CCNet, 4 November 1999


     "Previous estimates of fatality and damage rates on the 100 to
     10,000 year time scale are shown to be too low because they
     neglect rare, highly lethal outriders of the populations of
     bombarding objets, those with exceptional strength, unusually low
     entry velocity, and near-horizontal entry angles."
          -- John S. Lewis, Comet and Asteroid Impact Hazards on a
                Populated Earth, Academic Press Inc, 1999

     "In essence, I fancy Earth protection as an evolution of the
     function that national defense has held--attempting to minimize
     danger to citizenry while maintaining a status quo.  Obviously
     this is a social, philosophical, and funding issue; the question
     is whether resources will continue to flow most readily to
     short-term money-making projects or to endeavors that can enhance
     real wealth, which is accurate knowledge of how our world works.
     Perhaps increasing evidence of rapid climate change may help to
     tip various tills toward survival
             -- Bob Kobres, 3 November 1999

    Ron Baalke <>

    Andrew Yee <>

    Ron Baalke <>

    Bob Kobres <>

    New book by John S. Lewis (1999), Academic Press Inc

(6) ORBFIT 2.0
    Andrea Milani <>

    Andrew Yee <>



From Ron Baalke <>

Leonids on the Moon
Marshall Space Flight Center

Leonid meteorite impacts on the Moon might be visible from Earth and
provide a means for long-distance lunar prospecting.

Nov. 3, 1999: When the Leonid meteor shower strikes on the morning of
November 18, 1999, our planet won't be the only place in the cross
hairs. The Moon will also pass very close to the debris stream of comet
Tempel-Tuttle. Here on Earth, space-borne meteoroids will plummet into
the atmosphere and burn up, creating streaks of light called meteors.
The vast majority of meteoroids will burn and disintegrate well before
they hit the ground. The situation on the Moon, where there is no
appreciable atmosphere, is different. Every bit of comet debris that
rains down on our satellite will hit its surface. Some meteor
enthusiasts hope that will create a different sort of display. Rather
than streaks of light in lunar skies, there could be flashes of light
on the Moon's surface each time a sizable meteoroid hits the ground.

Last year, during the 1998 Leonid meteor shower, the phase of the
moon was new. It was so close to the sun in the sky that observing
faint lunar meteorite flashes was impossible. This year is different.
During the 1999 Leonid shower the phase of the Moon will be just 2
days past first quarter. That means the moon will visible in the
night sky during the early evening on November 17, and approximately
35% of the lunar disk as seen from Earth will not be illuminated by
sunlight. There will be plenty of dark lunar terrain where flashes
might be visible.

Is it possible to observe such flashes?

Maybe, say researchers. It depends a great deal on the mass spectrum
of particles in the Tempel-Tuttle debris stream and how efficiently
kinetic energy is converted into optical light as a result of the
impacts. Both factors are poorly known. Although flashes are unlikely
to be seen with the naked eye, they may be detectable through amateur

"The impact of a one gram particle would generate of the order of
1023 to 1024 photons in the peak sensitivity range of the human eye,"
says Dr. Bo Gustafson of the University of Florida Laboratory for
Astrophysics. "Given the distance to the Moon, we could expect a few
times 106 photons per square meter at the Earth. This should be
barely detectable using a small telescope."

In June 1999, Ciel & Espace reported that a Spanish team of
astronomers led by J.L. Ortiz had reached similar conclusions:

     Watching meteorites fall on the moon ... is within reach of
     (modest) amateur telescopes. Because the Moon doesn't have a
     substantial atmosphere, meteorite impacts there are much more
     violent than here on Earth liberating much more energy: 20 million
     joules for a 1-kg block. As seen from the Earth, this would
     produce a flash of magnitude 9 to 15. From Ciel & Espace, No. 349
     - Juin 1999, p. 17: Si, c'est possible! (Translation courtesy
     Bernd Pauli HD).

"The Leonid debris stream is in a retrograde orbit, and it's inclined
just 22 degrees from the plane of Earth's orbit around the sun," says
Professor George Lebo of the University of Florida Department of
Astronomy. "That's why the Leonids enter the atmosphere with such a
high velocity [72 km/s]. The Earth and the Leonids hit head-on, like
a head-on collision between two speeding automobiles."

"If you put yourself in the reference frame of the Earth it's pretty
easy to figure out where these meteoroids will hit the Moon,
"continued Lebo. "On November 18, at 0h UT the lunar sub-Leonid point
[the spot where Leonid meteoroids rain directly down on the Moon's
surface] will be 9.4 degrees north of the lunar equator and 9.5
degrees sun ward of the day-night terminator. In other words, the
greatest flux of Leonids are going to hit nearly dead center on the
lunar disk as seen from Earth, just over the terminator on the sunlit

It won't be possible to see flashes on the Moon's sunlit surface, so
amateurs will have to look where the terrain is dark. The best
approach will be to train a telescope -- higher powers are best for
discerning faint flashes -- at a spot near the lunar equator on the
night side of the terminator, keeping the sunlit side of the moon
completely out of the field of view. Flashes observed with the naked
eye would certainly be exciting, but might have little scientific
value. Instead, experienced observers suggest using a low-light
astronomical CCD video camera to make a permanent record.

The Leonids radiant, in the constellation Leo, rises above the
horizon at mid-northern latitudes around midnight on November 17/18.
That's about the same time that the Moon sets. It's an ideal
situation for observers who can monitor the Moon for the first half
of the night and then enjoy the Leonid meteor shower from midnight
until dawn.

Leonid Lunar Prospecting

Although optical flashes were not observed on the moon during last
year's meteor shower, a team of scientists from the Boston University
Center for Space Physics discovered indirect evidence for Leonid

The Moon has an extremely tenuous atmosphere that contains, among
other things, sodium atoms. Just above the Moon's surface the density
of sodium is 50 atoms per cubic centimeter. For comparison, the
sodium density in Earth's lower atmosphere is 1019/cc! Although the
Moon's atmosphere is incredibly thin, researchers at Boston
University's space physics lab have built sensitive cameras that can
trace its sodium component out to several lunar radii.

In mid-November 1998 the Boston University group were using their
sodium camera to monitor Earth's atmosphere for changes due to Leonid
meteors. To their surprise they detected a bright sodium spot on
November 17 that grew in brightness, peaked on November 19, and then
faded away. The spot was almost 180 degrees away from the new Moon in
the night sky. Nevertheless, the source of the sodium was apparently
Earth's satellite. When Leonid meteoroids crashed into the Moon's
dusty soil they kicked up an extra helping of sodium atoms,
increasing the density of the Moon's thin atmosphere. A long lunar
sodium tail formed (much like the tail of a comet) which swept by our
planet two days later.

The Boston University experiment showed for the first time that
intense meteor showers might be one way of "lunar prospecting" from a
distance -- by looking at materials blasted off the surface as
meteoroids strike. A team of scientists from the University of Texas
and NASA tried something similar earlier this year when they crashed
NASA's Lunar Prospector spacecraft into the Moon. The probe was sent
hurtling into a south polar crater on July 31 in hopes that the
impact would vaporize shadowed water-ice and send a cloud of water
vapor and OH flying over the lunar limb. Telescopes, including the
Hubble Space Telescope, looked near the impact site after the crash,
but failed to detect evidence for water. That doesn't mean there's no
water on the moon, say scientists. Lunar Prospector may simply have
hit a dry spot, or perhaps the water vapor didn't rise high enough to

Dr. David Goldstein, a professor at the University of Texas who
proposed the Lunar Prospector impact experiment, is wondering if the
Leonids might succeed where the Lunar Prospector crash failed. Data
from Lunar Prospector's neutron spectrometer indicate that water-ice
on the moon is concentrated around the Moon's poles where shadowed
areas would allow pockets of water to remain frozen (see the figure
below). The 1999 Leonids won't reach the Moon's south pole, but many
meteoroids should strike the north pole.

"The Leonids will be coming in from above the ecliptic plane," says
Goldstein. "Given the Earth-moon geometry on November 18th that means
that the lunar north pole will be exposed, but not the south pole.
That's unfortunate because there's thought to be more water around
the south pole where we crashed Lunar Prospector. There's no chance
of a Leonid meteoroid hitting the crater where Prospector crashed.
Near the north pole the meteoroids will be coming in at several
degrees above the horizon -- very similar to the Lunar Prospector

"Compared to Lunar Prospector, Leonid meteoroids are light weight and
tiny, but they move a lot faster," Goldstein continued. "The mass of
Lunar Prospector was 160 kg and it was moving 1.7 km/s when it hit
the moon on July 31. Leonid particles are going about 72 km/s. That
means that a Leonid the mass of a golf ball (about 0.1 kg) would
deliver the same kinetic energy as the Lunar Prospector crash."

"If a Leonid meteoroid did hit a spot near the north pole with frozen
water, it's not clear what we would see. The Lunar Prospector
collision was like a car crash -- it was moving at relatively slow
speed. When it hit, we hoped it would kick up water vapor that would
be dissociated into OH by ultraviolet sunlight. In theory we would
then see the OH by looking above the sunlit lunar limb with
appropriate spectrometers. A Leonid crash would be much more violent.
Instead of water vapor gently wafting above the lunar limb, we might
see ionized, hot plasma. It's possible that we would also get some
warm water vapor that didn't sustain such a damaging shock wave, but
it's really hard to say. We haven't done the high speed simulations yet."

Goldstein says that he and his colleagues may not have time to
organize a search for signs of water kicked up by Leonids this year,
following so closely on the heels of the Lunar Prospector experiment.
However, with some experts predicting significant Leonid activity
into the next millennium, there will be time to arrange an observing
campaign for next year and beyond.


From Andrew Yee <>

Air Force Space Command News Service

Released: 3 Nov 1999

Air Force, NASA to observe 1999 Leonid meteor storm

PETERSON AIR FORCE BASE, Colo. (AFPN) -- The Air Force and NASA are
teaming with the international scientific community to monitor
November's rare and potentially hazardous Leonid meteor storm.

The Earth is scheduled to pass through the debris stream from the comet
Tempel-Tuttle Nov. 17 and 18. The collision of this debris with the
Earth's atmosphere could produce a spectacular display of hundreds to
thousands of meteors per hour. The Leonid shower hits its peak every 33

The University of Western Ontario, the Canadian Space Agency, Canada's
Department of National Defence, and the European Space Agency are
teaming with NASA and the Air Force to set up monitoring sites at seven
locations around the world.

Special electro-optical video equipment will be set up at sites in
Hawaii, Florida, the Canary Islands, Kwajalein Atoll in the Marshall
Islands and at two sites in the Negev Desert, Israel, to record the
storm as it develops. The data collected from these seven sites will be
transferred to a communications center at NASA's Marshall Space Flight
Center in Huntsville, Alabama. From Alabama, NASA and UWO researchers
will compile and profile the data so satellite operators can access it.

The monitoring sites were chosen because they lie along what is
expected to be the best longitude for viewing. The storm is predicted
to peak Nov. 17.


From Ron Baalke <>

Forwarded from George Varros (
Subject: Near-Live Leonid Watching System

In anticipation of "higher than normal" meteor activity during this
November's annual Leonid Meteor Shower, NASA has created an image
library and invites amateur astronomers, photographers and individuals
with Single Lens Reflex (SLR) cameras or other imaging equipment,
to upload their Leonid  meteor photographs or images to the Near-Live
Leonid Meteor Watching System.


A Brief Background on the Leonid Meteors:

Every 33 years, there is a higher probability that the Leonid Meteor
Shower will turn into a meteor storm. This is caused by the parent
comet 55P/Temple-Tuttle and its 33 year orbit around the sun, which
nearly intersects that of Earth's. Fortunately, this occurs with Earth
and the comet on different sides of Earth's orbit.
As it approaches the inner solar system and is heated by the sun, the
comet replenishes its path with tiny bits of material eroded away by
the solar wind and radiation. As Earth travels in its path around the
sun and encounters this debris stream, the small grains of material in
this stream slam into Earth's upper atmosphere at a very high rate of
speed becoming incandescent and leaving an ionized and luminous trail
that we see as meteor or "falling star". 

On an average year, 15 to 20 Leonid meteors per hour can be seen,
depending on your local viewing conditions. During a storm year,
anything can happen as history has shown. The last major Leonid Meteor
Storm occurred on November 16, 1966, peaking for observers in the
mid-western United States. Hourly meteor rates were estimated to be as
high as 144,000! Historical accounts dating back to the 1833 and 1866
Leonids are fascinating to read! The 1899 and 1932 Leonids were largely
missed and it is suspected that Jupiter may have altered the meteor
stream's orbit for those years.  Studies also suggest 2000, 2001 or
even 2002 could be much better than normal years, with significantly
higher meteor counts than normal years! The 1999 Leonid Meteor Shower
is an event that has been long anticipated by the astronomy community.


The peak of the meteor shower or "storm component" has been predicted
by the experts to interact with Earth some time between 01:48 and 04:15
Universal Time, November 18, 1999. Observable hourly rates should be
significantly higher than normal years, perhaps on the order of several
hundred to several thousand per hour during the peak. However, it must
be emphasized that the various components of a meteor shower, such as
peak time and hourly rates are extremely hard to predict.  The peak
time can be off by several hours and recorded counts will certainly
vary with local sky conditions, the moon and light pollution, visual
obstructions and location on Earth. 

If the peak occurs during the earlier predicted time, Asia and Europe
will be positioned favorably with the radiant high overhead. If it
occurs a few hours past the later predicted time, the western portions
of Europe and Africa, along with the East Coast of the United States,
will be positioned favorably. This is certainly an event not to be
missed and it would be well advised to look for the Leonids during the
early morning hours of November 17th and November 19th, due to the

A Scenario For US East Coast Observers:

The radiant or apparent area of origin of the meteors, in the
constellation Leo, rises in the east shortly before midnight local time
November 17th (November 18, 1999 05:00 Universal Time). No Leonid
meteors should be expected to be seen prior to this due to the
direction that the meteors travel. The moon will interfere with meteor
visibility shortly after the radiant rises. It will be waxing gibbous
or just past half full and will be setting around 1:00AM local time. 
It should be noted that the radiant does rise just after the predicted
peak for US East Coast observers. However, if the peak, which is very
hard to predict is a few hours late, the US will be able to observe the
peak with the radiant higher in the sky!

George Varros


From Bob Kobres <>

Hi Benny

Regarding abrupt climate change and the Younger Dryas climate crisis: 
An interesting site that I had not seen in past queries has been put
together by William H. Calvin of the University of Washington in

Calvin goes into how human evolution might have been affected by such
changes as well as speculative ways that certain rapid changes (NADW
induced) might be mitigated. 

The one thing that I have found a bit disturbing about the notion of
'Spaceguard' is the tendency to define this project exclusively as a
way to protect Earth from impacts with celestial bodies. Personally I
can see no reason for restricting the idea of Earth defense to dueling
with asteroids and comets. As I suggested years ago , &

there are many benefits that would come from accelerated Space
development focused on protecting our environment. The most immediate
boon being a rapid increase in the ability to gather real-time
knowledge of how Life support systems on Earth are being affected by
our own activities as well as by variations in the immediate solar
environment. A well endowed, internationally coordinated, effort could
provide much greater information return than the various marginally
funded projects can at present. This would basically be an expansion
and institutionalization of the International Geosphere-Biosphere

In essence, I fancy Earth protection as an evolution of the function
that national defense has held--attempting to minimize danger to
citizenry while maintaining a status quo.  Obviously this is a social,
philosophical, and funding issue; the question is whether resources
will continue to flow most readily to short-term money-making projects
or to endeavors that can enhance real wealth, which is accurate
knowledge of how our world works. Perhaps increasing evidence of rapid
climate change may help to tip various tills toward survival

An interesting example of unusual climate change occurred around 1740
AD. This, according to Mike Baillie (Exodus to Arthur, page 143),
produced a tree-ring event that coincides with the largest temperature
reduction in Manley's Central England temperature record, which runs
from 1659 to the present. Years ago I culled some 'meteor' observations
from Philosophical Transactions and, upon running across them again and
realizing they were from right around this time period (December 1737),
I put them on my web-site in the DjVu format:

As an inducement to obtain and install the DjVu plug-in, I'll provide a
few interesting lines:

"6) This meteor was seen at Venice at the same time; and, over Kilkenny
in Ireland, it appeared like a great Ball of Fire; which burst with an
Explosion that shook [a] great Part of the Island, and set the whole
Hemisphere on Fire; which burnt most furiously, till all the
sulphureous Matter was spent."

Point five is also intriguing:

"5) The whole Time was attended with an extraordinary Heat of the Air
for the Season [early December]; for I was obliged to strip to the
Shirt, though abroad in the Air all the time."

What was going on here? I'm curious to hear the views of other readers.
To me such observations underscore how little we actually know of what
can happen within this dynamic environment we depend upon.

Links pertinent to 1737: [i.e. begin 1736 end 1740] [Caution! Alien noise. ;^)]
[ ]

There are heaps of interesting reports that we need to better understand:

It's a shame that so few resources are directed toward uncovering past
observations--the present often does not explain what occurred earlier.

But hey, if we fail to maintain the biosphere to our advantage and
run-away change starts to stress us out, there is a fall-back. We can
just wait for good-old Hsp90 to kick in and make us over again:

--Wonder if we can get even more pig-headed?/! 

Signaling noisily.

Bob Kobres
Main Library
University of Georgia
Athens, GA  30602


New book by John S. Lewis (1999): Comet and Asteroid Impact Hazards on
a Populated Earth, Academic Press Inc; ISBN: 0124467601

This work explores the anticipated consequences of comet and asteroid
impact. It presents the first computer simulations of the hazards of
comet and asteroid bombardment of a populated Earth. Previous estimates
of fatality and damage rates on the 100 to 10,000 year time scale are
shown to be too low because they neglect rare, highly lethal outriders
of the populations of bombarding objets, those with exceptional
strength, unusually low entry velocity, and near-horizontal entry
angles. This is an assessment of both the mean casualty rate and the
expected statistical fluctuations in that rate. A break down of
fatality and damage rates by impactor energy and compositional class
suggests lessons for both asteroid search strategies and interdiction
techniques. Key features of this title include: quantitative treatment
of impact hazards, including structural blast damage, firestorm
ignition and tsunami generation; a detailed and realistic Monte Carlo
simulation program; a realistic treatment of the impactor population,
composition, and orbits; attention to economic and public policy issues
of warning, interdiction and asteroid and comet search strategies;
quantitatively rigorous treatment of the state of impact hazards with
comparisons to historical records; and eight pages of colour plates
depicting impacts and hazards related to meteorites.

For orders see

(6) ORBFIT 2.0

From Andrea Milani <>

Dear OrbFitters and dear friends,

This message announces the new and significantly improved distribution
2.0 of the free software OrbFit.

The purpose of the software system we are distributing, maintaining and
continously upgrading, is to make available to observers of asteroids
an easy to use but accurate and reliable software to compute
preliminary orbits, ephemerides, improved orbits (by differential
corrections), identifications, and other auxiliary functions, to allow
the processing of astrometric observations and the planning of
observational campaigns (for example to recover lost objects).

Main improvements with respect to 1.9.0 are:

1) Automatic astrometric observation weighting, according to past
performance of each observatory (for each observing technology) on
numbered asteroids.

2) Radar observations are handled, with input from JPL data files.

3) Graphical interface to run the programs and an online help with
TCL/TK interface (see doc/README.tcl).

4) New MOID computation using Lowell Obs. subroutine based on method of

5) The MS-Windows version is now more stable, and includes plotting

6) Generation of ephemerides (on the sky) from fitobs. 

We are presently working toward several improvements, described in the
file README.workinprog which is enclosed with the distribution; the
ones most likely to be available with the next release, or even as
patches, are the following:

1) Weighting of photometric observations based upon past performances
of each observatory. 

2) Star maps superimposed on observation predictions.  This will
require gnuplot 2.7, which is not yet available for some operating

3) Light version that can run without JPL ephemerides.

4) Yarkovsky effect.  Already available as an undocumented feature, but
not properly tested.

Please note the ftp server has moved. The software can now be obtained

A README file to be found therein provides all the necessary
instruction for installation on all flavours of UNIX and WINDOWS

This software system has been developed by a consortium including A.
Milani and S. Chesley (Pisa University), M. Carpino (Astronomical
Observatory Milano/Brera), Z. Knezevic (Astronomical Observatory
Belgrade) and G. B. Valsecchi (CNR Rome).

Another new feature is the availability of the free software Orbit9 as
an add-on to OrbFit. This software, previously distributed separately,
is used to propagate orbits of asteroids for long time spans (tens of
millions of years for main belt asteroids). To get this, you should ftp
the archive orbit9.tgz from

and unpack it following the instructions in the file ./doc/README.orbit9.

Copyright (C) 1997-1999 OrbFit Consortium

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.
To contact us:,,


From Andrew Yee <>

Particle Physics and Astronomy Research Council
Swindon, England

2 November 1999


Astrophysicists will be able to predict in detail the effect of
solar-storms on Earth. Using a powerful new computer called MIRACLE*,
PPARC scientists are researching techniques to provide early warning
of the potentially devastating impact of solar storms on satellites
and power supplies.

Solar storms are caused by huge explosions on the surface of the sun,
which stream out into space, sometimes towards Earth. The heat from
solar storms has caused low orbiting satellites to drop out of the
sky. This happens when the Earth's atmosphere expands causing the
satellites to 're-enter' the atmosphere and burn-up. Solar storms
also affect the magnetic composition of the ionosphere. This disrupts
radio signals, causes electrical power blackouts and surges in oil

"Space weather prediction is an exciting area of research. Using this
new computer we are able to develop models that can be used to warn
telecom network operators, power suppliers and radio operators about
the effects of solar storms -- they can then take action to minimise
damage." said PPARC researcher Dr Alan Aylward.

Research satellites like SOHO warn scientists that a solar storm is
heading towards Earth, the computer models take over from there to
predict the impact of each storm.. PPARC fund both the UK's
participation in SOHO (an ESA mission) and the theoretical work to
interpret data from spacecraft.

Prediction of solar storms is only one of the uses for the new
computer. It will make it possible to investigate how stars and
planetary systems form and predict the fate of giant stars several
times hotter than the Sun. Other planets can also be modelled by
MIRACLE. "It used to take 7 earth-days to model one Jupiter day,
MIRACLE should allow us to run models in 'real time' " said Dr Steve
Miller. "It will also let us model the giant planets that have been
discovered orbiting nearby stars, which leads us into whole new areas
of research".

The computer, which can perform 15 billion calculations per second,
was financed by PPARC, the UK's strategic science investment agency
and has been provided as a research tool for the consortium of
astronomers from University College London, University of
Hertfordshire, Imperial College of Science, Technology and Medicine,
and Queen's University, Belfast.


Particle Physics and Astronomy Research Council
Press Office:
Charlotte Allen, Press Officer
Tel: 01793 442012   Mobile: 07881 645121

University College London
Press Office:
Patrick Edwards, Press Officer
Tel: 0171 391 1621
Department of Physics and Astronomy:
Dr Steve Miller
Tel: 0171 419 3443/3490 (work)

Notes for Editors
*MIRACLE is an acronym for Multi-Institutional Research Astrophysics
Computing. The MIRACLE Consortium is a group of research astronomers at
the leading edge of modelling the astronomical environment from the Milky
Way to the upper levels of the Earth's atmosphere.

The MIRACLE computer is Silicon Graphics Origin 2000. The computer has
24 individual processors, each of which can be harnessed to produce over
15 gigaflops (15 billion calculations per second) of computing power and
access 6 gigabytes of memory.

MIRACLE is one of two new computers in UCL's HiperSpace Centre officially
opened by Lord Sainsbury on Friday November 5th 1999.

PPARC, the UK's strategic science investment agency, funds the MIRACLE
computer through a research grant to University College London. The grant
includes provision of the SG Origin 2000 machine and support staff to
operate it. The value of the grant is approximately 250,000.00.

PPARC delivers world leading science, technologies and people.

Technologies developed by PPARC research can be found in business, defence,
industry and education. There are direct benefits to society in terms of
development of new materials and products, raising the skills base, and
maintaining the UK as a world leader in this field.

Minister for Science Lord Sainsbury will join Professor Chris Llewellyn
Smith, UCL Provost and John Fleming of SGI, for the launch of the new
HiperSPACE Centre on Friday 5 November 1999 at 2.00pm in the Eisai Lounge,
University College London, Gower Street. Members of the press wishing to
attend should contact UCL Media Relations on 0171 391 1621.



Donald Savage
NASA Headquarters, Washington, DC            November 3, 1999
(Phone:  202/358-1547)

Amber Jones
National Science Foundation, Arlington, VA
(Phone:  703/306-1070)

RELEASE:  99-127


Astronomers have found evidence of the first known planet orbiting a
pair of stars.  Previously, planets have been found circling only
single stars.

The Microlensing Planet Search (MPS) project, led by David Bennett and
Sun Hong Rhie of the University of Notre Dame, South Bend, IN, used a
technique called gravitational microlensing that may have revealed a
planet about three times the mass of Jupiter orbiting a binary star
system.  The researchers, who are supported by NASA's Astronomical
Search for Origins Program, the National Science Foundation (NSF) and
the Research Corporation, report their results in the November 4 issue
of Nature.

"Between half and two-thirds of the stars in our solar neighborhood are
known to be members of binary or multiple star systems," said Morris
Aizenman of NSF's Astronomical Sciences Division.  "To find evidence of
a planet orbiting a pair of stars means there could be more planetary
systems than we previously thought."  Astronomers have detected only
about 20 planets outside our solar system, all orbiting single stars,
although some of those stars are in binary systems.

Gravitational lensing is based on a property first noted by Albert
Einstein in the 1930s.  When an object such as a star or planet moves
in front of a more distant star, the gravity of this star or planet
serves as a "lens," magnifying the light from the distant star and
making it appear brighter.  The Microlensing Planet Search astronomers
analyzed data from such an event that occurred in 1997, referred to as
MACHO-97-BLG-41 -- the 41st microlensing event discovered by the
Massive Compact Halo Objects (MACHO) collaboration that year.  During
this 100-day event, the pattern of brightness appeared too complex to
be produced by a single-star lens.

While Bennett and his colleagues believe the best model for explaining
this microlensing event is a planet orbiting a binary star system,
other astronomers have proposed alternative models they believe could
also fit the data.  One possibility is that the orbital motion of the
binary star system itself could have caused the change in the observed
brightness of the distant star. Another possibility is that the distant
star may itself be part of a binary system.  These scenarios will be
tested in future observations.

The MACHO project, which is supported by NSF as part of the National
Science and Technology Center for Particle Astrophysics at the
University of California at Berkeley, routinely makes data on
microlensing events available to other astronomers. MACHO is
using microlensing to explore tens of millions of stars in a search for
the "dark matter" that dominates the mass of our galaxy. Dark matter is
believed to exist because the combined gravity of the known matter in
the universe is not enough to account for the observed gravitational

The MPS astronomers are using the microlensing technique to search for
planets orbiting stars other than our Sun. For this analysis, they used
observations from telescopes at the Mount Stromlo Observatory in
Australia and the Wise Observatory in Israel as well as data from the
NSF's Cerro-Tololo Inter-American Observatory in Chile.  Astronomers at
the Wise Observatory co-authored the Nature report. 

More information on MPS can be found on the Internet at:

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CCCMENU CCC for 1999