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(meteorobs) Excerpts from "CCNet 116/2001 - 8 November 2001"
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From: Peiser Benny <B.J.Peiser@livjm.acdot uk>
To: cambridge-conference <cambridge-conference@livjm.acdot uk>
Subject: CCNet 116/2001 - 8 November 2001
Date: Thu, 8 Nov 2001 12:13:34 -0000
CCNet 116/2001 - 8 November 2001
================================
[...]
(4) MILITARY SATELLITES BRACE FOR LEONID METEOR SHOWER
Space.com, 7 November 2001
[...]
(6) CANADIAN SCIENTISTS SEEKING HELP IN SEARCH FOR METEOR
Ron Baalke <baalke@zagami.jpl.nasadot gov>
[...]
(11) SERVING UP METEORITES ON ICE
Planetary Science Research, 7 November 2001
[...]
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(4) MILITARY SATELLITES BRACE FOR LEONID METEOR SHOWER
>From Space.com, 7 November 2001
http://www.space.com/businesstechnology/technology/leonids_satellites_011107-1.html
By Jim Banke
Senior Producer, Cape Canveral Bureau
CAPE CANAVERAL, Fla. -- Satellite operators will keep a close eye on their
Earth-orbiting spacecraft during the upcoming Leonid meteor shower, and
though the risk of damage from a stray speck of dust is greater than normal,
officials are confident there will be no natural disasters in space.
Nevertheless, if a Leonid meteoroid hits a satellite, the small grain can
destroy an imaging mirror or plow through fragile parts such as an
electricity-generating solar panel, possibly creating electrical shorts that
can disable the craft. Just the momentum imparted by an impact can throw a
satellite off course.
Especially sensitive at this time -- but not necessarily vulnerable -- are
the nation's reconnaissance, communications, navigation and weather
forecasting satellites, which are playing a key role in the United States'
efforts to combat terrorism in Afghanistan, and around the globe.
Not to worry, officials say.
"Satellites are designed with information about past storms and other things
that can happen in space," said Capt. Adriane Craig, a spokesperson for the
U.S. Air Force Space Command at Peterson Air Force Base near Colorado
Springs, Colo.
"Our satellites are robust and in the event that there is a problem we have
backup systems and contingency plans to help get them back online."
Air Force controllers at Peterson are responsible for monitoring the various
constellations of military satellite systems around the clock, Craig said,
but she wouldn't say exactly what additional measures -- if any -- are being
taken to minimize the threat from the Leonids.
"For the Leonids we have models that help us predict when the storm will
peak, so certainly (the satellite operators) can be more attentive during
that time, but we monitor the spacecraft pretty vigilantly every day of the
year," she said, politely refusing to elaborate. "I will not reveal anything
operationally about any actions we might or might not take."
The story is the same at the National Reconnaissance Office (NRO), which is
responsible for operating the many clandestine spy satellites responsible
for so much of the nation's space-based intelligence gathering efforts.
"We're working closely with the Air Force to fully understand the
implications of the Leonid storm, and we'll take precautions that we feel
are appropriate," said Art Haubold, a spokesman for the National
Reconnaissance Office. "However, we don't discuss operational details of our
satellites."
It's possible that in some cases a satellite may be turned off as the best
defense against being struck by a Leonid meteoroid. However, industry
observers and others agree that military and NRO spacecraft are constructed
with extra shielding and back up systems inside the spacecraft itself,
allowing continuing operation no matter what.
"Military satellites are much more hardened and much more capable of
surviving such things than normal satellites," said Bill Cooke, a meteor
forecaster at NASA's Marshall Space Flight Center in Huntsville, Ala.
So to, Cooke said, is the International Space Station, where the current
Expedition Three crew of Frank Culbertson, Vladimir Dezhurov and Mikhail
Turin are wrapping up a four-month stay in space. Shuttle Endeavour is to be
launched Nov. 29 -- long after the Leonid's peak -- to bring up a new crew
and then return to Earth on Dec. 10.
"The space station has armor to protect it against stuff as much as an inch
across," Cooke said. "We're not expecting anything that big from this year's
Leonids."
Remnants from the icy comet Tempel-Tuttle, the Leonid meteor shower will
result when planet Earth sweeps through the comet's trail of debris next
week and the tiny particles encounter our atmosphere and burn up, sparking
what are commonly called shooting stars.
Earth will enter the heavier parts of the stream at about 11 p.m. EST on
Nov. 17 (0400 GMT Nov. 18). Activity will peak around 5 a.m. EST Nov. 18
(1000 GMT), when as many as 13 meteors per minute could be visible, likely
for a stretch of time that lasts less than one hour.
No larger than a grain of sand, the Leonid meteroids tend to vaporize at
about 60 miles (100 kilometers) above the surface. Satellites, however, are
orbiting the planet much higher and so could be hit by the bits before they
burned up.
Satellites that orbit between 200 and 600 miles (325 and 965 kilometers)
above Earth will face meteor rates roughly the same as what is expected to
be seen from the ground, Cooke said.
However, high-flying geostationary satellites, which sit 22,300 miles
(35,900 kilometers) above the planet will be closer to the densest part of
the debris stream. Moreover, geostationary satellites in the Western
Hemisphere would be at the greatest risk, Cooke said.
Because Tempel-Tuttle orbits the Sun in the opposite direction compared to
Earth -- a backward motion called retrograde -- its debris would hit a
satellite with much greater velocity than other meteors created by the
debris from other comets.
"It's like two cars hitting head-on," Cooke said, adding that the
penetration power is 16 times that of a normal meteor.
The greatest danger, Cooke says, is the generation of a plasma cloud -- a
byproduct of high-speed impacts that could cause an electrical short
circuit.
When a meteor as fast as a Leonid strikes something, it vaporizes, creating
a cloud of plasma, or electrically charged particles. An electrical current
can then flow from one part of the craft, through the plasma cloud, and then
destroy an instrument on another part of the craft.
Few such instances have been documented.
In 1993, during the August Perseid meteor shower, a meteor hit an Olympus
communications satellite. The impact formed a plasma cloud, and the craft's
attitude control system was zapped. By the time operators could stabilize
it, they had depleted all of its attitude-control propellant and the
satellite was lost.
Copyright 2001, Space.com
============================================================================
(6) CANADIAN SCIENTISTS SEEKING HELP IN SEARCH FOR METEOR
>From Ron Baalke <baalke@zagami.jpl.nasadot gov>
http://wwwdot canada.com/calgary/news/story.asp?id={5DDF144D-650D-4470-80EA-9E4
29C036EC5}
Scientists seeking help in search for meteor canada.com
November 7, 2001
CALGARY -- Researchers are hoping someone has a photograph or video of the
biggest meteor to fall in Alberta in 40 years so they can tell where it
landed.
Alan Hildebrand, a planetary scientist at the University of Calgary, says
the meteor was an asteroidal fragment that weighed five to 10 tonnes, about
1.5 meters in diameter.
Hildebrand says it was travelling at roughly 20 kilometres per second and
this was probably the biggest rock to fall on Alberta since 1960.''
The flaming rock was seen streaking north across the Alberta sky near the
British Columbia boundary on October 14th at around 2:20 a.m.
It exploded over the northern part of Banff National Park with a deafening
boom that could be heard 150 kilometers away.
Eyewitnesses reported seeing hundreds of pieces of the rock falling to the
ground, however, freshly fallen snow may delay the hunt for particles until
next spring.
============================================================================
(11) SERVING UP METEORITES ON ICE
>From Planetary Science Research, 7 November 2001
http://www.psrd.hawaiidot edu/Nov01/metsOnIce.html
- --- Antarctic meteorites provide a continuous and readily available supply
of extraterrestrial materials, stimulating new research and ideas in
cosmochemistry, planetary geology, astronomy, and astrobiology.
Written by Linda M.V. Martel
Hawai'i Institute of Geophysics and Planetology
Annual collections of meteorites from Antarctica are a steady source of new
non-microscopic extraterrestrial material including lunar and Martian
samples and rare and unusual flotsam from asteroids. This article summarizes
research on new kinds of Antarctic meteorites that is not simply changing
how meteorites are classified but causing a revolution in our knowledge of
the materials and processes in the solar nebula, our solar system, and the
formation of asteroids, planets, and ultimately our world. When the
2001-2002 Antarctic Search for Meteorites (ANSMET) field party begins
scouting for meteorites on the ice this season, we will be continuing a
25-year tradition of exploration along the Transantarctic Mountains. As a
new ANSMET meteorite hunter, I will report to PSRD on this season's search
and recovery of specimens and how studies of Antarctic meteorites are
unraveling the secrets of solar system formation.
Finding Rocks That Fall From Outer Space
The U. S. Antarctic Search for Meteorites (ANSMET) program is a
collaborative effort of the National Science Foundation (NSF), NASA, and the
Smithsonian Institution. Field collection is supported currently by a grant
from the NSF Office of Polar Programs to Principal Investigator Dr. Ralph
Harvey at Case Western Reserve University in Cleveland, Ohio. NASA and the
Smithsonian Institution provide for the classification, curation, and
distribution of Antarctic meteorites. All three agencies sponsor research on
the specimens which remain the property of the National Science Foundation.
The Meteorite Working Group (MWG) reviews requests for samples by scientists
of all countries. The MWG is a peer-review committee that meets twice a year
to guide the collection, curation, allocation, and distribution of the U. S.
collection of Antarctic meteorites.
The National Institute for Polar Research (NIPR) in Tokyo manages their own
expeditions to Antarctica and oversees the curation, allocation, and
distribution of Japanese collections of Antarctic meteorites. The Committee
on Antarctic Meteorites, which also meets approximately twice a year,
reviews all requests for meteorite samples. The samples are the property of
the NIPR, and allocations are generally only made for a period of 1 to 2
years.
European expeditions and collection programs in Antarctica include the
Italian (PNRA) and German GANOVEX programs. European specimens currently
curated at the Open University, UK are available for study and can be
requested through the Department of Mineralogy of the Natural History Museum
in London.
These international collection programs require nothing less than strategic
trips to the ice by sturdy, trained individuals working together in a
well-coordinated way to survive and succeed in this extraordinary
environment. What motivates us to venture to a place that was only a
hypothesized landmass until it was actually sighted in 1820-21? The thrill
of living in an extreme, remote environment (likened by some to a space
outpost) with a rich history of heroic exploration, for the golden chance of
finding pieces of rock from space that tell stories of creation. From the
beginning, the Antarctic collection programs have aimed to recover large
enough numbers of meteorites each season so that something unusual might be
served up, possibly one day a sedimentary rock from Mars showing evidence of
the planet's watery history.
Tents at Meteorite Hills during the 2000-2001 ANSMET field season. This
photo was taken from the helicopter while two of the planetary geologists,
Ben Bussey and Ralph Harvey, began a six-day reconnaissance trip to ice
fields near Bates Nunatak.
Meteorites Found on the Blue Ice
Since 1976, ANSMET has recovered more than 10,000 specimens from meteorite
stranding surfaces along the Transantarctic mountains. The total number of
Antarctic meteorites is closer to 30,000 when you include Japanese
collections (beginning in 1969) and European collections. This large number
is uncorrected for pairing--when laboratory examinations show that two or
more specimens are actually broken pieces of the same rock. Antarctica (the
highest, driest, coldest, windiest, and emptiest place on Earth) has proven
to be an exceptionally good hunting ground because meteorites that have been
falling on the surface through the millennia become buried in the ice moving
slowly seaward. Where mountains or subsurface obstructions block the forward
movement of the ice, the old, deep ice, laden with meteorites, is pushed up
to the surface against the barrier. Strong katabatic winds (winds blowing
down the slopes) clear the surface of loose ice and snow and aid sublimation
and mechanical erosion which expose the meteorites on the blue ice. These
concentrations of meteorites, called stranding surfaces, are not permanent
but appear and disappear as the ice cap changes.
The Antarctic Meteorite Location and Mapping Project (AMLAMP) maintains
databases of meteorite locations for each ice field searched by ANSMET; see
the map below. The Allan Hills-David Glacier Region includes samples from
Allan Hills, Beckett Nunatak, David Glacier Icefields, Elephant Moraine,
MacKay Glacier Icefields, Outpost Nunataks, and Reckling Moraine. The
Darwin-Byrd Glacier Region includes Bates Nunatak, Derrick Peak, Lonewolf
Nunataks, and Meteorite Hills. The Beardmore Region includes Bowden Neve,
Dominion Range, Geologists Range, Grosvenor Mountains, Lewis Cliff,
MacAlpine Hills, Miller Range, and Queen Alexandra Range. The Wisconsin
Range-Scott Glacier Region includes Gardner Ridge, Graves Nunataks, Klein
Glacier, Mt. Howe, Mt. Prestrud, Scott Glacier Icefield, Wisconsin Range,
and Mt Wisting. The Thiel Mountains-Patuxent Region includes Lapaz Icefield,
Patuxent Range, Pecora Escarpment, Stewart Hills, and Thiel Mountains.
A complete set of maps, meteorite listings, and explanations are available
from AMLAMP.
Samples are identified by location (using a three-letter abbreviation), year
of collection, and unique sample number. For example, the Allan Hills
location is abbreviated as ALH, Elephant Moraine is EET, Queen Alexandra
Range is QUE, and Meteorite Hills is MET. Meteorite ALH 81005 was recovered
in Allan Hills during the 1981-1982 ANSMET field season and was the fifth
rock analyzed in the lab. It was a significant find because it turned out to
be a piece of the Moon. The next paragraphs summarize some of the
extraordinary discoveries enabled by ANSMET.
A Suite from the Moon
Scientists have identified 21 meteorites from the Moon. About half are from
Antarctica and half from hot desert regions. They recognized the first one,
ALH 81005, in 1982 on the basis of chemical, mineralogical, and isotopic
compositions. These rocks provide lunar scientists with samples from places
far from the U. S. Apollo and Russian Luna landing sites, allowing a much
better understanding of the composition of the lunar crust. More
importantly, the mere fact that impacts could blast rocks off the Moon
without melting them, gave some credence to the idea that we might also have
meteorites from Mars. See Randy Korotev's web site at Washington University
in St. Louis for more information about meteorites from the Moon.
First Martians
The idea that bits of Mars have fallen to Earth was hotly debated from the
late 1970s to the mid-1980s. The evidence centered around the relatively
young ages of a group of rocks called the SNC meteorites. They were a mere
1.3 billion years old, some even younger. Since the Moon's volcanic engine
stopped more than 2 billion years ago, the argument went, these meteorites
must come from a much large body. The logical choice was Mars. The evidence
was circumstantial.
All that changed when scientists measured the gases trapped in melted
pockets inside EET 79001, a SNC meteorite found at Elephant Moraine. The
abundances of the gases and the isotopic compositions of them were dead
ringers for the atmosphere of Mars, as measured by the Viking landers in
1976. The results stopped all arguments about where the SNC meteorites came
from--they are our first Martians. There are now 19 Martian meteorites, six
of which come from Antarctica and seven from hot deserts.
Diamond-studded Rocks
Ureilites may be the most mysterious of all the meteorites. They were named
for Novo Urei, a small rock that fell in Russia in 1886. Until people
started collecting meteorites in hot and cold deserts, only six ureilites
were known. All contained small grains of diamond (a high-pressure form of
carbon), along with graphite (low-pressure carbon). This was a startling
discovery because diamonds form at high pressure. Many scientists proposed
that the diamonds formed deep inside a large body. But as we understood the
effects of large impacts, it became clear that the diamonds were the
products of high-pressure shock waves caused by a large impact event on the
ureilite body. The key question became the source of the diamond. Was it
originally present in the rocks as graphite that crystallized along with the
silicate minerals, and was then converted to diamond by shock? Or was the
diamond forcibly injected into the rocks by an impact event?
During the past 15 years or so, the number of ureilites has increased
dramatically from only six to 110. Some of the new ones are not severely
damaged by shock and preserve the original state of the rock and its carbon
minerals. Examination showed that they contain long lath-shaped crystals of
graphite intergrown with the silicate minerals. The intergrowth clearly
indicates that the carbon was not mixed in by a shock event. The original
six ureilites fell into distinct groups on the basis of the amount of FeO
(iron oxide) in their olivine and pyroxene. This suggested that the rocks
within a group were related to each other, but unrelated to the other
groups. Analyses of the new samples indicate something different, that there
is a complete gradation in the amount of FeO, not separate groups. The
relationships among the ureilites are not so simple and researchers are
continuing to try to understand the geologic processes on the ureilite
parent body.
Leftovers From the Birth of the Solar System
Chondrites are meteorites that contain rounded objects (called chondrules)
that cooled very rapidly from a molten state. For a long time most
scientists thought chondrules formed directly in the solar nebula--the cloud
of gas and dust surrounding the primitive Sun. However, chemical and
mineralogical properties of chondrules and experiments designed to reproduce
the mineral intergrowths in chondrules showed that they could not possibly
have condensed from a gas. The condensation idea gave way in the 1980s to
the hypothesis that chondrules formed from small aggregations of dust (like
those fluffy dust balls that accumulate under your bed) that were melted by
some mysterious process in the solar nebula. Thus, meteoriticists concluded
that chondrules were secondary products.
Three chondrites found in Antarctica (ALH 85085 and QUE 94411) and the
Sahara (Hammadah al Hamra 237) are changing that view. Investigators in the
U. S. and Europe may have found direct condensates from the solar nebula in
those meteorites. Chondrules and grains of metallic iron-nickel chondrules
tell the story of heat and wind in the solar nebula. The chemical
compositions of the chondrules indicate formation from a cloud that had
become enriched in dust before being completely evaporated. When the gas
cloud cooled, the tiny droplets condensed, but were blown into much cooler
regions far from the Sun before they had a chance to acquire moderately
volatile elements such as sodium, potassium, and sulfur. They appear to have
accreted into asteroids before other processes affected them, thus
preserving the record of heating and jetting in the nebula that surrounded
the infant Sun. The results support new astrophysical theories of chondrule
and star formation. (For details on these interesting meteorites, see the
PSRD articles: Relicts from the Birth of the Solar System and The Oldest
Metal in the Solar System.)
Meteorite Bonanzas in Cold and Hot Deserts
We know that extraterrestrial materials fall randomly on Earth; it is simply
easier to find them in deserts where they are well preserved (due to lack of
weathering) and concentrated on a plain background so that they are easily
recognized. Successful meteorite searches in cold and hot deserts have
dramatically increased the number of meteorite finds. While Antarctica is
the premier cold desert hunting ground, researchers Ralph Harvey (Case
Western Reserve University), Anders Meibom (Stanford University), and
Henning Haack (University of Copenhagen) have been using remote sensing
images to look at Earth's other ice sheet, Greenland, for evidence of
meteorite stranding surfaces. Their work suggests that Greenland would be an
excellent place for future meteorite hunts. Several hot desert regions are
yielding huge numbers of meteorites, namely the Sahara Desert (Algeria and
Libya), the Nullarbor Plains (Western and South Australia), Mojave Desert
(Southern California), and high plains of Texas and New Mexico. The three
most productive areas in the Sahara are the Reg el Acfer in Algeria (at
least 320 meteorites), Dar al Gani (at least 256 meteorites) and Hammahah al
Hamra (at least 520 meteorites) in Libya. Over 200 specimens have been
collected from an unknown Saharan location (undisclosed by the private
collectors). An additional 280 meteorites have been collected in Australia's
Nullarbor Region.
To Boldly Look for Meteorites
Antarctic meteorites are collected, preserved, and documented very
carefully. They've proven their extraordinary value to science and to our
understanding of the history of the Solar System from its origin in the
solar nebula to the formation of our Sun and planets. Collecting meteorites
in Antarctica is like going on a field trip to the Moon, Mars, and
asteroids. Last year, the eight ANSMET team members recovered 740 meteorite
specimens during their two-month field trip. This season's team of ten will
return to Meteorite Hills to continue searching this portion of the vast
East Antarctic Ice Sheet. These annual systematic collection programs offer
the best chance of finding Martian meteorites and brand new types of
meteorites inspiring new research, ideas, and discoveries.
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