PLEASE NOTE:


*

CCNet DIGEST, 25 February 1999
--------------------------------------------------------------
The fully indexed archive of the CCNet, from February 1997 on,
can be found at http://abob.libs.uga.edu/bobk/cccmenu.html
---------------------------------------------------------------


       QUOTE OF THE DAY
       "The most likely explanation is that [the object] is a chip
       off the Moon" (Brian Marsden, in New Scientist 27 February)


(1) THERE'S A MYSTERY OBJECT NOT FAR FROM THE EARTH
    Andrew Yee <ayee@nova.astro.utoronto.ca>

(2) LEONID MAC WORKSHOP
    Peter Jenniskens <peter@max.arc.nasa.gov>

(3) MORE ON ASTEROID 8793 THOMASMULLER
    Andrew Yee <ayee@nova.astro.utoronto.ca>

(4) GENE SHOEMAKER'S POSTHUMOUS PAPER ON THE CONTROVERSIAL
    AUSTRALITES OF PORT CAMPBELL
    Eugene M. Shoemaker and H. Ralph Uhlherr, U.S. Geological Survey

(5) MARTIAN METEORITE ALH 84001 & THE IMPLICATIONS FOR SIGNS OF LIFE
    C. K. Shearer et al., University of New Mexico

(6) THE AGE OF THE SOUTH RAY LUNAR IMPACT CRATER
    Otto Eugster, University of Bern

(7) GEOCHEMICAL SIGNALS OF THE MJOELNIR IMPACT CRATER
    Henning Dypvik and Moses Attrep, University of Oslo

(8) THE FUSION CRUSTS OF STONY METEORITES
    Matthew J. Genge and Monica M. Grady,The Natural History Museum

(9) IMPACT SHOCK MELTING AT THE RIES CRATER, GERMANY
    Gnther Graup, Max-Planck-Institut fr Chemie

(10) THE INTERNAL STRUCTURES AND DENSITIES OF ASTEROIDS
     Lionel Wilson et al., University of Hawaii at Manoa

=======================
(1) THERE'S A MYSTERY OBJECT NOT FAR FROM THE EARTH

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

New Scientist

UK CONTACT -- Claire Bowles, New Scientist Press Office, London
Tel: 44-171-2751 or emailclaire.bowles@rbi.co.uk

US CONTACT -- Barbara Thurlow, New Scientist Washington Office
Tel: 202-452-1178 or email newscid@idt.net

EMBARGOED FOR RELEASE: February 24, 1999, 2 p.m. EST

There's A Mystery Object Not Far From The Earth

A CHUNK of rock some 50 metres across has been found circling the Sun
in an orbit close to Earth's. The object, which was discovered on 10
February by an automated asteroid-hunting telescope in New Mexico
called Linear, is probably a chip off the Moon, say astronomers.

After six nights of observations, Gareth Williams of the
Harvard-Smithsonian Center for Astrophysics in Cambridge,
Massachusetts, calculated that it circles the Sun every 1.09 years. Its
nearly circular orbit is just nine million kilometres farther from the
Sun than the Earth's.

The object's orbit is extremely unusual. Comets and asteroids that
cross the Earth's orbit normally have eccentric orbits. There is only
one asteroid-like object, called 1991 VG, that has a similar orbit to
that of the Earth. When it was discovered, eight years ago, astronomers
thought it might be a spacecraft that had escaped the Earth's gravity.

The new object, designated 1999 CG9, is considerably brighter than 1991
VG, indicating that it is much larger. Brian Marsden of
Harvard-Smithsonian estimates it to be between 30 and 50 metres across,
too big to be the final stage of a rocket. "The most likely explanation
is that it's a chip off the Moon," he says.

Although the Moon is small, its low gravity makes it easy to blast
debris into orbit. "We have seen there are chips off the Moon," says
Marsden. "Twelve small lunar meteorites have been found on the Earth."

"If you can shoot things off the Moon, they would continue to go around
the Sun in an orbit not too different from the Moon," Marsden adds. So
far, astronomers do not know the object's composition, which could cast
light on its origins. However, the astronomers hope to analyse the
rock's spectrum to see how it compares with that of the Moon.

Author: Jeff Hecht, Boston
New Scientist issue 27th Feb 99

PLEASE MENTION NEW SCIENTIST IF YOU USE THIS ARTICLE - THANK YOU

=======================
(2) LEONID MAC WORKSHOP

From Peter Jenniskens <peter@max.arc.nasa.gov>

Second announcement

Leonid MAC Workshop / NASA-Ames Research Center / April 12-15, 1999
-------------------------------------------------------------------
 
This is to remind you that the deadline for registration for the
Leonid MAC Workshop is coming up on:
                                         March 1.

Automatic registration: http://leonid.arc.nasa.gov/workshops/

Purpose of the workshop is to review the first results of the 1998
Leonid campaigns, both ground-based and airborne campaigns, discuss the
relevant science, and make recommendations for the upcoming campaigns
in November 1999 (in time to help the necessary preparations).

Researchers from the fields of meteor physics, atmosphere science, 
planetary astronomy, and astrobiology are invited to attend, as well as
those concerned with the satelite impact hazard of meteor storms. The
meeting is international and open to amateurs.

We anticipate an exciting 3-day meeting that is very interdisciplinary
in nature and that will set the stage for the organisation of next
year's campaigns, our last chance to witness a meteor storm in our
lifetime.

Sincerely,

Dr. Peter Jenniskens
LOC Leonid MAC Workshop (chair)

==================
(3) MORE ON ASTEROID 8793 THOMASMULLER

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

European Space Agency
Press Information Note No 02-99
Paris, France 17 February 1999

Asteroid named after ESA astronomer, as a reward for his discoveries

If you want an asteroid named after you, make a valuable scientific
contribution to the study of these rocky mini-planets of the Solar
System. That is what 32 year old ESA astronomer Thomas Mueller did,
and now the International Astronomical Union has rewarded him by
giving the name 'Thomasmuller' to asteroid number 8793. "It's been a
great surprise", Mueller said. He is part of the team working at
ESA's Infrared Space Observatory (ISO) Data Centre at Villafranca,
Spain, and his research is mostly based on ISO data (see footnote on
ISO).

Mueller's scientific work has proved to be crucial in describing the
physical properties of an asteroid. But that is not all: it will
improve the performance of the next millennium's infrared space
telescopes, since these instruments will be able to check the
accuracy of their observations by using the new data on asteroids.
Mueller has therefore shown that asteroids can be very useful tools
for astronomy.

"Many astronomers tend to look at asteroids as boring objects. I've
always disagreed. Take the infrared sky: if our eyes were able to see
in the infrared, and of course if we could get rid of the Earth's
atmosphere which is opaque to most infrared radiation, we would see
hundreds of asteroids sparkling and very few stars. I love this
idea", he says.

Thomas got his reward for his dedication on 10 December, when his
collaborator Johan Lagerros, of the Astronomiska Observatoriet in
Uppsala, Sweden, surprised him with the news about "Thomasmuller". "I
didn't expect it, I didn't even know I had been proposed!", the ESA
astronomer exclaimed.

The proposal to the International Astronomical Union (IAU) came from
astronomer Claes-Ingvar Lagerkvist, also at the Astronomiska
Observatoriet, who is entitled to name the 47 asteroids he has
discovered throughout his life. Asteroid 8793 was one of them. The
name "Thomasmuller" was immediately accepted by the IAU.

There are at present almost 10,000 asteroids with a known orbit, of
which a few hundred are named after a living astronomer. (See "How to
name a minor planet" at
http://cfa-www.harvard.edu/iau/info/HowNamed.html). The orbit is the
minimum every discoverer needs to know to get an object catalogued,
and often it is all that is known about an asteroid. That is the case
with "Thomasmuller".

"It puzzles me the fact that we know nothing about "Thomasmuller" but
its orbit and luminosity, although it was discovered in 1979 and it
has been observed 43 more times", Mueller confessed. (see also
Official homepage of asteroid 'Thomasmuller':
http://www.astro.uu.se/planet/asteroid/astdiv/8793.html)

A hard task

It has been precisely this scarce knowledge on asteroids that has
added value to the work of Mueller and Lagerros. They have developed
a very accurate model to predict the brightness of asteroids at any
given time, a type of data that will be useful in the calibration of
future infrared space telescopes such as ESA's FIRST (due for launch
in 2007).

Predicting the brightness of an asteroid is a very hard task.
Asteroid sizes range from a few to one thousand kilometres. They have
very irregular shapes and spin quickly, approximately once every five
to ten hours. Their infrared brightness is caused by heating due to
sunlight, and this heating strongly depends on the surface material
and the surface structures, like craters, and the irregular shape.
So, to know the infrared brightness of an asteroid at any given time,
one has to find out which "face" it is showing to the Sun and to the
observer, as well as its internal thermal behaviour and its distance
to the Earth.

The researchers set up a large database with 650 individual
observations, including those from the spectrophotometer ISOPHOT on
board ISO, of the "top-ten" main asteroids. They were then able to
model the egg-like shape of the ten asteroids, and to predict exactly
how much energy they would be emitting at any given time. They could
then derive the brightness with a very high accuracy.

The model has been tested against ISO observations. As Mueller
explains, "We compared hundreds of observations and predictions one
by one, and all test cases confirmed the quality of our model. We can
now predict flux densities from mid-infrared to submillimetre
wavelengths for all ten asteroids, including thermal and lightcurve
effects."

A further application of this work is that it is now possible to
infer diameters and albedos (the ability to reflect light) for all
asteroids observed by the infrared with unprecedented accuracy.

The model applications are not only limited to ISO observations: all
infrared measurements from ground, airborne or space telescopes can
now be used to improve our knowledge about asteroids.

The description of the model and the technique has been published in
the scientific journal "Astronomy and Astrophysics" ("Asteroids as
far-infrared photometric standards for ISOPHOT", by T.G. Mueller and
J.S.V. Lagerros, Vol 338, p340-352, 1998).

Footnote on ISO

ISO was put into orbit in November 1995, by an Ariane 4 launcher from
the Guiana Space Centre, Europe's Spaceport in Kourou, French Guiana.
As an unprecedented observatory for infrared astronomy, able to
examine cool and hidden places in the Universe, ISO successfully made
almost 30,000 scientific observations. These are now available to the
scientific community via the archive at the ISO Data Centre (IDC),
located at ESA's Satellite Tracking Station in Villafranca (Spain).

For more information and ISO pictures:

Thomas Mueller at the ISO Data Centre at Villafranca (Spain):
Tel: +34 91 8131100
e-mail: tmueller@iso.vilspa.esa.es

ESA Public Relations Division:
Tel: +33(0)1.53.69.71.55   Fax: +33(0)1.53.69.76.90

Visit the ISO web sites (hi-res images available) at:
http://www.iso.vilspa.esa.es
http://sci.esa.int/iso

==================
(4) GENE SHOEMAKER'S POSTHUMOUS PAPER ON THE CONTROVERSIAL
    AUSTRALITES OF PORT CAMPBELL

Eugene M. Shoemaker* and H. Ralph Uhlherr: Stratigraphic relations of
australites in the Port Campbell embayment, Victoria. METEORITICS &
PLANETARY SCIENCE 34, May (1999)

*) U.S. Geological Survey and Lowell Observatory, Flagstaff, Arizona
86001, USA; e-mail address: cshoemaker@flagmail.wr.usgs.gov

In the Port Campbell Embayment of Victoria, australites have been found
in situ in channel deposits of the Hanson Plain Sand of Pliocene and
Pleistocene age. The large majority of the australites, however, occur
as a lag deposit at the basal contact of the Sturgess Sand of late
Pleistocene and Holocene age and are spatially correlated with
ferruginous sandstone clasts that are derived from the Hanson Plain
Sand. Some of the tektites are imbedded in or bonded to the ferruginous
sandstone clasts, but most are found as individual tektite fragments. A
few percent of the tektites have nearly perfectly preserved, complete
aerodynamically shaped forms. The sandstone clasts and associated
tektites have been reworked from the much older underlying Hanson Plain
and have been locally concentrated in the lag deposit. Some tektites
also occur at higher levels in the Sturgess Sand, almost invariably in
association with stone flakes, exotic stones transported by the
aborigines, and, locally, with middens of mollusc shells.
Circumstantial evidence indicates that the aborigines transported the
tektites found in the upper part of the Sturgess, particularly at
Stanhope Bay. As Port Campbell australites unequivocally occur in
strata much older than the late Pleistocene and Holocene Sturgess,
there is no longer any conflict between the apparent stratigraphic age
of the tektites and the middle Pleistocene ages obtained by various
chronometric methods. Meteoritical Society, 1999.

===================
(5) MARTIAN METEORITE ALH 84001 & THE IMPLICATIONS FOR SIGNS OF LIFE

C. K. Shearer*), L. A. Leshin and C. T. Adcock: Olivine in Martian
meteorite ALH 84001: Evidence for a high-temperature origin and
implications for signs of life. METEORITICS & PLANETARY SCIENCE 34,
May (1999)

*) Institute of Meteoritics, Department of Earth and Planetary
Sciences, University of New Mexico, Albuquerque, New Mexico 87131-1126;
e-mail address: chearer@unm.edu

Olivine from martian meteorite ALH 84001 occurs as clusters within
orthopyroxene adjacent to fractures containing disrupted carbonate
globules and feldspathic shock-glass. The inclusions are irregular in
shape and range in size from approximately 40 m to sub-micron. Some of
the inclusions are elongate and boudinage-like. The olivine grains are
in sharp contact with the enclosing orthopyroxene, and often contain
small inclusions of chromite. The olivine exhibits a very limited range
of composition from Fo65 to Fo66 (n= 25). The (18O values of the olivine
and orthopyroxene analyzed by ion microprobe range from +4.3 to +5.3‰
and are indistinguishable from each other within analytical uncertainty.
The mineral chemistries, oxygen isotopic data, and textural
relationships indicate that the olivine inclusions were produced at a
temperature greater than 800C. It is unlikely that the olivines formed
during the same event that gave rise to the carbonates in ALH 84001,
which have more elevated and variable (18O values, and were probably
formed from fluids that were not in isotopic equilibrium with the
orthopyroxene or olivine. The reactions most likely instrumental in the
formation of olivine could be either the dehydration of hydrous
silicates that formed during carbonate precipitation or the reduction of
orthopyroxene and spinel. If the olivine was formed by either reaction
during a post-carbonate heating event, the implications are profound
with regards to the  interpretations of McKay et al. (1996). Due to the
low diffusion rates in carbonates, this rapid, high-temperature event
would have resulted in the preservation of the fine-scale carbonate
zoning, while partially devolatilizing select carbonate compositions on
a sub-micron scale (Brearley, 1998). This may have resulted in the
formation of the minute magnetite grains that McKay et al (1996)
attributed to biogenic activity. Meteoritical Society, 1999.

=========================
(6) THE AGE OF THE SOUTH RAY LUNAR IMPACT CRATER

Otto Eugster: Chronology of dimict breccias and the age of South Ray
crater at the Apollo 16 site. METEORITICS & PLANETARY SCIENCE 34, May
(1999)

Physikalisches Institut, University of Bern, Sidlerstrasse 5, 3012
Bern, Switzerland; e-mail address: eugster@phim.unibe.ch

We report the noble gas isotopic abundances of five dimict breccias and
one cataclastic anorthosite that were collected at the Apollo 16
landing site. Orbital and surface photographs indicate that rays from
South Ray crater, an almost 1 km wide young crater in the Cayley plains,
extend several km from their source into the area that was sampled by
the Apollo 16 mission. Previous studies have shown that South Ray
crater formed 2 Ma ago and that a large number of rocks might originate
from this cratering event. Based on cosmic-ray produced nuclei we find
that the six rocks investigated in this work yield the same lunar
surface exposure age. Using literature data we recalculate the exposure
ages of additional 16 rocks with suspected South Ray crater origin and
obtain an average exposure age of 2.010.10Ma. In particular, all nine
dimict breccias, a type of rock essentially restricted to the Apollo-16
area consisting of anorthosite and breccia phases, dated until now
yield an average ejection age of 2.060.17 Ma. We conclude that they
must originate from the Cayley formation or from bedrock underlying the
Cayley plain. We determined the gas retention ages for the dimict
breccias based on the 40K-40Ar and U,Th-136Xe dating methods: rock
64425 yields a 40K-40Ar age of 3.96 Ga and rock 61016 a U,Th-136Xe age
of 3.97 Ga. These results, together with 39Ar-40Ar ages, obtained by
other workers for rocks 64535 (3.98 Ga) and 64536 (3.97 Ga) show that
the dimict breccias formed 3.97 Ga ago. Meteoritical Society, 1999.

==================
(7) GEOCHEMICAL SIGNALS OF THE MJOELNIR IMPACT CRATER

Henning Dypvik*) and Moses Attrep, Jr.: Geochemical signals of the Late
Jurassic, marine Mjlnir impact. METEORITICS & PLANETARY SCIENCE 34,
May (1999)

*) Department of Geology, University of Oslo, P.O.Box 1047, Blindern,
N-0316 Oslo, Norway; e-mail address: henning.dypvik@geologi.uio.no

Of the only seven submarine impact craters that have been found
globally, the Mjlnir Crater is one of the best preserved and retails
crater and ejecta. Geochemical studies (organic pyrolysis: Rock Eval,
major elements, Co, Cr, Ir, Ni, Pb, Rb, Sr, Th, U, V, Zr, Y) of the IKU
(Institute for Petroleum Research) core 7430/10-U-01, which is located
about 30 km north-northeast of the crater-rim show gradual
establishment of anoxic sea floor conditions through the late Jurassic.
These poorly ventilated water conditions were overturned due to the
Mjlnir impact event. Waves and currents transported impact glass,
which is now partly weathered to smectite, into the depositional area
where the drillhole is located. The succeeding crater collapse
transported impact material (e.g., shocked quartz and iridium) from the
crater rim and deeper levels to the core site. Normal marine
depositional conditions were established a short time after the crater
collapsed. Meteoritical Society, 1999.

===================
(8) THE FUSION CRUSTS OF STONY METEORITES

Matthew J. Genge*) and Monica M. Grady: The fusion crusts of stony
meteorites: Implications for the atmospheric reprocessing of
extraterrestrial materials. METEORITICS & PLANETARY SCIENCE 34, May
(1999)

*) Department of Mineralogy, The Natural History Museum, Cromwell Road,
London SW7 5BD, Great Britain; e-mail address: mjg@nhm.ac.uk

Fusion crusts develop on all meteorites during their passage of the
atmosphere but have been little studied. We have characterised the
textures and compositions of the fusion crusts of 73 stony meteorites
to identify the nature of meteorite ablation spheres (MAS) and
constrain the processes operating during the entry heating. Most
chondrite fusion crusts are porphyritic and dominated by olivine, glass
and accessory magnetite whereas those of the achondrites are mainly
glassy. Chondrite fusion crusts contain sulphide droplets with high-Ni
contents (>55 wt%). The partially melted substrate of OCs, underlying
the outer melted crusts, are dominated by silicate glass and composite
metal, sulphide and Cr-bearing Fe-oxide droplets that form as
coexisting immiscible liquids. Enstatite chondrite substrates contain
Cr- and Mn- bearing sulphides. The substrates of the CCs comprise a
sulphide-enriched layer of matrix. The compositions of melted crusts
are similar to those of the bulk meteorite. Differences from whole
rock, however, suggest that three main processes control their chemical
evolution: 1) the loss and reaction of immiscible Fe-rich liquids, 2)
mixing between substrate partial melts and bulk melts of the melted
crust, 3) the loss of volatile components by evaporation and degassing.
Data from fusion crusts suggests that MAS produced at low altitude have
compositions within the range of those of silicate-dominated cosmic
spherules (CSs) that are formed by the melting dust particles.
Meteorite ablation spheres produced at high altitude probably have
compositions very different from bulk meteorite and will resemble CSs
derived from coarse-grained precursors. Meteoritical Society, 1999.

==================
(9) IMPACT SHOCK MELTING AT THE RIES CRATER, GERMANY

Gnther Graup: Carbonate-silicate liquid immiscibility upon impact
melting, Ries Crater, Germany. METEORITICS & PLANETARY SCIENCE 34, May
(1999)

Max-Planck-Institut fr Chemie, Abteilung Geochemie, Postfach 3060,
D-55020 Mainz, Germany

The 24-km-diameter Ries impact crater in southern Germany is one of the
most studied impact structures on Earth. The Ries impactor struck a
Triassic to Upper Jurassic sedimentary sequence overlying Hercynian
crystalline basement. At the time of impact (14.87 0.36 Ma; Storzer
et al., 1995), the 350 m thick Malm limestone was present only to the S
and E of the impact site. To the N and W, the Malm had been eroded
away, exposing the underlying Dogger and Lias. The largest proportion
of shocked target material is in the impact melt-bearing breccia
suevite. The suevite had been believed to be derived entirely from the
crystalline basement. Calcite in the suevite has been interpreted as a
post-impact hydrothermal deposit. From optical inspection of 540 thin
sections of suevite from 32 sites, I find that calcite in the suevite
shows textural evidence of liquid immiscibility with the silicate
impact melt. Textural evidence of liquid immiscibility between silicate
and carbonate melt in the Ries suevite includes: carbonate globules
within silicate glass, silicate globules embedded in carbonate,
deformable and coalescing carbonate spheres within silicate glass,
sharp menisci or cusps and budding between silicate and carbonate melt,
fluidal textures and gas vesicles in carbonate schlieren, a quench
crystallization sequence of the carbonate, spinifex textured quenched
carbonate, separate carbonate spherules in the suevite
mineral-fragment-matrix, and inclusions of mineral fragments suspended
in carbonate blebs. Given this evidence of liquid immiscibility, the
carbonate in the suevite has, therefore, like the silicate melt a
primary origin by impact shock melting. Evidence of carbonate-silicate
liquid immiscibility is abundant in the suevites to the SW to E of the
Ries crater. The rarer suevites to the W to NE of the crater are nearly
devoid of carbonate melts. This correspondence between the occurrence
of outcropping limestones at the target surface and the formation of
carbonate melt, indicates that the Malm limestones are the source rocks
of the carbonate impact melt. This correspondence shows that the
suevites preserve a compositional memory of their source rocks. From
the regional distribution of suevites with or without immiscible
carbonate melts, it is inferred that the Ries impactor hit the steep
Albtrauf escarpment at its toe, in an oblique impact from the north.
Meteoritical Society, 1999.

====================
(10) THE INTERNAL STRUCTURES AND DENSITIES OF ASTEROIDS

Lionel Wilson, Klaus Keil*) and Stanley J. Love: Report: The internal
structures and densities of asteroids. METEORITICS & PLANETARY SCIENCE
34, May (1999)

*) Hawaii Institute of Geophysics and Planetology, University of
Hawai'i at Manoa, Honolulu HI 96822; e-mail address:
keil@kahana.pgd.hawaii.edu

Four asteroidal bodies (the martian satellites Phobos and Deimos and
the main-belt asteroids 243 Ida and 253 Mathilde) have now been the
subjects of sufficiently close encounters by spacecraft that the masses
and sizes and, hence, the densities of these bodies can be estimated to
~10%. All of these asteroids are significantly less dense than most
members of the classes of meteorites identified as being
compositionally most nearly similar to them on the basis of spectral
characteristics. We show that two processes can act, independently or
in concert, during the evolutionary histories of asteroids to produce a
low bulk density. One of these processes is the result of one or more
impact events and can affect any asteroid type, whereas the other can
occur only for certain types of small asteroids which have undergone
aqueous alteration. Meteoritical Society, 1999.

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