PLEASE NOTE:
*
CCNet DIGEST, 18 February 1999
------------------------------
QUOTE OF THE DAY
"Mistaken reports that the IAU
intended to strip Pluto of its
planetary status caused an uproar among
astronomers and in the
popular press. It seems that Pluto is a
sentimental favorite to
remain a planet among both scientists
and the public. However, if
more trans-Neptunian objects are
discovered that are even larger
than Pluto, the debate could begin
anew" (NASA Science News, 17
February 1999).
(1) UPON MY SOUL: NASA TO KEEP PLUTO DEBATE WIDE OPEN
NASA Science News <expressnews@sslab.msfc.nasa.gov>
(2) STARDUST REPORT
Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>
(3) ANCIENT VOLCANIC CATACLYSMS DISCOVERED IN THE INDIAN OCEAN
Michelle R. Edwards <medwards@nsf.gov>
(4) THE IMPACT OF ANTARCTIC METEORITES ON PLANETARY SCIENCE
http://viking.eps.pitt.edu/public/cassidy.html
(5) REVOLUTION IN DISASTER RISK ASSESSMENT
ABCNEWS.com
http://abcnews.go.com/onair/DailyNews/wnt_weatherseries.html
(6) IMPACT MELTS & METAMORPH OF THE EARLY LUNAR CRUST
G. Jeffrey Taylor et al., Hawai'i Institute of
Geophysics & Pl.
(7) ORIGIN OF POLYMICT BRECCIAS ON ASTEROIDS
Kazuto Saiki and Hiroshi Takeda, Akita
University
(8) 'PATHOLOGICAL' MARTIAN IMPACT CRATERS
William Hartmann & G. Esquerdo, Planetary
Science Institute/SJI
============
(1) UPON MY SOUL: NASA TO KEEP PLUTO DEBATE WIDE OPEN
From NASA Science News <expressnews@sslab.msfc.nasa.gov>
NASA Space Science News for Feb. 17, 1999
http://science.nasa.gov/newhome/headlines/ast17feb99_1.htm
Much ado about Pluto
Recent discoveries of Pluto-like objects in the outer solar
system have
sparked debate about the nature of the tiniest "planet"
Marshall Space Flight Center
http://science.nasa.gov/newhome/headlines/ast17feb99_1.htm
Feb 17, 1999:
In 1979 the Solar System became a bit mixed up. That's when
Pluto,
which travels in a highly elliptical orbit, temporarily moved
closer to
the sun than Neptune. Every 248 years the two planets swap places
and
for about 20 years Pluto becomes the eighth planet and Neptune
the
ninth. This topsy-turvy situation was rectified last Thursday,
Feb. 11,
when Pluto crossed Neptune's orbit and became the ninth planet
once
again.
Pluto is the only planet that has not been visited by a
spacecraft.
Even the Hubble Space Telescope can resolve only the largest
features
on its surface, shown in this image of one hemisphere. The
brightness
variations could be due to craters and basins, methane and
nitrogen
frosts, or even areas of primordial organic matter. No one knows,
and
the mystery may remain until some future spacecraft pays a visit
to this
distant planet.
One of these things is not like the others
But is Pluto really a planet? That's what astronomers have been
discussing since late last year when some members of the
International
Astronomical Union suggested that Pluto be given a minor planet
designation. Why? For one thing Pluto is very small. It's 6 times
smaller than Earth, and even smaller than seven of the solar
system's
moons (the Moon, Io, Europa, Ganymede, Callisto, Titan and
Triton).
Pluto's own moon, Charon, is larger in proportion to its planet
than
any other satellite in the solar system. Some astronomers
consider the
pair to be a double planet.
Pluto's elliptical orbit is also unusual. It is the only
planetary
orbit which crosses that of another planet (Neptune), and it is
tilted
17 degress with respect to the plane of the solar system.
Astronomers
once thought that Pluto may have been a satellite of Neptune's
that was
ejected to follow a tilted elliptical path around the sun.
However,
careful simulations of the orbits and dynamics of Pluto and
Neptune
indicate that this is an unlikely scenario.
Pluto's composition is unknown, but its density (about 2 gm/cm3)
indicates that it is probably a mixture of rock and ice. All the
other
rocky planets -- Mercury, Venus, Earth and Mars -- are located in
the
inner solar system, close to the Sun. Except for Pluto, all of
the
outer planets -- Jupiter, Saturn, Uranus and Neptune -- are
gaseous
giants. Once again, Pluto is a misfit.
Pluto behind the 8 ball
Despite its well-known peculiarities, Pluto's official status as
a
planet was never in jeopardy until 1992 when David Jewitt and J.
Luu
discovered a curious object called 1992 QB1. QB1 is a small icy
body,
similar in size to an asteroid, orbiting 1.5 times further from
the sun
than Neptune. QB1 was the first hint that there might be more
than just
Pluto in the distant reaches of the solar system.
Since then nearly 100 objects like QB1 have been found. They are
thought to be similar to Pluto in composition and, like Pluto,
many
orbit the sun in a 3:2 resonance with Neptune. This swarm of
Pluto-like
objects beyond Neptune is known as the Kuiper Belt, after Gerard
Kuiper, who first proposed that such a belt existed and served as
a
source of short period comets. Astronomers estimate that there
are at
least 35,000 Kuiper Belt objects greater than 100 km in diameter,
which
is several hundred times the number (and mass) of similar sized
objects
in the main asteroid belt.
So, is Pluto really a planet or is it more like a dormant comet,
simply
the largest known member of the Kuiper Belt? That's the question
that
astronomers have recently been debating.
Other than its relatively large size, Pluto is practically
indistinguishable from the Kuiper Belt objects (KBOs) and short
period
comets. The main difference is Pluto's reflectivity, which is
much
higher than that of known KBOs.
"Pluto has a higher albedo (60%) than we suspect for the
other KBOs,"
explains Dr. David Jewitt of the University of Hawaii. "But
this is an
artifact of size - Pluto has enough mass & gravity to retain
a tenuous
atmosphere from which bright surface frosts may be deposited on
the
surface."
David Jewitt and his colleagues at the Institute for Astronomy
are
leaders in the search for new members of the Kuiper Belt. They
are
presently scanning a 50 sq. degree area of the sky for KBO's
using the
University of Hawaii's 8192 x 8192 pixel CCD camera, and are
experimenting with an even larger 12,000 x 8,000 pixel camera for
faster searches. So far their efforts have met with considerable
success. They have discovered over 40 KBO's in recent years, some
of
which are comparable in size to Pluto.
"We've already found objects 1/3rd the diameter of
Pluto," says David
Jewitt," even though we have examined only a tiny fraction
of the sky.
An example is 1996 TO66, which is 800 km diameter. It would be
incredible in its own right if Pluto proved to be the only 2000
km
object. I think we'll have Pluto II, Pluto III....within a few
years."
Nine's a charm
Dr. Jewitt raises the interesting possibility that Kupier Belt
objects
might one day be discovered that are even larger than our ninth
planet.
If that happens, what does it mean for Pluto? Should it be
stripped of
planetary status and reclassified as a member of the Kuiper Belt?
Or
should newly discovered "Plutos" be classified as
planets as well?
These are difficult questions that await the astronomical
community.
For now, however, Pluto's status as a planet seems secure. In a
press
release dated Feb. 3, 1999 the International Astronomical Union
stated
that "No proposal to change the status of Pluto as the ninth
planet in
the solar system has been made by any Division, Commission or
Working
Group of the IAU responsible for solar system science. Lately, a
substantial number of smaller objects have been discovered in the
outer
solar system, beyond Neptune, with orbits and possibly other
properties
similar to those of Pluto. It has been proposed to assign Pluto a
number in a technical catalogue or list of such Trans-Neptunian
Objects
(TNOs) so that observations and computations concerning these
objects
can be conveniently collated. This process was explicitly
designed to
not change Pluto's status as a planet."
Mistaken reports that the IAU intended to strip Pluto of its
planetary
status caused an uproar among astronomers and in the popular
press. It
seems that Pluto is a sentimental favorite to remain a planet
among
both scientists and the public. However, if more trans-Neptunian
objects are discovered that are even larger than Pluto, the
debate
could begin anew.
===============
(2) STARDUST REPORT
From Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>
STARDUST Status Report
February 12, 1999
Ken Atkins
STARDUST Project Manager
STARDUST is on its way to Wild 2! After a one-day delay because
of a
range safety interaction with the Delta 2's C-band transponder,
the
launch was accomplished with a virtual "bullseye" on
the targeted
outbound trajectory. All injection parameters were well within
the
3-sigma dispersion. The second stage "rocket camera"
provided a
spectacular view of the ride into space on a beautiful, cloudless
Florida day. This triggered a big press response with great
national
coverage. The time of launch was 4:04:15.238 EST, against the
instantaneous window. Spacecraft separation came at about
28 minutes
after lift off.
After separation from the Star-37 upper stage, STARDUST did its
own
de-spin, deployed the solar arrays, got to its on-sun attitude,
and
performed a status check to be ready to telemeter data as soon as
possible. Signal acquisition was near the earliest possible time,
just
after 5 P.M. EST and showed that the spacecraft was de-spun and
on the
sun. STARDUST passed the moon the next day at 12:16 p.m.
EST at a
distance of 33,200 miles and speed of almost 12,000 mph.
Hand-offs from
Canberra to Madrid tracking was very smooth.
The spacecraft is demonstrating excellent performance in all
respects.
Temperatures are tracking close to those from system thermal
vacuum
testing, but are generally a little warmer, which should provide
some
margin for aphelion when the spacecraft is at is farthest
distance from
the Sun. Initial trajectory tracking indicates that no
trajectory
correction maneuver (TCM) is required for February 22 as
originally
called for by the nominal flight plan. Tracking data will
continue to
accrue, and an assessment early next week will confirm whether a
maneuver will be needed on Feb 22, or whether it should be simply
delayed (which requires re-coordination of Deep Space Network
(DSN)
time) until better correlation of the actual accelerations with
those
predicted can be achieved.
Current plans indicate we may turn on the Dust Flux Monitor (DFM)
next week
and the Cometary & Interstellar Dust Analyzer (CIDA) within
two weeks. We
are also looking at turning on the Navigation Camera and imaging
the moon,
if we do not need the Feb 22 TCM.
It's great to have the "voyage" begun. I'm sure
everyone is enjoying the
pictures and new "movies" on the Web Site. It's
great to be able to see
where STARDUST is at any time.
After the launch, Don Brownlee and I made a
"pilgrimage" back to the launch
pad. It was impressive to see that place where so much of our
last
3 1/2 years work had been just hours before...now empty.
Launch Pad
17-A (SLC-17A) holds an important historic role in being the
place
where the first attempt to bring back cometary material launched
off
the planet . And other robotic explorers have also departed
the planet
from there: Mars Global Surveyor and Mars Climate Orbiter.
It was a
moving experience.
And, now all the "passengers" on the chip are in deep
space, beyond the
moon and moving outbound. Let's have a wondrous journey of
adventure
and discovery.
For more information on the STARDUST mission - the first ever
comet
sample return mission - please visit the STARDUST home page:
http://stardust.jpl.nasa.gov
=================
(3) ANCIENT VOLCANIC CATACLYSMS DISCOVERED IN THE INDIAN OCEAN
From Michelle R. Edwards <medwards@nsf.gov>
Media
contacts:
February 17, 1999
Cheryl Dybas,
NSF
NSF PR 99-10
(703) 306-1070/cdybas@nsf.gov
Pamela Baker-Masson, ODP
(202) 232-3900 ext. 226/pbaker@brook.edu
Program contact:
Bruce Malfait, NSF
(703) 306-1581/bmalfait@nsf.gov
Scientists from the largely National Science Foundation (NSF)
supported
Ocean Drilling Program (ODP) have completed an expedition to one
of the
most remote places on Earth, the Kerguelen Plateau. The
results of
their expedition will shed new light on how and when continents
formed
and broke apart millions of years ago.
The international team of 45 scientists conducted their research
aboard
the world's largest scientific drilling vessel, the JOIDES
Resolution.
The drillship departed Fremantle, Australia, on December 13,
1998, and
returned to Fremantle on February 11, 1999.
Kerguelen Plateau is located in the southern Indian Ocean, is
one-third
the size of the United States, and is described as a large
igneous
province (LIP). LIPs are areas where magma wells up from
deep beneath
Earth's surface and forms molten rock. The major objectives of
the ODP
expedition, explains Bruce Malfait, director of ODP at NSF, were
to
determine through drilling when volcanism was active; how much of
the
plateau formed above sea level and how long portions of the
feature
remained above sea level; and if continental fragments form part
of the
plateau.
Using evidence from fossils as well as terrestrial plant remains,
the
scientific team constrained the time period during which the
Kerguelen
LIP formed. They found that the southern Kerguelen Plateau,
only
hundreds of kilometers from Antarctica, formed approximately 110
million years ago. To the north, the central Kerguelen
Plateau and the
once-contiguous Broken Ridge formed between 85 and 95 million
years
ago. In contrast, the northern Kerguelen Plateau is much
younger,
having formed less than 35 million years ago. These results
indicate
that several intense episodes of volcanism formed this large
plateau
over a long time period, rather than from a single massive
volcanic
event.
"We found abundant evidence that much of the Kerguelen LIP
formed above
sea level," states co-chief scientist Mike Coffin of the
University of
Texas Institute of Geophysics. "Wood fragments, a seed,
spores and
pollen recovered in 90-million-year-old sediment from the central
Kerguelen Plateau, just southeast of Heard Island, unambiguously
indicates that this region was above sea level."
A spectacular result was finding uniquely continental rocks in a
conglomerate that was probably deposited in a river on Elan Bank
near
the central and southern Kerguelen Plateau, explains co chief
scientist
Fred Frey of the Massachusetts Institute of Technology.
"Knowing how
pieces of an ancient continent were incorporated into the oceanic
environment of Elan Bank will have significant impact on our
understanding of the approximately 130-million-year-old break-up
of
Australia, India and Antarctica."
A surprising finding at three drill sites was evidence for
large-scale
explosive volcanism, apparently a common phenomenon as volcanic
construction of the plateau came to an end. Explosive volcanism
can
perturb the earth-atmosphere system significantly by injecting
material
into the stratosphere where, depending on the magnitude and
altitude of
the material, it may persist for several years. This can
cause
considerable short-term environmental effects, such as those
resulting
from the recent eruption of Mount Pinatubo in the Philippines.
-NSF-
============================
(4) THE IMPACT OF ANTARCTIC METEORITES ON PLANETARY SCIENCE
From http://viking.eps.pitt.edu/public/cassidy.html
April 30 - May 1, 1999
The Impact of Antarctic Meteorites on Planetary Science:
A Symposium in Celebration of the Retirement of William A.
Cassidy
Pittsburgh, Pennsylvania.
Contact: Cassidy Symposium, Department of Geology and Planetary
Science, 321 Old Engineering Hall, University of Pittsburgh,
Pittsburgh
PA 15260, USA.
Phone: 412-624-8780; fax: 412-624-3914
E-mail: geology@pop.pitt.edu
http://viking.eps.pitt.edu/public/cassidy.html
Dear Colleague:
You are cordially invited to attend a symposium on Antarctic
meteorites
and planetary science. Most of you know of Bill Cassidy as an
explorer
and as the founder and former leader of the ANSMET Antarctic
Meteorite
Recovery Program. After over 40 years of studying impact craters
and
finding meteorites, Bill has decided to spend a little less time
in
the field and a little more with his family. His colleagues
and
friends will honor Bill's lifetime of service to the planetary
science community with this symposium, and we request the
pleasure of
your presence at this event.
Sincerely,
The Organizing Committee
Thomas Anderson
David Crown
Bruce Hapke
Ralph Harvey
Robert Witkowski
================
(5) REVOLUTION IN DISASTER RISK ASSESSMENT
From ABCNEWS.com
http://abcnews.go.com/onair/DailyNews/wnt_weatherseries.html
Computer Modeling Reveals Where Risk Is Greatest
By Ned Potter
It was Mark Twain who said, “Everybody talks about the
weather, but
nobody does anything about it.” We still cannot do anything
about
nature, but we may have unlocked some of its mysteries.
Weather and other natural disasters claimed 32,000 lives last
year. The
financial cost is also staggering — an estimated $1 billion
a week in
the United States alone.
Now, a whole new science can show with stunning accuracy where
the risk
for natural disasters is greatest. The technology, called
computer
modeling, requires engineers to first chart the strength and
location
of every storm, every quake, and every flood of the last century.
They then combine it with current data on where people live, and
what
types of structures they live in. Some programs can rate the risk
on a
house-by-house basis. They cannot forecast disaster, but they can
tell
you your chance of being in one.
FULL STORY at
http://abcnews.go.com/onair/DailyNews/wnt_weatherseries.html
==================
(6) IMPACT MELTS & METAMORPH OF THE EARLY LUNAR CRUST
Janet A. Cushing, G. Jeffrey Taylor*, Marc D. Norman, and Klaus
Keil:
The granulitic impactite suite: Impact melts and metamorphic
breccias
of the early lunar crust. Meteoritics & Planetary Science 34,
March
(1999)
*) Planetary Geosciences, Hawai'i Institute of Geophysics and
Planetology, 2525 Correa Rd., Honolulu, Hawai'i 96822, USA;
e-mail
address: gjtaylor@pgd.hawaii.edu
An important and poorly understood group of rocks found in the
ancient
lunar highlands is called "feldspathic granulitic
impactites." Rocks of
the granulite suite occur at most of the Apollo highlands sites
as hand
samples, rake samples, clasts in breccias, and soil fragments.
Most
lunar granulites contain 70-80% modal plagioclase, but they can
range
from anorthosite to troctolite and norite. Previous studies have
led to
different interpretations for the thermal history of these rocks,
including formation as igneous plutons, long-duration
metamorphism at
high temperatures, and short-duration metamorphism at low
temperatures.
This paper reports on a study of 24 polished thin sections of
lunar
granulites from the Apollo 15, 16, and 17 missions. We identify
three
different textural types of granulitic breccias: poikilitic,
granoblastic, and poikilitic-granoblastic breccias. These
breccias have
similar equilibration temperatures (1100 ± 50 °C), as well as
common
compositions. Crystal size distributions in two granoblastic
breccias
reveal that Ostwald ripening took place during metamorphism.
Solid-state
grain growth and diffusion calculations indicate relatively rapid
cooling during metamorphism, 0.5 to 50 °C/year, and thermal
modeling
shows that they cooled at relatively shallow depths (<200 m).
In
contrast, we conclude that the poikilitic rocks formed by impact
melting, whereas the poikilitic-granoblastic rocks were
metamorphosed
and may have partially melted. These results indicate formation
of lunar
granulites in relatively small craters (30-90 km in diameter),
physically associated with the impact-melt breccia pile, and
possibly
from fine-grained fragmental precursor lithologies. ©
Meteoritical
Society, 1999.
============================
(7) ORIGIN OF POLYMICT BRECCIAS ON ASTEROIDS
Kazuto Saiki* and Hiroshi Takeda: Origin of polymict breccias on
asteroids deduced from their pyroxene fragments. Meteoritics
&
Planetary Science 34, March (1999)
*) Research Institute of Materials and Resources, Faculty of
Engineering and Material Science, Akita University, 1-1 Tegata
Gakuen
machi, Akita 010-8502, Japan; e-mail address: ksaiki@rimr.akita-u.ac.jp
Cumulate eucrite, noncumulate eucrite, and diogenite meteorites
are
considered to have come from the crust of one (or similar) parent
asteroids. Howardites are regarded as regolith breccias of
eucrites and
diogenites, and polymict eucrites are regarded as polymict
breccias of
eucrites. These polymict breccias show many textural and chemical
features. In order to gain a better understanding of the origin
of
polymict breccias and the origin of their components, we
investigated
four polymict breccias, Yamato(Y)791439, Y791192, Y82009 and
Y82049 by
a SEM equipped with a chemical mapping system and by electron
probe
microanalysis (EPMA). We analyzed all pyroxene grains with
chemical
maps, classified them by chemical composition, and observed their
chemistry and mineralogy in detail. The characteristics of
pyroxenes
suggest that the polymict breccias were generated by gathering
locally
ordinary eucrites and cumulate eucrites. The
chemical-evolutionary
features of the pyroxenes, such as homogenization, chemical
zoning, and
exsolution lamellae, suggest that there were at least two long
annealing events and one short (or low temperature) annealing
event
separated by mixing events. Local heterogeneity on the asteroidal
crust
is also suggested. © Meteoritical Society, 1999.
================
(8) 'PATHOLOGICAL' MARTIAN IMPACT CRATERS
William K. Hartmann*) and Gilbert Esquerdo:
"Pathological" Martian
craters: Evidence for a transient obliteration event? Meteoritics
&
Planetary Science 34, March (1999)
*) Planetary Science Institute/SJI, 620 North 6th Avenue, Tucson,
Arizona 85705 USA; e-mail address: hartmann@psi.edu
We have detected three unusual, low-relief circular features, 1.2
to
2.1 km in diameter, in the northwest Noachis highlands, which may
be
craters that have undergone isostatic deformation. They may shed
light
on the existence, nature, and timing of suspected widespread
Martian
erosion/obliteration events, and offer clues to a type of Martian
terrain softening. In the surrounding area we find an anomalous
deficiency of craters in the 3-11 km diameter range, and evidence
that
larger, older craters have undergone relief-softening and infill.
We
discuss three different hypotheses to explain these features, two
of
which involve Martian ice. This region may have undergone a
transient
event in which a near-surface permafrost layer, several hundred
meters
deep, underwent partial melting or softening. This would allow
relaxation of kilometer-scale craters, and softening of larger
craters.
Crater data presented here suggest that this event happened some
time
in mid-Martian history. Whether the event was regional or related
to
global-scale events is uncertain, though it may represent a class
of
events that happened in other Martian areas. © Meteoritical
Society,
1999. Printed in USA.
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