telescope on the dynamic so-called
'transition region' of the Sun's atmosphere, between the relatively
cool surface and lower atmosphere of the Sun where temperatures are
about 6,000 degrees Fahrenheit, and the extremely hot upper atmosphere
called the corona, where temperatures are up to 16 million degrees
Fahrenheit. Using instruments sensitive to extreme-ultraviolet and
ultraviolet wavelengths of light, TRACE will study the detailed
connections between the fine-scale surface features and the overlying,
changing atmospheric structures of hot, ionized gas, called plasma. The
surface features and atmospheric structures are linked by fine-scale
solar magnetic fields.

The power of the TRACE telescope to do detailed studies of the solar
atmosphere makes this observatory unique among the current group of
spacecraft studying the Sun.

"The spacecraft has roughly ten times the temporal resolution and five
times the spatial resolution of previously launched solar spacecraft.
Its findings are eagerly awaited by the solar science community," said
Dr. Alan Title, TRACE principal investigator from the Stanford Lockheed
Institute for Scientific Research in Palo Alto, CA. "We can expect to
resolve some present mysteries of the Sun's atmospheric dynamics as
well as discover new and exciting phenomena."

TRACE will be launched into a polar orbit to enable virtually
continuous observations of the Sun, uninterrupted by the Earth's shadow
for months at a time. This orbit will give the mission the greatest
chance of observing the random processes which lead to flares and
massive eruptions in the Sun's atmosphere.

The TRACE telescope is really four telescopes in one. Its 30-centimeter
(12-inch) primary and six-centimeter (2-inch) secondary super-polished
mirrors are individually coated in four distinct quadrants to allow
light from different bandwidths (colors) to be reflected and analyzed.
An electronic detector collects images over a 231,000-by-231,000-mile
field of view, nearly 25 percent of the Sun's disk. A powerful data
handling computer enables very flexible use of the detector array
including adaptive target selection, data compression and image
stabilization.

"TRACE was completed on time, under budget, and met all performance
goals," said Jim Watzin, Small Explorer project manager, NASA Goddard
Space Flight Center, Greenbelt, MD. "I'm really proud of this team.
They have produced a magnificent observatory in a manner that saved
NASA nearly $9.7 million over the initial cost estimate." TRACE, which
costs $49 million, is the third launch in the Small Explorer series of
small, quickly developed, relatively low-cost missions.

TRACE will be launched on an Orbital Sciences Corp., Dulles, VA,
Pegasus-XL rocket released from an L-1011 jet aircraft at the Western
Range, Vandenberg Air Force Base, CA. The launch window is open for 10
minutes.

TRACE will be the first space science mission with an open data policy.
All data obtained by TRACE will be available to other scientists,
students and the general public shortly after the information becomes
available to the primary science team.

The TRACE telescope was designed and developed in cooperation between
Lockheed Martin Corp. and Stanford University. The spacecraft was
designed and tested at Goddard, which manages the mission for the
Office of Space Science at NASA Headquarters, Washington, DC.

Further information about the TRACE mission can be found on the
Internet at:

http://sunland.gsfc.nasa.gov/smex/trace

TRACE science information can be found at:

http://www.space.lockheed.com/TRACE/welcome.html

==========================
(3) NATIONAL SPACE SOCIETY TEAMS WITH TIME MAGAZINE AND PARAMOUNT
PICTURES FOR IN-DEPTH EXPLORATION OF COMET THREAT
(Sorry, but this Internet discussion took already place last night).

From: meteorobs@latrade.com

Washington, DC) - March 18 - The National Space Society, in cooperation
with Paramount Pictures, announces a live Internet discussion about the
potential threat of planetary impact by asteroids or comets. The
discussion, hosted by TIME.com, the online component to TIME magazine,
will be held on March 19, at 7:00 pm ET/4:00 pm PT on Yahoo! Chat.

The live forum comes only one week after the announcement and later
retraction of news that an asteroid might impact Earth in 2028. The
scare renewed debate over the likelihood of a collision and whether
more steps should be taken now to plan for such a disaster. The news
was timely for Hollywood, which on May 8th releases Paramount
Pictures/Dreamworks' "Deep Impact," the story of the world's reaction
to an impending collision with a comet. The Internet chat brings
together the science and Hollywood views of such an event.

Joining the live forum will be:

- Richard D. Zanuck, co-producer of "Deep Impact." He, along with
David Brown, first presented the idea for the film to Paramount in the
late 1970s. After the discovery that Earth had indeed suffered from
shattering comet impacts in its distant past, the Zanuck/Brown team
decided the most powerful script was one based on science fact. Zanuck,
in partnership with Brown, also produced "Jaws," Academy Award winner
"The Sting," the Academy Award nominated film "The Verdict" and
"Cocoon."

- Dr. Pete Worden, member of the National Space Society Board of Directors, an
astronomer, and former director of advanced programs for the National Space
Council during the Bush Administration. He was recently involved with a
proposed space mission to intercept an asteroid for the purpose of
gathering data. Dr. Worden is currently active in the defense space
program.

- Gerry Griffin, science consultant to "Deep Impact." Griffin was former
director of NASA's Lyndon B. Johnson Space Center in Houston. He also served
as a Flight Director during the Apollo 13 mission. Griffin previously
consulted on the making of the films "Apollo 13" and "Contact."

- Jon Favreau, "Gus Partenza" in "Deep Impact," the medical officer on a space
shuttle headed for an Earth-crossing comet. Favreau previously wrote,
produced, directed and starred in the independent feature "Swingers."

In preparation for the live discussion the National Space Society is hosting a
website offering background information and a directory of related resources.

The National Space Society, founded in 1974, is an independent, nonprofit
space advocacy organization headquartered in Washington, DC. Its 23,000
members and 90 chapters around the world actively promote a spacefaring
civilization. Information on NSS and space exploration is available at
http://www.nss.org. TM & Copyright ) 1998 by Paramount Pictures and
DreamWorks L.L.C. ALL RIGHTS RESERVED.

========================
(4) WORKNOTES ON THE JOSHUA IMPACT EVENT

From: Ed Grondine epgrondine@hotmail.com

Many researchers have noted the impact event set out in the biblical
book of Joshua. Recently I have been working on some material which
appears to provide indepedent corraborative evidence as to the
historicity of this event and as to its date and location. From the
evidence, it appears that there was an impact event in about 1584 BC,
just to the west of what is now Jerusalem, and that this Nagasaki-sized
impact destroyed the military forces of a large number of Hittite
appenages, which were under the command of the Hittite king
T'Hantilish, known to the Greeks as Tantalus. So far I have three
independent sources for this event, a summary of which follows,
(including contemporary Hittite records, second summary below), as well
as a broad archaeological sequence that supports the occurence of this
impact event.

The first written source for the event, one with which the conference
participants are probably familiar, is the biblical book of Joshua,
which is admittedly quite distant from the event itself. To summarize
once again the account there, the Israelites leave Egypt at the time of
the eruption of Thera in 1628 BC. They are repulsed at Rephidim, return
to the desert, eliminate the Kohath faction, and establish themselves
on the east bank of the Jordan in lands which were long before under
Horim (Hurri) control. This brings us to 1588 BC. The Israelites begin
to move across the Jordan, and after a particularly savage attack on
Ai, a "multi-national" force is assembled to stop them. Under the
leadership of Joshua, the Israelites launch a night attack, and as the
"multi-national" force regroups the impact event occurs:

"And it came to pass, as they fled from before Israel, and were going
down to Beth-horon, that the Lord cast down great stones from heaven
upon them unto Azekah, and they died. More died with hailstones than
they whom the children of Israel slew with the sword."

The Israelites then went on to slaughter and enslave a large region,
dividing the land in 1583 BC.

The second group of written sources for this impact event are the
Hittite records of Hantilish's (Hantili's) defeat. To summarize,
Hantilish's predecessor Murshilish I (Musili I)is deafened by the
explosion of Thera as a child, and takes the throne in 1604 BC.

[The dating used here follows the Hittite scholar Michael Astour's
sequence of dates (Hittite History and Absolute Chronology of the
Bronze Age, page 2), but adjusted back by 64 years using the middle
chronology Babylonian astronomical cycle observation. The dates thus
arrived at coincide very well with those independently arrived at from
the ice cores for the Thera explosion and Joshua.] Murshilish I marches
on Babylon in 1595 BC. On his way home Murshilish I is attacked and
defeated by the Hurrians. There is a treaty (KUB XXXVI 106 + KBo IX 73)
with hapiru ("raiders") which was concluded by either Murshilish now,
or his successor Hantilish concluded it at a later date, some time
after his murder of Murshilish in 1594 BC.

Hantilish also campaigns against the Hurri, but the Hurri defeat him
and take his queen and heirs to Shugziya and kill them. (Edict of
Telepinush, 15-17) According to fragmentary record KBo III 46, someone
dies in Shugziya, after the death of 3 Hittite commanders, and an
unnamed Hittite king assembles 3000 Hapiru men and garrisons them in a
(name lost) city. (Astour, page 87)

The third group of written sources for this event are the Greek
mythological records. It appears that Hantilish was known to the
Achaeans as Tantalus, the god (Theos) Hantilish, or T'e-Hantilish: the
king of the coastal region of Sipylus, which has been correctly
identified as Hittite Zippasla. The direct Mycenean sense of humor
finds typical expression in its description of Tantalus's fate. After
Tantalus dies he is sent to hell, where though surrounded by food and
drink, he can not enjoy them, as he must hold up a large stone with both
hands, in order to keep it from falling on his head.

As for the archaeological record of this event, there are destruction
levels at Jericho, Hormah, Gibeon, and Arad which have been dated to
1550 BC, though I do not know if these dates are still valid. It also
appears that the Hittites were so weakened by this impact event that
they were unable to prevent the migration of the Gasgas (Kaskas) and
Achaeans, so every LM IB site could be added to the archaeological
support for this hypothesis.

From what I have experienced so far in the e-forums, I do not think
that any amount of argument over written records is going to persuade
the academic community to even consider the hypothesis. Physical
evidence of the event itself must be found. So far I have contacted a
friend who lives in Jerusalem about searching for the meteorites in the
fall field. I have also sent a message of inquiry with a specific
description of the location of the fall field to a meteorite collecting
group, and since these collectors pay the same price as gold for
meteorites, I hope that solid evidence should not be long in coming.

I think that additional text materials might justify a more
professional search for the meteorites by geologists, and I am going to
look for more text material, immediately as I can find the time. As a
final method of attack on this problem, I plan to investigate the work
which has been done on finds of meteoritic iron artifacts and the
records of their trade.

Altogether there is more than I can handle, so I thought I'd take
the opportunity to share my findings so far with the conference.

=========================
(5) MAKING A COMET NUCLEUS

J.M. Greenberg: Making a comet nucleus, ASTRONOMY AND ASTROPHYSICS,
1998, Vol.330, No.1, pp.375-380

LEIDEN UNIVERSITY, ASTROPHYSICS LAB, POSTBUS 9504, NL-2300 RA LEIDEN,
NETHERLANDS

The chemical composition of a comet nucleus can be very strictly
constrained by combining the latest results on: the core-mantle
interstellar dust model, the solar system abundances of the elements,
the space observed composition of the dust of comet Halley, and the
latest data on the volatile molecules of comet comae. The distribution
of the components in the comet nucleus fall naturally into two basic
categories - refractories and volatiles. The refractory components are
tightly constrained to consist of about 26% of the mass of a comet as
silicates (a generic term for combinations of the elements Si, Mg, Fe),
23% complex organic refractory material (dominated by carbon), and
about 9% in the form of extremely small (attogram) carbonaceous/large
molecule (PAH) particles. The remaining atoms are in an H2O dominated
mixture containing of the order of 2-3% each of CO, CO2, CH3OH plus
other simple molecules. The H2O abundance itself is very strictly
limited to similar to 30% of the total mass of a comet - not much more
nor much less. The refractory to volatile (dust to gas) ratio is
about 1:1, while the dust to H2O ratio is approximate to 2 : 1. The
maximum mean density of a fully packed nucleus would be approximate to
1.65g cm(-3). The morphological structure of the component materials,
following the interstellar dust into the final stage of the presolar
cloud contraction, is as tenth micron silicate cores with organic
refractory inner mantles and outer mantles of 'ices' with each grain
containing many thousands of the attogram carbonaceous/large molecule
particles embedded in the icy and outer organic fraction. Copyright
1998, Institute for Scientific Information Inc.

===========================
(6) THE RELEVANCE OF LABORATORY IMPACTS FOR THE STUDY OF COMETS

D. Koschny, The relevance of laboratory impacts into ice and
ice-silicate targets for the study of comets, ADVANCES IN SPACE
RESEARCH, 1997, Vol.20, No.8, pp.1569-1576

MAX PLANCK INSTITUTE, PO BOX 20, D-37189 KATLENBURG DUHM, GERMANY

This paper points out the relevance of impact experiments into ice and
ice-silicate mixtures for the study of comets. After a brief summary of
the properties of cometary surfaces, a short overview over the
available papers dealing with experimental impacts in ice and
ice-silicates is given. Then, the crater rate onto comet Wirtanen is
estimated. The conclusion identifies future necessary work. (C) 1997
COSPAR. Published by Elsevier Science Ltd.

--------------------------------
THE CAMBRIDGE-CONFERENCE NETWORK
--------------------------------
The Cambridge-Conference List is a scholarly electronic network
moderated by Benny J Peiser at Liverpool John Moores University,
United Kingdom. It is the aim of this network to disseminate
information and research findings related to i) geological and
historical neo-catastrophism, ii) NEO research and the hazards to
civilisation due to comets, asteroids and meteor streams, and iii) the
development of a planetary civilisation capable of protecting itself
against cosmic disasters. To subscribe, please contact Benny J Peiser
b.j.peiser@livjm.ac.uk . Information circulated on this network is
for scholarly and educational use only. The attached information may
not be copied or reproduced for any other purposes without prior
permission of the copyright holders.



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The content and opinions expressed on this Web page do not necessarily reflect the views of nor are they endorsed by the University of

The content and opinions expressed on this Web page do not necessarily reflect the views of nor are they endorsed by the University of Georgia or the University System of Georgia.