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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