PLEASE NOTE:
*
CCNet, 37/2000 - 22 March 2000
------------------------------
"The disappearance of NASA's Mars
Polar Lander last December
was no surprise to space officials, UPI
has learned. Prior to its
arrival at Mars, a review board had
already identified a fatal
design flaw with the braking thrusters
that doomed the mission,
but NASA withheld this conclusion from
the public. [...] A source
close to the panel probing the second
accident has told UPI that
its conclusions are
"devastating" to NASA's reputation. Unlike the
previous accident, where management
errors merely prevented the
recognition of other human errors, in
this case it was a
management misjudgment which caused the
fatal flaw in the first
place."
--
James Oberg, 21 March 2000
(1) IAU CALL FOR RECOMMENDATIONS ON MPC TERMS OF REFERENCE
Michael A'Hearn <ma@astro.umd.edu>
(2) IAU, MPML & A NEO-CONSPIRACY THEORY
Benny J Peiser <b.j.peiser@livjm.ac.uk>
(3) EARTH'S CLOSE SHAVE
BBC News Online, 21 March 2000
(4) NASA KNEW THAT MARS POLAR LANDER WAS DOOMED
James Oberg <JamesOberg@aol.com>
(5) NEW METHOD OF DETECTING NANNOBACTERIA
Andrew Yee <ayee@nova.astro.utoronto.ca>
(6) GLOBAL WARMING DUE TO NATURAL CAUSES:
BUT UNDERLYING MECHANISM REMAINS UNCERTAIN
Andrew Yee <ayee@nova.astro.utoronto.ca>
(7) CHEMICAL SEPARATION OF Fe-Ni PARTICLES AFTER IMPACT
Y. Miura et al., YAMAGUCHI UNIVERSITY
(8) COLLECTION OF MICROMETEOROID REMNANTS FROM LOW EARTH ORBIT
G. A. Graham et al., OPEN UNIVERSITY
(9) IN-SITU DETECTION OF MICROMETEOROIDS AND ORBITAL DEBRIS
J.C. Mandeville et al., OFF NATL ETUD &
RECH AEROSP
(10) A COMMENT ON GOLD DUST
Larry Klaes <lklaes@bbn.com>
=================
(1) IAU CALL FOR RECOMMENDATIONS ON MPC TERMS OF REFERENCE
From Michael A'Hearn <ma@astro.umd.edu>
[as posted on the MPML mailing list on 21 March 2000]
Dear Colleagues,
We note that there have been several messages circulated in this
forum
about the MPC and the proposed Terms of Reference drafted by a
small
group consisting of Andrea Carusi and the three of us. We are
gratified
by the keen interest of the community in the subject in general
and the
draft in particular, and thank all who have contributed to the
discussion. Regarding the further procedure, we wish to stress
that:
a) The messages circulated are not representative of the complete
set
of messages that have been received by us,
b) Every message received by us is given careful attention, but
we
assume that some may have been sent in confidence
and we do not
intend to circulate the complete set to a wide
audience.
Correspondents are, of course, free to disseminate
their views
as they see fit, but we cannot undertake to answer
them.
c) We are convinced that, to end the existing poorly-defined
state
of affairs, specific Terms of Reference are needed
to ensure the
long-term continuation of the MPC as an important
and effective
part of the astronomical research community,
especially at a time
when increasing international research activities
are placing
steeply increasing demands on its services,
d) We have explicitly solicited comments from a modest but very
diverse group of experts, including the Organizing
Committees of
Commission 20 and the WG NEO, several NEO
discoverers & astrometric
observers, and a set of orbit computers, and
e) We welcome further SPECIRIC recommendations for IMPROVING the
Terms of Reference. These should be directed to
Michael A'Hearn
(ma@astro.umd.edu).
When a satisfactory text has been prepared,
it will be submitted to the IAU Executive Committee
for decision.
Michael F. A'Hearn, President, Division III
Hans Rickman, President, Commission 20; and Assistant General
Secretary
Johannes Andersen, General Secretary
==============
(2) IAU, MPML & A NEO-CONSPIRACY THEORY
From Benny J Peiser <b.j.peiser@livjm.ac.uk>
In a somewhat peculiar statement to the MPML mailing list,
officials of
the International Astronomical Union (IAU) have called upon
amateur and
professional astronomers to come forward with "specific
recommendations
for improving the [MPC] Terms of Reference" (see the IAU
statement
above).
Strangely, the IAU officials claim that "there have been
several
messages circulated in this [MPML] forum about the MPC and the
proposed
Terms of Reference drafted by a small group consisting of Andrea
Carusi
and the three of us. We are gratified by the keen interest of the
community in the subject in general and the draft in particular,
and
thank all who have contributed to the discussion."
To the best of my knowledge, the so-called "MPC Terms of
Reference"
have never been published or mentioned on MPML, let alone
discussed on
the mailing list in question. It is the first time the issue has
been
brought to the attention of the interested public, and I am
starting to
wonder what the IAU is up to. Surely, the call for further
suggestions
and recommendations is incoherent as long as the IAU does not
inform the
NEO community what the whole fuss is about. Perhaps one of the
signatories would be happy to illuminate the interested public
what is
going on here.
In another development on the same mailing list, Andrea Milani
has
stepped up his public campaign against the MPC and leading NEO
search
programmes. In a statement to MPML on 21 March, the Italian
mathematician speculates that asteroid Hermes, first detected in
1937
but subsequently lost, may have been already re-discovered by an
astronomer. In his statement he hints at the possibility that the
crucial asteroid information may be "kept in some secret
[...] file" by
the MPC which Milani accuses of having "a private
agreement" with
leading NEO search programmes which, he alleges, wish to keep
observational data hidden from public inspection.
These are serious allegations indeed. The noticeable reticence by
the
IAU in face of accusations against one of their own institutions
as
well as internationally respected NEO search programmes is rather
distressing. Nevertheless, the allegations deserve to be
addressed and
clarified by the IAU in due course if further damage is to be
averted.
Benny J Peiser
==============
(3) EARTH'S CLOSE SHAVE
From the BBC News Online, 21 March 2000
http://news.bbc.co.uk/hi/english/sci/tech/newsid_685000/685539.stm
By BBC News Online science editor Dr David Whitehouse
A newly-discovered asteroid will pass moderately close to the
Earth in
the next few days.
Designated 2000 EW70, the space rock will come within about 1.9
million
kilometres (1.2 million miles) of the planet - or about five
times the
Earth-Moon distance. Suggestions of a collision sometime in the
future
have been exaggerated, say astronomers.
On 9 March, the Linear asteroid patrol camera in New Mexico
picked up a
fast-moving object. A preliminary calculation of its orbit
suggested it
would make a moderately close pass in a few weeks.
At that time, there was nothing very unusual about the situation
until
the alarm was raised by the US astronomy magazine Sky &
Telescope, that
claimed that the newly-discovered asteroid "could threaten
Earth at
some future date."
Since then, however, astronomers have tried to put 2000 EW70 into
perspective. "There is no evidence, to my knowledge, to
suggest that
asteroid 2000 EW70 poses any threat to collide with Earth in the
near
future," says Benny Peiser, of Liverpool John Moores
University in the
UK.
Orbit computations
In the astronomical world, Brian Marsden of Harvard University is
the
custodian of cometary and asteroid orbits and issues the
International
Astronomical Union (IAU) circulars that alert astronomers to
important
goings-on in space including threatening asteroids.
Asked to comment on 2000 EW70, he said that he was "not
aware of any
computations showing that any impact is remotely possible during
the
next several decades."
The asteroid may not be a problem but astronomers do have
concerns in
explaining the nature of the potential threat from so-called NEOs
(Near
Earth Objects).
In general, they want to give the public an accurate impression
of the
possible threat from NEO's but they do not want to set off a
series of
false alarms that would ultimately sour the public's and the
politicians' view of the subject.
Impact warnings
Benny Peiser commented: "Science writers, web authors and
net
moderators are well advised to consult with the experts in the
field
before publishing misguided or alarmist asteroid alerts.
"Mind you, this advice is perhaps even more valid for some
rash NEO
researchers who have been prone to issue rushed impact warnings,
often
quite unnecessarily."
According to astronomer Daniel Fischer "the moderately close
approach
of asteroid 2000 EW70 to Earth could be used to raise awareness
of
these kinds of objects and that they really exist and are not
just in
the movies."
You will need a powerful telescope to see the asteroid. It will
be
about as bright as Pluto, the most distant planet. But despite
its
faintness, the rock will be so close that it will appear to
almost
streak across the sky. The asteroid will move across the sky at
about
one degree per hour, or two diameters of the full Moon.
Copyright 2000, BBC
==============
(4) NASA KNEW THAT MARS POLAR LANDER WAS DOOMED
From James Oberg <JamesOberg@aol.com>
NASA knew Mars Polar Lander doomed
United Press International - March 21, 2000 15:01
By James Oberg, UPI Space Writer
HOUSTON, March 21 (UPI) -- The disappearance of NASA's Mars Polar
Lander last December was no surprise to space officials,
UPI has
learned.
Prior to its arrival at Mars, a review board had already
identified a
fatal design flaw with the braking thrusters that doomed the
mission,
but NASA withheld this conclusion from the public.
The probe was lost while attempting to land near the martian
south
pole on December 3. Two small microprobes which had deployed
separately also were never heard from again.
It was the second expensive setback for American interplanetary
exploration in less than three months. On September 23, a
companion
probe had been destroyed when a navigation error sent it skimming
too
deeply into the atmosphere of Mars.
Following these failures, NASA commissioned several expert panels
to
review the accidents and recommend improvements in NASA
procedures.
A source close to the panel probing the second accident has told
UPI
that its conclusions are "devastating" to NASA's
reputation. Unlike
the previous accident, where management errors merely prevented
the
recognition of other human errors, in this case it was a
management
misjudgment which caused the fatal flaw in the first place.
"I'm as certain as I can be that the thing blew up,"
the source
concluded.
As explained privately to UPI, the Mars Polar Lander vehicle's
braking thrusters had failed acceptance testing during its
construction. But rather than begin an expensive and
time-consuming
redesign, an unnamed space official simply altered the conditions
of
the testing until the engine passed.
"That happened in middle management," the source told
UPI. "It was
done unilaterally with no approval up or down the chain of
command."
The Mars Polar Lander employed a bank of rocket engines which use
hydrazine fuel. The fuel is passed through metal grates which
cause
it to decompose violently, creating the thrust used by the
engines.
These metal grates are called "catalyst beds," or
"cat beds." Their
purpose is to initiate the explosive chemical reaction in the
hydrazine.
"They tested the cat bed ignition process at a temperature
much
higher than it would be in flight," UPI's source said. This
was done
because when the cat beds were first tested at the low
temperatures
predicted after the long cruise from Earth to Mars, the ignition
failed or was too unstable to be controlled.
So the test conditions were changed in order to certify the
engine
performance. But the conditions then no longer represented those
most
likely to occur on the real space flight.
Following the September loss of the first spacecraft due to
management errors, NASA had initiated a crash review of the Mars
Polar Lander to identify any similar oversights. According to
UPI's
source, the flaws in the cat bed testing were uncovered only a
few
days before the landing was to occur on December 3.
By then it was too late to do anything about it.
Garbled rumors of some temperature-related design flaw circulated
in
the days before the landing attempt. However, as in the September
case when space officials possessed terrifying indications of
imminent failure even before the arrival at Mars, NASA made no
public
disclosure of these expectations.
The Mars Polar Lander investigation team has also reportedly
identified a second fatal design flaw that would have doomed the
probe even if the engines had functioned properly.
The three landing legs of the probe contain small microswitches
which
are triggered when the legs touch the surface. This signal
commands
the engines to cease firing.
Post-accident tests have shown that when the legs are initially
unfolded during the final descent, springs push them so hard that
they "bounce" and trigger the microswitches by
accident. As a result,
the computer receives what it believes are indications of a
successful touchdown, and it shuts off the engines.
Since this false signal actually occurs high in the air, the
engine
shutdown automatically leads to a free fall and destructive
high-speed impact.
Ground testing prior to launch apparently never detected this
because
each of the tests was performed in isolation from other tests.
One
team verified that the legs unfolded properly. Another team
verified
that the microswitches functioned on landing.
No integrated end-to-end test was performed due to budget and
time
constraints. But UPI has been privately told that "this has
been
reproduceable on a regular basis" in post-flight tests.
Perhaps by coincidence, in a safety memo to NASA employees
distributed on March 20, NASA administrator Dan Goldin stressed
"the
importance of adequate testing." Reliability, he said,
"requires
well-thought-out verification and test activities."
Goldin explicitly described the adverse impact of "our
difficulties
with recent failures in late stages of development -- such as
system
integration and testing -- and during mission operations."
The memo
did not specifically attribute these problems to the Mars
failures.
The Mars Polar Lander also deployed two small
"penetrator" probes,
both called Deep Space 2. They were designed to fall freely
through
the thin atmosphere, hit the ground at about 200 meters per
second
(400 miles per hour), and come to rest deep in the soil.
All attempts to pick up radio signals from these probes, relayed
via
another spacecraft already orbiting Mars, also failed.
Reportedly,
the review board believes that the probe radio equipment could
not
have survived the impact.
Alternately, the probes may simply have hit ground too rocky for
survival. Engineers also suspected that their batteries, which
had
been charged before launch almost a year earlier and not checked
since then, might not have retained sufficient power.
"Nobody in the know really expected either of the
penetrators to
work," UPI's primary source said.
Dr. Carl Pilcher, head of NASA's planetary program, talked with
space
scientists at last week's Lunar and Planetary Science Conference
in
Houston. While expressing disappointment at the setbacks and
skepticism of ambitious flight schedules -- "Our ambition
exceeded
our grasp," he told the scientists -- he would not discuss
the
results of the accident investigation.
The conclusions, he did admit, "make sober reading."
The
investigation was led by Tom Young, a former manager at NASA's
Jet
Propulsion Laboratory which runs most of NASA's deep space
probes.
"Goldin recently told his managers that the Young report
will be the
Rogers Commission of space science," Andrew Lawler wrote in
the March
10 issue of Science magazine, "referring to the devastating
critique
delivered by a panel that examined the 1986 Challenger
disaster."
And in a March 9 internal memo from JPL director Ed Stone, which
UPI
has obtained, space workers are warned that "the days ahead
may at
times be difficult."
According to Lori Garver, NASA's associate administrator for
plans,
the report on NSA's failures will be reviewed internally and then
will be sent to the White House before being released to the
public.
Copyright 2000, UPI
==============
(5) NEW METHOD OF DETECTING NANNOBACTERIA
From Andrew Yee <ayee@nova.astro.utoronto.ca>
University of Texas-Austin
Office of Public Affairs
P O Box Z
Austin, Texas 78713-7509
(512) 471-3151 FAX (512) 471-5812
Contact:
Mary Lenz, UT Austin Office of Public Affairs
March 20, 2000
New method of finding nannobacteria in rust could be used on Mars
rocks
AUSTIN, Texas -- Two geology professors at The University of
Texas at
Austin, Dr. Robert L. Folk and Dr. Kitty L. Milliken, have
demonstrated
that iron oxide filaments from a variety of geological periods on
Earth
are lifelike in form at microscopic levels. They say their
research
could have implications for Martian exploration and the search
for some
form of life on other planets.
Scientists have been debating for a century whether iron oxide,
commonly known as rust, results from biological or inorganic
processes.
The question of whether life forms such as bacteria or viruses
play a
role in the formation of rocks rich in iron oxide has not yet
been
settled, Folk said.
But Folk and Milliken say the microscopic shapes they found would
strongly suggest that living matter is intimately involved in the
process. Their findings will be presented at the Geological
Society of
America meeting on Wednesday (March 22) in Charleston, S.C.
Milliken is
a research scientist in the department of geological sciences.
Folk is a Dave P. Carlton Centennial Professor Emeritus in
Geology in
the department, who has done pioneering work on forms called
nannobacteria. Nannobacteria are incredibly small strands, along
with
spherical and egg-shaped objects found in rocks and minerals and
believed by a few scientists to be dwarf forms of bacteria. They
are
about 1,000 times smaller than normal bacteria. Folk said half a
billion nannobacterial cells could fit on a pinhead.
Many biologists say no living creature could be smaller than
about 0.2
microns because they say that is too small a size to contain the
genetic material necessary for life. (A micron is one-millionth
of a
meter in the metric system.) And other scientists deny the
structures
represent the presence of life, arguing that the suggestive
shapes are
merely the result of chemical actions or weathering.
Folk and other researchers admit that suspiciously lifelike shape
does
not necessarily prove or disprove the presence of life. But they
believe the forms are fossils of the most primitive and earliest
life
forms on found on Earth and beyond.
Folk discovered the first mineralized nannobacteria in an Italian
hot
springs deposit about 10 years ago. Folk's nannobacteria web page
contains a photo gallery of the mysterious shapes found in fossil
form
in mineral and rock samples from Italy and from carbonaceous
meteorites. The address is http://www.geo.utexas.edu/Illite/
.
Folk and Milliken's most recent research shows that modern iron
oxide
deposits (rust) contain these same tiny filamentous structures
shaped
like very small microbes. The iron oxides also contain a
veritable
"zoo" of other nano-sized bodies, which Folk said
indicate the presence
of life.
Folk found the same features in both the new forms and the
ancient
forms of the iron deposits. "Together we worked on iron
oxides ranging
from those that clog present-day pipes to ancient iron deposits
as old
as three billion years," Folk said. Folk said in modern
oxides "these
nano-scale features are clearly organic because they remain in
residue
after iron oxides have been leached out. Bacteria and
nannobacteria
leave abundant evidence of their presence in iron oxides in the
shapes
we see under the microscopes."
The scientists used a simple new technique to separate out the
nannobacteria. "Slightly dissolving iron oxide with
hydrochloric acid
reveals the entombed nannobacteria -- a method that has not
heretofore
been used, nor has investigation of the deposits been made at
such high
magnifications," Folk said. "These dwarf forms of
bacteria precipitate
the iron oxide in modern rust. The presence of these same forms
in
iron–rich sediments that are extremely ancient (billions of
years)
indicates their important role in chemical reactions."
Normal-sized iron bacterial filaments are seen best with a 3-D
microscope. Very minute nannobacterial cells -- cells 50-to-100
nanometers in diameter -- are visible only using an electron
microscope. These features are easily found in iron oxides of all
ages
in rocks on Earth by using the new microscope technology. If the
research is correct, Folk said the same methods could be useful
in
evaluation of iron-rich rocks that eventually may be retrieved by
Martian exploration vehicles.
When NASA scientists in 1996 announced that odd formations,
resembling
terrestrial nannobacteria, appeared to be present in a carbonate
vein
of a 4.57 billion-year-old Martian meteorite recovered in
Antarctica
some years earlier, they based their announcement on Folk's
research on
Italian travertines (a type of limestone). Folk said his work on
the
other carbon-bearing meteorites "implies that minute forms
of life may
have existed not only on Mars but also on other planets and
asteroids,
the source of most meteorites."
Folk and his nannobacteria research team include Dr. Brenda L.
Kirkland
of the UT Austin department of geological sciences, Dr. Leo Lynch
of
the Mississippi State University department of geosciences, Dr.
Ian J.
Molineux, a professor in the UT Austin department of molecular
genetics
and microbiology and Dr. Robert J.C. McLean of the Southwest
Texas
State University biology department.
For more information, contact Dr. Robert Folk at the Department
of
Geological Sciences at (512) 471-5294 and visit the Nannobacteria
Home
Page at http://www.geo.utexas.edu/Illite/
==============
(6) GLOBAL WARMING DUE TO NATURAL CAUSES:
BUT UNDERLYING MECHANISM REMAINS UNCERTAIN
From Andrew Yee <ayee@nova.astro.utoronto.ca>
Scripps Institution of Oceanography
University of California-San Diego
Scripps Contacts:
Mario Aguilera or Cindy Clark: (858) 534-3624
E-mail: maguilera@ucsd.edu,
cclark@ucsd.edu
New Research on Long-Term Ocean Cycles Reveals Rapid Global
Warming in
Near Future
Scientists at Scripps Institution of Oceanography at the
University of
California, San Diego, report evidence of pronounced changes in
the
earth's climate that can be tracked in cycles of ocean conditions
over
thousands of years. These cycles reveal that Earth is currently
in a
period in which a natural rise in global temperatures -- combined
with
warming from the greenhouse effect -- will push the planet
through an
era of rapid global warming.
Charles Keeling and Timothy Whorf report in the March 21 online
edition
of the Proceedings of the National Academy of Sciences (PNAS)
that
strong oceanic tides are the engines behind this warming-cooling
cycle
that may help determine future climates. This report is the first
comprehensive study of the effects of tidal mixing on climate
change
spanning millennia. The current phase in the cycle suggests that
a
natural warming trend began a hundred years ago, picked up in the
1970s, and should continue over the next five centuries.
"We have discovered an 1,800-year tidal cycle that appears
to match
with recent climate change," said Charles Keeling, the
study's first
author. "If this is a correct mechanism for understanding
climate
change over millennia, then temperatures will rise both because
of
weaker tidal mixing and because of the greenhouse effect, which
is on
the increase as well."
The researchers suggest that strong oceanic tides drive changes
in
climate due to their ability to increase vertical mixing in the
ocean
and thereby transport cold ocean water to the surface. The strong
tides
elicit cool conditions on the sea surface, which in turn lowers
temperatures in air and over land, resulting in cooler climates
around
the planet, often accompanied by drought conditions. Weak tides
lead to
less cold water mixing and result in warmer periods on Earth.
Keeling and Whorf's 1,800-year cycle, which arises because of
gradual
changes in the astronomical alignments of the sun, moon, and
earth, was
proposed as an explanation for nearly periodic millennial changes
in
temperature seen in ice and deep-sea sedimentary core records.
Previously (1997), they have reported on the effects of shorter
cycles
of tidal forcing on global temperature at periods near 18, 90,
and 180
years.
A maximum in tidal cooling near 1974 might have produced more
cooling,
but perhaps was masked by a simultaneous greenhouse warming,
according
to Keeling, a professor of oceanography at Scripps.
"If that is true, then it becomes pretty clear that if
today's natural
warming trend is combined with the greenhouse effect, then we'll
soon
see the effect of combined warming all over the world," said
Keeling.
In addition to climate change recognition, the research also
represents
a new mechanism for analyzing events in world history. The paper
reports on the near coincidence of major tidal fluctuations with
worldwide phenomena, including the Little Ice Age of 1400 A.D. to
1700
A.D., major dust layers in Minnesota lake sediments spaced about
1,800
years apart, a major drought in the Amazon Basin around 2200
B.C., and
a 2000 B.C. drought that may have contributed to the collapse
of
Akkadia, a Mesopotamian civilization regarded as the world's
first
empire. The Vikings inhabited Greenland in temperate conditions
in the
tenth century near the end of a period of weak tidal activity,
but
perished or left Greenland when tides strengthened near the
beginning
of the Little Ice Age in the 13th century.
"One of the principle benefits of the tidal hypothesis is
that
researchers can compare the timing of specific historical events
with
predicted times of warming or cooling to see whether they
coincide or
not," said Whorf, a research associate in the Geosciences
Research
Division of Scripps. "If we are correct, then the 1,800-year
tidal
cycle will be important in understanding future climates as well
as
events of the past." The study was supported by the National
Science
Foundation and the U.S. Department of Energy.
Scripps Institution of Oceanography, at the University of
California,
San Diego, is one of the oldest, largest, and most important
centers
for global science research and graduate training in the world.
The
National Research Council has ranked Scripps first in faculty
quality
among oceanography programs nationwide. The scientific scope of
the
institution has grown since its founding in 1903 to include
biological,
physical, chemical, geological, geophysical, and atmospheric
studies of
the earth as a system. More than 300 research programs are under
way
today in a wide range of scientific areas. The institution has a
staff
of about 1,300, and annual expenditures of approximately $100
million,
from federal, state, and private sources. Scripps operates the
largest
academic fleet with four oceanographic research ships for
worldwide
exploration and one research platform.
=============
(7) CHEMICAL SEPARATION OF Fe-Ni PARTICLES AFTER IMPACT
Y. Miura*), S. Fukuyama, M.A. Kedves, A. Yamori, M. Okamoto, A.
Gucsik:
Chemical separation of Fe-Ni particles after impact. ADVANCES IN
SPACE
RESEARCH, 1999, Vol.25, No.2, pp.285-288
*) YAMAGUCHI UNIV,DEPT EARTH SCI,YAMAGUCHI 7538512,JAPAN
Tiny grains of Fe-Ni system originated from planetesimals or
meteoroids
can remain under solid (or melt)-solid impact reactions even
after
impact process, probably together with high pressure form of Fe
phase.
Impact fragment with major Fe-Si (-Ni) system can be formed under
vapor
condition of impact reaction from terrestrial and artificial
impact
craters and spherules, and those with Ni-CI (-S) system in
composi-
tion are formed under vapor condition of artificial impact
experiments
on the Barringer iron meteorite. These impact grains of
Fe-bearing
composition or high pressure form of iron-rich phases will be
found
probably on the asteroids in future exploration. (C) 1999 COSPAR.
Published by Elsevier Science Ltd.
==========
(8) COLLECTION OF MICROMETEOROID REMNANTS FROM LOW EARTH ORBIT
G. A. Graham*), A.T. Kearsley, M.M. Grady, I.P. Wright,
J.A.M. McDonnell: The collection of micrometeoroid remnants from
low
earth orbit. ADVANCES IN SPACE RESEARCH, 1999, Vol.25, No.2,
pp.303-307
*) OPEN UNIVERSITY,PSRI,MILTON KEYNES MK7 6AA,BUCKS,ENGLAND
The solar array panel returned from the Hubble Space Telescope
after
3.62 years of space exposure offered the opportunity to study
individual solar cells for hypervelocity impact damage and
residue. A
detailed electron microscope investigation of impact craters
(100-1000
mu m diameters) has identified that most are residue-rich and by
digitised x-ray elemental mapping and semi-quantitative
micro-spot
analysis the original precursor composition of the impactor can
almost
unambiguously be identified. The residues contain diverse
elemental
compositions that can be associated with known meteorite
mineralogies
and directly compared with interplanetary dust particles and
micrometeorites, possibly the most likely source object. The
observation of a magnesium-rich residue with (Mg+Fe) / Si ratio
similar
to that of forsterite (end-member Mg-olivine identified in
meteorites),
indicates that it is possible in favourable conditions to define
clearly the compositional nature of the impactor. The
identification of
near-intact calcium-rich fragments, that are neither artefacts
nor
contamination, indicates that volatile chemistries can survive
hypervelocity impacts in brittle glass substrates. The abundance
of
micrometeoroid residues in the individual solar cells has
highlighted
that valuable information can be retained from impact craters in
returned space hardware which are essentially not designed as a
dust
collectors. (C) 1999 COSPAR. Published by Elsevier Science Ltd.
============
(9) IN-SITU DETECTION OF MICROMETEOROIDS AND ORBITAL DEBRIS
J.C. Mandeville*), C.R. Maag, C. Durin: In-situ detection of
micrometeoroids and orbital debris: The PIE experiment on MIR.
ADVANCES IN SPACE RESEARCH, 1999, Vol.25, No.2, pp.329-334
*) OFF NATL ETUD & RECH AEROSP,DESP,2 AV E
BELIN,TOULOUSE,FRANCE
During the last few years, investigation of impact features found
on
material retrieved after exposure to space for a long period of
time,
in low earth orbits, has provided us with a great deal of data on
the
particulate environment, either natural or man-made. The PIE
detection
device presented here has been deployed outside the Kvant-2
module
attached to the Russian MIR station, between June 1996 and April
1997.
Part of the experiment uses a detection technique similar to the
one
used in previous experiments flown on LDEF and MIR. Passive
sensors are
composed primarly of stacked thin metal foils (gold and
aluminium).
According to the size of the particles, they are either
decelerated or
fragmented upon high velocity impact. The size of holes or impact
craters give information on the size or shape of the impacting
particles. Samples have been retrieved for laboratory analysis.
Comparison with data from LDEF, EuReCa, I-IST and previous
experiments
on MIR provides insight in the long term evolution rf small
particle
population and in the debris environment of a permanently manned
station. Some of the samples show evidence of secondary
impact
cratering: an attempt is made to locate the origin of the primary
impact site. Some results about the possible origin of the
impactors
are provided by the chemical identification of particle remnants
inside
the craters. (C) 1999 COSPAR. Published by Elsevier Science Ltd.
=============================
*LETTERS TO THE MODERATOR *
=============================
(10) A COMMENT ON GOLD DUST
From Larry Klaes < lklaes@bbn.com
>
Hi Benny,
In regards to the March 20, 2000 CCNet article on Thomas Gold and
his
theory of oil creation, the ABC News item declares that in 1959
Gold
said the lunar surface was covered in dust when every other
scientist
said it was lava. They then said it was proven true with Apollo.
What the ABC News item fails to add is that Gold also said the
lunar
dust was thick enough to probably swallow up any vehicles that
landed
on the surface. This was proven wrong first by unmanned landers
like
Surveyor and then Apollo in the late 1960s.
Larry
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CCNet-ESSAY, 22 March 2000
--------------------------
THE 3.2+/- 0.1 B.Y. IMPACT CATACLYSM IN
THE EARTH-MOON SYSTEM
By Andrew Glikson <andrew.glikson@anu.edu.au>
Research School of Earth Science,
Australian National University, Canberra, ACT 0200;
The Late Heavy Bombardment (LHB) in the Earth-Moon system,
broadly
defined at 4.2-3.8 * 10^9 years [1], may represent the tail-end
of
planetary accretion or, alternatively, include a distinct
3.95-3.80*10^9 years bombardment episode [2]. Here I point out
that
combined evidence from terrestrial Archaean terrains and from the
Moon militate for a major impact cataclysm in the Earth-Moon
system
about 3.2+/-0.1*10^9 years. Older less-well-defined impact events
in
the Earth-Moon system are also marked about 3.47-3.46*10^9 years
- a
time of maximum greenstone-granite formation. The question is
whether
these events signify an extension of the LHB or represent
temporally
distinct episodes.
. . . [continued]