PLEASE NOTE:
*
CCNet, 38/2000 - 23 March 2000
------------------------------
"We'll have to be patient and await
more observations [of Eros],
especially from the lower orbits where
the x-ray and gamma ray
spectrometers were designed to operate.
Gene [Shoemaker] would
have had difficulty with the notion of
being patient at Eros - he
wanted to go there and bang on it with a
hammer - but he would
have understood."
-- Andrew Cheng,
NEAR-SHOEMAKER Project Scientist,
in his tribute to Gene Shoemaker
(1) NEAR-SHOEMAKER SCIENCE UPDATE
Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>
(2) WAS MARS SHAPED BY GLACIERS?
Andrew Yee <ayee@nova.astro.utoronto.ca>
(3) NASA REJECTS JAMES OBERG’S INVESTIGATIVE MPL FAILURE
STORY
NASANews@hq.nasa.gov
(4) NASA CHIEF ADMITS MANAGEMENT ERRORS
MSNBC Space News, 22 March 2000
(5) ASTRONOMERS DISCOVER FREE-FLOATING PLANETS IN THE
ORION
NEBULA
Jacqueline Mitton <jmitton@dial.pipex.com>
(6) FOSSILIZED BACTERIA FOUND IN ANCIENT METEORITE
Michael Paine <mpaine@tpgi.com.au>
(7) DEGRADATION SIGNATURES AROUND IMPACT CRATERS
J.A. Grant, SUNY COLL BUFFALO
(8) IMPACT CRATERS IN 3D
D. Wallis et al., UNIVERSITY OF KENT
(9) JAPANESE CONTRIBUTION TO METEOROID & SPACE
DEBRIS
MEASUREMENT
H. Yano, INST SPACE & ASTRONAUT SCI
(10) POSSIBLE CAUSES OF CYCLICAL IMPACT EVENTS
Michael Rampino <mrr1@is3.nyu.edu>
(11) RUMOURS AND ALLEGATIONS
Jeremy Tatum <UNIVERSE@uvvm.UVic.CA>
============
(1) NEAR-SHOEMAKER SCIENCE UPDATE
From Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>
NEAR-Shoemaker Science Update
March 22, 2000
http://near.jhuapl.edu/news/sci_updates/00mar22.html
Last week the NEAR spacecraft was renamed "NEAR
Shoemaker," in honor of
the late Eugene M. Shoemaker, a pioneer in the study of asteroid
and
comet impacts on Earth and other planets. It is largely because
of
Gene's work that we know that the famous Meteor Crater in Arizona
(also
called Barringer Crater) was indeed created by the impact of a
15-meter
iron-rich meteoroid and not by a volcano. While many scientists
suspected an impact origin, including Barringer himself, it was
Shoemaker and his colleague Chao's discovery of the high pressure
silicate mineral coesite that finally convinced skeptics.
Gene was also heavily involved in the Apollo missions that
resolved one
of the leading scientific controversies of our time, whether the
craters on the Moon were formed by volcanoes or by impacts. We
now know
that the surface of the Moon is actually saturated with impact
craters
and that even the largest features we see, those that make up the
"man
in the moon", lie within the scars of giant impacts. These
features are
dark because, later in the moon's history, the giant impact scars
were
filled with volcanic lavas. The Moon's surface records a period
of
violent bombardment in the early history of the solar system, a
bombardment which the Earth itself did not escape. Of course, on
Earth
the record of ancient giant impacts has been mostly erased by the
actions of weather and plate tectonics. Gene was among the first
to
recognize the importance of large impacts for the geologic
history of
the Earth and for the evolution of life on Earth.
Since the projectiles that bombarded the Moon, the Earth, and
other
terrestrial planets were asteroids and comets, Gene initiated
telescopic observing programs to search for such objects in
orbits
close to Earth's orbit (that is, near-Earth asteroids and comets)
as
well as in more distant orbits. He and David Levy discovered the
comet
Shoemaker-Levy 9 that plunged into Jupiter in 1994, after
splitting
into more than 20 fragments, temporarily creating dark spots in
Jupiter's clouds larger than the Earth.
NEAR Shoemaker is now orbiting one of the largest of the
near-Earth
asteroids, 433 Eros. Gene always thought of the near-Earth
asteroids as
"roadcuts in the heavens", which would have fascinating
and important
stories to tell about the formation of the planets. We all have
the
experience of driving through a roadcut on the highway and
looking at
exposed layers of sediment or rock on either side, which would
reveal
something of the geologic history of that particular site. How
appropriate it is that we now see fantastic systems of linear
features
- ridges, grooves, and chains of craters or pits - all around the
surface of Eros. Were the linear features formed by ancient
geologic
activity on the parent body of Eros, making Eros possibly a
'roadcut'
through the parent body from which it was derived? Or were the
linear
features formed by later processes? Our task is now to find the
evidence that would indicate which of these possibilities may be
correct.
One important line of evidence will come from NEAR's x-ray and
gamma-ray spectrometers, which will measure the elemental
compositions
of surface materials. Last week, NEAR recorded the first
detections of
x-ray emissions from an asteroid. NEAR's x-ray spectrometer was
able to
identify emission from the elements silicon, aluminum, magnesium,
calcium and iron during a large solar flare on March 2, 2000. The
flare
bombarded the asteroid's surface with an unusually high intensity
of
x-rays, enabling NEAR's x-ray spectrometer to detect the asteroid
emissions at a range of more than 200 kilometers from the
surface. From
that one observation, we were not able to determine quantitative
abundances of these elements, which is the information that might
tell
us whether Eros is from a differentiated parent body (one large
enough
to have melted in the interior and separated into heavier and
lighter
constituents) or from a more primitive parent body. We'll have to
be
patient and await more observations, especially from the lower
orbits where the x-ray and gamma ray spectrometers were designed
to
operate. Gene would have had difficulty with the notion of being
patient at Eros - he wanted to go there and bang on it with a
hammer -
but he would have understood.
Andrew Cheng
NEAR Project Scientist
==================
(2) WAS MARS SHAPED BY GLACIERS?
From Andrew Yee <ayee@nova.astro.utoronto.ca>
New Scientist
http://www.newscientist.com
UK Contact:
Claire Bowles, claire.bowles@rbi.co.uk,
44-207-331-2751
US Contact:
New Scientist Washington Office, newscidc@idt.net, 202-452-1178
EMBARGOED FOR RELEASE: March 22, 2000, 2 p.m. EST
Was Mars shaped by glaciers?
Melting glaciers rather than flowing surface water could have
carved
out the Red Planet's distinctive valleys.
Branching networks of small valleys have led many scientists to
conclude that rivers of running water once flowed freely across
the
surface of Mars. But this would mean that the Red Planet once had
a
much warmer climate than it does today and, apart from its
valleys,
there is no evidence to suggest that Mars was ever warm (New
Scientist,
17 April 1999, p 48).
But Pascal Lee, a planetary scientist at NASA's Ames Research
Center in
Mountain View, California, says the answer may be found on Devon
Island
in the Canadian Arctic, where he is studying valleys carved by
glacial
meltwater. "What we've been finding on Devon Island,"
says Lee, "is a wide
variety of valley types, from canyons to little networks of small
valleys, that bear an uncanny resemblance to specific
counterparts on
Mars."
In particular, he says, the Martian valleys "cut through a
desert that
otherwise has very little sign of water flowing nearby". The
constant
width and depth of Martian valleys over long distances, their
flat
floors and steep walls are all distinctive features also found on
Devon
Island, but uncommon on river networks.
Lee believes that other Martian landforms, notably some large
canyons
on the west end of Vallis Marineris, could actually have been
carved by
flowing glacial ice. Devon Island also has canyons like these, he
told
the 31st Lunar and Planetary Institute Science Conference in
Houston,
Texas, last week.
If Lee is correct, Mars may have had a cold climate, in which
snowfall
piled up to form glaciers that later melted in the heat generated
inside the planet. Mars expert Jim Head of Brown University,
Rhode
Island, welcomes Lee's work, saying the analogy to Devon Island
is
helping him visualise how melting snow might have produced
valleys on
Mars.
Reporter: Henry Bortman
New Scientist issue: 25th March 2000
PLEASE MENTION NEW SCIENTIST AS THE SOURCE OF THIS STORY AND, IF
PUBLISHING ONLINE, PLEASE CARRY A HYPERLINK TO:
http://www.newscientist.com
==============
(3) NASA REJECTS JAMES OBERG’S INVESTIGATIVE MPL FAILURE
STORY
From NASANews@hq.nasa.gov
Peggy Wilhide
Headquarters, Washington,
DC
March 22, 2000
(Phone: 202/ 358-1898)
Brian Welch
Headquarters, Washington, DC
(Phone: 202/ 358-1600)
Don Savage
Headquarters, Washington, DC
(Phone: 202/ 358-1547)
RELEASE: 00-43
NASA'S RESPONSE TO UPI'S MARCH 21 MARS POLAR LANDER STORY
James Oberg of UPI claims that NASA knew there was a problem with
the
Mars Polar Lander propulsion system prior to the Dec. 3 landing
attempt
and "withheld this conclusion from the public."
NASA categorically
denies this charge. Here's what NASA did and what NASA
said:
* The Stephenson report, phase 1, was released to the
public on
November 10, 1999 during a press conference at NASA
Headquarters.
* The report made 11 different references to
technical issues or
concerns involving the propulsion system and the Entry, Descent
and Landing (EDL) sequence.
* This issue was specifically addressed in the press
conference
and in "MPL Observation No. 5" and other public
recommendations of
the Stephenson Phase 1 report. It was entitled, "Cold
Firing of
Thrusters," and dealt in detail with the catalyst bed issue
cited
by Mr. Oberg of UPI in his March 21 story, "NASA Knew Mars
Polar
Lander Doomed."
* Had UPI researched the public documents released on
Nov. 10,
which have been available online at the NASA Home Page, the
reporter would have been able to conclude that NASA did indeed
publicly address propulsion issues, and specifically, the
propulsion system's "catalyst bed" temperature concern.
* Based on this review, NASA knew about the concerns
with the
propulsion system, NASA took corrective action, and NASA hid
nothing from the public. We made our concerns known in
early
November.
* Several failure scenarios have been reported in the
press over
the last few weeks, including the lander legs microswitch
issue.
Outlets such as the Denver Post, Space Daily, and National Public
Radio's "All Things Considered" have covered this
angle. There is
nothing new in the UPI report relating to this specific
issue.
The lander legs issue is among the failure modes we are studying.
* Both the Stephenson and Casani (John Casani,
retired JPL
flight programs head and also director of mission assurance)
teams
have conducted intensive reviews relating to Mars Polar Lander,
and their teams have surfaced no evidence relating to thruster
acceptance testing irregularities as alleged by UPI. In
fact,
members of the review teams are using words like
"bunk," "complete
nonsense," and "wacko," to describe their
reactions to UPI's
charge.
=================
(4) NASA CHIEF ADMITS MANAGEMENT ERRORS
From MSNBC Space News, 22 March 2000
http://msnbc.com/news/385617.asp?cp1=1
ASSOCIATED PRESS
Goldin absorbs criticism from senators, agrees that work force
was
‘too thin’
WASHINGTON, March 22 — NASA, trying to do more
missions with less
money and fewer people, made management mistakes that contributed
to a
string of recent failures in space, the chief of the agency said
Wednesday.
“WE PROBABLY cut too tight” in reducing the NASA work
force from 25,000
to 18,500 over the last seven years, Daniel Goldin, NASA’s
administrator, told the Senate Commerce subcommittee on space.
“We
found we were really too thin.”
Goldin said the agency lost many veteran engineers over those
years,
and there was inadequate training and mentoring for young,
inexperienced workers who were hired.
Additionally, he said, there was a failure in communication
between
engineers and technicians doing the work and the management
personnel
overseeing it. “There was no good communication
feedback,” Goldin
said. “People were talking and we weren’t hearing
them.”
FULL STORY at:
http://msnbc.com/news/385617.asp?cp1=1
============
(5) ASTRONOMERS DISCOVER FREE-FLOATING PLANETS IN THE
ORION
NEBULA
From Jacqueline Mitton <jmitton@dial.pipex.com>
Royal Astronomical Society Press Notice
Date: 22 March 2000
For immediate release
Ref. PN 00/04
ISSUED BY:
Dr Jacqueline Mitton
RAS Press Officer
Office & home phone: Cambridge ((0)1223) 564914
FAX: Cambridge ((0)1223) 572892
E-mail: jmitton@dial.pipex.com
RAS web: www.ras.org.uk/press/press.htm
----------------------------------------------------------------------------
Contacts for this release:
Dr Philip Lucas, University of Hertfordshire
Phone: 01707 286070
pwl@star.herts.ac.uk
Dr Patrick Roche, University of Oxford
Phone: 01865 273338
pfr@astro.ox.ac.uk
----------------------------------------------------------------------------
ASTRONOMERS DISCOVER FREE-FLOATING PLANETS IN
THE ORION NEBULA
The most sensitive survey ever undertaken of the region in the
Orion
Nebula where new stars are forming has revealed 13
"free-floating
planets" as well as more than one hundred very young brown
dwarfs.
The discovery was made by Dr Philip Lucas of the University of
Hertfordshire and Dr Patrick Roche of the University of Oxford
using
a new camera on the United Kingdom Infrared Telescope (UKIRT) in
Hawaii. Their results will be published in the Monthly Notices of
the
Royal Astronomical Society.
Brown dwarfs are objects that might have become stars, but never
accumulated sufficient material. With less than 8% of the Sun's
mass,
they did not heat up enough inside to trigger the nuclear
reactions
involving hydrogen that keep stars shining over long periods.
Nevertheless, they do produce some nuclear energy for a short
time
(from deuterium, a rare isotope of hydrogen) if their mass
exceeds
1.3% the Sun's mass -- about 13 times the mass of Jupiter.
Astronomers regard this as the minimum mass for a brown dwarf.
The new infrared survey of the Trapezium Cluster in the Orion
Nebula,
turned up 13 objects below the 13 Jupiter-mass threshold. The
mass of
the smallest is equivalent to no more than about 8 Jupiters.
These objects
have been dubbed "free-floating planets". They give off
only residual
heat left over from when they were born. By nature they are more
like
the giant planets of our solar system than stars. However, they
do
not orbit any star and drift through space by themselves. Only
two
similar objects have previously been discovered. (Japanese
astronomers found them in the southern Chamaeleon Nebula.) The
discovery of thirteen more in one cluster suggests that they
might be
very common.
Astronomers believe that most stars are born in giant molecular
clouds -- vast clumps of cold gas and dust. The nearest such
cloud
lurks just behind the glowing gas of the Orion Nebula. The
Trapezium
cluster at the heart of the Orion Nebula has recently broken out
of
the dark molecular cloud. It is therefore the best place to look
in
order to find out about the creation of stars, brown dwarfs and
free-floating planets in the rest of the Galaxy. The backdrop of
the
Orion Molecular Cloud obscures everything that lies behind it,
which
is very useful because it means that all the objects seen in this
part of the sky are members of the cluster, except for perhaps a
handful which lie in the foreground.
Because brown dwarfs and free floating planets quickly cool down,
they are easiest to find when they are young and still retain
some
heat from the formation process. The objects in the Trapezium
cluster
are mostly about one million years old -- very young compared to
the
five-billion-year age of the Sun.
An interesting feature of this study is that no planets have been
found under 8 Jupiter masses. It may indicate that there is a
limit
to how small these free-floating planets can be but even more
sensitive surveys will be needed to confirm this. In the meantime
UKIRT has been used to obtain spectra of about twenty of the
brown
dwarfs and planets. The results are still being analysed but they
show the signature of water vapour that is expected in relatively
cool stars and brown dwarfs, at a temperature of a mere 2700
degrees
Centigrade. The planets will eventually cool down to earthly
temperatures but it is unlikely that they could ever sustain
life.
Although the total number of brown dwarfs and planets in the
Trapezium may be similar to the number of stars, individually
they
have less mass. If this a typical cluster, brown dwarfs and
planets
do not contribute significantly to the dark matter that many
astronomers believe pervades the universe.
This survey is one of the first projects undertaken with the new
infrared camera UFTI, the UKIRT Fast Track Imager. It is the most
sensitive search yet conducted for low mass stellar and
sub-stellar
objects. For all the objects they detected, Lucas and Roche
measured
the strength of radiation given off at three standard wavelengths
in
the near infrared (known as I, J and H). They used this data to
deduce the mass, luminosity and temperature of the objects. UFTI
was
built by a team headed by Roche and Lucas at Oxford University in
1998, with the help of several British universities.
ILLUSTRATION
A low-resolution JPEG version is attached. This, and higher
resolution versions may be downloaded from the following web
pages:
http://www-astro.physics.ox.ac.uk/~pwl/trapl.jpg
http://www-astro.physics.ox.ac.uk/~pwl/trapl.gif
http://www-astro.physics.ox.ac.uk/~pwl/trapl.tif
Caption: An infrared picture of the central part of the Orion
Nebula
constructed from the three separate images taken with UFTI (the
UKIRT
Fast Track Imager) on the United Kingdom Infrared Telescope. The
three colours used in this false colour image (blue, orange and
red)
correspond to infrared radiation with wavelengths twice as long.
Hence, this picture shows Orion as we would see it if our eyes
were
sensitive to light of twice the wavelength they are actually
capable
of detecting. The picture shows stars, brown dwarfs and planets
together with diffuse starlight, which is scattered by tiny
particles
of cosmic dust, and light emitted by energised gas. Infrared
images
are vital for this work, as they penetrate the dusty clouds and
are
able to pick up faint objects which cannot be seen in visible
light
images.
NOTES
1. Both UFTI and UKIRT are funded by the Particle Physics and
Astronomy
Research Council.
2. The paper describing this work has been accepted for
publication in the
Monthly Notices of the Royal Astronomical Society,
but the date of
publication and is not yet available.
============
(6) FOSSILIZED BACTERIA FOUND IN ANCIENT METEORITE
From Michael Paine <mpaine@tpgi.com.au>
Dear Benny,
Re: The developmemts with the Martian meteorite ALH84001 reported
by
Bill Wheaton (CCNet 21 Mar 2000).
I hope the Yukon meteorite has been sufficiently protected from
contamination so that it can be examined for signs of ET. It now
seems
that even those that fall on Antarctica can become contaminated
with
local bugs after a few (thousand?) years.
regards
Michael Paine
(Claims of) Fossilized Bacteria Found in Ancient Meteorite
By Michael Paine,
Special to SPACE.com, posted: 07:51 am EST 21 February 2000
http://www.space.com/science/murchison_metor_000221.html
Russian scientists claim to have discovered fossils of primitive
extraterrestrial organisms in a meteorite thought to be a
leftover from
the formation of the solar system.
Similar theories have met with skepticism in the past and there
are
doubts about the latest claims. It seems that garden-variety
microbes
love to feast on these carbon-rich meteorites.
Last year, at a conference on Astrobiology held in Denver, Dr
Stanislav
Zhmur and colleagues from the Russian Academy of Sciences
revealed that
they had found what looked like fossilized microorganisms in
fragments
of several meteorites that fell on the rural town of Murchison in
South-East Australia in 1969.
Their electron microscope pictures and comments were recently
posted on
the web pages of "Cosmic Ancestry" -- part of the
Panspermia website,
devoted to research and conjecture about the spread of life
between star
systems.
Even to the un-trained eye the objects in the pictures look like
organisms.
"Since these objects look so much like the remains of
terrestrial
organisms, it seems most likely that they are remains of
terrestrial
organisms," said Allan Treiman from the Lunar and Planetary
Institute
in Houston. "Terrestrial bacteria and fungi infest
meteorites almost
immediately on landing on Earth, take up residence and consume
whatever
they can. The fungi worm their way into the meteorites along
cracks and
pores, and 'burrow' into the carbonaceous material as they eat
it".
Treiman has also been critical of the claims about microfossils
in the
famous martian meteorite ALH84001.
Dr Andrew Steele from the University of Portsmouth told SPACE.com
"meteorites become contaminated with Earth life within days
of landing,
yet some of the Murchison meteorites were in the open for four to
five
months before being collected."
Added Steele, "electron microscopes and morphology
[comparing the shape
of organisms] are powerful tools, but they are not conclusive.
More
detailed biological tests of other meteorite specimens point in
one
direction -- terrestrial microbial contamination."
Last year Steele found evidence of infestation by fungi and
bacteria in
another piece of Murchison meteorite. Crystals had even started
to grow
over some of the microbes while the rocks had been in storage. In
more
extreme cases this mineral growth could possibly be mistaken for
fossils.
Dr Matthew Genge, a meteorite researcher from the Natural History
Museum
in London, is also skeptical.
"Murchison meteorites are even more likely than most to have
experienced
contamination since they fell in a farmyard and, reputedly, at
least
some of the stones had to be recovered from a ditch filled with
manure,"
Genge said, adding that "any meteorite recovered outside
Antarctica has
had ample opportunity to become contaminated. Those in museum
collections have furthermore been handle many times."
Treiman wrapped up the case for the negative: "my opinion
[for what its
worth] is that the meteorites are infested with Earth bacteria --
the
meteorites are not infested with extraterrestrial bacteria. The
issue of
life in the solar system is fascinating, but [like all good
detective
stories] will have lots of false leads."
c2000 Space.com
References for this article are at
http://www1.tpgi.com.au/users/tps-seti/reading.html#ez8b
===============
(7) DEGRADATION SIGNATURES AROUND IMPACT CRATERS
J.A. Grant: Evaluating the evolution of process specific
degradation
signatures around impact craters. INTERNATIONAL JOURNAL OF IMPACT
ENGINEERING, 1999, Vol.23, No.1 Pt1, pp.331-340
SUNY COLL BUFFALO,1300 ELMWOOD AVE,BUFFALO,NY,14222
The pristine morphologies created during an impact event comprise
a
template for constraining how various environmental parameters
influence the mechanics of crater formation. Identification of
pristine morphologies used in defining and/or evaluating models
of
crater formation can be complicated or precluded however, by the
effects of post-formation degradation.. Field and/or remote
examination of simple, unglaciated impact craters on the Earth
(e.g.,
Meteor Crater, Arizona, and Roter Kamm crater, Namibia) can yield
results that help to define characteristic degradation signatures
for
use in placing first-order constraints on the number and
intensity of
processes that have been active. In turn, the presence of a suite
of
these degradation signatures can be used to define the amount and
style of crater degradation that has taken place, thereby
providing a
tool for possible distinction between pristine versus secondary,
post-formation characteristics. (C) 1999 Elsevier Science Ltd.
All
rights reserved.Copyright 2000, Institute for Scientific
Information
Inc.
===============
(8) IMPACT CRATERS IN 3D
D. Wallis*), C.J. Solomon, L. Kay: Use of Scanning Electron
Microscopy
for three dimensional stereo analysis of impact craters and
modelling
with Zernike polynomials. ADVANCES IN SPACE RESEARCH, 1999,
Vol.25,
No.2, pp.339-344
*) UNIVERSITY OF KENT,UNIT SPACE SCI & ASTROPHYS,CANTERBURY
CT2
7NR,KENT,ENGLAND
Examples will be presented to demonstrate the use of a Scanning
Electron Microscope to obtain detailed measurements of
hypervelocity
impact craters and to obtain the shapes of craters in three
dimensions
by comparing stereo pairs. The depth of each crater is sampled at
approximately 5000 points and the data is fitted using a set of
polynomials orthogonal over a unit disc ( the Zernike
polynomials). The
specific application to be presented is the study of groups of
craters
produced under identical impact conditions by firing a quantity
of
projectiles as buckshot from a light gas gun. Analysis of the
Zernike
polynomial spectrum of the crater shapes will show quantitatively
the
variations in crater shapes, both within groups of identical
craters
and between groups corresponding to different impact conditions.
In
this way the potential of the method for inferring properties of
impactors will be assessed, with the aim of applying the method
to
obtain velocity and density information from craters in retrieved
space-exposed surfaces. (C) 1999 COSPAR. Published by Elsevier
Science
Ltd.
==================
(9) JAPANESE CONTRIBUTION TO METEOROID & SPACE
DEBRIS
MEASUREMENT
H. Yano: Japanese contribution to in-situ meteoroid and debris
measurement in the near Earth space. EARTH PLANETS AND SPACE,
1999,
Vol.51, No.11, pp.1233-1246
INST SPACE & ASTRONAUT SCI,PLANETARY SCI DIV,3-1-1
YOSHINODAI,SAGAMIHARA,KANAGAWA 229851,JAPAN
This paper reviews major results of present studies and recent
developments for future missions in the Japanese space program
regarding in-situ measurement and collection of micrometeoroids
and orbital debris in the near Earth space. Japan's contribution
in
this area began with the post flight impact analysis of the Space
Flyer Unit (SFU) satellite which was returned to Earth in 1996
after
10-month exposure in space. Despite a decade later than similar
efforts first conducted in the USA and Europe, it resulted in a
record of over 700 hypervelocity impact signatures, which now
forms
the nation's first database of real space impacts being open to
public in the Internet. Together with laboratory impact tests,
both
morphological and elemental analyses of the impact craters
yielded
new insights of the meteoroid to debris ratio as well as flux
variation compared with the previous spacecraft. The next step
was a
passive aerogel exposure in the STS-85 shuttle mission in 1997.
No
hypervelocity impact was found there but its experience has been
incorporated for designing a microparticle collector to be
on-board
the Japan Experiment Module-Exposed Facility of the International
Space Station. All of such ''passive'' collection of micro-impact
features, however, still leave the significant uncertainty in the
quest of their origins. Therefore an aerogel-based ''hybrid''
dust
collector and detector (HD-CAD) is currently under the
development.
It measures time of impact and deduces impactors' orbital and
physical parameters by detecting impact flash while still
capturing
them intact. The system is suitable for both (1) sample return
missions in LEO as well as to parent bodies of meteoroids, i.e.,
comets and asteroids, and (2) one-way mission to where the
thermal
and plasma environment is such that impact induced plasma
detectors
may suffer from significant noise, e.g., a Mercury orbiter and a
solar probe. Together with unambiguous dust samples from a comet
by
STARDUST and an asteroid by MUSES-C as references, the HD-CAD in
the
LEO will be able to deduce the accretion rates of the cometary
and
asteroidal dust grains on the Earth. Copyright 2000, Institute
for
Scientific Information Inc.
===========================
* LETTERS TO THE MODERATOR *
=============================
(10) POSSIBLE CAUSES OF CYCLICAL IMPACT EVENTS
From Michael Rampino <mrr1@is3.nyu.edu>
Benny:
A nice up-to-date discussion of the possible causes of cyclic
impacts
and extinctions is given by John and Mary Gribbin in their book
"Fire
on Earth (St. Martin's Press, New York, 1996; see Chapter 8,
Cycles of
Doom).
After reviewing the evidence, they conclude that it makes:
"the
galactic carousel is our best buy to account for the 30 Myr cycle
of
death."
Mike Rampino
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)
and NASA, Goddard Institute for Space Studies, 2880 Broadway, New
York, NY
10025. mrampino@giss.nasa.gov
===========
(11) RUMOURS AND ALLEGATIONS
From Jeremy Tatum <UNIVERSE@uvvm.UVic.CA>
What is the matter with solar system scientists these days? We
used to
do astronomy because we enjoyed it. Nowadays the field seems all
too
full of people who seem to make it their business to find fault
with
the efforts of others, by making unfounded allegations and
spreading
rumours about the personal deficiencies of colleagues, and
keeping it
up for month after month. Anyone will be able to think of recent
examples. Yet another one turned up in today's peisergrams. This
time a
"source" explained "privately" to UPI that an
"unnamed space official"
had altered something or other, and it was therefore someone's
fault
that the Mars Polar Lander failed. Such rumours about unnamed
persons
by unnamed persons should be ignored and I am surprised that they
would
be further distributed in a peisergram.
Exploring planets by spacecraft is an enormously difficult
undertaking,
and there are certain to be failures along the way, and probably
many
of them. Certainly when there is a failure, there needs to be an
enquiry to determine its cause, whether by human failure or not -
but
anonymous accusations of wrongdoing and of coverups (whether in
this
instance or in others that will doubtless come to mind) are about
as
unhelpful as it is possible to imagine.
No one and no organization is beyond constructive criticism, but
to
anyone who feels he has to find fault with a failed spacecraft
excursion to a distant planet I would just say: "Well, you
go ahead and
do it, and show us how it ought to be done."
Jeremy Tatum
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