CCNet 103/2000 - 11 October 2000

     "Astronomers who predicted the 1999 Leonid meteor storm with
     unheard-of accuracy say there could be a modest outburst
     of Leonids in 2000 -- the prelude to more powerful storms in 2001
     and 2002. [...] 'We're very, very confident of the storms coming in
     2001 and 2002,' says David Asher of the Armagh Observatory in Scotland.

     'Peak rates during those years should reach at least 10,000 meteors per

     hour as Earth passes through debris trails from comet Tempel-Tuttle.'
     Asher expects Leonids activity to reach 100 per hour on Nov. 18, 2000,
     similar to the recent Perseids display. Other forecasters anticipate higher
     rates -- around 700 per hour."
       -- NASA News, 10 October 2000

    NASA News Service, 10 October 2000   

    Mark Bailey <>

    The British Interplanetary Society <

    D.J. Scheeres et al.

    F. Vilas, A.L. Cochran, K.S. Jarvis

    M.T. Zuber et al.,

    CO2 Science, 11 October 2000

    Petr Pravec <>

    Michael Paine <>

     Neil Bone <>

     Andy Smith <>

     Bob Kobres <>



Our planet is heading for a minefield of cosmic dust streams laid
down by periodic comet Tempel-Tuttle. The result could be a series
of meteor outbursts on Nov. 17 and 18, 2000.

October 10, 2000 -- Astronomers who predicted the 1999 Leonid meteor
storm with unheard-of accuracy say there could be a modest outburst
of Leonids in 2000 -- the prelude to more powerful storms in 2001
and 2002. Although Europeans and North Americans will have the best
chance to spot Leonids activity this year, meteor watchers everywhere
should be on the alert. Brief flurries of shooting stars could materialize
over any part of the globe between local midnight and dawn on November
17th and 18th.

"We're very, very confident of the storms coming in 2001 and 2002,"
says David Asher of the Armagh Observatory in Scotland. "Peak rates
during those years should reach at least 10,000 meteors per hour as
Earth passes through debris trails from comet Tempel-Tuttle." Asher
expects Leonids activity to reach 100 per hour on Nov. 18, 2000, similar to
the recent Perseids display. Other forecasters anticipate higher rates --
around 700 per hour.

"The last quarter Moon will be in the constellation Leo on Nov. 18th,
practically on top of the Leonids radiant," says Mitzi Adams, an astronomer
at the NASA Marshall Space Flight Center. "Moonlight will make fainter
meteors hard to spot, but if there's a strong outburst stargazers could see
plenty of Leonids in spite of the bright Moon."

Leonid meteors are caused by tiny meteoroids that burn up in our planet's
atmosphere as Earth passes close to the dust-strewn orbit of periodic comet
Tempel-Tuttle. Every 33 years when the comet swings through the inner solar
system it lays down a new trail of dusty debris. For Tempel-Tuttle, no two
circuits through the solar system are exactly alike. Jupiter's powerful
gravity slightly alters the comet's orbit each time around. As a result,
each new debris trail is in a different spot. The comet's many dust streams form
a sort of cosmic minefield that Earth navigates every year in mid-November.

Most years the Leonids are a minor event -- boasting no more than 10 to 15
shooting stars per hour. That's what happens when Earth passes through the
rarefied zones between Tempel-Tuttle's debris trails. On the rare occasions
when our planet plows directly into a dense filament of dust, meteor rates
can soar to 100,000 per hour or more.

James Young, who watched such a storm in 1966 from JPL's Table Mountain
Observatory, recalls:

"This very noteworthy [1966] meteor shower was nearly missed altogether...
The shower was expected to occur over the European continent. There were 2-5
meteors every second as we scrambled to set up the only two cameras we had. The
shower peaked around 4 a.m. with some 50 meteors falling each second. We all felt
like we needed to put on 'hard hats'! To further understand the sheer intensity
of this event, we blinked our eyes open for the same time we normally blink
them closed, and saw the entire sky full of streaks ... everywhere!" 

The Leonids, which surprised Young in 1966, are notoriously difficult to
predict. They tend to happen at 33 year intervals when the parent comet is in the
neighborhood -- but not always. For instance, after major Leonid meteor
storms in 1833 and 1866, astronomers confidently forecast another historic display
on Nov. 18, 1899. Millions around the world were watching and waiting as Earth
glided by Tempel-Tuttle's orbit. And nothing happened.

"[It was] the worst blow ever suffered by astronomy in the eyes of the
public," wrote 19th century astronomer Charles Olivier after the much-touted storm
failed to materialize.

Times may be changing, though, as astronomers are finally learning the
whereabouts of Tempel-Tuttle's many dust trails. Like the comet itself, Tempel-Tuttle's
debris streams can be nudged into different orbits by gravitational encounters with
Jupiter, Saturn, and Uranus. By carefully tracking the orbit and shape of each
filament, several groups of astronomers now believe they can predict when Earth will
hit one.

"[Gravitational perturbations by planets] are the mechanism that determines
whether the relevant sections of dust trails are shifted inwards or outwards or
exactly on to the Earth's orbit," explains David Asher. "Ejection velocities from the
comet nucleus and/or radiation pressure change the orbital period of [cometary
debris] particles, which causes them to stretch into trails -- those with longer
periods fall behind in the stream and vice versa. But planetary perturbations are
the most important factor in moving the debris streams towards or away from our
planet's orbit." If comet Tempel-Tuttle were to disappear entirely, he added, the
existing dust streams could continue to exist and to trigger Leonid meteor storms for
hundreds of years before they dispersed.

In 1999, Asher and colleague Robert McNaught (Australian National
University) predicted a strong Leonid outburst on Thursday, Nov. 18th. In years past,
astronomers had struggled to decide whether a storm might occur within a day or so of
Earth's closest approach to the comet's orbit. Asher and McNaught's audacious
prediction was for 0208 UT plus or minus 10 minutes. No one had ever dared predict the
Leonids with such precision.

The 1999 Leonid meteor storm broke over Western Europe, right on schedule,
at 0205 UT. It was an unprecedented success in Leonids forecasting.

According to the Asher-McNaught model of Leonid dust streams, the 1999
outburst of 1500 meteors per hour occurred when our planet passed through a trail
deposited by Tempel-Tuttle in 1899 -- the very year that astronomy suffered its "greatest
blow" at the hands of the Leonids!

The same model predicts that Earth is now heading for encounters with two
dust streams on November 18th, 2000: one from the year 1733 and another from
1866. Unfortunately for meteor lovers, we won't pass as close to these streams as
we did to the one in 1999. Astronomers aren't sure how wide the dusty ribbons
really are -- gliding through the outskirts might not produce much of a display.
This year's likely encounters with dust streams are tabulated below. The
higher estimates for Leonid meteor rates, in the range 200 to 700 per hour, come
from astronomers Esko Lyytinen and Tom van Flandern, who are analyzing the
streams in much the same fashion as Asher and McNaught have done.

"They've done some interesting work on the effect of radiation forces in
dispersing meteoroids," says Asher of Lyytinen and van Flandern, "and their predictions
could well turn out to be correct. If pushed, I would go with our lower estimates
of 100 per hour."

Asher also noted that sky watchers should be alert for a possible outburst
on Nov. 17th, when Earth skirts by the 1932 dust trail. "There should be some
activity although the level may not be very high."

Predictions for Leonids 2000

Date (2000), Time (UT), Dust Stream, Maximum visual meteor rate, Best seen

Nov. 17, 07:50
 215 N. America, Central America & NW S. America

Nov 18, 03:44
 100-700 W. Africa, W. Europe, NE S. America

Nov 18, 07:51
 100-700 N. America, Central America & NW S. America

Above: A careful analysis of Leonid dust streams by Asher & McNaught and by
Lyytinen & van Flandern suggest as many as three meteor outbursts on Nov. 17 and 18,
2000. In the table, gray-colored values are the predictions of Lyytinen & van Flandern;
black-colored text comes from Asher & McNaught.

Leonid Observing Tips

With the science of Leonid forecasting still in its infancy, meteor
enthusiasts might not wish to place too much confidence in the exact times of this year's
predicted outbursts -- they could be wrong. Earth will be passing through comet Tempel-Tuttle's
"minefield" of debris for two full days spanning Nov. 17th to 18th. Flurries of shooting
stars could erupt at any time during that interval.

No matter where you live, the best time to look for Leonids will be between
local midnight and sunrise on Nov. 17th and again on Nov. 18th. Observers in the northern
hemisphere are favored because the constellation Leo reaches a maximum altitude of 60
degrees at mid-northern latitudes, but only 20 degrees in, say, Australia.

In mid-November, Leo rises above the eastern horizon just after midnight
local time. (Local time means the time it is where you live.) Finding Leo will be easy
because the waning quarter Moon will lie inside the boundaries of the constellation --
you can't miss it! Once you've located Leo, look away toward a darker area of the sky.
Although meteors will stream from the general direction of Leo, they can appear
anywhere overhead. In fact, they are often easiest to spot about 90 degrees from the shower's
radiant point.

If you begin observing before Leo rises -- that is, before local midnight --
and a Leonid meteor outburst occurs, then you may spot a rare variety of shooting star
called "Earth-skimmers." These are disintegrating meteoroids that fly over the horizon
nearly parallel to the atmosphere. They produce long colorful tails.

Contrary to some reports, 2000 is not a make-or-break year for the
Asher-McNaught model. If there are no outbursts this November, it may simply be that Earth passed
too far from the dusty filaments that lie ahead. The real test will come in November 2001
when our planet is due to pass through the hearts of at least two dust streams.

What will happen? The only way to know in either year is to be outside on
November 18th, under clear skies and looking up!


From Mark Bailey <>

Theoretical and Observational Solar System Astronomy

A Research Astronomer position funded by the Northern Ireland
Department of Culture, Arts and Leisure (DCAL) is available from 1
February 2001 for a suitably qualified candidate to work at Armagh
Observatory. The Observatory has full access to all UK facilities, and
is eligible for research grants from the Particle Physics and
Astronomy Research Council (PPARC) and other funding organizations.
Facilities for computing and data reduction are excellent and include
a local Starlink node funded in part by the PPARC and partly by the
DCAL, and an Origin 2000 supercomputer. The Observatory is also a
member of the UK Southern African Large Telescope Consortium.

Applicants must have a PhD in an appropriate discipline, experience of
post-doctoral research in astronomy, and preferably experience of
managing grants and running research programmes. Candidates with
research interests in any area of solar system astronomy, including
extra-solar systems, are encouraged to apply, but preference may be
given to those with experience of observational or theoretical work on
small bodies, particularly comets, asteroids and near-Earth objects.
The successful candidate will be expected to develop an independent
research programme in his or her field of expertise, to make a leading
contribution to the Observatory's research profile, to attract
research grants and personnel into Armagh, and to play a full role in
Observatory activities including Public Understanding of Science.

The salary, which is pensionable, is based on the Northern Ireland
Civil Service (NICS) Grade 7, currently in the range 27478 to 43064
pounds sterling (under review). Starting salary will depend on
qualifications and experience, and progression on the scale will be
based on performance in accordance with NICS regulations. The
appointment is for an initial five-year period, after which the Board
of Governors of the Armagh Observatory and Planetarium reserves the
right to offer the successful candidate a renewal appointment for a
further term or conversion to an established post.

Enquiries and requests for further information may be made to the
Director, Professor M.E. Bailey, at the address below, or by e-mail
to Information about the Armagh Observatory may be
obtained by consulting the Armagh Observatory web-site:

The closing date for receipt of applications is 8 December 2000.
Applicants should obtain an application pack from the Administrator
and send this together with a full curriculum vitae, a statement of
research interests and complete bibliography to: The Administrator,
Armagh Observatory, College Hill, Armagh BT61 9DG, Northern Ireland
(Tel: +44-(0)28-3752-2928; FAX: +44-(0)28-3752-7174; e-mail: References from three referees should be sent to
the Administrator by the closing date.

Armagh Observatory is an equal opportunities employer and welcomes
applications from candidates irrespective of ethnic origin, religion,
gender, political opinion, marital status, sexual orientation, or

From  The British Interplanetary Society <
TWO DAY Meeting
UK Manned Rocket Aircraft to be held at
The RAF Museum Cosford, Cosford, Shifnal, Shropshire
on Friday 10 and Saturday 11 November 2000
At the start of the 1950's the Air Ministry issued a tender for a rocket
fighter capable of intercepting high flying, nuclear capable, Soviet jet
bombers. Contracts to build such an aircraft were awarded to both Saunders
Roe (S.R.) and AVRO. Changes in defence policy were to mean cancellation for

the project but by the time this occurred, the S.R.53 had already flown.
However, the designers at S.R. had other ideas for their plane. In July
1958, presentations were made to the Ministry requesting that a modified S.R.53 be

developed as an air launched, manned re-entry test vehicle to aid in the
development of a British manned satellite (in the same way that America's
X-2 and X-15 were forerunners of the Space Shuttle).
The aim of this symposium is to bring together (possibly for the last time)
those people who worked on what, with hindsight, was the nearest thing that
Britain ever had to a rocket-powered "X-Plane"!
Provisional Programme
Spectre Engine, Peroxide APU & Turbo Starter, S.R.53 & S.R.177 Projects
 P.R. Stokes, former de Havilland Engine Co & Rolls Royce Heritage
The M.52 (UK's ill-fated contender to break the sound barrier)
 Dennis Bancroft, Chief Aerodynamicist on M.52.
 Presented by TBA
The M.52, RAE 1947 and the Me163B 'Komet'
 Capt E.M. Brown, RN (retd)
The Scorpion Rocket Engine
The Screamer Rocket Engine
Political and Technical Issues Pertaining to the Development and
Cancellation of the UK Rocket Fighters
 C.N. Hill, Charterhouse
The AVRO 720
The S.R.53
 R.B. Stratton, S.R.53 Project Manager
The SR177
 D. Hardy, S.R.177 Chief Project Engineer
Development of the S.R.177 Pressure Suit
 Air-Vice Marshal J. Ernsting CB OBE, RAF (retd) former Commandant of the
Institute of Aviation Medicine
P.187 & P.209 (and equivalent plans to modify the X-2 to meet X-15
 C.N. Hill, H. Matthews, I.A. Moule
Look at the exhibits at Cosford, in particular the S.R.53 and the V-Bombers
(the Valiant was proposed as the Carrier for the air launched S.R.53, i.e.
P.209), and to photograph speakers and attendees next to their respective
For an Information Pack on: Registration, Hotel Booking, Gala Evening and
Accompanying Person Social Tours, please contact: The Executive Secretary,
The British Interplanetary Society, 27/29 South Lambeth Road, London SW8 1SZ


D.J. Scheeres, S.J. Ostro, R.A. Werner, E. Asphaug, R.S. Hudson: Effects
of gravitational interactions on asteroid spin states, ICARUS, 147:
(1) 106-118 SEP 2000

We demonstrate that mutual gravitational interactions between an asteroid
and a planet or another asteroid can play an important role in shaping an
asteroid's spin state. We focus on two situations that asteroids may encounter during
their lifetimes. The first is the environment after creation from a disrupted
parent asteroid, when there may be many asteroid fragments interacting
gravitationally with each other before their mutual escape. The other is the interaction
between an asteroid and a planet during a hyperbolic flyby. In each case the mutual
gravitational interaction can alter the asteroid's spin state. We derive
analytical descriptions of the effects and perform numerical simulations to explore the
interactions and to give examples, The net effect of many small
interactions, taken in isolation, is to cause the asteroid to spin at a faster rate-although
this must be balanced against all other effects that influence spin rates. Conversely,
the effect of a single, strong interaction can fundamentally change an asteroid's spin
state, causing it to tumble and significantly increasing or decreasing its overall
angular momentum. We simulate interactions of a sphere of arbitrary mass with
Toutatis and find that these types of gravitational interactions can provide partial
explanations for the current Toutatis rotational state. (C) 2000 Academic Press.

Scheeres DJ, Univ Michigan, Dept Aerosp Engn, Ann Arbor, MI 48109 USA.
Univ Michigan, Dept Aerosp Engn, Ann Arbor, MI 48109 USA.
CALTECH, Jet Prop Lab, Pasadena, CA 91109 USA.
Univ Calif Santa Cruz, Dept Earth Sci, Santa Cruz, CA 95064 USA.
Washington State Univ, Sch Elect Engn & Comp Sci, Pullman, WA 99164 USA.


F. Vilas, A.L. Cochran, K.S. Jarvis: Vesta and the Vestoids: A new rock
ICARUS, 147: (1) 119-128 SEP 2000

Moderate spectral resolution observations of the 505-nm Fe2+ pyroxene
absorption feature were obtained for 13 asteroids dynamically linked to 4 Vesta, or
located between Vesta and the 3:1 resonance gap. Eleven showed spectra with deep
0.9-mu m mafic silicate absorptions suggesting a pyroxene composition (Binzel and Xu
1993). Spectra of only six of these asteroids show the absorption feature centered
at 506.5 nm, suggestive of an augite (high-calcium) component to the surface
pyroxenes consistent with previous spectral observations across the surface of Vesta
(Cochran and Vilas 1998). Five of the six asteroids include all objects observed at
heliocentric distances between Vesta and the 3:1 resonance gap. The spectrum of only one
asteroid interior to Vesta's orbit showed this feature. No correlation between the
presence or absence of this feature and the strength of the 1-mu m mafic silicate
feature was found. (C) 2000 Academic Press.

Vilas F, NASA, Lyndon B Johnson Space Ctr, Houston, TX 77058 USA.
NASA, Lyndon B Johnson Space Ctr, Houston, TX 77058 USA.
Univ Texas, Austin, TX 78712 USA.
Lockheed Martin Space Operat, Houston, TX 77058 USA.


M.T. Zuber, D.E. Smith, A.F. Cheng, J.B. Garvin, O. Aharonson, T.D. Cole,
P.J. Dunn, Y.P. Guo, F.G. Lemoine, G.A. Neumann, D.D. Rowlands,
M.H. Torrence: The shape of 433 Eros from the NEAR-Shoemaker Laser
SCIENCE, 289: (5487) 2097-2101 SEP 22 2000

Measurements from the Near Earth Asteroid Rendezvous (NEAR)-Shoemaker Laser
Rangefinder (NLR) indicate that asteroid 433 Eros is a consolidated body
with a complex shape dominated by collisions. The offset between the asreroid's
center of mass and center of figure indicates a small deviation from a
homogeneous internal structure that is most simply explained by variations
in mechanical structure. Regional-scale relief and slope distributions show
evidence for control of topography by a competent substrate. impact crater morphology
is influenced by both gravity and structural control. Small-scale topography
reveals ridges and grooves that may be generated by impact-related fracturing.
Copyright 2000 Institute for Scientific Information

Zuber MT, MIT, Dept Earth Atmospher & Planetary Sci, Cambridge, MA 02139
MIT, Dept Earth Atmospher & Planetary Sci, Cambridge, MA 02139 USA.
NASA, Earth Sci Directorate, Goddard Space Flight Ctr, Greenbelt, MD 20771
Johns Hopkins Univ, Appl Phys Lab, Laurel, MD 20723 USA.
Raytheon Informat Technol & Sci Serv, Greenbelt, MD 20771 USA.



From CO2 Science, 11 October 2000

In the October 2000 issue of Physics Today, there is a Special Report
entitled "Presidential Candidates Speak Out on Science Policy," wherein ten questions
are posed to Texas Governor George W. Bush and U.S. Vice President Al Gore.

The fourth of the questions deals with Global warming; they are asked if
they see global warming as a threat, and if they do, what they would do
about it if elected President of the United States.

With respect to the first question, Governor Bush states that scientific
data show average temperatures have increased slightly over the past century,
which is indeed correct. He then says that "both the causes and the impact of this
slight warming are uncertain," which is also correct. And he adds that these
phenomena "require much more extensive scientific analyses," which is only

The rest of Governor Bush's comments concern what should be done about the
situation.  He begins by saying "I oppose the Kyoto Protocol," but the reasons he gives
for opposing it have nothing to do with the science of global warming.
Nevertheless, he does say "I will work ... to develop the technologies to reduce
greenhouse gas emissions."

Vice President Gore begins by stating his belief that "global temperatures
are rising and that human activities such as the burning of fossil fuels are at
least partly to blame." The way this statement reads suggests that global
temperatures are rising now, or at least have done so in the very recent past, which is
highly debatable. The Vice President's belief that humanity's burning of fossil
fuels is partly to blame for the putative recent warming and the acknowledged
longer-term warming is also debatable, having been challenged by the very scientist -
NASA's James Hansen - Gore once embraced as a paragon of wisdom on this

Mr. Gore also says "studies have shown that the 20th century has been the
warmest century in the past 1000 years, the 1990s have been the warmest decade in
the period, and 1998 was the single warmest year on record." In truth, however,
only a handful of studies of this subject have made that claim, while many more
provide contrary evidence.

In referring to climate model predictions of an eventual greenhouse
gas-induced global warming on the order of 2.0 to 6.5F, the Vice President states that
likely consequences would be "more extreme weather events, expanded geographic
ranges for diseases like malaria and dengue fever, sea level rises, and damage to
ecosystems that cannot adapt quickly enough."  All of these claims are contradicted by
a wealth of real-world observations that have appeared in the scientific literature,
many of which are referenced in our Subject Index.  For information on extreme weather see
Extreme Weather; for materials related to diseases like malaria see Disease; for
studies of sea level see Sea Level; and for "damage to ecosystems that cannot adapt quickly
enough" see Extinction.

Another claim of Vice President Gore is that the climate change predicted to
result from the CO2 emitted by the burning of fossil fuels imperils the reliability
of agricultural production.  However, experimental evidence that looks at the
consequences of simultaneous increases in the air's temperature and CO2 concentration
suggests just the opposite, as indicated by the materials discussed in our Editorials Give
Peace a Chance by Giving Plants a Chance, In Search of the Second "Green
Revolution", and The Fortunate Coupling of Atmospheric CO2 and Temperature Trends.  So compelling
is the scientific information on this subject, in fact, that Sharon Cowling (1999)
of the Institute of Ecology's Climate Impacts Group at Lund University in Sweden
writes in Science (285: 1500-1501) that "maybe we should be less concerned about
rising CO2 and rising temperatures and more worried about the possibility that future
atmospheric CO2 will suddenly stop increasing."

With respect to how he would respond to the "catastrophic changes" he claims
will result from the continued burning of large amounts of fossil fuels, Mr. Gore says
"I will work with Congress to ensure the earliest possible ratification and most
sensible implementation of the [Kyoto] Protocol."

In summary, Governor Bush says little about the science of global warming;
but what he says is correct. Vice President Gore, on the other hand, says much; but most
of what he says is hotly contested. Besides differing in these respects, each man comes
down on opposite sides of the debate to ratify the Kyoto Protocol, candidate Gore
saying he is in favor of it, and candidate Bush saying he opposes it. Their reasons
for their different stances are also different, Bush citing economic reasons and Gore
citing his view of the science.

These are the facts of the matter as we see them.  They suggest that
Governor Bush, like NASA's James Hansen and colleagues (and many others, including us), is
not at all convinced that the historical rise in the air's CO2 content is
responsible for whatever warming may have occurred over the past century.  Vice President
Gore, however, is thus convinced. On the science, therefore, we would give Bush the edge,
but not with great enthusiasm; for he still advocates the development of
technologies to reduce greenhouse gas emissions.  Perhaps this could be forgiven, however,
as a prudent insurance policy against the remote possibility that something more
akin to Gore's presumed scenario may ultimately be found to be correct; it is
also possible that Bush may be thinking of non-CO2 greenhouse gases within this context,
which would, of course, significantly re-endear him to us.
Craig D. Idso
Keith E. Idso
Cowling, S.A. 1999. Plants and temperature - CO2 uncoupling.  Science 285:



From Petr Pravec <>

Dear Benny,

Michael Paine asked "How close would the parent body need to get to the
Earth or Mars (or the Moon?) to break apart?"  Erik Asphaug gave some good answers
to it. I note that he forgot to mention one important physical characteristic
that can make a tidal disruption of asteroids during their close planetary
approaches much easier and therefore more likely to happen even at somewhat
greater distances than otherwise would be. It is a rotation of the

Richardson et al. (Icarus 134, 47-76, 1998) presented results of their
modeling of such tidal disruptions of rotating rubble-pile asteroids.
They found that a fast rotation of the progenitor can facilitate its
tidal disruptions a lot, thus effectively increasing the distance from
Earth (or another planet) at which the disruption can happen.  In other
words, the tidal disruption cross-section of Earth is much greater for a fast
rotating progenitor than it is for a non-rotating one.  A geometry of the approach
and orientation of the body play their role, too, but generally fast
rotating rubble-pile asteroids are much more likely to be tidally disrupted during
close encounters with the planet than to collide with it.

In fact, all seven binary near-Earth asteroid candidates that I and others
have found from their double-period lightcurves (see, e.g., Icarus 146, 190,
2000) have fast rotating primaries with periods in the range 2.3-3.6 hours.
(I write here "candidates" because their binary nature was not confirmed by
another technique but the evidence for the binary nature we have is strong
for at least five of them; so 2000 DP107 is at least No. 6 and possibly No.
8 in my list of binary near-Earth asteroids.)  Here are some estimated
parameters of the eight NEA binary systems:

Object      d_p  d_s/d_p a/d_p  P_orb   P_rot   A_rot   Orb.Class
            (km)                 (h)     (h)    (mag)
1991 VH     1.2    0.40   2.7   32.69   2.6238   0.11   PHA
1994 AW1    0.9    0.53   2.3   22.40   2.5193   0.16   PHA
(3671)      0.9   >0.28   2.6   27.72   2.7053   0.16   PHA
1996 FG3    1.4    0.31   1.7   16.13   3.5942   0.09   PHA, Venus-crosser
1998 PG     0.9    0.30  (1.7) (14.01)  2.5162   0.13   Amor
(5407)      4.0  >=0.30  (1.7) (13.52)  2.5488   0.13   Mars-crosser
1999 HF1    3.7  >=0.20   1.7   14.01   2.3191   0.14   Aten, Venus-crosser
2000 DP107  0.8    0.37   3.2   42.2    2.7756   0.21   PHA

d_p is the diameter of the primary
d_s/d_p is the secondary-to-primary diameter ratio
a is the semimajor axis of the orbit
P_orb is the orbital period
P_rot and A_rot is the primary's rotation period and amplitude, respectively
(For references and uncertainties, see Pravec et al., Icarus 146, 190, 2000;
Pravec and Harris 2000, "Fast and slow rotation of asteroids", Icarus,
in press; IAU Circulars 7503 and 7504.)

The observed fast rotations of all the primaries are not far from their
rotation break-up limit (Pravec and Harris 2000) and indicate that the
rotation is an important characteristic that must be taken into account
when estimating the probability of formation of the binary systems.

Petr Pravec


From Michael Paine <>


I appreciate that, over geological timescales, NEAs will usually pass
"close" (eg 12 lunar distances) to the Earth millions of times before
impact. My comments were based on predictable collisions - those that
might occur in the next century or so. In other words, IF an object is
going to collide within the next century then it is likely to make
several close approaches to the Earth before impact. If referred to this
in my article
"There is an unexpected benefit with a scheme to detect large asteroids.
[Alan] Harris's calculations suggest that an ongoing search using six
telescopes will also detect many of the most threatening smaller NEOs
because, before hitting us, they are likely to buzz the  Earth during
several orbits of the sun. Being close to the Earth  means they are
likely to be picked up by a vigilant [ongoing] Spaceguard  program."

In an earlier article
I also pointed out that close approaches before impact should make the
task of deflecting the object much easier. That is, deflecting an object
away from a "keyhole" about 100km across during a close approach instead
of a deflection of several thousand km needed to miss the Earth on a
subsequent orbit.

These points go some way towards addressing two common, but
questionable, criticisms of Spaceguard - that smaller objects won't be
detected before they hit us and that the task of deflecting a
threatening NEA is beyond our capability.

Spaceguard is an exceptionally good investment for mankind to make -
even more so with recent developments. I wonder how the current debate
over the number, location and size of telescopes will be viewed in a
century or so, when I fully expect that the type of protection envisaged
by Arthur C Clarke (Rendezvous with Rama, 1973) will be in place and
taken for granted. Hopefully this will not be achieved under the
circumstances described by Sir Arthur (a "small" but deadly impact to a
heavily populated region) but by a coordinated international effort.
Like the impact issue itself, not a matter of IF but WHEN.

Michael Paine


From Neil Bone <>

In discussing the relation between the classes of potentially hazardous
NEOs, Duncan Steel cites 3200 Phaethon as an example of an object which
has 'quite recently made the comet-asteroid transition' partly, at
least, on the basis of the presence of a meteor stream, (the
Geminids). I wonder, however, whether this assertion doesn't neglect
some of the fundamental differences between Geminids and meteors of
defintely-established cometary origin.

Orionids (from 1P/Halley), Taurids (2P/Encke), Leonids
(55P/Tempel-Tuttle) or Perseids (109P/Swift-Tuttle), to give some
obvious examples, all have observational and physical properties which
differ considerably from the Geminids. They seldom penetrate more deeply
into the atmosphere than 80-90 km, for example, whereas Geminids have
been triangulated in luminous flight down to end-heights as low as 50
km. Neither do Geminid meteors tend to produce ionisation trains with
anything like the frequenct of those of cometary origin (20-30% for the
latter, roughly 5% for the Geminids).
Both these characteristics are, as I understand it, ascribable to the
greater density and physically 'robust' nature of Geminid meteoroids
(2gcm^3) copmpared with the 'dust-balls' shed by comets (0.2-0.3 gcm^3).
In the case of the Geminids, are we not dealing with rocky fragments -
for which, I agree, an ejection mechanism has to be found - and which
are quite different from those which populate cometary meteor
streams? Surely the presence of a meteor stream is not, in itself, a
reason to suggest that Phaethon was once a comet?

Neil Bone
Director, BAA Meteor Section


From Andy Smith <>

Hello Benny,

Much of our volunteer time is now being spent explaining the
asteroid/comet emergency (ACE) danger, prevention and preparedness
to interested individuals and groups and promoting the need
for preparedness and especially tsunami emergency preparedness,
in the coastal cities.

In these discussions we have found the use of a simple ACE comparison
scale to be very helpful. We use a ten-step exponential scale which
starts with the nominal 50 meter Tunguska or Barringer (Arizona)
object. This is magnitude #1 on our scale. We equate this to about
20 megatons (TNT) of destructive energy and we estimate the risk
interval to be about 100 years.

With each step, we double the object diameter. ACE magnitude #10 is about
the size of Hale-Bopp (25.6 kilometers). With each step, we increase
the kinetic energy(KE) by a factor of 8 and the risk interval by a
factor of 10.

This scale is similar to the Richter Scale(RS). Our steps result in an
8 fold increase in KE and the RS steps represent about a 30 fold
increase. We find the Torino index is difficult to explain to many
people, because it combines risk with the kinetic energy. We use it
only with technical groups, as an additional tool.

We also associate object absolute magnitude, crater diameter and burn
area width with the steps in our scale. We indicate the start of significant
ACE winter effects at about ACE magnitude 6 (1.6 kilometers).

We are continuing to refine this approach and we welcome inputs from the
CCNet community.

SPE 2000

We are anxiously awaiting feed-back from the Space Shield Conference, last
month. If anyone has seen abstracts, summaries, etc. from this important meeting
we would appreciate references.

Asteroid/Comet Workshop (ACW)/ ISDC 2001

We are compiling an Honor Roll of the pioneers in the ongoing development of
our global planetary defense capability. It will cover the last 400 years
and include people like Galileo, Piazzi, Witt, Wolf, Teller, Shoemaker, Rahe,
Simonenko, Carusi, Gehrels, and Morrison. We already have about 50 names and
we invite nominations from CCNet members and all countries. There is a lot of
good information in Clark Chapman's Web chronology.

We are planning a special evening tribute to these outstanding colleagues,
during our workshop, along with the playing of Beethoven Symphony #1 in C major (Op.21).
We understand this music was being played by our celebrated colleagues when
they got confirmation of the SL-9 string-of-pearls discovery from Jim
Scotti, at Spacewatch (National Geographic) and we think it will be a fitting theme
for our tribute. Opus 21 was first performed in 1800, within months of the
discovery of Ceres. Beethoven was then about 30 years old.

Our workshop, for the International Space Development Conference (ISDC 2001
on the Web), is developing nicely and we are extending the submission deadline. One
highlight area will be tsunami preparedness and structural responses.


Andy Smith


From Bob Kobres <>

US government blurb on Space development:

[. . .]

In order to fully allow and facilitate the commercialization of the
tremendous potential market of space, the cost of the basic space
infrastructure must be reduced dramatically. The government will also be
required to play a role to promote, entice, and aid the development of a
private sector presence in space.

The unique near zero-gravity of space would allow industries to manufacture
new materials simply due to the fact that the absence of gravity allows for
the creation of perfectly even and consistent mixtures of materials with
vastly different mass and densities. These alloys would have "unique
physical properties no nation on Earth could duplicate" and could lead to
the production of much faster computers, smaller and much more powerful
batteries that could power future electric cars, and many other new

Another potentially profitable space activity is the disposal of nuclear
waste and other hazardous materials. The disposal of hazardous waste
material has long been a problem for government and industry and continues
to be today. A report by the Aerospace Research and Development Policy
Committee of IEEE Inc. projects that "by the year 2000 the accumulation of
irradiated fuel from commercial nuclear plants alone will approach 200
thousand metric tons and will be increasing at a rate of 10 thousand metric
tons per year". With the development of new technology and reduced costs,
the potential to transport hazardous materials into space from remote
locations on Earth and the propulsion of this material into far-out orbit
can become a realistic and desirable option.

Space can also provide an optimum location for orbiting platforms that can
be used to transmit electrical energy via optical mirrors and microwave
energy transmission technology. This electrical energy can then be sent from
remote sources on the surface of the planet to the locations where it is
needed. This would provide a new and environmentally safe method of
electrical power generation and transmission.

Continues at:

Developing the infrastructure required to avoid future impact events would
also provide the means to further Space development in general. Monies for
this should and could come from contemporary military budgets. It is a
defense issue! And effecting a planetary defense system is certainly more
cost effective than producing more nuclear subs, B-1s, and other costly
military hardware!


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From Hans Rickman <>

Dear Benny,

from recent email correspondence that has been copied to me,
I have noted some apparent confusion about the IAU position
with regard to the conclusions and recommendations of the UK
Task Force report. Since such confusion can only be detrimental
to the aims of increasing the efforts to study NEOs that we
all share, I have published the following Press Release on
behalf of the IAU and undersigned by both myself and David
Morrison. It has been posted on Alpha-Galileo and on the IAU
web page. I sincerely hope it leaves no doubt about the IAU
support for the TF recommendations!

Best regards,  Hans Rickman

IAU PRESS RELEASE, 11 October 2000

International Research on Near-Earth Objects

The hazard posed to humanity by cosmic impacts is international in
character. While km-sized impactors would cause important, global
perturbations to the Earth's biosphere and climate, those of somewhat
smaller size could also have serious international consequences,
affecting densely populated coastal areas in several countries.
Those well-known circumstances, and the fact that a more detailed
assessment of the impact hazard requires a survey and study of the
Near-Earth Object population, for which an effort by the international
astronomical community is necessary, form the basis for the IAU's
engagement in the issue, as laid down by the IAU Executive Committee
already in 1998.

The recent report of a Task Force (UKTF) appointed to advise
the Government of the United Kingdom on research policies related to
potentially hazardous Near-Earth Objects gives a clear summary of
the current situation with a proper and welcome emphasis on the
international aspects. It provides a follow-up on earlier planning
efforts initiated in the US, that resulted in defining the Spaceguard
System for the inventory of the population of km-sized Earth-crossers,
while now pushing the goals further.

The IAU and its Working Group on Near-Earth Objects (WGNEO) welcome the
report of the UKTF as a very constructive step towards a concerted
programme of action on the subject.

To this end new resources will be required, and in all likelihood,
those can not be found solely within any one country. Nonetheless,
international efforts naturally grow out of national initiatives.
The exploration of the potential impactor population has so far
been carried out mostly thanks to search programmes carried out in
the US but has nevertheless been international, e.g. with the
IAU offering its resources for gathering the scientific expertise.
We now look forward to a deepening search which will still profit
essentially from national and multilateral funding, as proposed
by the UKTF to the British Government, but which will continue to draw
upon the contributions of scientists all over the world and,
in particular, the support of the IAU Minor Planet Center.

The formation of national centers to provide other kinds of support
was in fact one of the recommendations of last year's IMPACT
meeting in Torino, for which the IAU was one of the sponsors. The
IAU will be pleased to collaborate with governmental and other partners
both in Europe and elsewhere to secure the role of the international
scientific community in setting up or reinforcing the necessary
structures, and hopes that the government of the UK and other
interested countries will decide to follow up the Task Force
recommendations with appropriate initiatives. The WGNEO will continue
to be the main forum of discussions within the IAU of all related
scientific matters.

Hans Rickman,    IAU General Secretary
David Morrison,  Chairman of the WGNEO

CCCMENU CCC for 2000

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