PLEASE NOTE:


*

CCNet, 21 October 1999
------------------------

   QUOTE OF THE DAY

   "But what about Jerry Garcia, and especially what about this
   asteroid named Zappafrank? Marsden said both were chosen after
   campaigns organized by individuals. He said the push for Zappafrank
   resulted in more than 200 e-mails. Aha! So we can name an asteroid?
   So we checked. Madonna is not on the list. Elvis in not on the list.
   Even Ricky Martin has been overlooked, leading us to wonder if
   Marsden considered the likely flood of e-mail requests that will
   come now that the real truth behind the asteroid naming convention
   is out of the bag."
        -- Rob Britt, 20 October 1999


(1) P-T BOUNDARY EXTRATERRESTRIAL IMPACTS
    Andrew Glikson <geospectral@spirit.com.au>

(2) POSSIBLE FALKLAND IMPACT STRUCTURE
    Michael Rampino <mrr1@is3.nyu.edu>

(3) METEORITE CONTAINS MARTIAN SOIL
    Harvey Leifert <HLeifert@agu.org>

(4) FROM CLAPTON TO ZAPPA: ASTEROID NAMES THAT ROCK
    EXPLOREZONE, 20 October 1999

(5) YAWN, YAWN: LATEST ROCKY HORROR TALL STORY IS ANOTHER   
    SLOWCOACH 
    Jeremy Tatum <UNIVERSE@uvvm.UVic.CA>

(6) UNUSUAL ORIGIN OF EUROPE'S LARGEST VOLCANO EXPLAINED
    Stanford News Service <stanford.report@forsythe.stanford.edu>

(7) A PHYSICAL MODEL OF ASTEROID GEOGRAPHOS
    R.S. Hudson & S.J. Ostro, WASHINGTON STATE UNIVERSITY

(8) RADAR OBSERVATIONS OF 37 MAINBELT ASTEROIDS
    C. Magri, et.al.,  UNIVERSITY OF MAINE

(9) WHY ASTEROID 1997 XF11 WAS POTENTIALLY HAZARDOUS
    A. Milani & G.B. Valsecchi, UNIVERSITY OF PISA

(10) COMETARY TRAVEL: FROM INTERSTELLAR SPACE TO EARTH'S OCEANS
     D. Laufer et al.,TEL AVIV UNIVERSITY

(11) COMETS, ICE & ORGANIC MOLECULES
     R.L. Hudson, ECKERD COLLEGE

(12) ORBITAL HISTORY OF COMET P/LAGERKVIST (1996 R2)
     G. Hahn & C.I. Lagerkvist, DLR BERLIN

(13) POLARIMETRY OF ASTEROID 2100 RA-SHALOM
     N.N. Kiselev ET AL., KHARKOV AM GORKII STATE UNIVERSITY

================
(1) P-T BOUNDARY EXTRATERRESTRIAL IMPACTS

From Andrew Glikson <geospectral@spirit.com.au>

Dear Benny
 
With reference to Michael Paine's communication (CCNet 20.10.1999),
several indicators exist for extraterrestrial impacts contemporaneous
with the Permian-Triassic boundary - which saw the largest extinction
recorded in Earth history - including:
 
1.  Araguainha impact structure, Brazil - ~247 +/-5.5 Ma; D=40 km (see
    R.A.F. Grieve's crater listing).

2.  Lorne Basin - New South Wales - a candidate P-T boundary impact
    structure, 35x30 km large (Tonkin, P.C., 1998, Aust. J. Earth Sci.
    45, 669-671).

3.  shock features in quartz (PDF) along the P-T boundary in Antarctic
    and New South Wales (Retallack G.J., Geology, Jan. 1999; for other
    references re-P-T boundary conditions refer to Retallack and Krull,
    1999, Aust. J. Earth Sci. 46:785-812.

4.  Weak Ir anomalies reported from China and Japan, remaining
    unconfirmed due to possible analytical problems.
 
On the basis of known stratigraphic constraints, more than one impact
structures may prove to be of a P-T boundary age by future isotopic age
studies. The Falkland structure (M.R. Rampino) and Bedout structure (off
NW Australia, J.D. Gorter) are only candidate P-T impact structures
inferred from geophysical and in the latter case drilling data, as yet
unconfirmed and undated. As yet the magnitude of the confirmed impact/s
is not large enough to link them to the P-T boundary extinction and/or
as triggers of the Siberian volcanic traps (248.4+/-2.4 Ma), although it
is definitely possible further crater/s identification and isotopic
dating may shed light on these questions.
 
Andrew Glikson
21.10.1999

Research School of Earth Science
Institute of Advanced Studies
Australian National University
Canberra  ACT 0200 Australia
andrew.glikson@anu.edu.au <mailto:andrew.glikson@anu.edu.au>

===================
(2) POSSIBLE FALKLAND IMPACT STRUCTURE

From Michael Rampino <mrr1@is3.nyu.edu>

Benny:

There is a large, circular gravity anomaly on the Falkland Plateau that
resembles anomalies associated with large impact craters.  It is quite
large; greater than 200 km in diameter.

The basin that is indicated could be Late Paleozoic or Early Mesozoic in
age, but not much more is known about it. Recent papers have suggested that
it is of tectonic origin, but more study is needed.

I suggested that it might be an impact structure, and should be more
closely studied back in 1992.

Mike R.


Dr. Michael R. Rampino
Earth & Environmental Sciences Program, New York University, 100 Washington
Square East, Rm. 1009, New York, NY 10003
212-998-3743; 212-995-3820 (fax)
NASA, Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025
mrampino@giss.nasa.gov

==================
(3) METEORITE CONTAINS MARTIAN SOIL

From Harvey Leifert <HLeifert@agu.org>

Geophysical Research Letters, 1 November 1999

Rao et al. ["Martian soil component in impact glasses in a martian
meteorite"] use electron microprobe analysis to determine the chemical
compositions of veins of impact glass, called Lithology C (Lith C), in
the Martian meteorite EET79001. The meteorite also consists of two
known basaltic lithologies. The authors identify and estimate the
relative proportions of the precursor components in the mixture that
produced Lith C glass by impact melting. Lith C is found to have not
only one of the known basaltic lithologies as a component, but also
plagioclase and Martian soil. Lith C also shows significant enrichments
of sulfur, aluminum, calcium and sodium.

M. N. Rao, L. E. Borg, David S. McKay, NASA Johnson Space Center,
*Houston, Texas; S. J. Wentworth, Lockheed Martin, Houston, Texas.

==================
(4) FROM CLAPTON TO ZAPPA: ASTEROID NAMES THAT ROCK

From EXPLOREZONE, 20 October 1999
http://explorezone.com/archives/99_10/20_asteroids_rock.htm

By Robert Roy Britt, explorezone.com

You would expect asteroids, if they need to be named, to get labels
like Apollo or Zeus. And they do. But who would have thought Frank
Zappa was up there, zipping irreverently through the cosmic vacuum?

Then again, maybe that's not so surprising. Which is also perhaps why
Ringo Starr makes the official list of Minor Planet names
(John, Paul and George are there too, of course).

So who's behind all this folderol, this pop-culture naming of chunks of
iron and rock, some of which might one day collide with a planet, maybe
even the pale blue one carving the third arc from the Sun? Surely the
scientists are not responsible.

"On the whole, we enjoy as many different things as the rest of the
world and try not to take ourselves too seriously -- only seriously
enough that we are still respected as the ultimate authority for
names," says Michael A'Hearn, chairman of the International
Astronomical Union's Small Bodies Names Committee. The committee
oversees the process of giving names to some of the nearly 12,000 such
objects discovered to date. "Recognition of pop culture is not a
problem for us any more than recognition of classical musicians, for
whom lots of other asteroids are named."

"Classical music has been used quite a lot," according to Brian G.
Marsden, secretary of the naming group. "The first one was Mozart.
Bach, Beethoven and Brahms followed some years after that."

Marsden, an asteroid hunter himself, chose Duke Ellington to be
immortalized in a semi-stable orbit around the Sun.

"I'm happy to see imaginative names," Marsden said with a level of
enthusiasm that might hint at how little it takes to get some of these
folks excited. After all, they sit around and stare at numbers,
trajectories, and fuzzy radar images all day long. "It doesn't have to
be serious. If it is somewhat entertaining, that's great. Some of the
best names are whimsical names."

Like Purple Mountain. Or Clapton. Or Colemanhawkins. The list seems
endless, though only 60 percent of space rocks have gotten a name --
the naming process is woefully behind the more immediate and structured
numbering convention. But only a near-endless list could combine
travelling rocks (Acapulco and Africa, just to name a couple in the
A-section), just plain cool-sounding rocks (Pravdo, Protea and Pushkin)
and, of course, the inevitable recognition of Asimov and Sagan.

Come to think of it, the alphabetical list of Minor Planet Names could
serve as the perfect baby-naming resource for the space cognoscenti.
Then again, there's Humperdinck. And Hippo. No word on whether these
were of the whimsical variety or not.

Who picks the names?

So how are the names decided? In most cases, the discoverer makes a
suggestion -- 16 characters or less and nothing offensive, please. Oh,
and no pets (Rover and Fido are deemed less worthy than Zappa and
Ringo, et al.) The suggested name, along with a brief defense of it,
goes before the eleven-person naming committee, which has the final
say.

The official argument for putting Ringo on the list goes like this: 
He's "a Liverpudlian of lively personality and deadpan humor who
occasionally sat in as drummer with The Beatles during their early
days in Hamburg."

Definite material for the name of an orbiting object.

A host of concerns can flag a name. Confusing pronunciations or 
spellings are frequently rejected. After all, if an asteroid is found
to be on a collision course with Earth, scientists want people of many
languages to be able to recognize it.

Politicians and military notables have to be dead a while to get their
name on a space rock.

"We have guidelines against this, until at least 100 years after the
individual has died, but the names keep coming in," A'Hearn said. "In
recent times these have included anti-Nazi activists and prominent
politicians who have been active in civil rights. The basis of
disallowing them is that even though most of us would agree that the
person is deserving of honor, there are just so many cases near the
borderline in which some would consider the name honorable while
others would consider it offensive, that we just keep a rigid guideline."

But what about Jerry Garcia, and especially what about this asteroid
named Zappafrank? Marsden said both were chosen after campaigns
organized by individuals. He said the push for Zappafrank resulted in
more than 200 e-mails. Aha! So we can name an asteroid?

"After 10 years have elapsed (from the time of discovery), it's fair
game and almost anybody can propose a name," Marsden said.

So we checked. Madonna is not on the list. Elvis in not on the list.
Even Ricky Martin has been overlooked, leading us to wonder if
Marsden considered the likely flood of e-mail requests that will come
now that the real truth behind the asteroid naming convention is out of
the bag. ez

Copyright 1999, Explorezone

==================
(5) YAWN, YAWN: LATEST ROCKY HORROR TALL STORY IS ANOTHER   
      SLOWCOACH 
 
From Jeremy Tatum <UNIVERSE@uvvm.UVic.CA>

From Weekly World News, October 26 (sic), picked up at my local
friendly supermarket check-out.
 
                GIANT ASTEROID THREATENS EARTH!
         Space rock has 87% chance of hitting THIS planet!
          GIANT ASTEROID MAY SLAM INTO EARTH THIS JANUARY
     Nuclear weapons will NOT be able to stop it, warn experts!


Washington - Unless a miracle occurs in the next two months, an
asteroid the size of Rhode Island could strike Earth just after New
Year's day - and the impact will kill a staggering 3 billion people and
virtually destroy civilization as we know it!
 
The asteroid, discovered in 1989, is moving at 134,000 mph. At the time
of its discovery, the space rock did not appear to pose a threat to our
planet.  But over the past 10 years, it has become clear that we are
directly in its path.  It has an 87% chance of striking Earth on Sunday
January 2 - the day after the turn of the century.
 
That's the shocking conclusion of a team of seven scientists who have
met secretly with President Bill Clinton at least five times since
October 1, when it became clear that the collision seems inevitable.
 
Their task:  To determine what, if anything, can be done to avoid the
approaching disaster.  The results are not heartening. The most
brilliant minds - not only American but international - have been
unable to see any way to divert the giant space rock. White House
officials remain tight-lipped on the subject, fearing worldwide panic.
But one scientist, noted astronomer Dr Robert Clemson, believes it's
time to speak out.  "Clinton has instituted a top-secret plan and
appropriated $3.2 billion that the Pentagon and NASA say they will need
to shoot the asteroid out of the sky with nuclear weapons", Dr Cremson
said. "The trouble is, most scientists now agree that destroying the
asteroid or altering its course would be a million-to-one longshot, if
not a total impossibility. We have run computer-simulated tests and the
plan has failed dismally. Military officials are proceeding with the
plans to modify land-based nuclear weapons for an assault on the
asteroid because at this point it's the only plan anyone has come up
with.  But if we don't come up with something better - and fast -
chances are that life as we know it will be over" ."
 
Dr Cremsom says that he doesn't like to speculate on what will happen
if the asteroid strikes, but says there are two - dismal - scenarios. 
"The impact could shatter a giant section of Earth into a million
pieces, sending fragments hurtling into space", he said. "Billions will
die.  In the second scenario, the Earth will remain intact but the
force of the blow will kick enough dirt and dust into the atmosphere to
block out the sun, plunging us into a devastating deep-freeze similar
to the one believed to have killed off the dinosaurs 65 million years
ago."
 
So what can be done?  Dr Cremson recommends:
 
* If you have a bomb shelter left over from the 1960s, use it. If not,
  build one.
 
* Stock the shelter with nonperishable foods and plenty of water.
 
* If you don't have a shelter or can't afford to build one, you can
  outfit a basement or other room in your home for survival.  These
  areas won't be as effective as bomb shelters but they will be better
  than nothing.
 
* Gasoline or kerosene heaters will be extremely valuable as will
  wood to burn for cooking.
 
* And - perhaps most important of all - pray.  At this point, prayer
  may be the only thing that can avert this world-shattering
  catastrophe.
 
                 -------------------------------
 
And in case the asteroid should miss, we have another problem,
because the same issue of Weekly World News carries an article pointing
out that THE EARTH'S ROTATION IS SLOWING...AND MAY STOP ALTOGETHER.
Apparently it will come to a complete halt within 30 years.

===================
(6) UNUSUAL ORIGIN OF EUROPE'S LARGEST VOLCANO EXPLAINED

From Stanford News Service <stanford.report@forsythe.stanford.edu>

10/20/99

CONTACT:  Kathleen O`Toole, News Service (650) 725-1939;
                    e-mail kathleen.otoole@stanford.edu
COMMENT: Amos Nur, Geophysics (650) 723-9526
                    e-mail nur@pangea.stanford.edu

Mt. Etna, Europe`s highest, active volcano, has perplexed geophysicists
for years because it sits alone on the east coast of Sicily and spews
out lava that is chemically different from that of volcanoes caused by
the clashing of Earth`s tectonic plates.

Now Amos Nur of Stanford`s Geophysics Department and his former
student, Zohar Gvirtzman of the Institute of Earth Sciences at Hebrew
University of Jerusalem, propose an explanation for Etna in the Oct. 21
issue of the journal Nature.

Etna`s voluminous flows are the consequence of "slab rollback" where a
chunk of the Tyrrhenian plate broke off, rapidly opening a narrow
basin of magma that is sucked up from under the nearby African plate,
they say. This magma, or pool of viscous asthenosphere, is what has
erupted periodically from Etna over thousands of years. Mt. Vesuvius on
the other side of the Tyrrhenian Sea from Etna may be the same sort of
volcano, Nur adds, but that awaits further research.

Most of the earth`s volcanoes are situated over subduction systems -
places where one tectonic plate is sliding under the other. As the
whole system converges, partial melting occurs in the wedge between the
plates and is spewed through faults or cracks in the Earth`s crust.

Mt. Etna sits near but not on a subduction zone where three plates of
Africa and Europe are converging. Sicily was once part of Corsica and
Sardinia but separated, and the Tyrrhenian Sea opened up, geologists
believe. The geologic record suggests the opening of a basin between
the plates occurred very fast - at centimeters per year, and such
basins have been a puzzle for a long time in plate tectonics,`` Nur
says. "We asked why does something extend in the middle of
convergence?"

Nur and Gvirtzman first calculated the suspected thickness of the solid
upper mantle of the earth`s crust, known as the lithosphere, based on
the observed surface elevations of the region and what they knew about
the Earth`s crustal structure and buoyancy. Using a three-dimensional
mechanical model of the three plates involved and a fair amount of
recorded geologic data on Etna, they determined that a localized
disturbance could release a narrow part of the subducted plate so that
it would sink fast, creating what they call a "back-arc" basin. This
basin would be shallow enough to permit a sideways flow of magma, which
would be sucked out of the basin as the descending slab migrates into
the earth`s mantle, leaving low pressure behind it.

"A plate with some type of topography that doesn`t want to subduct
could cause that type of tear," in the plate, Nur said. "The tear
allows the viscous material underneath to rise from the sides, and you
have a passageway to the surface."

Etna`s numerous, voluminous eruptions show that it has a large
underground fuel tank. Aeschylus wrote about eruptions occurring in 475
B.C. The most devastating eruptions occurred in 1169 and 1669 and the
most recent, in 1971. The volcano is now about 93 miles in
circumference and has 260 lesser craters on its slopes.

Perhaps 15 or 20 other volcanoes in the world have similar origins, Nur
says, as they seem to defy the more conventional plate tectonics
model. This may be a case of "the exception proving the rule," he says.
"I`ve never really known what that phrase meant, but I`m taking it to
mean that one way to learn a lot more about plate tectonics is by
understanding these exceptions."

Downloadable illustrations, named Etna 1 and Etna 3 may be found at
ftp://36.15.0.2271/images

-By Kathleen O`Toole-

================
(7) A PHYSICAL MODEL OF ASTEROID GEOGRAPHOS

R.S. Hudson*), S.J. Ostro: Physical model of asteroid 1620 Geographos
from radar and optical data. ICARUS, 1999, Vol.140, No.2, pp.369-378

*) WASHINGTON STATE UNIVERSITY,SCH ELECT ENGN & COMP
   SCI,PULLMAN,WA,99164

We develop a physical model of asteroid 1620 Geographos using Goldstone
delay-Doppler radar images obtained August 1994 (Ostro et al. 1996,
Icarus 121., 46-66) with resolution as fine as 75 m, and optical
lightcurves obtained in 1969, 1983, and 1993-1994 (Magnusson et al.
1996, Icarus 123, 227-244). The data set admits a geometric ambiguity
that precludes a unique model. Within this constraint, our model has
maximum dimensions of (5.0, 2.0, 2.1) +/- 0.15 km and a volume of less
than or equal to 8.8 km(3), equivalent to a sphere of less than or
equal to 2.56 km diameter. The radar equivalent spherical albedo is
greater than or equal to 0.12. The photometric solution provides Hapke
parameters w greater than or equal to 0.22, g = -0.34 +/- 0.10, and
<(theta)over bar> = 25 +/- 10 degrees with assumed values h = 0.02 and
B-0 = 1.32. The spin state solution does not differ significantly from
that of Magnusson et al, having lambda = 55 +/- 6 degrees, beta = -46
+/- 4 degrees, and P = 5.2233270 +/- 0.00000072 h. We identify seven
main features in the delay-Doppler images and their corresponding
locations on the model. (C) 1999 Academic Press.

=================
(8) RADAR OBSERVATIONS OF 37 MAINBELT ASTEROIDS

C. Magri*), S.J. Ostro, K.D. Rosema, M.L. Thomas, D.L. Mitchell,
D.B. Campbell, J.F. Chandler, I.I. Shapiro, J.D. Giorgini, D.K.
Yeomans: Mainbelt asteroids: Results of Arecibo and Goldstone radar
observations of 37 objects during 1980-1995. ICARUS, 1999, Vol.140,
No.2, pp.379-407

*) UNIVERSITY OF MAINE,39 HIGH ST,PREBLE HALL,FARMINGTON,ME,04938

We report detailed results of Arecibo and Goldstone radar observations
of 30 mainbelt asteroids (MBAs) during 1980-1995, In addition to
estimates of radar cross section, radar albedo, and circular
polarization ratio, we obtain new constraints on pole direction for
several asteroids, with those for 21 Lutetia being particularly
restrictive. We carry out statistical analyses of disk-integrated
properties (radar albedo and polarization ratio) of all 37
radar-observed MBAs. M asteroids seem to have higher radar albedos and
a wider range of albedos than do asteroids from the other taxonomic
classes; there is no evidence that C and S MBAs have different albedo
distributions; and there is some suggestion, worthy of future study,
that primitive B, F, G, and P asteroids are not as radar-bright as C
and S objects. There is no statistically significant evidence that
different taxonomic classes have different polarization ratio
distributions, despite suggestions to the contrary based on visual
inspection of these distributions. The similarity between the C and S
albedo distributions implies similar near-surface regolith bulk
densities. The hypothesis of ordinary chondritic composition for the
S-class asteroids is reasonably consistent with the radar data,
provided that these asteroids have typical lunar porosities.
Nevertheless, it is possible that some of these targets have
high-porosity regoliths of stony-iron composition. Our M-class sample
presumably contains both metallic objects (such as 216 Kleopatra and,
probably, 16 Psyche) and less metallic objects. (C) 1999 Academic
Press.

===============================
(9) WHY ASTEROID 1997 XF11 WAS POTENTIALLY HAZARDOUS

A. Milani*) & G.B. Valsecchi: The asteroid identification problem -
II. Target plane confidence boundaries. ICARUS, 1999, Vol.140, No.2,
pp. 408-423

*) UNIVERSITY OF PISA,DIPARTIMENTO MATEMAT,VIA BUONARROTI 2,I-56127
   PISA,ITALY

The nominal orbit solution for an asteroid/comet resulting from a least
squares fit to astrometric observations is surrounded by a region
containing solutions equally compatible with the data, the confidence
region. If the observed are is not too short, and for an epoch close to
the observations, the confidence region in the six-dimensional space of
orbital elements is well approximated by an ellipsoid. This uncertainty
of the orbital elements maps to a position uncertainty at close
approach, which can be represented on a Modified Target plane (MTP), a
modification of the one used by Opik. The MTP is orthogonal to the
geocentric velocity at the closest approach point along the nominal
orbit. In the linear approximation, the confidence ellipsoids are
mapped on the MTP into concentric ellipses, computed by solving the
variational equation. For an object observed at only one opposition,
however, if the close approach is expected after many revolutions, the
ellipses on the MTP become extremely elongated, therefore the linear
approximation may fail! and the confidence boundaries on the MTP, by
definition the nonlinear images of the confidence ellipsoids, may not
be well approximated by the ellipses. In theory the Monte Carlo method
by Muinonen and Bowell (1993, Icarus 104, 255-279) can be used to
compute the nonlinear confidence boundaries, but in practice the
computational load is very heavy. We propose a new method to compute
semilinear confidence boundaries on the MTP, based on the theory
developed by Milani (1999, Icarus 137, 269-292) to efficiently compute
confidence boundaries far predicted observations. This method is a
reasonable compromise between reliability and computational load, and
can be used for real time risk assessment. These arguments can be
applied to any small body approaching any planet, but in the case of a
potentially hazardous object (PHO), either an asteroid or a comet whose
orbit comes very close to that of the Earth, the application is most
important. We apply this technique to discuss the recent case of
asteroid 1997 XF11, which, on the basis of the observations available
up to March 11, 1998, appeared to be on an orbit with a near miss of
the Earth in 2028. Although the least squares solution had a close
approach at 1/8 of the lunar distance, the linear confidence regions
corresponding to acceptable size of the residuals are very elongated
ellipses which do not include collision; this computation was reported
by Chodas and Yeomans. In this paper, we compute the semilinear
confidence boundaries and find that they agree with the results of the
Monte Carlo method, but differ in a significant way from the linear
ellipses, although the differences occur only far from the Earth. The
use of the 1930 pre-discovery observations has confirmed the
impossibility of an impact in 2028 and reduces the semilinear
confidence regions to subsets of the regions computed with less data,
as expected. The confidence regions computed using the linear
approximation, on the other hand, do not reduce to subsets of the
regions computed with less data. We also discuss a simulated example
(Bowell and Muinonen 1992, Bull. Am. Astron. Soc. 24, 965) of an Earth-
impacting asteroid. In this hypothetical case the semilinear confidence
boundary has a completely different shape from the linear ellipse, and
indeed for orbits determined with only few weeks of observational data
the semilinear confidence boundary correctly includes possible
collisions, while the linear one does not. Free software is available
now, allowing everyone to compute target plane confidence boundaries as
in this paper; in case a new asteroid with worrisome close approaches
is discovered, our method allows to quickly perform an accurate risk
assessment. (C) 1999 Academic Press.

=================
(10) COMETARY TRAVEL: FROM INTERSTELLAR SPACE TO EARTH'S OCEANS

D. Laufer*), G. Notesco, A. Bar Nun: From the interstellar medium to
Earth's oceans via comets - An isotopic study of HDO/H2O. ICARUS, 1999,
Vol.140, No.2, pp.446-450

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

The isotopic enrichment of HDO over H2O when water vapor freezes into
ice at 60-170 K was studied experimentally. No such enrichment was
detected (1.003-1.007 in the 95% confidence interval). Thus HDO cannot
be enriched when ice is formed by freezing of water vapor. The very
similar D/H ratio in the water of Comets Halley, Hyakutake, and
Hale-Bopp(similar to 3 x 10(-4)) is 10-20 times larger then the D/H
ratio in the solar nebula. Therefore the cometary water had to
originate in a giant molecular cloud, where the HDO is enriched by ion-
molecule reactions. We cannot determine whether the ice grains which
agglomerated into these comets were formed in a similar to 50 K warm
clump in the giant molecular cloud and settled intact to the solar
nebula or sublimated and refroze in the similar to 50 K Uranus-Neptune
region. The HDO/H2O ratio in Earth's oceans suggests that the water was
delivered by both comets and rocky material formed in Earth's region of
the solar nebula. (C) 1999 Academic Press.

==============
(11) COMETS, ICE & ORGANIC MOLECULES

R.L. Hudson: Laboratory studies of the formation of methanol and other
organic molecules by water plus carbon monoxide radiolysis: Relevance
to comets, icy satellites, and interstellar ices. ICARUS, 1999,
Vol.140, No.2, pp.451-461

ECKERD COLLEGE,DEPT CHEM,ST PETERSBURG,FL,33733

Radiation processing of cometary, planetary, and interstellar ices has
been investigated by irradiating mixtures of H2O and CO near 16 K with
0.8-MeV protons. IR spectroscopy and isotopic substitution showed that
H and OH, from H2O, added to CO to form HCO, H2CO, HCOOH, and CH3OH. A
values (integrated spectral absorbances) for HCOOH and HCO trapped in
H2O ice were measured for the first time. These new values, along with
published A's for H2CO and CH3OH, were used to calculate radiation
yields (G values) and conventional percentage yields. Significantly
higher percentage yields of HCOOH and CH3OH were observed, compared to
previous solid-state H2O + CO experiments. This suggests that radiation
processing may help explain the discrepancy between the observed
gas-phase abundances of small organic molecules and the abundances
predicted by current theoretical models and previous laboratory
experiments. In contrast to previous experiments on one-component ices,
no spectral evidence for long-chain molecules was found in the present
work. This demonstrates that ice composition is a critical factor in
applying laboratory results to cometary, icy satellite, and
interstellar ices. (C) 1999 Academic Press.

==========
(12) ORBITAL HISTORY OF COMET P/LAGERKVIST (1996 R2)

G. Hahn*) & C.I. Lagerkvist: The recent orbital history of periodic
Comet P/Lagerkvist (1996 R2). ICARUS, 1999, Vol.140, No.2, pp.462-463

*) DLR,INST PLANETARY EXPLORAT,RUDOWER CHAUSSEE 5,D-12489
   BERLIN,GERMANY

Numerical integrations of 99 orbits centered on that of Comet
P/Lagerkvist (P/1996R2) and of the original orbit were made 70
years backward in time and 200 years into the future. The
integrations show that this comet, belonging to the quasi-
Hildas (G. Tancredi et al., 1990, Astron. Astrophys. 239, 375-
380), most likely has been transferred into its present orbit
as recently as 1990, ending a phase of temporary satellite
capture by Jupiter. The future orbital evolution indicates a
stable period for about 100 years, when another close encounter
with Jupiter may Lead to further drastic changes. (C) 1999
Academic Press.

============
(13) POLARIMETRY OF ASTEROID 2100 RA-SHALOM

N.N. Kiselev*), V.K. Rosenbush, K. Jockers: Polarimetry of asteroid
2100 Ra-Shalom at large phase angle. ICARUS, 1999, Vol.140, No.2,
pp.464-466

*) KHARKOV AM GORKII STATE UNIVERSITY, ASTRON OBSERV,UA-310077
   KHARKOV, UKRAINE

Two-color polarimetric observations of C-type asteroid 2100 Ra-Shalom
were conducted when its phase angle was 59.7 degrees. No other C-type
asteroid has so far been observed at such a large phase angle. We
relate the new data point to the available data on C-type asteroids and
on Phobos and Deimos and compare the phase curve of these objects with
the phase curve of dusty comets. The observed polarization of Ra-Shalom
is slightly lower than expected from a common curve of the other C-type
asteroids and the martian moons. We conclude that this may be caused by
the immature regolith on the surface of this small asteroid. (C) 1999
Academic Press.

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