PLEASE NOTE:


*

CCNet DIGEST, 18 December 1998
------------------------------

(1) COSMIC LOVE GAME: HELP NAME THE CRATERS ON EROS
    (BUT NO SEX PLEASE, SAY TPS)
    Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>

(2) WHERE TO FIND FULL INFORMATION ON CASSINI RISK
    Dave Hostetter <davehostetter@linknet.net>

(3) I M O  S h o w e r  C i r c u l a r
    Rainer Arlt <100114.1361@compuserve.com>

(4) SIBLING SANDBLASTING AND THE SMOOTHNESS OF GASPRA AND IDA
    D.W. Hughes*) & I.P. Williams, UNIVERSITY OF SHEFFIELD

(5) COMPOSITIONAL VARIATION AND MIXING OF IMPACT MELT
    T.H. See et al., NASA, JOHNSON SPACE CTR

(6) THE K/T BOUNDARY & PLATINUM GROUP ELEMENTS
    Q.L. Hou et al., CHINESE ACADEMY OF SCIENCE

(7) THE PROBLEMS OF INTERPRETING PLATINIUM-GROUP ELEMENTS IN
    GEOCHEMISTRY
    I. McDonald, UNIVERSITY OF GREENWICH

(8) PRESERVATION OF EXTRATERRESTRIAL HELIUM IN MARINE LIMESTONES
    D.B. Patterson et al., CALTECH


========================
(1) COSMIC LOVE GAME: HELP NAME THE CRATERS ON EROS
    (BUT NO SEX PLEASE, SAY TPS)

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

Help name the Craters on Eros

The Planetary Society
http://planetary.org/news/hot-topics-name-eros.html

As NEAR approaches its target -- 433 Eros -- the mission team is faced
with the daunting challenge of naming more than 100 craters that may be
found on Eros and for which names will be useful, as when making
reference to unique features of geographic position. The team would
like a little help.

The NEAR team has asked Planetary Society members and others to suggest
crater names, which will later be submitted to the International
Astronomical Union (IAU) for official consideration. The selection
process will follow the strict rules laid down by the international
organization to ensure that the names chosen are appropriate and
worthy.

Once a planetary body's discoverer has selected a name, there follows a
theme for naming the geologic features such as craters. For example,
Gaspra, the first asteroid imaged by Galileo, was named for a resert in
the Crimea. Its craters are called after spas of the world. Galileo's
next asteroidal target, Ida, was named for a nymph who lived on the
shores of Crete. Its craters are called after caverns and grottos of
the world.

The name Eros suggests an obvious theme: love. The craters of Eros can
be named after famous lovers, legendary romantic locales, aspects of
love, and so on. (Please, no obscene or offensive names.)

You are invited to submit names for Eros' craters. Each suggestion
should be accompanied by a short explanation (50 words maximum) of why
the name is appropriate. Please
use a separate sheet of paper for each suggestion. Send
your entries to:

                              Names on Eros
                              The Planetary Society
                              65 N. Catalina Avenue
                              Pasadena, CA 91106
                              USA

A complete overview of the IAU's naming process is at:

http://wwwflag.wr.usgs.gov/USGSFlag/Space/nomen/nomen.html

=========================
(2) WHERE TO FIND FULL INFORMATION ON CASSINI RISK

From Dave Hostetter <davehostetter@linknet.net>

Dr. Peiser:

For those interested in NASA's viewpoint regarding the risk due to
Project Cassini, I recommend looking at the Cassini home page at
http://www.jpl.nasa.gov/cassini/.  The nuclear safety section is
extensive.

Dave Hostetter
Curator of the Planetarium
Lafayette (LA) Natural History Museum & Planetarium

=========================
(3) I M O  S h o w e r  C i r c u l a r

From Rainer Arlt <100114.1361@compuserve.com>

GEMINID Activity 1998

Although the total Geminid number of 5633 sounds impresive, the number
of observers who contributed to this little analysis with many
excellent reports, is relatively small. Systematic effects resulting in
overestimated or underestimated ZHRs cannot be excluded. Few
observations are available from Europe, whence the gaps in the mornings
of Dec 14 and 15.

A maximum at lambda=262.05+-0.10 degrees is found with a maximum
activity of ZHR=103+-4. Apart from the statistical error, we should
assume that the total error including systematic effects is certainly
larger. The actual peak ZHR will certainly settle at a slightly
different value, once the full data set is available. The data given
here suggest that the Geminids showed a 1998 activity level which is
comparable to previous years.

The ZHR graph below is based on the observational reports of the
following observers:

Jim Bedient (BEDJI)                Matthew Collier (COLMA)
Tim Cooper (COOTI)                 Shlomi Eini (EINSH)
Frank Enzlein (ENZFR)              Raul Fernandez (FERRA)
Wayne T. Hally (HALWA)             Takema Hashimoto (HASTA)
He Jingyang (JINHE)                Niladri Kar (KARNI)
Rhishikesh Kulkarni (KULRH)        Siddharth Kulkarni (KULSI)
Anna S. Levina (LEVAN)             Vladimir Lukic (LUKVL)
Robert Lunsford (LUNRO)            Pierre Martin (MARPI)
Antonio Martinez (MARTI)           Mark Mikutis (MIKMR)
Eran Ofek (OFEER)                  Kazuhiro Osada (OSAKA)
Bruce Patterson (PATBR)            Alfredo Pereira (PERAF)
Tushar Purohit (PURTU)             Jurgen Rendtel (RENJU)
Qi Rui (RUIQI)                     Shashank Shalgar (SHASH)
Brian Shulist (SHUBR)              Richard Taibi (TAIRI)
Neelima Thatte (THANE)             Josep M. Trigo Rodriguez (TRIJO)
Elena Valero Rodriguez (VALEL)     Erwin van Ballegoy (VANER)
Jin Zhu (ZHUJI)

------------------------------------
Date   Time  Sollong   ZHR  +-  nGEM
------------------------------------
Dec 10 2000  258.576   3.0  1.6   12
Dec 11 0800  259.090   6.2  0.8   54
Dec 12 0000  259.746  17.4  1.6  114
Dec 12 0500  259.981  16.7  1.5  128
Dec 13 0030  260.799  25.5  1.8  202
Dec 13 1230  261.313  38.6  2.1  335
Dec 13 1600  261.462  47.7  1.6  929
Dec 13 1840  261.571  47.4  1.6  879
Dec 14 0040  261.825  57.8  2.5  537
Dec 14 0600  262.048 102.7  3.6  807
Dec 14 0930  262.201  68.2  2.1 1087
Dec 14 1220  262.319  43.4  1.6  779
Dec 14 1550  262.464  29.8  1.9  247
Dec 14 1820  262.576  45.6  1.9  585
Dec 14 2140  262.714  37.8  1.5  628
Dec 15 0820  263.165  11.6  1.7   43
------------------------------------

The ZHR-profile was calculated with a population index of r=2.6 and a
zenith correction of 1/sin(hR).

Rainer Arlt, 1998 Dec 17.

=============
(4) SIBLING SANDBLASTING AND THE SMOOTHNESS OF GASPRA AND IDA

D.W. Hughes*) & I.P. Williams: Sibling sandblasting and the smoothness
of Gaspra and Ida. PLANETARY AND SPACE SCIENCE, 1998, Vol.46, No.8,
pp.929-935

*) UNIVERSITY OF SHEFFIELD, DEPT PHYS, SHEFFIELD S3 7RH, S
   YORKSHIRE, ENGLAND

Both Asteroid 951 Gaspra and 243 Ida look like smooth, rounded pebbles
and neither have the expected angular, jagged-faceted appearance of a
rock fragment produced by a hypervelocity impact. We suggest that they
were both rough and sharp-edged at 'birth' and that the rounding off
that we now see is the result of a multitude of low-velocity collisions
(at around 0.065 to 0.1 km s(-1)) with the much smaller sibling
asteroidal fragments that were born at the same time by the collisions
that produced the respective asteroidal families. (C) 1998 Elsevier
Science Ltd. All rights reserved.

========================
(5) COMPOSITIONAL VARIATION AND MIXING OF IMPACT MELT

T.H. See*), J. Wagstaff, V. Yang, F. Horz, G.A. McKay: Compositional
variation and mixing of impact melts on microscopic scales. METEORITICS
& PLANETARY SCIENCE, 1998, Vol.33, No.4, pp.937-948

*) NASA, JOHNSON SPACE CTR,PLANETARY SCI BRANCH,SN4,HOUSTON,TX,77058

We investigated the compositional characteristics of schlieren-rich,
holohyaline impact glasses from Ries, Wabar, and Meteor Crater using a
Cameca SX 100 scanning electron microprobe. This instrument is capable
of producing detailed maps of major elements at spatial resolutions of
<10 mu m. The objective was to characterize the composition of an
unusually large number of individual schlieren and to evaluate details
of the process that causes melts of lithologically diverse target rocks
to mix on scales of micrometers. The Ries and Meteor Crater impacts
involved lithologically heterogeneous targets; whereas, Wabar Crater
formed in relatively uniform dune sand. Texturally heterogeneous,
schlieren-rich glasses from the Ries Crater illustrate that schlieren
of highly variable color can be surprisingly similar in composition, as
first detailed by Stahle (1972). Consistent with these earlier
findings, most schlieren represent mixtures of diverse rock melts;
their compositions deviate only subtly from the average melt and do not
resemble monomineralic melts nor binary mixtures of major rock-forming
minerals. A specific population of schlieren is enriched in mafic
elements (Mg, Fe: and Ca), which suggests incomplete homogenization of
an amphibolite progenitor. In the case of Wabar Crater, a
compositionally simple melt of dune sand mixed with projectile (IIIA
iron meteorite) materials, and specific schlieren are variable mixtures
of these two progenitors. The optically homogeneous glass from Meteor
Crater is compositionally homogeneous as well, which suggests ideal
mixing of such diverse lithologies as platform carbonates, sandstone,
and a class IIIA iron meteorite. The mixing of projectile and target
melts at Wabar and Meteor Crater unambiguously demonstrates that melts
initially produced in distinctly different stratigraphic/structural
locations will undergo wholesale mixing, if not homogenization. Also,
the projectile melts unquestionably formed relatively early in the
cratering process, and their dissemination throughout the prospective
melt volume, albeit at variable concentration levels, suggests that the
entire mixing process may be an early cratering feature. This also
follows from the fact that we investigated ballistic melt ejecta, which
thereby eliminates all of those mixing processes that may additionally
operate during the pooling and generation of massive melt-ponds
following gravitational collapse of large, structurally complex
craters. Substantial turbulence ranging from field dimensions to
microscopic scales seems inescapable to accomplish the observed degree
of mixing, yet this is not readily inferred from current models of
macroscopic material motions during hypervelocity impact. Copyright
1998, Institute for Scientific Information Inc.

=======================
(6) THE K/T BOUNDARY & PLATINUM GROUP ELEMENTS

Q.L. Hou*), P.X. Ma, X. Ju: K/T boundary: Discussion of the platinum
group elements as indicators of extraterrestrial materials. CHINESE
SCIENCE BULLETIN, 1998, Vol.43, No.19, pp.1585-1593

*) CHINESE ACADEMY OF SCIENCE, INST GEOL,LAB LITHOSPHERE TECTON EVOLUT,
   BEIJING 100029, PEOPLES R CHINA

Whether the platinum group elements (PGE) can be taken as the
indicators of extraterrestrial materials is a very important and
interesting scientific problem. It is discussed on the basis of
systematic investigation and study of a great amount of related
literature. The following conclusions can be obtained: (i)
extraterrestrial impact event can cause the PGE anomaly; conversely,
the PGE anomaly may not represent the existence of extraterrestrial
impact event, because the PGE anomaly can be caused by many terrestrial
events (e.g. volcanic activity); ( ii) the PGE anomaly, especially the
global PGE anomaly can inspire us to think it from extraterrestrial
event, but it may not be as useful as previously thought as unambiguous
identifiers of large extraterrestrial impact event in the earth's
history. Copyright 1998, Institute for Scientific Information Inc.

========================
(7) THE PROBLEMS OF INTERPRETING PLATINIUM-GROUP ELEMENTS IN
    GEOCHEMISTRY

I. McDonald: The need for a common framework for collection and
interpretation of data in platinum-group element geochemistry.
GEOSTANDARDS NEWSLETTER-THE JOURNAL OF GEOSTANDARDS AND GEOANALYSIS,
1998, Vol.22, No.1, pp.85-91

UNIVERSITY OF GREENWICH, SCH EARTH & ENVIRONM SCI, LITHOSPHER PROC &
RESOURCES GRP,CHATHAM ME4 4AW,KENT,ENGLAND

Platinum-group element (PGE) concentrations and the distribution of the
metals in rocks serve as important tracers of mantle processes, as well
as extraterrestrial input into crustal environments, but common
standards regarding the gathering and presentation of PGE data have
never been formalized. Effective modelling assumes that concentration
data are within acceptable levels of precision, yet the practices used
in some studies to determine precision do not adequately assess
precision and, as a result, the uncertainties on PGE concentrations and
PGE ratios are sometimes consistently underestimated. This article
argues that replicate analyses of unknowns must be adopted more widely
in order to overcome this problem. Related to the issue of
uncertainties on PGE concentrations, is the issue of uncertainty
associated with normalisation. Arguments have recently been put forward
as to the significance of small positive or negative anomalies on
chondrite normalized plots. At least four CI chondrite PGE datasets (of
varying age and quality) are currently used for normalisation and
significantly different patterns can be derived simply by using one
dataset rather than another. This article is intended to open a debate
within the PGE research community by asking whether more consistency
needs to be applied in PGE analysis and in the subsequent
interpretation of data. A rigorous assessment of the real uncertainties
on PGE concentrations and the adoption of ct standard CI chondrite PGE
dataset, in order to eliminate bias from normalisation, are suggested
to be central to this. Copyright 1998, Institute for Scientific
Information Inc.

===============
(8) PRESERVATION OF EXTRATERRESTRIAL HELIUM IN MARINE LIMESTONES

D.B. Patterson*), K.A. Farley, B. Schmitz: Preservation of
extraterrestrial He-3 in 480-Ma-old marine limestones. EARTH AND
PLANETARY SCIENCE LETTERS, 1998, Vol.163, No.1-4, pp.315-325

*) CALTECH, DIV GEOL & PLANETARY SCI,MS 170-25,PASADENA,CA,91125

We have measured the helium abundance and isotopic composition of a
suite of Lower Ordovician marine limestones and associated fossil
meteorites from Kinnekulle, Sweden. Limestone He-3/He-4 ratios as high
as 11.5 times the atmospheric value in fused samples and up to 23 times
atmospheric in a single step-heat fraction indicate the presence of
extraterrestrial helium, and demonstrate that at least a fraction of
the extraterrestrial He-3 carried by interplanetary dust particles must
be retained against diffusive and diagenetic losses for up to 480 Ma.
The carrier phase has not been identified but is not magnetic.
Extrapolation of high-temperature He-3 diffusivities in these sediments
is consistent with strong retention of extraterrestrial He-3 under
ambient Earth-surface conditions. Combination of the observed helium
concentrations with sedimentation rates estimated from conodont
biostratigraphy suggest that the flux of extraterrestrial He-3 in the
Early Ordovician was about 0.5 x 10(-12) cm(3) STP cm(-2) ka(-1),
ignoring potential post-deposition helium loss. This value is
indistinguishable from the average He-3 flux estimated for the
Cenozoic Era. In contrast, previous studies of fossil meteorites, Ir
abundances, and Os isotopic ratios in the limestone suggest that the
total accretion rate of extraterrestrial material during the studied
interval was at least an order of magnitude higher than the Cenozoic
average. This disparity may reflect significant post-depositional loss
of He-3 from IDPs within these old limestones; if so, the match between
the Ordovician flux and the Cenozoic average would be fortuitous.
Alternatively, the size distribution of infalling objects during the
Early Ordovician may have;been enriched only in extraterrestrial
material too large to retain He-3 during atmospheric entry heating
(>similar to 30 mu m) The fossil meteorites themselves also preserve
extraterrestrial helium. Meteorite He-3 concentrations of 2 to 9 x
10(-12) cm(3) STP g(-1) are several orders of magnitude lower than
found in most modern meteorites, suggesting very substantial helium
loss (probably >99.9%) from these chemically altered objects. The
meteorites carry He-3 concentrations only a factor of a few higher than
the host limestones. The meteorites themselves cannot be the source of
the extraterrestrial He-3 observed in the limestones. (C) 1998 Elsevier
Science B.V. All rights reserved.

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