PLEASE NOTE:
*
CCNet, 16 November 1999 - LEONIDS SPECIAL III
---------------------------------------------
QUOTES OF THE DAY
"The scene was truly awful and
indescribably sublime; ... it
carried to the bosoms of many terror and
consternation. Some
imagined the world was coming to an end
and began to pray;
and a gentleman from the counrty states
that such was the
alarm produced in the neighborhood where
he was that the
welkin every where around him resounded
with cries of
distress."
- Reporting the 1833 Leonids,
Raleigh Star, 15 November 1833
"Such scientific matters are of
little interest to the
increasing numbers of apocalyptic
Christian groups gathered
in Israel and the United States. They
have been moved to
paroxysms of excitement by recent
earthquakes in Turkey and
Greece, which they believe are portents
of a coming
Armageddon. Their doomsday predictions,
which involve mass
destruction and the "rapture",
when believers ascend to
heaven, will be further encouraged by
the meteor storm,
which, like the star that led the Three
Wise Men to the
birthplace of Christ, will rise in the
east over Jerusalem."
-- The Times, 16 November 1999
(1) THE LEONIDS ARE BACK. IS A STORM BREWING?
Andrew Yee <ayee@nova.astro.utoronto.ca>
(2) NASA PLANES AID ISRAEL TO MONITOR METEORS
The Times, 16 November 1999
(3) AVOIDING LEONID STORMS
Andrew Yee <ayee@nova.astro.utoronto.ca>
(4) ELUSIVE METEOR STORM OFFERS LAST GLIMPSE
Andrew Yee <ayee@nova.astro..utoronto.ca>
(5) LEONIDS WARNING 1999
Andrew Yee <ayee@nova.astro.utoronto.ca>
(6) ASTROBIOLOGISTS FLYING HIGH TO STUDY LEONID METEORS
John Bluck <jbluck@mail.arc.nasa.gov>
(7) SOHO PREPARES TO WEATHER THE LEONID'S METEOR STORM
Andrew Yee <ayee@nova.astro.utoronto.ca>
(8) PUTTING THE SQUEEZE ON LIGHTWEIGHT ASTEROIDS
SpaceViews, 16 November 1999
==========
(1) THE LEONIDS ARE BACK. IS A STORM BREWING?
From Andrew Yee <ayee@nova.astro.utoronto.ca>
European Space Agency
Press Information Note Nr. 17-99
Paris, France 15 November 1999
THE LEONIDS ARE BACK. IS A STORM BREWING?
Will the night sky be illuminated with thousands of 'shooting
stars' --
known to scientists as the Leonid meteors -- on the night of
17-18
November? No one knows for sure, but some experts are predicting
a
dramatic display over Western Europe which will rival any
millennium
celebrations.
What are the Leonids?
Each year, the night sky is illuminated by dozens of meteor
showers.
During these showers, pieces of cosmic debris -- mostly coming
from
giant dirty snowballs called comets -- leave glowing trails as
they are
incinerated during entry to the Earth's upper atmosphere. We see
them
as short-lived trails of light streaking across the sky.
One of the most famous meteor showers is known as the Leonids,
so-called because their light trails all seem to originate from
the
constellation of Leo. The Leonid meteors are associated with dust
particles ejected from Comet P/55 Tempel-Tuttle, which pays
periodic
visits to the inner Solar System once every 33.25 years.
Actually, the Leonids appear every year between November 15-20,
when
the Earth passes very close to the comet's orbit. However, the
numbers
on view vary tremendously. In most years, observers may see a
peak of
perhaps 5-10 meteors per hour around 17 November.
But, roughly every 33 years, the Leonids generate a magnificent
storm,
when thousands of them illuminate the night sky: they are
renowned for
producing bright fireballs which outshine every star and planet.
Their
long trails are often tinged with blue and green, while their
vapour
trains may linger in the sky like enormous smoke rings for 5
minutes or
more.
Although the incoming particles are small, ranging from specks of
dust
to the size of small pebbles, the Leonids glow brightly because
they
are the fastest of all the meteors. A typical Leonid meteor,
arriving
at a speed of 71 km/s (more than 200 times faster than a rifle
bullet),
will start to glow at an altitude of about 155 km and leave a
long
trail before it is extinguished.
The Unpredictable Leonids
Based on past behaviour, a meteor storm was predicted for 1998 or
1999.
Last year, some very bright fireballs appeared unexpectedly 18
hours
before the predicted maximum. They were associated with a
previously
unknown dust band which had been shepherded into a narrow stream
by
Jupiter's gravity. Unfortunately, although there was also a peak
in
meteor activity at the predicted time, their trails were not very
bright and hard to see with the naked eye.
"In hindsight people found out that actually in 1965 we saw
a similar
display ... these fireballs the night before and then not quite
the
activity that was expected at the real maximum and you might know
that
in 1966, that was when the real storm occurred" said Detlef
Koschny,
scientific coordinator of the ESA's Leonids observation campaign.
"So
that was one year after. So some scientists say, 'Ok, for this
year we
really expect a big storm or we hope; you can never be
sure."
So what about this year? In 1999, although the Earth will reach
Tempel-
Tuttle's orbit 622 days after the comet passed by, the
distribution of
its dust ribbons means that a notable display is still possible.
One
encouraging sign is that the 1998 shower was similar to that of
1965,
the year before the storm of 1966. Most astronomers are not
expecting a
comparable display in 1999, but a spectacular show cannot be
ruled out.
Activity will probably reach a peak on the night of 17-18
November,
though earlier fireballs are always a possibility. Nothing will
be
visible until the 'sickle' of Leo rises above the eastern horizon
around 22.30 GMT. At first, the fainter meteors will be swamped
by
light from the first quarter Moon, but once this sets soon after
midnight, conditions should be ideal as long as the sky is cloud
free.
The maximum activity should occur around 02.00 GMT, at the time
when
the Earth passes closest to the comet's orbit. At this time, Leo
will
be well above the horizon over Western Europe.
Some scientists predict that 2000 or 2001 may provide even better
viewing opportunities for the Leonids, but no one can be sure if
these
unpredictable cosmic travellers will live up to expectations.
"We just know from past history that, in the two years after
the
perihelion of Comet Tempel-Tuttle, there is enhanced
activity," said
Dr. Walter Flury of the European Space Operations Centre (ESOC).
"A storm is possible, but these things are very
uncertain," he added.
"Predictions are based on models of the way material is
distributed
along the comet's orbit. But the models are quite inaccurate. We
just
don't have enough information."
There are two main reasons why scientists study meteors: the
clues they
hold about the formation of the planets and the potential threat
they
pose to Earth-orbiting satellites:
1. ESA Scientists Seek to Study the Leonids
Since the Leonids ejected from a comet and since comets are
thought to
be left-overs from the formation of the planets, studying the
Leonids
helps scientists to learn more about the physical and chemical
characteristics of their 4.5 billion year-old parents.
If the storm does materialise, scientists from ESA's Space
Science
Department intend to be ready. Armed with a variety of equipment,
including image-intensifier video cameras, CCD cameras with
wide-angle
lenses and a spectrograph, they are planning an observational
campaign
at two observatories in southern Spain (Calar Alto and Sierra
Nevada)
from 11 to 19 November.
The main science goals are:
* To determine the varying rates in the number of meteors and
their
magnitudes (visual brightness).
* To study the physical properties of individual meteors by
measuring their
light output and changing velocity, then compare these to
other meteor
streams.
* To use the 1.5 m telescope at the Sierra Nevada Observatory to
perform
spectroscopy of persistent trains and so determine their
composition.
There will also be an ESA scientist with a meteor camera on board
an
aircraft operated by the American SETI (Search for
Extraterrestrial
Intelligence) Institute. Results from the meteor count
experiments will be
sent to ESOC in Germany so that spacecraft operators can
determine the
level of threat posed by the space dust.
2. Hazards to spacecraft: how ESA is preparing
Although they are very small, the tremendous speed of the Leonids
means
they pack a mighty punch. Apart from knocking a spacecraft off
alignment
or causing physical damage in the form of an impact crater, such
collisions
can also generate a cloud of plasma (gas composed of neutral and
electrically charged particles) which may cause electrostatic
discharges
or damage a spacecraft's sensitive electronics.
This threat is not simply theoretical. In 1993, an ESA's
satellite called
Olympus spun out of control due to an electrical disturbance
caused by the
impact of a particle from the Perseid meteor shower.
The situation is further complicated by the fact that there are
currently more satellites in orbit around the Earth than ever
before,
all of which pose a tempting target for one of nature's miniature
missiles. Despite this spacecraft population explosion, few, if
any,
satellites are likely suffer significant problems from meteors,
even
during a storm. Researchers estimate that the chance of one
getting hit
by a Leonid meteor is only about 0..1 percent.
This low hit rate was born out by an absence of damage during the
1998
Leonids event. Nevertheless, driven by uncertainty over the
future of
their high-tech hardware, satellite operators will once again be
taking
precautions to protect their multi-million Euros charges this
November.
One of the largest targets, the NASA-ESA Hubble Space Telescope
will
be manoeuvred so that its mirrors face away from the incoming
meteors
and its solar arrays are aligned edge on to them. These
precautions
will continue for several Earth orbits, a duration of seven
hours,
during the Leonids' predicted peak.
Apart from reducing the exposed area of giant solar arrays,
operators
may shut off power to vulnerable electrical components of
satellites,
or switch them off entirely during the peak of the Leonid
activity.
Even spacecraft located some distance from the Earth may be at
risk.
ESA's Solar and Heliospheric Observatory (SOHO) studies the Sun
from a
vantage point 1.5 million kilometres away, but it, too, will roll
so
that its main navigational aid, the star tracker, is pointing out
of
harm's way.
"There could be a lot of activity, but we just don't know
for sure,"
commented Walter Flury. "It's better to take precautions now
than be
sorry later."
ESOC issued a warning to all satellite operators in August,
explaining key
protective measures to be taken such as switching off the payload
and
modifying the angle of the solar panels in relation to the
Leonids
storm.
By November 17, 1999 ESOC will have secured both earth
observation
satellites ERS-1 and ERS-2 by switching off the payload. The risk
does
not only lie in the damage caused by direct impact but rather in
plasma
discharge that could disrupt the functioning of the on-board
electronics. Teams of operations experts will be on shift
throughout
the night to assess any potential damage and take necessary
action.
The press is welcome to attend the press briefing that will take
place on
Thursday 18th November at 8:00 am at ESOC after a night's watch.
Please
contact Jocelyne Landeau-Constantin, Public Relations Office,
Tel +496151902696, Fax +496151902961 for accreditation.
Possibility
for interviews is available as from 17th November 1999.
More information, including live images and reports, and an 'Ask
the
experts' forum, can be found on the ESA Science Leonids 99
website at:
http://sci.esa.int/leonids99
Information on the Leonids flux and events at ESOC is available
at:
http://www.esoc.esa.de/pr/leonids.php3
For further information please contact:
ESA Public Relations Division
Tel: +33 (0)1.53.69.71.55
Fax: +33 (0)1.53.69.76.90
Further information on the ESA science programme and a subscriber
service for news can be found on the Worldwide Web at:
http://sci.esa.int
More information about ESA at http://www.esa.int
===============
(2) NASA PLANES AID ISRAEL TO MONITOR METEORS
From The Times, 16 November 1999
FROM SAM KILEY IN JERUSALEM
TWO specially equipped Nasa aircraft will arrive in Israel
tomorrow as
part of an international effort to monitor the Leonid meteor
storm and
to help to protect satellites from debris entering the Earth's
upper
atmosphere.
Up to 100 scientists from Britain and elsewhere will join Israeli
astronomers in the effort to warn satellite operators around the
globe
to shut down or move their systems. The satellites are in danger
of
being hit by debris travelling at 150,000mph, as well as from
plasma, a
cloud of electronically charged particles that follows the
meteors.
"Air Force satellite operators are reviewing contingency
plans to
protect and recover, if necessary, military communications,
missile-warning and navigation satellites that could be affected
by the
storm," the US Air Force said.
The meteors, which form the tail of the Temple-Tuttle comet,
could also
damage the expensive optical equipment of spy satellites, which
are
likely to be temporarily or even permanently blinded by the
celestial
display. Scientists say it could generate up to 1,200 visible
flashes an hour, far higher than the last storm in 1966. The
shower
will be seen best in Israel, but it will also be visible in
Canada,
Florida and the Canary Islands tomorrow night.
Aby Har-Evan, director-general of the Israeli Space Agency, said
yesterday that in addition to the scientists on board the
aircraft,
others in the Negev Desert would link to amateurs working at
observatories across Israel to collect data. "There is a
great danger
of collision to satellites from particles no bigger than a grain
of
sand," he said. "The Canadians will be able to alert
systems
operators to shut down their equipment, or change its orientation
so
that the smallest face is turned towards the meteor storm. We
hope that
this event will give us some insights into how the universe was
created. There is a possibility that one day we will collect
organic
matter from a comet tail of this kind, which would unlock a lot
of
secrets by giving some indication to the foundation of the
universe."
Such scientific matters are of little interest to the increasing
numbers of apocalyptic Christian groups gathered in Israel and
the
United States. They have been moved to paroxysms of excitement by
recent earthquakes in Turkey and Greece, which they believe are
portents of a coming Armageddon.
Their doomsday predictions, which involve mass destruction and
the
"rapture", when believers ascend to heaven, will be
further encouraged
by the meteor storm, which, like the star that led the Three Wise
Men
to the birthplace of Christ, will rise in the east over
Jerusalem.
Ed Daniels, 54, a former surveyor from Denver, Colorado, who
emigrated
to Israel two months ago, said that he had seen signs of the
"end time"
so frequently during the past year that he was convinced that
Armageddon was fast approaching.
"I don't think it, I know it," he said. "The end
time is approaching,
and we are expecting the rapture."
Copyright 1999, Times Newspapers Ltd.
=============
(3) AVOIDING LEONID STORMS
From Andrew Yee <ayee@nova.astro.utoronto.ca>
[From Cooperative Research Centre for Satellite Systems (CRCSS)
Space Industry News, Issue 84, September 1999
http://www.crcss.csiro.au/spin/spin84/SPIN8407.htm]
Avoiding Leonid storms
Leonid meteor storms, particles from Comet Tempel-Tuttle, reach a
peak
every 33 years. In Novembers near this peak, the meteoroids
threaten
satellites. New predictions can pinpoint the storms to five
minutes;
they will help agencies protect their satellites. Robert McNaught
explains.
Research in meteor science was well established before the space
age. A
big worry was the potential threat meteoroids could pose to
satellites
or humans in space. But experience has shown the threat was
mostly
slight.
However, several times each century, meteor activity has
increased to
intense levels, called storms. Although storms are related to the
dust
released from specific comets, their occurrence has been largely
unpredictable. With their potential catastrophic consequences for
satellites, much attention is now being focused on meteor
storms.
Meteor storms result from Earth passing through dense narrow
streams of
debris from comets. Comet Temple-Tuttle produces the Leonid
meteor
storms. Storms have been largely unpredictable, but closely
related to
the orbital period of the parent comet; they occur within a few
years
of the comet passing Earth. The most intense Leonids occurred
1833 and
1966. The 1966 storm was the only one within the space age. No
satellite damage occurred, but few satellites were in orbit
then.
As comets approach the Sun, the increasing solar radiation
sublimates
ices which are swept away by the solar wind. Fine dust grains are
released with the gasses.
The size of particles in a comet's visible dust tail are too
small to
produce naked-eye meteors. Particles causing visible meteors are
only
slightly affected by solar radiation wind and begin in orbits
close to
the comet's. The particles eventually scatter around the
orbit.
The traditional approach to predicting meteor storms involved
examining
the correlation between comets' orbital geometry, and the
historical
dates and times of storms. The best this approach could do was
suggest
likely storm-years, and estimate peak intensity to within a day,
or
maybe a few hours. This is inadequate to assess the potential
risk or
organise evasive action.
New theories
To improve, it's necessary to look at how particles evolve from
comet-
ejection to collision with Earth's atmosphere. Dust ejected as a
spherical cloud each time the comet is nearest the Sun, becomes a
narrow dust trail, elongated along the original comet orbit. The
precise position of the dust trail in relation to the Earth can
be
calculated for each year, a direct hit with the a trail being
necessary
to produce a storms.
We know the solar wind has some influence on the particles
producing
visual meteors. The radiation counteracts the Sun's gravitational
attraction, so particles orbit the Sun more slowly. This is why
storms
occur in years shortly after passage of the parent comet. The
exact
time lag for the main bulk of the particles depends on the range
of
masses and ejection velocities, and the number of orbital
revolutions
before encounter.
David Asher and I have checked Earth's predicted times of
approach to
these dust trails. We could back-predict the peak times to within
5
minutes of the observed times, for all years when the maxima were
timed
(1866, 1867, 1869, 1966 and 1969). We also developed a model of
dust
trail density; our model closely fits the observed rates for all
storm years (1833, 1866, 1867, 1869 and 1966).
We believe we can predict storms to within 5 minutes, and perhaps
50%
in visual rates. Our model predicts the main activity will occur
between
1999 and 2002, with the highest rates in 2001 and 2002. We
predicted no
activity from dust trails in 1998.
Predictions & countermeasures
Although no storm occurred in 1998, we still saw impressive
Leonid
fireballs (bright meteors). The explanation came in a separate
study; as
comet Tempel-Tuttle is in an orbital resonance with Jupiter, any
particles
ejected at low enough velocity (generally big ones), also inhabit
this
resonance zone. The zone only covers about 1/30 of the comet's
orbit,
so encounters with Earth only occur within a year of the comet
passing.
Detailed calculations showed the Earth had a direct encounter
with large
resonant meteoroids ejected from Comet Tempel-Tuttle in
1333.
The highest activity over the next few years will be due to
encounters
with young dust trails:
* 1999, Nov. 18 02:08 UT 3-rev ZHR 1,200
* 2001, Nov. 18 18.19 UT 4-rev ZHR 13,000
* 2002, Nov. 19 10.36 UT 4-rev ZHR 25,000
Additional dust trail encounters in these years will be at
different times
with lower rates.
The geometry of encounter with the dust trails results in the
more
southerly parts of Earth experiencing the peak first. It then
moves
roughly northwards at around 600 km/min., leaving the northern
extreme
about 22 minutes later.
Given this model, and the small uncertainty in the predicted
maximum
time, there are specific consequences in mitigating the threat to
satellites.
For a satellite that can be maneuvered to any point in its orbit
at the
maximum time, and having the appropriate orbital geometry, the
two
obvious strategies are to place the satellite in the "Leonid
shadow"
produced by the Earth, or at the point in the orbit furthest from
the
center of the Leonid dust trail. With the maximum of a Leonid
storm
being around 30 minutes, the period in shadow can be very
significant. If
the satellite orbit is oriented perpendicular to the dust trail,
the rates
furthest from the dust trail can be a small fraction of those
closest to
the dust trail. Combinations of these, and additional strategies,
can
result in a substantial reduction of the overall risk.
[Robert McNaught works in the Research School of Astronomy and
Astrophysics at the Australian National University, studying the
discovery and tracking of Near-Earth objects. He previously
worked in
optical satellite tracking.]
==============
(4) ELUSIVE METEOR STORM OFFERS LAST GLIMPSE
From Andrew Yee <ayee@nova.astro.utoronto.ca>
Centre for Research in Earth and Space Technology
Toronto, Ontario
Contact:
Andre Bellefeuille
Director, Communications
CRESTech
office (416) 665-5464, cell (416) 707-9120,
email: andre@admin.crestech.ca
Press Release - November 12, 1999
Elusive Meteor Storm Offers Last Glimpse
Toronto -- The debris of Comet Tempel-Tuttle, better known as the
Leonid Meteor Storm, is once again on Earth's radar screen for
the
night of November 17 and likely for the last time until roughly
the
year 2032.
The mysterious debris field is of great concern to scientists and
satellite owners. As Earth passes through the path of
Tempel-Tuttle's
highly elliptic orbit, satellites within Earth's gravitational
field
will face their greatest risk of physical damage since the huge
Leonids
storm of 1966.
The Centre for Research in Earth and Space Technology (CRESTech)
is
once again leading a global observation and risk-reduction
program to
try and build a comprehensive model of the Leonid meteor storm.
Though
the Leonids only appear every 32-33 years, they offer immense
insight
toward building forecasting technology that could help protect
the
world's satellite fleets from similar astral activity.
CRESTech's clients for the 1999 program include the Canadian
Space
Agency (CSA), the Department of National Defence (DND), NASA, the
United States Air Force Space Command (USAF) and the European
Space
Agency (ESA).
Last year's program surprised many scientists when instead of
seeing a
massive quantity of "shooting stars," many viewers in
the Far East were
treated to a show of large fireballs, few in number but highly
visible.
As a result of travelling through a different "slice"
of the meteor
field, this year's event is anticipated to result in massive
quantities
of shooting stars, but few large fireballs.
Through the involvement of researchers at the University of
Western
Ontario and other Canadian and international institutions, the
CRESTech-led team will set up electro-optical camps in Israel's
Negev
desert and the La Palma Observatory on the Canary Islands,
considered
to be the two best viewing points globally. Additional optical
data
will be collected by the USAF in Florida, Hawaii and the
Kwajalain
Atoll. Radar data will be collected in Northern Canada at a
station in
Alert, Nunavut.
A full backgrounder on the Leonids program is available at
"www.crestech.ca/leonids"
as are links to NASA and ESA descriptions of
the event.
CRESTech is made possible through the Ontario government's
Centres of
Excellence Program.
For more information, please contact:
Andre Bellefeuille
Director, Communications
CRESTech
(416) 665-5464, cell (416) 707-9120
www.crestech.ca
==============
(5) LEONIDS WARNING 1999
From Andrew Yee <ayee@nova.astro.utoronto.ca>
European Space Operations Centre
European Space Agency
Darmstadt, Germany
November 1999
Leonids Warning 1999
Earth orbiting spacecraft are at risk of being hit by Earth
orbiting
debris but to some extent also by meteoroids. For example, the
demise
of ESA's Olympus spacecraft may be attributed to the Perseid
meteoroid
stream. The Leonid meteoroid stream is expected to pose a
particular
risk in the coming years around November 17-18, the time in the
year
when the Earth passes closely the orbit of comet Tempel-Tuttle,
which
is the progenitor of this stream.
ESOC Leonids Document
For more information about Leonid and the risks it poses, feel
free to
download this PDF report.
[http://www.esoc.esa.de/pr/documents/leonids-warning99.pdf]
The objective of this note is to provide background information
about
the expected Leonid meteor shower around 18 November 1999 and to
give
advice for spacecraft operators what kind of precautions can be
taken
to minimize the risk of damage to operational spacecraft. In this
note
updated predictions for the expected time and intensity of the
Leonid
1999 meteor shower are given.
==========
(6) ASTROBIOLOGISTS FLYING HIGH TO STUDY LEONID METEORS
From John Bluck <jbluck@mail.arc.nasa.gov>
Nov. 15, 1999
Kathleen Burton
NASA Ames Research Center, Moffett Field, CA
(Phone: 650/604-1731, 650/604-9000) kburton@mail.arc.nasa.gov
Laura Lewis
NASA Ames Research Center, Moffett Field, CA
(Phone: 650/604-2162, 650/604-9000) llewis@mail.arc.nasa.gov
RELEASE: 99-71
NOTE TO EDITORS/NEWS DIRECTORS: You are invited to observe video
footage of the Leonid meteors from the mission on Wednesday, Nov.
17,
from 2 p.m. to 6 p.m. (PT) in the main auditorium, N-201, at NASA
Ames
Research Center, Moffett Field, CA. To gain entry, show
press
credentials and photo ID at the Visitor Badging Office, located
at the
Main Gate, Moffett Federal Airfield.
ASTROBIOLOGISTS FLYING HIGH TO STUDY LEONID METEORS
To gain a better understanding of the way life may have evolved
on
Earth, a team of scientists has begun a multinational airborne
mission
to study the Leonid meteors.
The Astrobiology mission began when two U.S. Air Force planes,
the ARIA
and the FISTA, lifted off from Edwards Air Force Base, Edwards,
CA, on
Nov. 13 at 11:15 a.m. (PT) enroute to Royal Air Force Mildenhall
Airbase in the United Kingdom. During the mission, an
international
cadre of scientists will point their instruments towards the sky
to
study the Leonid meteors from the unique vantage-point of the
aircraft.
"The planes provide a perfect platform for viewing the
meteors," said
Peter Jenniskens, chief scientist for the Leonids mission.
"They lift
us above the weather to ensure a fantastic view. By flying
over 35,000
feet in the air, we are above most of the atmospheric water
vapor, and
our instruments get the best data possible."
The Leonid meteor showers occur each November when the Earth
passes
through the debris shed from periodic comet
55P/Temple-Tuttle. The
meteors, named the Leonids because they appear to stream from the
constellation Leo, are about the size of a grain of sand.
Studying
comets and meteors, which are made from ice and dust that existed
when
the universe was formed, may help scientists develop a better
understanding of how life began on Earth.
"Comets and meteors are fascinating to study because they
are a frozen
record from the time when the universe formed," explained
astrobiologist Dr. Scott Sandford of NASA's Ames Research Center,
Moffett Field, CA. "Due to geological activity, all of
Earth's
materials have been reformed several times over, and we must
study
comets, meteors and meteorites to get an early view of our
universe."
Most years, observers with ideal viewing conditions can see 10 to
20
meteors per hour during the Leonid showers. Every 33 years
when the
parent comet Temple-Tuttle passes particularly close to the
Earth, as
it did in 1998, meteor storms with hundreds or thousands of
meteors per
hour are possible. In 1998, following Temple-Tuttle's pass by
Earth,
counts of 250 meteors per hour were recorded. Predictive
models have
indicated that, in 1999, it may be possible to see 200 to 5000
meteors
per hour around the longitudes of Europe and the Middle
East. The 1999
Leonid Multi-instrument Airborne Campaign (MAC), a mission
jointly
funded by NASA and the United States Air Force, has been designed
to
fly over these longitudes for three consecutive observation
nights,
Nov. 16-18.
Both aircraft being used for the mission have been specially
outfitted
with a variety of instruments, including spectrometers and
cameras, to
study the meteors. The FISTA, an NKC-135 aircraft, has been
modified
with 20 upward-facing viewing ports. The ARIA, an EC-18
airplane, has
telemetry equipment that will allow researchers to send images
and near
real time data regarding comet flux, or counts, to the ground.
Research objectives for the mission involve taking many
measurements
that have never been done in airborne astronomy, including
real-time
meteor counts, spectroscopy (mid-infrared, near-infrared,
ultraviolet
and visible) and stereoscopic viewing of meteors using
intensified
high-definition television cameras. The stereoscopic view,
obtained
when instruments on both aircraft image a meteor, will provide
the
first-ever three-dimensional model of meteor trajectories.
About half of the scientists on the current mission participated
in the
1998 Leonid MAC mission that flew over Japan. That highly
successful
mission is credited with observing more than 3,200 meteors,
obtaining
the first differential spectrometry data from meteors as they
burned
through the sky, and obtaining the first stereoscopic images of a
persistent meteor train.
After departing Edwards Air Force Base Nov. 13, the planes flew
to
Mildenhall Airbase in the United Kingdom. During the
night-time
crossing of the Atlantic Ocean, scientists tested and calibrated
their
instruments and completed initial observations, including taking
measurements of the Aurora Borealis.
The mission will begin Nov. 16 when the planes depart England and
fly
the scientists overnight to Tel Aviv. The following night,
Nov. 17,
during the expected peak of the storm, the scientists will fly
from Tel
Aviv to Lajes Air Base in the Azores. The final night, Nov.
18, the
planes will fly from the Azores to Patrick Air Force Base in
Florida.
The peak of the storm is expected to occur at 0200 (UT) Nov. 18
(9:00
p.m. ET, Nov. 17) over Europe and the Middle East. While
the best
viewing of the storm will be in these locations, it may be
possible to
see the Leonid meteors in the United States, particularly in the
predawn hours of November 17 and 18.
For current information about the Leonid MAC Astrobiology
mission,
visit: http://leonid.arc..nasa.gov/
=======================
(7) SOHO PREPARES TO WEATHER THE LEONID'S METEOR STORM
From Andrew Yee < ayee@nova.astro.utoronto.ca
>
ESA Science News
http://sci.esa.int
11 Nov 1999
SOHO prepares to weather the Leonid's meteor storm
The Earth will have another close encounter with Comet
Tempel-Tuttle's
dust trail in the early hours of 18 November, and the resulting
meteor
storm, called the Leonids, could be spectacular.
But the storm so eagerly awaited by astronomers is also making
spacecraft controllers take precautions. Like a ship caught in a
tempest, ESA's Solar and Heliospheric Observatory (SOHO) will try
to
stay as safe as possible during the meteor storm.
The scintillating effect produced by the friction between the
comet's
dust particles and the upper layers of our atmosphere should be
visible
in North America, Europe, Africa, and part of Asia.
With the Earth remaining at a distance of about 1 million
kilometres
from the comet's path, the danger for SOHO and other satellites
may be
considered minimal, say scientists. But given that the flow of
dust
particles is hundreds of thousands of kilometres wide, space
agencies
and satellite operators have decided the risk should not be
disregarded.
The loss of ESA's Olympus communications satellite in the early
1990s
was thought to have been caused by the Perseid meteor shower.
The relative velocity between our planet and the particles left
behind
by comet Tempel-Tuttle will be about 70 km/s, that is more than
250 000
km/h. "At that speed, if you had a hit by a discrete
particle, it would
pierce right through the spacecraft like a bullet," says
Bernhard
Fleck, SOHO Project Scientist.
During the coming peak of activity of the Leonids, as many as
1000
meteors per hour are expected to strike the Earth's atmosphere.
To avoid the danger of a sandblasting effect on the optical
systems of
its instruments, the protective doors on SOHO will be commanded
to
close.
In 1986, the camera on ESA's Giotto spacecraft suffered -- as
expected
-- severe damage as it passed in front of Halley's comet nucleus.
Since
cometary dust could cause similar problems to SOHO's vital star
trackers, ground controllers will command the spacecraft to
rotate 120
degrees around its axis. The star trackers are used by the
spacecraft
to determine its position in space as it observes the Sun from
its
vantage point 1.5 million kilometres from Earth.
Ten of SOHO's 12 scientific instruments will also be turned off,
to
minimise the risk that any instrument hit by a particle would be
severely damaged by the combination of incandescent debris from
the
impact and the high-voltage power supply.
During the peak of the storm, SOHO will be placed in a safety
configuration, known as the Coarse Roll Pointing mode. The 10
instruments will remain switched off for a period of almost 70
hours
starting 16 November.
USEFUL LINKS FOR THIS STORY
* ESA Leonids99 page
http://sci.esa.int/leonids99
* More about SOHO
http://sohowww.nascom.nasa.gov/
* SOHO near-real time image screen saver
http://www.estec.esa.nl/spdwww/soho/SohoScreens.exe
[NOTE: An image supporting this release ia available at
http://sci.esa.int/missions/newsitem.cfm?TypeID=12&ContentID=7591
]
====================
(8) PUTTING THE SQUEEZE ON LIGHTWEIGHT ASTEROIDS
From SpaceViews, 16 November 1999
http://www.spaceviews.com/1999/11/16a.html
Craters on some asteroids may be caused by the compression of
porous
material, rather than the excavation of material as previously
assumed,
scientists reported last week.
The results, presented in the November 11 issue of Nature, could
explain how small asteroids like Mathilde have such large craters
without breaking apart, and could make it harder to protect the
Earth
from such asteroids.
Kevin Housen, a scientist at Boeing, and colleagues at the
University
of Washington, performed laboratory tests to see how craters form
in
low-density materials. By creating small impacts at high
accelerations,
they were able to scale up their results to much larger craters
at low
accelerations, as on the surface of an asteroid.
To their surprise, they found that craters formed not by digging
out
material, as is the general case for impact craters, but by
compressing
the material. The porous material effectively absorbs the energy
of then impact, compressing and increasing its density as a
result.
This would explain who asteroids like Mathilde, which was
observed up
close by the Near-Earth Asteroid Rendezvous (NEAR) spacecraft
during a
June 1997 flyby, can have large craters on its surface that are
remarkably free of the debris usually associated with an impact.
Scientists had previously assumed that the impact debris was
accelerated beyond the escape velocity of the asteroid and thus
never
landed.
The results, if they hold up, would have an effect on both
planetary
formation and planetary defense. Erik Asphaug, a planetary
scientist at
the University of California Santa Cruz, notes in an accompanying
article that low-density objects, like primitive asteroids in the
early
solar system, would be able to accrete material "like a
celestial
Pac-Man." That would make planetary accretion easier to
understand, he
believes.
On the other hand, a porous asteroid like Mathilde on a collision
course with the Earth would be difficult to deflect, since it
would be
able to effectively abosrb the energy of bombs designed to
deflect it off course. The object would simply become slightly
more
dense, rather than be deflected off course as intended.
Asphaug isn't terribly concerned about this, however. "We
would have to
live ten million years or more, on average, to experience the
type of
asteroid collision that could wipe out mankind," he writes.
"I am not
betting on that horse."
Copyright 1999, SpaceViews
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