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(meteorobs) Excerpts from "CCNet 121/2000 - 23 November 2000"
Note the LAST LINE of item #6... Extraordinary is a good word. ;>
Clear skies,
Lew Gramer
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CCNet 121/2000 - 23 November 2000
---------------------------------
(1) PREDICTING LEONID METEORS OFFICIALLY BECAME A SCIENCE LAST WEEKEND
NASA Science News for November 21, 2000
[...]
(6) UK SCIENTISTS REPORT 'ALIEN' LIFE
Environmental News Network, 22 November 2000
(7) FAST ROTATING ASTEROIDS
P. Pravec et al.
(8) RADAR OBSERVATIONS OF ASTEROID 2100 RA-SHALOM
M.K. Shepard MK et al.
[...]
==============================================================
(1) PREDICTING LEONID METEORS OFFICIALLY BECAME A SCIENCE LAST WEEKEND
>From NASA Science News for November 21, 2000
http://science.nasadot gov/headlines/y2000/ast21nov_1.htm?list20392
LEONIDS GALORE
The art of predicting Leonid meteors officially became a science this
weekend as sky watchers around the globe enjoyed three predicted episodes of
shooting stars.
November 21, 2000 -- A bright moon, city lights and scattered clouds weren't
enough to keep the 2000 Leonid meteor shower at bay. Sky watchers who
ventured outdoors after midnight on Nov. 17th and 18th enjoyed sporadic
flurries of bright shooting stars numbering more than 200 per hour over
parts of Europe, Africa, and the Americas.
"I could see plenty of Leonids from [brightly-lit] downtown Boston,"
reported a reader on Saturday morning after a break in cloudcover briefly
revealed clear skies. "One meteor was even brighter than the Prudential
Building!"
This year's Leonid meteor shower consisted of three main episodes lasting
several hours each. There was a modest flurry of 50 to 100 meteors per hour
on Nov. 17th, followed by two more outbursts of 150 to 450 per hour on the
18th.
For many North Americans the times of greatest activity coincided with local
midnight when the constellation Leo was lying low on the eastern horizon.
Normally, low-hanging radiants are bad news because they make shooting stars
hard to see. In this case, however, sky watchers were treated to a vivid
display of Earthgrazing meteors. "Earthgrazers" are shooting stars that
emerge from just below the horizon and streak through the upper atmosphere
nearly parallel to the ground. They often display colorful halos and
long-lasting trails stretching 90 degrees or more across the sky.
"I [started watching] just before 11:00 pm on Friday," recounted Pierre
Martin from eastern Ontario. "Even with the Leonid radiant only 3 degrees
over the eastern horizon, it was obvious that some fairly high activity was
in progress. Several spectacular Earthgrazers appeared! .... A most
impressive orange-colored Leonid split the sky in half. It traveled 70
degrees. A multi-colored one at 11:55 pm really blew me away... It went from
vivid blue to green to orange before it extinguished and left behind a train
that lingered for 3 seconds."
The bright Moon was not a serious impediment to meteor watching as many
feared it would be. The Leonids were bright and they tended to streak far
from the shower's moonlit radiant.
At 2:45 am EST on Saturday, the Moon was high in the sky when Marjory
Moeller of Atol, NY, peered out her bedroom window. "I was immediately
rewarded by a long yellow meteor coming from the east," she said.
"Incredible sight! It would have been scary if I hadn't known what it was!"
Minutes later, Jeannie Moorhead of Warwick, NY, says "I saw an incredible
fireball explode as white as the moon -- it left a very thick trail that
remained in the sky for at least 5 minutes."
"I never expected a shower [to be] this good with the Moon up," added Ted
Nichols of the Astronomical Society of Harrisburg, PA. "During one 15 minute
interval I counted 45 meteors!" Altogether, he saw 275 shooting stars
between 10:30 pm on Friday and 3:30 am on Saturday.
But, not everyone was so fortunate.
"Like a lot of people in the southeastern US, all we saw in Louisiana were
rain showers -- about 10.5 inches worth at my house," lamented meteor
enthusiast Dave Hostetter. "We've been having a drought for a year and a
half -- I should have known which weekend would get rain!"
"The experts had predicted a strong Leonid shower... and by golly, that's
what happened here," agreed Kim Youmans in Georgia. "I can't remember when
it last rained so hard."
Fortunately for such observers, more Leonids are on the way. The
triple-peaked character of this year's shower appears to confirm new
research that predicts powerful Leonid meteor storms in the future.
"We're very confident that Leonid storms are coming in 2001 and 2002," says
forecaster David Asher of the Armagh Observatory in Northern Ireland. "Peak
rates during those years should reach at least 10,000 meteors per hour when
Earth passes through debris streams from comet Tempel-Tuttle."
Asher and collaborator Robert McNaught (Australian National University) drew
attention last year when they predicted the onset of a Leonid meteor storm
over Europe within minutes of the time it actually occurred. They had
carefully studied the orbits of myriad debris streams shed by comet
Tempel-Tuttle during its periodic 33-year visits to the inner solar system.
By noting the time when Earth passed close to one of those dust trails,
Asher & McNaught were able to forecast the 1999 Leonids with unheard-of
precision.
Astronomers have long regarded the Leonids as stubbornly unpredictable. The
failure of a major Leonid storm to appear in 1899, after scientists had
urged millions to stay up and watch it, was "the worst blow ever suffered by
astronomy in the eyes of the public," according to 19th-century astronomer
Charles Olivier. For the next hundred years astronomers fared little better
with hit-or-miss forecasts based on historical records.
As mid-November 2000 approached, meteor watchers were anxious to learn if
the dust stream models developed by Asher & McNaught would work again. It
seemed to be a testable question because -- according to the models -- Earth
was heading for the outskirts of three debris streams. Expectations were
tempered by the fact that the expected encounters were not very close. Earth
would pass half a lunar distance (LD) from one stream and 0.3 LD from two
others. Researchers suspected that these might be great distances compared
to the average width of a dust filament. If the outer reaches of the debris
fields were rarefied, observers might see very little meteor activity or
possibly none at all. (Note: one "lunar distance" or LD equals 384 thousand
km, the average separation of the Earth and the Moon.)
The doubters became believers by day's end on Nov. 18th as sky watchers
reported strong meteor activity during all three encounters. There is still
some uncertainty about the exact times of the maxima and their amplitudes,
and how those compare to the predictions, but the essentials are clear:
Asher & McNaught-style models can predict Leonid meteor showers, and for
more than one year in a row. Other researchers are already working to
improve the basic predictive models by, e.g., adding the effects of
radiation pressure on meteoroids and considering in detail the trajectories
of debris particles ejected from the parent comet. Decades of uncertain
Leonid meteor forecasts may soon be a distant memory.
Indeed, the future looks bright for Leonid meteors. In mid-November 2001
Earth will pass almost directly through three more Leonid dust streams.
Observers in the Americas, east Asia, Australia and the Pacific Ocean will
be favored for a good display. Even the Moon is expected to cooperate -- its
phase will be nearly New, affording dark skies for observers.
So, if rain or clouds (or simply a faulty alarm clock) spoiled your view of
the 2000 Leonids, don't despair. The best may be yet to come!
==============================================================
(6) UK SCIENTISTS REPORT 'ALIEN' LIFE
>From Environmental News Network, 22 November 2000
http://www.enn.com/news/wire-stories/2000/11/11222000/upi_alien_40377.asp
Wednesday, November 22, 2000
By United Press International
Scientists in Wales said they discovered what may be a tiny form of
primitive alien life that a passing comet may have dropped into Earth's
atmosphere, London's Daily Mail newspaper reported today.
Researchers said that in the filter of a high-flying balloon operated by the
Indian Space Research Organization, they found a strain of bacteria unlike
anything on Earth. The bacteria were found at an altitude of 10 miles and
scientists from the ISRO, Cardiff University and the University of Wales
College of Medicine said it may have come from a comet on a close approach
to earth, according to the Daily Mail.
Prof. Chandra Wickramasinghe, who is based at Cardiff University, said the
discovery marked "the first time we have had direct evidence for the
hypothesis that comets seed life on other planets."
Wickramasinghe and astronomer Fred Hoyle suggested the theory of
"panspermia" more than two decades ago, that the seeds of life, either DNA
or microbes, could be carried by asteroids or comets and dropped off on
planets such as earth to germinate life.
The bacteria found in the balloon's filter "is a hitherto unknown strain,"
Wickramasinghe said. "It is so different from anything we've seen before
that there are only two possible explanations."
One, he told the Daily Mail, is that "organisms have been lifted from the
earth to great heights in the skies and have somehow multiplied there and
changed over time." The second, he said, is "that this is an example of
primitive alien life."
The newspaper said samples of the bacteria are under study at Cardiff's
Astrobiology Center, which Wickramasinghe and other scientists from ISRO,
Cardiff University and the College of Medicine have teamed up to form.
Wickramasinghe rejected suggestions that the bacteria might the result of
contamination by earthly organisms. He said ISRO had imposed stringent
sterile conditions aboard the balloon.
"The most recent geological evidence now suggests life on earth may be 4
billion years old," the professor was quoted as saying. "That is a very
significant time because it was a period when the earth was pounded by
comets and meteors."
But his theory is not universally accepted in scientific circles. The Daily
Mail quoted Alan Penny, an astronomer at Britain's Rutherford Appleton
Laboratory, as warning that "we would be cautious about jumping to
conclusions."
"Extraordinary claims," he said, "need extraordinary evidence."
Copyright 2000, United Press International
All rights reserved
==============================================================
(7) FAST ROTATING ASTEROIDS
Fast rotating asteroids 1999 TY2, 1999 SF10, and 1998 WB2
Pravec P, Hergenrother C, Whiteley R, Sarounova L, Kusnirak P, Wolf M
ICARUS 147: (2) 477-486 OCT 2000
An analysis of our photometric observations of near-Earth asteroids 1999
TY2, 1999 SF10,and 1998 WB2 has revealed their rotation periods to be 7.2807
+/- 0.0003, 2.4663 +/- 0.0005, and 18.8 +/- 0.3 min, respectively, Their
rotations are so fast that the bodies cannot be held together by
self-gravitation alone, and must therefore be monoliths. Their absolute
magnitudes, 23.1 +/- 0.3, 24.0 +/- 0.5, and 22.1 +/- 0.2, respectively,
indicate that they are small bodies with mean diameters in the range 60-120
m. The current statistics of asteroid spin rates vs size suggest that the
range where monoliths start to dominate among asteroids is below a diameter
of about 200 m, corresponding to H approximate to 22, as suggested by
P.Pravec and A. W. Harris (2000, Icarus, in press). (C) 2000 Academic Press.
Addresses:
Pravec P, Acad Sci Czech Republ, Inst Astron, CZ-25165 Ondrejov, Czech
Republic.
Acad Sci Czech Republ, Inst Astron, CZ-25165 Ondrejov, Czech Republic.
Univ Arizona, Lunar & Planetary Lab, Tucson, AZ 85721 USA.
Univ Hawaii, Inst Astron, Honolulu, HI 96822 USA.
Charles Univ Prague, Astron Inst, CZ-18000 Prague, Czech Republic.
Copyright ) 2000 Institute for Scientific Information
==============================================================
(8) RADAR OBSERVATIONS OF ASTEROID 2100 RA-SHALOM
Radar observations of Asteroid 2100 Ra-Shalom
Shepard MK, Benner LAM, Ostro SJ, Harris AW, Rosema KD, Shapiro II, Chandler
JF, Campbell DB
ICARUS 147: (2) 520-529 OCT 2000
We report Doppler-only (cw) radar observations of near-Earth Asteroid 2100
Ra-Shalom obtained at the Arecibo Observatory using a transmitter frequency
of 2380 MHz (12.6 cm) on 1984 Aug. 18-22. Weighted and filtered sums of cw
echoes achieve a maximum signal-to-noise ratio of 74 and cover the asteroid
in rotation phase. A weighted sum of all cw spectra gives an opposite
circular (OC) radar cross section of 1.13 +/- 0.40 km(2) and a circular
polarization ratio of 0.31 +/- 0.02. Inversion of echo edge frequencies
yields a convex hull with an elongation (maximum breadth/minimum breadth) of
1.15 +/- 0.03 and places a lower bound on the maximum pole-on dimension of
2.4 km/cos delta, where delta is the angle between the radar line-of-sight
and the asteroid's apparent equator. Ra-Shalom has one of the least
elongated pole-on silhouettes of the near-Earth asteroids for which similar
shape information from radar observations is available. Ra-Shalom's
effective diameter (diameter of a sphere with equal cross-sectional area) is
constrained to a range of 2.4-3.6 km. We use a two-component radar
scattering model to remove the "diffuse" contributions from Ra-Shalom's
radar cross section and obtain a surface bulk density estimate of 1.1-3.3 g
cm(-3). When compared with reported bulk densities and porosities of
meteorites, our results are consistent with either: (1) a C-class asteroid
with carbonaceous-chondritic composition, effective diameter 2.6-3.6 km, and
surface porosity <70%; or (2) an S-class asteroid with ordinary-chondritic
or stony-iron composition, effective diameter 2.4-2.6 km, and little or no
surface regolith. Ra-Shalom's near-surface roughness appears to be globally
heterogeneous. (C) 2000 Academic Press.
Addresses:
Shepard MK, Bloomsburg Univ Penn, Dept Geog & Geosci, Bloomsburg, PA 17815
USA.
Bloomsburg Univ Penn, Dept Geog & Geosci, Bloomsburg, PA 17815 USA.
CALTECH, Jet Prop Lab, Pasadena, CA 91109 USA.
Harvard Smithsonian Ctr Astrophys, Cambridge, MA 02138 USA.
Cornell Univ, Natl Astron & Ionosphere Ctr, Ithaca, NY 14853 USA.
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