PLEASE NOTE:


*

CCNet DIGEST, 21 December 1998
------------------------------

(1) ASTEROID 1998 XB AND ITS IMPLICATIONS FOR IMPACT PROBABILITY
    ESTIMATES
    Andrea Milani Comparetti <milani@copernico.dm.unipi.it>

(2) 1998 XB NOT SUCH A SURPRISE AFTER ALL
    Alan W. Harris <awharris@lithos.jpl.nasa.gov>

(3) THE NEAR BRIEFING (AND A SHORT CHAT WITH DON YEOMANS)
    E.P. Grondine <epgrondine@hotmail.com>

(4) DEFINING THE EFFECTS OF SUB-CRITICAL COSMIC IMPACTS ON THE EARTH
    A few thoughts from Jay Tate <fr77@dial.pipex.com> of    
    Spaceguard UK.

(5) PLATINUM-GROUP ELEMENTS AND COMETS.
    Jeremy B. Tatum <UNIVERSE@UVVM.UVic.CA>

(6) NEAR'S FIRST RENDEZVOUS BURN
    Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>

(7) NASA NEWS SERVICE
    Louis Friedman <tps.ldf@mars.planetary.org>

(8) SEARCHING FOR EXTRATERRESTRIAL LASER SHOWS
    Andrew Yee <ayee@nova.astro.utoronto.ca>

========================
(1) ASTEROID 1998 XB AND ITS IMPLICATIONS FOR IMPACT PROBABILITY
    ESTIMATES

From Andrea Milani Comparetti <milani@copernico.dm.unipi.it>

Pisa, December 19, 1998.

Dear Benny,

I would like to contribute to the discussion on the implications
of the discovery of 1998 XB, started on CCNet DIGEST, 15/12/98 by
David Morrison, including remarks by Alan Harris, Ted Bowell and
David Rabinowitz.

The fact that such a large Near Earth Asteroid has been discovered
is indeed remarkable, and can suggest a change to population
models of the NEO. How this changes the estimated probability of
collisions with Earth is, however, less obvious, and depends upon
the time span considered.. If you allow me, I would like to use
this remarkable example to illustrate the complexity of these
`risk estimate' arguments.

We (myself and my coworkers S. Chesley, G.F. Gronchi and A. Rossi)
have redetermined the orbit of 1998 XB and computed its long term
evolution. The orbit was fitted to all observations, including the
very recent ones (taken until December 17), by using the same free
software advertised on CCNet DIGEST, 16/12/98, and available at
ftp://copernico.dm.unipi.it/pub/orbfit. We found that a solution
with semimajor axis close to 1 AU is not any more compatible with
the observations: the best value is now 0.907 AU. (The new best
fit solution is enclosed.) Thus the discussions about the
observing conditions of this asteroid (both in the future and in
the past) have to be revised.

We have propagated this best fit orbit for the time span between
3,000 BC and 3,000 AD (that is, for the time span of the JPL
ephemerides DE406) and found that it does not undergo close
approaches to Earth until after the year 2,800, and very shallow
approaches (0.095 AU) even then. To the contrary, our sample
integration contains 76 close approaches to Venus (0.087 to 0.1
AU), beginning around 400 AD and until the end of our propagation.
Of course the orbit, as it is known from the short observed arc we
have now, cannot be used to predict in a deterministic way
specific close approaches, but the frequency and depth of the
close approaches have a meaning. The question is, why there are no
close approaches to Earth for a time span of at least 5,800 years?
The answer is simply that the nodes of this orbit, the points
where the ellipse intersects the plane of the orbit of the Earth,
are now at 0.601 and at 1.178 Astronomical Units (AU) from the
Sun. Thus approaches to Venus, orbiting the Sun at a distance of
approximately 0.7 AU, are now possible within 0.1 AU, although
very close approaches are excluded; close approaches to Earth at
about 1 AU are not currently possible.

From this simple geometrical argument, as well as from the
numerical integration, it is possible to conclude that the
contribution of 1998 XB to the risk of impact on our planet in the
near future (a few hundred years) is zero. It is important to
stress this, since an impact by an object of the size of 1998 XB
belongs certainly to the civilisation threatening class, and
probably also to the exctinction threatening class. It is our
responsibility as scientists to keep the public aware of the
dangers, but certainly we should not raise unjustified alarm. 
This discovery might imply that some previous estimates of the
completeness of our searches were optimistic, but in itself the
discovery of such an object, in an orbit which can not result in
an impact in the near future, does in fact decrease the overall
risk of impact over the next few centuries.

I do not know if you are keen about adding multimedia capabilities
to your mailing list [not yet, BJP]; in case you are, I am
enclosing a figure (gif encoding) showing the future evolution of
these nodal points. Alternatively, your readers can access this
figure at http://copernico.dm.unipi.it/neo/XB98.gif .

The figure shows the evolution of the nodal points of 1998 XB on 
the (mean) ecliptic plane; crosses indicate the present positions.
The continous lines are from a numerical integration over 6,000
years; the dotted lines are from the averaged integration, and
show the approximate future evolution for 25,000 more years.

To extend our study of the evolution of the orbit of 1998 XB
beyond 3,000 AD we have used, rather than a full numerical
integration, an averaged (semianalytic) computation. To give an
idea of the power of this method, note that we have used a
stepsize of 1,000 years, somewhat reduced only near the node
crossing singularities. The long term orbits obtained in this way
are only approximate; on the other hand a full numerical
integration would give an illusory precision, since the initial
conditions are still poorly known. The theory is in 3 papers by
Gronchi and myself now in press; preprints can be obtained at
http://copernico.dm.unipi.it/milani/preprints/preprint.html.

This averaged integration shows that 1998 XB will eventually
undergo a node crossing with the Earth, and thus very close
approaches, even impacts, will become possible, but this will
happen only somewhere between 9,900 and 10,000 AD. If the asteroid
escapes from collision, and also from approaches so close that the
orbit would be completely changed, it will undergo a node crossing
with Venus about 2,800 years later. Note that the node crossing
point is now approaching the Earth from the night side, while the
other node crossing point is approaching Venus from the day side.
This has also some implications on the discussion, reported by
Morrison (also by Boattini and Carusi on CCNet DIGEST, 16/12/98)
on the strategies for detecting all the dangerous asteroids, in
particular Atens.

The conclusion is that 1998 XB indeed contributes significantly to
the collision rate with the Earth for asteroids of its size class,
if this rate is averaged over a long time span (e.g. longer than
10,000 years), while it does not contribute at all to the impact
risk for the near future.

This asteroid has also a significant probability of impact on
Venus, again only in the remote future. Because of our
chauvinistic geocentric attitude, we actually hope that it hits
Venus, thus never coming back to a node crossing with our planet.
On the other hand, why do we care about asteroids hitting the
Earth 8,000 years from now? By that time, asteroid deflection will
be a petty solar system maintenance operation (unless another one
has hit much earlier). 

Yours Andrea Milani

Dipartimento di Matematica
Via Buonarroti 2
56127 PISA ITALY
tel. +39-50-844254 fax +39-50-844224
E-mail: milani@dm.unipi.it
WWW: http://virmap.unipi.it/~milani/homemilani.html

1998XB
Keplerian elements: a, e, i, long. node, arg. peric., mean anomaly
KEP     0.906337    0.351125      13.524      75.688     202.817     247.511
MJD   51200.0000 TDT
MAG  14.200  0.150
RMS    1.336E-03   8.591E-05   6.676E-02   2.056E-01   2.320E-01   1.723E-01
COV          1.78531712E-06         6.21949246E-08         8.91546110E-05
COV          2.73852251E-04        -3.09785443E-04         2.30061620E-04
COV          7.38050507E-09         3.25733117E-06         1.06906372E-05
COV         -1.14565324E-05         8.40898215E-06         4.45661998E-03
COV          1.37089373E-02        -1.54893703E-02         1.15003193E-02
COV          4.22612049E-02        -4.76654254E-02         3.53764033E-02
COV          5.38386605E-02        -3.99704581E-02         2.96766124E-02
COR                  1.0000                 0.5418                 0.9995
COR                  0.9970                -0.9992                 0.9995
COR                  1.0000                 0.5680                 0.6053
COR                 -0.5747                 0.5682                 1.0000
COR                  0.9989                -1.0000                 1.0000
COR                  1.0000                -0.9993                 0.9989
COR                  1.0000                -1.0000                 1.0000

==========================
(2) 1998 XB NOT SUCH A SURPRISE AFTER ALL

From Alan W. Harris <awharris@lithos.jpl.nasa.gov>

Dear Benny,

It now appears, based in part on the revised orbit (cf. Milani's
message) that 1998 XB is not really so large after all. The current
best estimate of its absolute magnitude H is 16.0 +/-0.5.  This
corresponds to a diameter of around 2.5 km, and makes is one of the
larger NEAs, but by no means largest, discovered in the last couple
years.  At 16.0, it is unremarkable. Using the latest orbit, I computed
an ephemeris for it a year ago, when it should have been even more
favorably placed for discovery. It was in as sense, mag. 13.8 and only
10 degrees or so from the opposition point. But it was dead center in
the milky way and the moon interferred by the time it got out of the
milky way. Before that, no good apparitions for about 10 years.  So it
is in fact not even remarkable that it wasn't discovered before.

Alan Harris

===================
(3) THE NEAR BRIEFING (AND A SHORT CHAT WITH DON YEOMANS)

From E.P. Grondine <epgrondine@hotmail.com>

Benny -

This last Wednesday a briefing on the NEAR probe was held at NASA
Headquarters, and afterwards I had an opportunity to speak with Don
Yeomans on how things are going at the new NASA NEO Office. Here
goes...

The briefing started with an introduction by Dr. Carl Pilcher, who set
forth NASA's reasons for funding NEAR, in what he identified as
their order of importance.  First in Dr. Pilcher's list came the
probe's value to NASA's Origins program, which is that it will throw
light on the fundamental building blocks of the Solar System, including
the organic chemicals from which life formed. This is in keeping with
the current NASA emphasis on the search for life, including life on
Mars. Second in Dr. Pilcher's list came the value of NEAR for planetary
defense, and Dr. Pilcher placed a limit on the threat to asteroids 1 km
in diameter.  This limit probably reflects current NASA emphasis in
this area, with Sub-Critical Impactors ignored, at least for the time
being. Third came the possible future resource use of asteroids in
manned space development.

Dr. Pilcher noted that the results from Mathilde had come as a
surprise, in that the large crater on Mathilde showed that some
asteroids could absorb the force of a massive collision without
shattering.  He emphasized that it was clear from this that a better
understanding of the physical properties of the asteroids would be
necessary if we ever had to stop one of them.

Bob Farquhar of John Hopkins APL spoke next on the actual mechanics of
scheduled rocket firings for the Eros rendezvous.  The science
experiments are timed with these burns so as to maximize the science
return for the probe at any time in the event of failure, so more on
these later.

Andy Cheng of the APL, the mission's primary scientist, spoke next on
the basic classes of asteroids, which he grouped in laymen's terms into
differentiated and undifferentiated.  The undifferentiated asteroids he
described as the basic building blocks, while the differentiated
asteroids he described as the remains of planetisimals which formed,
differentiated, and then broke apart under collision. Cheng went on to
discuss how it was hoped that the spectrometry results from NEAR would
allow S type asteroids to confirmed as the source for common chondrite
meteorites.

Cheng also discussed the low density of asteroids, using Phobos as
an example this time instead of Mathilde, and compared Phobos'
collisional history with Mathilde's.

Don Yeomans spoke next emphasizing the necessity of getting good
density data for Eros.  The first rocket burn will put NEAR in range of
Eros' gravity, and the first images and radar data will be available at
that time, so an initial density calculation should be possible. In
laymen's terms Don divided the asteroids into monolithic and rubble
pile, and it is hoped NEAR will provide better information to refine
models of interior voids.

Don emphasized the problems that are likely to be encountered trying to
put NEAR into orbit around Eros. Since Eros is likely to be
non-spherical in shape, it will not be possible to leave NEAR in one 
fixed orbit around Eros, but instead it will be necessary to modify
NEAR's orbit every week to week and an half to prevent it from
colliding with Eros. In turn, orbital data will then be used to refine
density models for Eros.

Joe Veverka of Cornell spoke next on the camera and spectrometer. The
first images of Eros against its star field are currently being used
for navigation, as well as to map Eros' rotation .  As NEAR approaches
Eros, additional images will be used for navigation and initial
science. The researchers are concerned about companions and the threat
they may present for NEAR.  Additional images at a resolution of 250 m
per pixel will be taken by NEAR before it orbits Eros, and these will
be assembled into a movie and released sometime around 14 January. 

The team hopes to place NEAR into orbit around Eros by January 10, with
an initial orbit planned for 1,000 kilometers from Eros's center. The
next orbit is planned for 200 kilometers, with camera data in 32 meter
pixels and spectrometry data in 1 kilometer pixels. It is hoped that
the differing orbits will allow spectrometry data to gathered on the
same scale as was obtained for camera data on earlier orbits. Thus
NEAR's orbit will then be lowered to 35 kilometers (15 to 20 kilometers
from Eros' surface), with camera data in 2.5 - 4.5 meter pixels, and a
last orbit planned for 100 meters above Eros' surface, with spectrometry
data in 2.5 - 4.5 meter pixels.

Finally, assuming that NEAR survives, and that sufficient fuel remains
onboard, (and NEAR has a factor of 3 times the minimum fuel estimated
for nominal operations), hovering operations and/or a possible soft
landing are contemplated.

Lidar data and infrared or gamma ray spectrometry data will be taken in
all orbits.  All of these orbits are subject to change depending on how
irregular Eros actually turns out to be.  Deep Space Network
communication time is currently not scheduled beyond February, 2000.

During questioning, Don spoke on the usefulness of NEAR rendezvous
operations for possible future asteroid interception.  In this regard
it should be noted that NEAR's instrument mass is 56 kilograms, and
fuel mass is 325 kilograms. 56 kilograms is barely the working mass of
a back pack nuclear weapon, with a charge of say 10 kilotons; and even
then part of NEAR's instrument suite is used to aid navigation. The
fuel safety factor of 3 might leave say 200 kilograms available for a
nuclear charge; enough for a boosted fission or fusion charge of 125
kilotons or so, but I don't believe enough for a really large fusion
charge. (N.B.-I'm sure others on the list have more accurate numbers for
the masses of nuclear charges.)

NEAR was launched aboard a Delta 2 in February 1996, with a travel time
to Mathilde of 4 months, and a travel time to Eros of 22 months.

A CHAT WITH DON

After the briefing, I spoke with Don Yeomans about the new NASA NEO
Office.  The initial plans are working their way through the NASA
planning process, and this review is being done in co-ordination with
the Air Force. Don has some good news for us, that there will be
additional funding for the MPC, and he hopes that he will have some more
good news for the Conference members shortly.

Well Benny, that's it for now.  Until next time...

Best wishes -
Ed

=================
(4) DEFINING THE EFFECTS OF SUB-CRITICAL COSMIC IMPACTS ON THE EARTH

A few thoughts from Jay Tate < fr77@dial.pipex.com > of Spaceguard UK.

On 11 December 1998 a meeting entitled "Defining The Effects Of
Sub-Critical Cosmic Impacts On The Earth", jointly sponsored by the
Royal Astronomical Society, the British Interplanetary Society and the
Geological Society was held at the London headquarters of the
Geological Society.  The event was expertly organised by Richard L. S.
Taylor, Julian A. Hiscox and David Hughes.

The definition of a Sub-Critical Impactor (SCI) is based on the work of
Morrison et al., who determined that the impactor diameter threshold
for a globally threatening impact was 1.5 to 2 kilometres. In the
light of the impact of Comet Shoemaker-levy 9 this estimate was
revised downwards to 1 kilometre. An SCI therefore is an object that
impacts with the surface of the Earth, or has an effect on that
surface, that has a diameter of less than 1 kilometre.

Benny has recently published the abstracts of the papers presented at
the meeting, so I don't intend to plough the same furrow, bit I think
that it is worth examining some overall impressions of the
discussion, and to consider the overall significance of the event.

The first thing to note is that the meeting happened at all.  As
recently as three years ago it is unlikely that anyone would have
considered the subject of "sub-critical impacts" worthy of a dedicated
conference!  Events over the past few years have brought the theme of
impact studies to the attention of the scientific community and the
general public, and the interest generated is spreading.

The second important aspect of this gathering was the
multi-disciplinary nature of the speakers and audience. The threat of
asteroidal and cometary impact is often considered to be in the
province of astronomy, but it is becoming increasingly clear that there
are multi-disciplinary ramifications. Indeed, it was geological and
palaeontological data that led to the linking of the Chicxulub feature
with the K-T boundary event. The multi-disciplinary nature of impact
studies was emphasised at the Spaceguard 2 conference at the Royal
Greenwich Observatory in July 1997, and it was most encouraging to see
that the message is spreading through the scientific community.

The third overwhelming impression was that the fact that cosmic impacts
play and have played a significant part in the geological and
biological evolution of our environment now appears to be widely
accepted. The only controversy seems to be the extent to which these
events have had an effect when stacked up against other natural
processes such as volcanism and continental drift. This paradigm shift
is fertile ground for debate and research, with a frisson of urgency
given the risk of future catastrophic events.

Although there were a number of areas where interpretations of data
were matters of debate, the only major area of disagreement to emerge
during the meeting's deliberations concerned the rate at which impacts
(in this case, sub-critical impacts) occur on the Earth. I presented
the "party line", developed by individuals such as Shoemaker, Muinonen,
Rabinovitz, Steel and Bailey (amongst many others). Dr. David Hughes
presented a view that would involve a substantial reduction in the
impact flux, and supported his contention with expertly derived data. 
In discussions after the presentations it became clear that there is a
distinct need for better empirical data to reduce the uncertainties in
the estimates presented by both sides of the argument. The available
data sets are very limited, and are thus open to different
interpretations.  Only when reliable population figures are available
and the dynamical properties of Earth threatening objects are better
understood will the estimated impact rates derived by different methods
converge towards the true figure.

The following two speakers addressed geological evidence of past
impacts, but I fear that much of what they had to say was quite beyond
me! I have no doubt that details of their papers will be available from
the Geological Society in due course, but the bottom line appeared to
be that there is considerable work to be done in the field, and once
again the multi-disciplinary nature of the required research was
emphasised. It was interesting to note that one of the suggested
reasons that impact evidence has not been found before was that
"existing concepts in geology do not permit reconstruction of these
abrupt events".

Professor Chandra Wickramasinge described how the stable ice ages
experienced by the Earth in the past could have been ended by the
injection of water into the atmosphere by cometary impacts - a
fascinating perspective given the usual preoccupation with "cosmic
winter" effects after a significant impact.

Dr Norman MacLeod warned the conference against developing a new,
possibly flawed paradigm concerning mass extinctions.  He clearly
demonstrated that the "big five" mass extinction events that we are
aware of need not have been caused by single events (such as large
impacts or volcanism), but were probably the result of a combination of
circumstances.  He again stressed the need for more research into the
subject on a multi-disciplinary basis.

Julian Hiscox then discussed the bioevolutionary consequences of
sub-critical impacts, describing the probability that the majority of
the water on Earth was delivered by cometary impacts.  He then
considered the possibility that the range of organic compounds also
present on cometary nuclei could have played a key role in the genesis
of life.  He pointed out that the rise of mammals was as a direct
consequence of Chicxulub impact that hastened the demise of the
dinosaurs, and that there are bound to be many other examples of
advantage or disadvantage to species resulting from impact events.

Moving somewhat closer to home, Dr Marie-Agnes Courty presented new
findings that appear to link the destruction layers in the Near
East around 2300 BC with an extra-terrestrial impact, rather than
volcanic activity as previously thought. She suggested that "the
ambiguity lies partly in the weak knowledge of the geoscience community
of minor collisions with Earth" and the inability of conventional
science to discriminate between instantaneous and extended events. Her
evidence points to a major event, somewhere in the Middle East at
around 4000 BP that might have caused global environmental
consequences. This ties in nicely with other work pointing to the
collapse of other civilisations world-wide at that time.  Her data was
(at least to the lay person) extremely convincing, but there is clearly
more work to be done in the field.

Dr Benny Peiser then considered the multi-disciplinary search for
evidence of recent, i.e. Holocene impacts. He pointed out that such a
search is significant, not just for historical interest, but as an
indicator of the current impact flux that reflects the present hazard
to our own civilisation.  He called upon current knowledge of
historical and pre-historical environmental punctuations that could
be linked to impacts, and made a convincing case for the role of
sub-critical cosmic events in the development of human societies
throughout history. This theme was continued by Dr Victor Clube who
traced the human concern about comets throughout history, and the
possible (probable?) reasons for that concern and fear.

I have deliberately not gone into the subjects discussed in detail for
a number of reasons; the full papers will no doubt be published in the
fullness of time, I am not qualified to comment on technical points and
time and space do not permit.  But, there were a number of recurring
themes throughout the day. I have mentioned them before, but they bear
repeating.

There is a clear need for a multi-disciplinary approach to impact
studies.

There is a clear need for research into the impact flux on the Earth.

There is a clear need for research into the effects of impact events.

There is a clear need for education, both within and without the scientific
community, on the significance of impact studies.

I believe that the meeting held on 11th December could be the beginning
of a new era in Earth studies, where researchers of many disciplines
co-operate to understand one of the basic formative processes of our
planet, and one of the greatest hazards that face our civilisation. 
The meeting was a first faltering step, but it would be criminally
irresponsible to let this opportunity slip through our fingers.

Jay Tate

====================
(5) PLATINUM-GROUP ELEMENTS AND COMETS.

From Jeremy B. Tatum < UNIVERSE@UVVM.UVic.CA >

Since it now seems to be universally accepted that the presence of
iridium or other platinum-group elements in geological samples is
incontrovertible evidence of cometary impact, can someone please post
on the peisergrams a list of the comets in which these elements have
been detected and how their cometary abundance was determined?

====================
(6) NEAR'S FIRST RENDEZVOUS BURN

From Ron Baalke < BAALKE@kelvin.jpl.nasa.gov >

http://near.jhuapl.edu/

On Dec. 20, at 5 p.m. EST, NEAR's large bipropellant engine will be
turned on for the first of a possible four engine burns that will put
the spacecraft at optimum speed and location for its Jan. 10
rendezvous with asteroid Eros. The burn will be executed from the
NEAR Mission Control Center and will last 20 minutes, expending more
than half of NEAR's onboard fuel.

Presently, NEAR and Eros are traveling in approximately the same
direction. Like a vehicle on an onramp trying to merge onto the
interstate, NEAR is speeding up to merge with Eros, which is coming
from behind at a speed of 2,180 mph (974 meters per second), relative
to the spacecraft.

The next burn will occur on Dec. 28.

======================
(7) NASA NEWS SERVICE (CCNet DIGEST 17/12/98)

From Louis Friedman < tps.ldf@mars.planetary.org >

Did the NASA press release really say "Mars Observer" spacecraft?!
What an embarassing error for them.

Louis Friedman

===========================
(8) SEARCHING FOR EXTRATERRESTRIAL LASER SHOWS

From Andrew Yee < ayee@nova.astro.utoronto.ca >

Harvard University

3 December 1998

Researchers Searching for Light from E.T.
By Maria Cristina Caballero and John Lenger, Harvard Gazette

If E.T. won't call, maybe he'll shine a light on us instead.

That's the hope of Harvard researchers involved in the search for
extraterrestrial intelligence (SETI) who have unveiled a new experiment
that involves scanning the heavens for flashes of laser light.

Professor of Physics Paul Horowitz's laboratory recently installed the
experiment at the Harvard-Smithsonian Oak Ridge Observatory in Harvard,
Mass. The optical SETI (or OSETI) experiment has occasionally
registered a signal similar to what one would expect if another
civilization's laser were aimed at us. None of those signals has shown
the regular repetitions that could indicate an intelligent hand behind
them; but then, the researchers have just begun looking. Though such
searches for laser lights from beyond our solar system have been done
before, in an isolated and sporadic way, the Harvard experiment is the
first broad-based and systematic search.

Horowitz has had his ears to the skies for interstellar radio messages
for the past 20 years. He directs Harvard's BETA project, which for the
past three years has searched 600 million channels for radio signals
broadcast by an intelligent civilization. Before BETA there was META,
an 8.4 million-channel searching device that went on-line in 1985 and
was supported in part by funds from E.T. director Steven Spielberg.
While BETA continues its radio-wave search in full force, collecting
the equivalent of a compact disc's worth of data every two seconds,
none of the radio signals collected has yet been shown to be of
intelligent origin. "After 20 years, maybe it's time to try something
else," Horowitz says.

The idea of analyzing light flashes from distant parts of the galaxy is
not a new one, Horowitz explains. Charles Townes, who shared the Nobel
Prize in Physics in 1964 for his work on masers and lasers, first
raised the idea in a paper co-authored with R.N. Schwartz,
"Interstellar and Interplanetary Communication by Optical Masers," that
was published in the journal Nature in April 1961. But technology
developed just within the past five years finally made it a viable
project. "This is very much an experiment of the '90s," Horowitz says.

The beauty of the new experiment, Horowitz explains, is that flashes of
concentrated light are easy to detect and show up as distinct from
other sources of illumination. If, for instance, Earthlings aim a
high-intensity pulsed laser at a distant star, anyone watching from
that star with a moderate-sized telescope will suddenly see a flash
1,000 times brighter than the light of our Sun -- "an efficient
interstellar beacon."

And since the brightness of starlight and laser light both decrease at
the same rate, that particular high-intensity laser beam shot from
Earth would always be 1,000 times brighter than the light from our Sun,
no matter how far it travels.

Reversing the direction, any extraterrestrial flash pointed the way of
Earth would be easily distinguishable from the light of a distant star.
That could make pulsed light the preferred method for communicating
across galactic distances instead of radio waves. If you remember
childhood games involving walkie-talkies and messages communicated by
flashlight beams, you'll recall that flashlight beams were much more
reliable than static-filled walkie-talkie transmissions, if not as
dramatic.

Horowitz, who has long been an optimist regarding the idea of
extraterrestrial civilizations, cautions, however, that, "Maybe they're
using 'zeta rays' to communicate, and the problem is we haven't
discovered zeta rays yet."

Still, the elegance and simplicity of the new laser-detection
experiment is appealing. BETA took four years to build (at a cost of
hundreds of thousands of dollars), involves enough high-end computer
equipment to fill a large truck, and uses an 84-foot radio telescope.
The OSETI equipment, funded by the Planetary Society, the SETI
Institute, and the Bosack-Kruger Charitable Foundation, was put
together in three months by Horowitz and fellow researchers Jonathan
Wolff, Chip Coldwell, and Costas Papaliolios at a cost of less than
$10,000.

"It fit in the back seat of my Corolla," Horowitz says, describing the
monitoring device as being as big as a box "for a large loaf of bread."
It uses leftover light from a 61-inch telescope that already was
engaged in a survey of 2,500 nearby solar-type stars, an experiment run
by researchers Joe Caruso, David Latham, Robert Stefanik, and Joe
Zajac.

The simplicity of the new OSETI equipment means the experiment could
easily be duplicated elsewhere. Researchers at the University of
California at Berkeley, who have done some preliminary looking, are
setting up an optical SETI experiment along the same lines, and their
experiment will be operational soon.

A more detailed description of Harvard's optical SETI experiment is
on-line at http://mc.harvard.edu/hgroup.html, and contains a call for
the SETI research community "to consider alternative OSETI strategies
-- choice of wavelength, pulse widths and repetition rates, revisit
times, etc. -- in an attempt to identify a particularly compelling a
priori strategy, involving both sender and receiver, that could be the
basis for major Earth-based OSETI receiving efforts in the near term."

Optical SETI is an added tool for searching the heavens that has
emerged just as the more traditional searches of radio frequencies are
getting tougher. Darren Leigh, a recent Harvard Ph.D. in applied
physics who oversees the BETA project, says that cellular phones in
particular have made it harder to hear signals from outer space. As
satellite transmissions increase, Leigh says, we are confronted by the
possibility that our interest in talking with each other might mean
less chance of hearing a call from extraterrestrials.

Horowitz is optimistic about the optical SETI project, but 20 years of
waiting have made him cautious. "I'll be excited when we get results,"
he says.

PHOTO CAPTIONS:
[ http://www.news.harvard.edu/science/current_stories/3.Dec.98/seti.3.dec.98.html ]

[Image 1]
Part of the experiment's crew poses with the telescope being used for
the SETI experiment.  From left to right are researchers Costas
Papaliolios, Chip Coldwell, Paul Horowitz, and Jonathan Wolff.  A more
detailed description of Harvard's optical SETI experiment is online
[ http://mc.harvard.edu/hgroup.html ].

[Image 2]
The OSETI equipment fit in Horowitz's Corolla; Jonathan Wolff (above)
built most of the device.

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