CCNet DIGEST, 8 June 1998
"Being before the time, the astronomers are to be killed without
respite; and being behind the time, they are to be slain without
reprieve." [Shu Ching, before 250 BC]
[Today's 'Quote of the Day' was sent in by Duncan Steel]
(1) I'M SORRY, CLARK, BUT 1997 XF11 WAS DANGEROUS
Brian G. Marsden (firstname.lastname@example.org)
(2) AT LONG LAST: US SCIENTISTS REJECT NASA'S INTERIM PROCEDURES ON
(3) NEW DEEP SPACE 1 TRAJECTORY INCLUDES ASTEROID FLYBY
Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>
(4) ANOTHER DEEP IMPACT VS REALITY STORY
Daniel Fischer <email@example.com>
(5) GIANT SHRIMP POISED TO TARGET BIG QUESTIONS WITH TINY ION BEAM
Andrew Yee <firstname.lastname@example.org>
(1) I'M SORRY, CLARK, BUT 1997 XF11 WAS DANGEROUS
From Brian G. Marsden (email@example.com)
On March 12, Eleanor Helin and Ken Lawrence quickly responded to my
plea to search for past images of 1997 XF11. Using the ephemerides
included in the infamous "Press Information Sheet" in the MPC's Web
pages (rather than any calculations originating at JPL), they located
the 1990 images that were essential for resolving the issue of whether
XF11--at an estimated 1-2 km in diameter a particularly large
NEO--could conceivably be a threat to the earth a few decades from now.
Once the 1990 images were found and measured, the deduction that there
would be a miss distance of 950 000 km from the earth in 2028 (and no
closer approaches during the next couple of centuries) was a
straightforward computation, done essentially simultaneously at both
the MPC and JPL and formally announced separately by each group shortly
However, despite the millions of words written about XF11, nobody
seems to have considered that the earth was in danger of being hit by
it during the couple of decades following 2028. Among Clark Chapman's
numerous ill-founded criticisms, the one that I overplayed the
significance of searching for pre-1997 observations is perhaps the most
ridiculous. Far from being the "icing on the cake", such observations
were absolutely essential if one wanted a quick answer to the question
of whether the earth could be hit by XF11 during the next half century.
As everybody knows by now, even the initial 15-day arc of
observations made it clear that XF11 would miss the earth by some
modest distance, possibly a very small distance, at its descending node
in 2028. Since the object will be near opposition, its heliocentric
distance is then larger than the earth's. But the node regresses with
time, and after 2028 the earth's distance from the sun in the direction
of the node slowly increases. At the same time, and more rapidly, the
nodal distance of XF11 decreases. The distances will therefore become
identical at some time a decade or so after 2028, and the uncertainty
in our knowledge of the object--prior to the discovery of the crucial
1990 data--was such that there was in fact a small, but real,
possibility of a collision.
One could not say when the orbital distances would become
identical, because this depends on how the orbit of 1997 XF11 is
perturbed by the earth during the 2028 encounter. Likewise, one could
not immediately say if and when the earth and the object would be
unlucky enough to occupy the same point in space. This was a beautiful
problem in mathematical chaos! It was actually a pity that the 1990
data came along to spoil it before we could work out all the possible
1997 XF11 currently has a revolution period about the sun of about
1.73 years. The 2028 encounter changes this period. If XF11 were to
come in 2028 to the minimum distance reasonably prescribable by the
data available prior to the 1990 precovery (i.e., about 30 000 km), the
period could increase to about 1.99 years. Since 2.00 years seems to be
excluded, the minimum distance 1997 XF11 could therefore have
approached us in 2030 would therefore be more than 8 million km. But
there are rational numbers between 1.73 and 1.99 that could indeed
bring another very close encounter by, say, mid-century. Furthermore,
one such close encounter can beget another. What about 1.75 years?
This would bring XF11 close in 2035. Likewise, 1.7777... years could
make life interesting in 2044, 1.8 years in 2037, 1.8181... years in
2048, 1.8333... years in 2039, etc.
Some of my colleagues think it important to compute an "impact
probability". In order to do that properly for XF11 between now and
2050 would require all the possible encounters to be carefully
examined. More work for someone! Much more important, it seems to me,
is the need for an awareness of what is possible and what is not.
One of the things that makes this problem so interesting is that the
larger the desired change in the period from the initial 1.73 years,
the closer one has to make XF11 go to the earth in 2028, with the
result that the orbits of XF11 and the earth go through their point of
coincidence earlier. For example, if one aims at an impact in 2039, the
2028 miss distance has to be as small as 130 000 km, the crossing point
takes place in the mid-2030s, and one may be able to do only somewhat
better than in 2028, with an inferior-conjunction miss of perhaps 19
000 km. But this drops down to something like 13 000 km (from the
earth's center) on the inferior-conjunction side for a 2044 encounter,
which requires a 2028 miss distance of 310 000 km and yields an orbit
coincidence closer to 2040.
This suggests that a good time to look for an actual impact would be
in 2037. Given a passage 210 000 km from the earth on 2028 Oct. 26.8
UT, one can indeed engineer an impact between 1997 XF11 and the surface
of the earth around 2037 Oct. 27.0 UT! Thanks to the Helin-Lawrence
1990 observations, we know that this cannot happen, but some readers
may like to check that the following orbital elements (or something
very much like them, given possible rounding differences) both yield
the impact and appropriately satisfy the set of 95 observations used
between 1997 Dec. 6 and 1998 Mar. 4 (with a mean residual of 0.5
Epoch 1998 July 6.0 TT = JDT 2451000.5 Marsden
M 210.52123 (2000.0) P Q
n 0.56929194 Peri. 102.48610 +0.72523349 +0.68733692
a 1.4418255 Node 214.11864 -0.65617522 +0.67239344
e 0.4837551 Incl. 4.09494 -0.20849570 +0.27469076
P 1.73 H 17.0 G 0.15
Residuals in seconds of arc
J97C6 691 0.7- 0.0 J97CQ 046 0.4+ 0.4+ J981H 046 0.1+ 0.2-
J97C6 691 0.9- 0.0 J97CQ 046 0.2+ 0.0 J981H 046 0.3+ 0.0
J97C6 691 0.6- 0.1- J97CR 104 1.2+ 0.8+ J981H 046 0.4- 0.7-
J97C8 587 0.9+ 1.3+ J97CR 104 0.6- 1.0+ J981H 046 0.0 0.0
J97C9 402 0.1- 0.5- J97CS 897 0.7+ 1.5+ J981M 691 0.6- 0.7-
J97C9 402 0.1+ 0.4- J97CS 897 1.2- 1.3+ J981M 691 0.8- 0.6-
J97C9 402 0.0 0.5+ J97CV 118 0.2+ 0.5- J981M 691 0.7- 0.7-
J97C9 402 0.2+ 0.1- J97CV 118 0.1- 0.5- J981N 118 0.4+ 0.1+
J97C9 402 0.1- 0.3+ J97CV 118 0.3+ 0.5- J981N 118 0.4+ 0.0
J97C9 402 0.5+ 0.3+ J97CV 897 0.1- 0.6- J981N 118 0.3+ 0.1-
J97CI 402 (2.6+ 1.2-) J97CV 897 0.2- 0.5+ J981Q 118 0.8+ 0.0
J97CI 402 0.0 0.0 J97CV 897 0.7- 0..5+ J981Q 118 0.6+ 0.4+
J97CI 402 (0.8+ 2.6-) J9812 900 0.0 0.4+ J981Q 118 0.8+ 0.0
J97CI 402 0.7+ 1.2- J9812 900 0.6+ 0.3+ J981T 360 0.1+ 0.4+
J97CL 897 0.8+ 0.4+ J9813 587 0.0 0.0 J981T 360 0.0 0.5+
J97CL 897 (2.2+ 0.8+) J9813 587 0.2- 0.5- J981T 360 0.7+ 0.5+
J97CL 897 0.5+ 0.8- J9816 360 0.1+ 0.1- J981U 402 0.3+ 0.5-
J97CL 897 0.4- 0.4+ J9816 360 0.5+ 0.2- J981U 402 0.8- 0.8-
J97CL 897 0.7- 0.4+ J9816 360 0.4+ 0.1+ J981U 402 0.0 0.3+
J97CL 897 1.9- 0.2+ J9816 118 0.6+ 0.7- J9822 557 0.1- 0.3+
J97CN 900 0.3- 0.1+ J9816 118 0.6+ 0.6- J9822 557 0.8- 0.8+
J97CN 900 1.4+ 0.0 J9817 691 0.5- 0.3- J9822 557 0.2- 1.1+
J97CO 360 0.1- 0.4- J9817 691 0.6- 0.2- J9823 711 0.7- 0.2+
J97CO 360 0.1- 0.2- J9817 691 0.5- 0.3- J9823 711 1.0+ 0.2+
J97CO 360 0.2- 0.3- J9818 658 0.4- 0.2- J9823 046 0.5- 0.3+
J97CO 104 0.5+ 0.4- J9818 658 0.3- 0.3+ J9823 046 0.2- 0.4+
J97CO 104 0.2+ 0.3+ J9818 658 0.3- 0.0 J9824 711 0.4+ 0.2+
J97CP 402 0.1+ 0.1- J9819 658 0.5- 0.7- J9824 711 0.3+ 1.3+
J97CP 402 0.1+ 0.1- J9819 658 0.4- 0.2- J9833 711 0.3- 0.0
J97CP 402 0.5+ 0.0 J9819 658 0.9- 0.5- J9833 711 0.2+ 0.1-
J97CQ 046 0.3+ 0.5- J981A 118 0.5- 0.1- J9834 711 0.1- 0.3-
J97CQ 046 0.1- 0.4- J981A 118 0.0 0.2- J9834 711 0.2+ 0.7-
J97CQ 046 0.5+ 0.0 J981A 118 0.2+ 0.2-
As I say, I find it surprising that nobody has remarked on this type
of danger before. The calculation did not require the use of any
observations Chapman has accused me of withholding. Others could
certainly have reached the same conclusion. Since they didn't, I offer
my calculation for "peer review", if anybody cares. So much, too, for
the idea that NEO dangers can be properly accepted or dismissed by
"consensus" over a 48-hour period!
Some might quibble that this 2037 scenario is rather improbable. But
it is far from impossible and flatly contradicts Chapman's statement
that the three-month data set "and those data alone, were sufficient to
demonstrate that 1997 XF11 would NOT hit the Earth at ... any other time
in the foreseeable future". In fact, the scenario lends support to my
March 11 remark that "the chance of an actual collision is small, but
one [a little more than 30 years from now] is not entirely out of the
Things like this do happen in nature, as in the celebrated example of
Lexell's comet, captured from a large-perihelion orbit by Jupiter into
resonance with it in 1767, slingshot to miss the earth by only 2
million km in 1770, and dismissed onto another large-perihelion orbit
by Jupiter in 1779.
It is undoubtedly true at the present time that the chance that the
earth will be hit by an NEO so far undiscovered is greater than that it
will be hit by one so far recorded. But that does not mean that we can
be hurt only by what we don't know. New discoveries are added to the
list of potentially hazardous asteroids for good reason. If we then
persist in ignoring them, we may do so at our peril.
Brian G. Marsden
(2) AT LONG LAST: US SCIENTISTS REJECT NASA'S INTERIM PROCEDURES ON
From CNN http://cnn.com/TECH/space/9806/06/asteroid.conference.ap/
Scientists discuss how to warn about asteroids without causing
June 6, 1998
IRVINE, California (AP) -- Following March's false alarm about an
asteroid coming dangerously close to Earth in the 21st century and
two Hollywood summer blockbusters about cosmic collisions, experts
met Saturday to plan asteroid warnings that won't trigger mass
"Collisions with the Earth is a topic that is so prone to
sensationalism that we must be extremely careful about how we
communicate new discoveries," said Richard P. Binzel, a planetary
science professor at the Massachusetts Institute of Technology.
"It took the (March) event to wake us up."
A March 11 report that Asteroid 1997XF11 was headed to within
30,000 miles of Earth's center -- and could hit in October 2028 --
was front page news and the top story on evening TV news
The report from the International Astronomical Union was quickly
debunked by astronomers at NASA's Jet Propulsion Laboratory in Pasadena
who recalculated the asteroid's likely path and found it would miss the
Earth by 600,000 miles.
"There's a great misperception in the public that for one day there was
a possibility that the asteroid would hit in 2028," said Paul W.
Chodas, the JPL astronomer whose calculations put those frightened by
the report at ease. "According to our calculations, there never was a
chance the object would hit the Earth."
Chance of possible collision is rare
In the aftermath, scientists began thinking about how they could avert
another scare, although efforts to delay release of data could be
difficult given the increasingly free flow of scientific information
through the Internet.
Since that time, Hollywood has put killer asteroids and comets into the
public mind with the "Deep Impact" and "Armageddon," as well as
made-for-TV movies earlier this year.
In light of the heightened awareness, the National Research Council's
Committee on Planetary and Lunar Exploration brought together
astronomers who identify and track asteroids, experts in risk
management, seismologists with experience in earthquake and volcano
warnings and reporters.
The main problem in reporting new asteroid discoveries is that only a
fraction that initially seem potentially hazardous turn out to be
headed close to Earth once scientists refine orbital calculations.
"It is extremely unlikely that we're going to have an asteroid come
with a real possibility of a collision," Chodas said, adding that 15
minutes after he had the XF11 data in hand, his calculations found
Scientists agree that peer review of initial observations -- standard
procedure in science -- is essential.
In April, the National Aeronautics and Space Administration drafted
"Interim Roles and Responsibilities for Reporting Potentially Hazardous
Objects," which recommends consultation and coordination among experts
before any public announcements.
NASA wants longer delay before any announcement
It might take up to 48 hours for experts to consult with each other,
Chodas said. NASA wants an additional 24 hours before the information
Chodas, who computes orbits for asteroids and comets, went into the
meeting with an open mind about giving NASA the extra 24 hours,
although he wondered what the agency planned to do during that time.
But participants suggested eliminating the delay. They also suggested
encouraging, rather than requiring, scientists to contact NASA.
An earthquake expert urged openness about any potential threat, as long
as the uncertainty of initial observations is clearly explained.
"You can't control the flow of news but you can be as truthful as
possible up front," said Allan Lindh of the U.S. Geological Survey.
"The press, public and public officials seem to deal well with
uncertainty, but they don't deal well with the suggestion you might
hold out on them."
Controlling false alarms
Binzel, who opposes mandating a set waiting period, suggested that NASA
or the International Astronomical Union establish a code of conduct
under which amateur or professional astronomers would seek verification
from colleagues before going public.
Without that, false alarms will create "total loss of credibility
among the astronomers."
Scientists have so far identified 123 potentially hazardous asteroids
that could pass within 5 million miles of Earth. They've discovered 200
of the estimated 2,000 large asteroids that could pass within 30
million miles of Earth.
Chodas noted that just Friday, scientists using a radar antenna in
Goldstone, California, observed that a 100-foot- wide asteroid
discovered days earlier will pass within 476,000 miles of Earth on
Monday. That's the closest future passage of any asteroid now being
tracked, he said.
NASA is spending more money in the next decade to scan space for others.
One of the giant rocky chunks is thought to have slammed into Mexico's
Yucatan Peninsula 65 million years ago, wiping out dinosaurs and most
Scientists know that in 1908, an asteroid exploded over Siberia,
flattening nearly 1,000 square miles of forest.
Harry Y. "Hap" McSween, the University of Tennessee geologist who
chaired the daylong workshop, said it was important that the event
was getting U.S. scientists talking, but added that "this is going to
have to be an international discussion."
Copyright 1998 Associated Press
(3) NEW DEEP SPACE 1 TRAJECTORY INCLUDES ASTEROID FLYBY
From Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>
MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109 TELEPHONE (818) 354-5011
Contact: John G. Watson
NEW DEEP SPACE 1 TRAJECTORY INCLUDES ASTEROID FLYBY
Mission planners for NASA's Deep Space 1 have selected a near-Earth
asteroid, 1992 KD, as a flyby destination.
Last April, NASA announced that the launch date for this technology
validation mission was to be rescheduled from July 21 to October 15,
with the launch period extending to October 30. The new launch date
precluded flying by planned destinations, including the previously
announced asteroid McAuliffe, making it necessary to choose a new
target. Deep Space 1 is scheduled to fly by the newly chosen asteroid
1992 KD on July 28, 1999.
This asteroid was chosen from more than 100 flyby possibilities.
Its elliptical orbit curves within and outside of Mars' orbit of the
Sun, at its farthest going out more than three times farther from the
Sun than Earth. Although scientists believe its diameter is
approximately three kilometers, they know little else about the body.
With this flyby, they can learn more about its shape, size, surface
composition, mineralogy, terrain and rotation speed.
"This new mission offers excellent opportunities for us to test our
payload of advanced technologies that are so important for future space
exploration," said Dr. Marc Rayman, Deep Space 1's chief mission
engineer. "At the same time, the potential for bonus scientific return
Deep Space 1 is the first launch of the New Millennium Program, a
series of missions designed to test new technologies so that they can
be confidently used on science missions of the 21st century. Among the
12 technologies that the mission is designed to validate is an ion
propulsion engine that fires electrically charged xenon atoms from its
thrusters; this is the first time it has ever been used as the primary
propulsion system in deep space. Also being tested are autonomous
optical navigation, a solar concentrator array and an integrated camera
and imaging spectrometer.
The latter instrument, also known as the Miniature Integrated
Camera Spectrometer, or MICAS, will be validated by making science
observations of asteroid 1992 KD, among several other methods. The
flyby will also help to test both a miniature integrated ion and
electron spectrometer instrument, also termed the Plasma Experiment for
Planetary Exploration (PEPE), and the spacecraft's autonomous optical
navigation system. The remaining new technologies will be tested during
cruise and thrusting phases both before and after the flyby.
By October, 1999, Deep Space 1 will have completed its primary
mission of demonstrating new technologies and will be on a trajectory
that could result in a flyby of comet Borelly two years later.. Comet
Borrelly is one of the most active comets that regularly visit the
inner solar system.
Further information about Deep Space 1 is available at
http://nmp.jpl.nasa.gov/Deep Space 1/ . The New Millennium Program and
Deep Space 1 are managed by JPL for NASA's Office of Space Science. JPL
is a division of the California Institute of Technology.
(4) ANOTHER DEEP IMPACT VS REALITY STORY
From Daniel Fischer <firstname.lastname@example.org>
... can be found at http://www.hollywood.com:80/news/berlin/06-05-98
(with a rather creative spelling of Shoemaker-Levy but otherwise good).
(5) GIANT SHRIMP POISED TO TARGET BIG QUESTIONS WITH TINY ION BEAM
From Andrew Yee <email@example.com>
This release is about studying minute samples of meteorites and minerals.
CONTACT: David F. Salisbury, News Service
Giant SHRIMP poised to target big questions with tiny ion beam
Picture the solar nebula, that hot cloud of gas and dust that collapsed
to form our solar system. Where did the gas and dust molecules come
from? And what was the sequence of events that transformed them from a
swirling amorphous blob into the well-organized planets and atmospheres
that we know today?
A brand new $2.5 million, 12-ton instrument called the SHRIMP arrived
at Stanford this past April and is poised to answer these and other
fundamental questions about the origins of our Earth and solar system.
The SHRIMP is not a time machine, and it's not an overgrown crustacean.
It's a Sensitive High Resolution Ion MicroProbe, arguably the most
coveted instrument of its type in the world, equaled only by its twin
at the Australian National University in Canberra, where both machines
were designed and built.
This is the machine whose predecessors determined the ages of the
oldest minerals on Earth in 1983, the oldest rocks on Earth (3.96
billion years) in 1989, and the oldest minerals in the solar system
(4.56 billion years) in 1992.
The SHRIMP was purchased jointly by the Stanford School of Earth
Sciences and the U.S. Geological Survey as a result of an agreement
signed in 1989. Geological and environmental sciences Professor Gary
Ernst, who was dean of earth sciences at the time, saw the SHRIMP as a
remarkable opportunity to attract collaborative world-class geochemical
research to Stanford and to enhance ties with the U.S. Geological
The SHRIMP is located in the basement of the Green Earth Sciences
building and operates under the direction of Trevor Ireland, assistant
professor in geological and environmental sciences, who came to
Stanford from the Australian National University, and Joe Wooden of the
U.S. Geological Survey. Brad Ito, also of the USGS, plays a critical
role as full-time electronics technician. Mike McWilliams, associate
professor of geophysics and geological and environmental sciences at
Stanford, and Charlie Bacon of the USGS contribute to planning and
coordinating the SHRIMP's busy research schedule.
Earth and planetary scientists already are lining up to get bits of
their favorite rocks into the new SHRIMP, because this machine is not
only shiny-new, super-fast and highly precise, it's also very easy to
use. Give it a tiny grain of Earth, Mars, interstellar dust or other
solid material, and the SHRIMP can divine the exact chemical
constituents of the sample down to minuscule differences in atomic mass
within 15 minutes. Four sample analyses per hour, 30-some analyses per
day -- that's enough information to satisfy a data junkie's habit
Rocks and minerals that Stanford scientists are preparing for the
SHRIMP include bits of stardust from very old meteorites, minerals from
far-traveled sedimentary basins in western Canada, and samples from
deep crustal rocks coughed up by volcanoes in the Bering Strait region,
near the border between Alaska and Russia.
The creators of the new SHRIMP assert that it is endowed with a
combined sensitivity and mass resolution that far surpasses that of any
previous ion probe. This instrument has the sensitivity to detect very
small concentrations of atoms, down to a few parts per billion. And its
mass resolution is 40,000, meaning that it can distinguish between
atoms that differ in mass by as little as one part in 40,000. That's
analogous to discriminating between a 20-ton whale (that's 40,000
pounds) and a 20-ton whale who just ate a pound of plankton (that's
Several earlier ion probes, including the SHRIMP's predecessors, SHRIMP
I and SHRIMP II, and its closest competitors, the French CAMECA probes,
have comparable sensitivity ratings, but much lower mass resolution, on
the order of 5000 for the CAMECA probes and 10,000 for the earlier
Here's how the SHRIMP works. It shoots the sample, usually an
individual mineral grain from a rock or meteorite, with high-energy
oxygen ions fired at speeds of 350 kilometers per second or nearly
800,000 miles per hour. The oxygen ions are focused into a very fine
beam about the width of a single strand of human hair. The ions have a
negative electrical charge, and when they hit the sample they kick off
positively charged ions and leave impact craters like tiny potholes on
This process, called "sputtering," liberates ions from the sample and
sends them traveling down a tube into a curved magnet about 1 meter
long. The magnet separates the ions according to their mass and energy,
so that lighter and slower ions hug the inside lane, whereas heavier
and faster ones are accelerated to the outer lanes.
The ions exit the magnet in a broad beam, then enter an electrostatic
compensator, which re-organizes them according to mass only, removing
the effects of energy differences between ions of the same mass. The
result, on the exit end of the electrostatic compensator, is a spectrum
of ions perfectly organized in order of increasing mass -- from
hydrogen, with an atomic mass of one, up to uranium, with an atomic
mass of 238. The scientist can inspect the part of the mass spectrum of
interest, at the collector, and ascertain the exact proportions of
chemical elements sputtered out of the sample.
So how do these sputtered ions lead to the age of a rock, or better
yet, the origins of the solar system? By way of radiometric dating and
isotopic fingerprinting. In both cases, the key is the isotopes --
atoms of the same element that have slight differences in mass.
Radiometric dating uses certain isotopes of uranium and thorium which
over time turn to lead by radioactive decay. By measuring relative
abundances of the original isotopes and their decay products, it is
possible to calculate the age in millions of years of a very old rock.
Isotopic fingerprinting is applied mainly to extraterrestrial samples,
usually from meteorites. The presence of particular isotopes can be
used to link samples of unknown origins to a probable source inside or
outside the solar system. For example, scientists believe certain
meteorites came from Mars because they have that unusual mix of
hydrogen isotopes that is peculiar to Mars. The SHRIMP is well equipped
for both these types of isotopic studies, because it has the resolution
to measure and compare ions with very small mass differences and the
sensitivity to obtain good results from very small samples, typically a
limiting factor in extraterrestrial research.
Although the more conventional applications for the SHRIMP are in
radiometric dating, its greatest potential may lie in isotopic studies
of the early solar system. Until recently, all of the gas and dust
particles in the solar nebula were thought to have been thoroughly
heated and mixed -- that is, totally homogenized -- prior to that
momentous collapse that led to agglomeration of the sun and orbiting
planets. This explains why most bodies in our solar system show broadly
similar isotopic trends.
However, recent isotopic studies, some of which were conducted on
earlier models of the SHRIMP by Trevor Ireland and his colleagues at
the Australian National University, have shaken the long-standing
homogenization theories. Some star dust particles embedded in
early-formed meteorites contain highly anomalous isotope concentrations
when compared with normal abundances for the Earth, sun and normal
meteorites. How these bits of dust escaped homogenization is not clear,
but their pristine chemistry makes them an important link to possible
interstellar sources for the stuff in the solar nebula. Some particles
may have drifted in on prevailing interstellar winds. Others may have
been catastrophically blown into our solar nebula by the explosion of a
neighboring star. Could such an explosion have triggered the collapse
of the solar nebula? This is a scientific frontier rife with new
questions and rapidly changing theories, and the new SHRIMP promises to
feed this debate with much-needed isotopic data.
Scientists at Stanford and the U.S. Geological Survey also have plans
for more down-to-Earth applications for the SHRIMP. Kathy Degraaff,
Stanford doctoral student and recipient of the U.S. Geological Survey
fellowship award, will delve into a hot controversy over the geographic
origins of a big chunk of western Canada. It has been proposed that
most of what we call British Columbia is a recent arrival from a
position near Baja California. By analyzing mineral grains in
sedimentary rocks from British Columbia and comparing their isotopic
signatures with possible source terrains up and down the western part
of North America, DeGraaff hopes to see where these rocks may have
originated -- if they are indeed immigrants from Mexico.
Stanford geological and environmental sciences Professor Elizabeth
Miller and doctoral student Jeremy Hourigan, along with Russian
colleagues Slava Akinin and Julia Apt from the Northeastern
Interdisciplinary Scientific Research Institute in Magadan, plan to use
the SHRIMP for radiometric dating of rocks in the Bering Strait region
between Alaska and Russia. Over the past 30 million years, volcanoes in
the Bering Strait region have been coughing up fragments of rock
thought to have originated deep in the continental crust at depths of
10 kilometers or more. Miller and her colleagues hope that age-dating
these crustal blocks will help them to develop better models for the
history of tectonic stretching and crystallization of the Earth's crust
in this poorly understood region.
Stay tuned for new developments with the SHRIMP by visiting the web
site -- http://shrimprg.stanford.edu, which includes a time-lapse tour
of the SHRIMP's installation and assembly. You can also e-mail SHRIMP
gurus Trevor Ireland, firstname.lastname@example.org, and Joe Wooden,
email@example.com for further information on what the SHRIMP
can do and how it works.
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CCCMENU CCC for 1998