PLEASE NOTE:


*

CCNet DIGEST, 17 May 1999
-------------------------

     QUOTES OF THE DAY - BETWEEN SCIENCE AND FICTION

     FIRST THE SCIENCE....

     "Man had, from the beginning, devised ways and means of averting
     impending disasters due to the forces of nature. The present case
     differed in no respect from the others except in magnitude. The
     evolution of defense against nature had been steady and
     progressive, from the stone age, when prehistoric man sought
     shelter in caves from the pelting hailstones, to the present one
     in which they were about to whip out of its course a planet that
     was running wild through the solar system. [...]
     And in the midst of all this rumpus, Professor Benjamin Hooker
     suddenly stated that he purposed going out in the Flying Ring to
     meet the asteroid in its fall through space, attack it with the
     famous lavender ray that had disrupted the Atlas mountains, and
     either deflect it from its course so that it should not strike the
     earth at all or blow Medusa into smithereens! Yet his announcement
     that he intended to sally forth and slay the celestial monster -
     like a little scientific David - did not tend to assuage the
     universal terror in the slightest" (Arthur Train & Robert Wood,
     THE MOON MAKER, first published in 1916)



     "NASA's goal is to inventory the population of NEO's larger than 1KM
     and to characterize a sample of them. If we are able to inventory the
     NEO population and obtain good orbits for these NEOs, we will not need
     to monitor them further" (Guenter Riegler, NASA HQ, May 1999)



(1) PLANETARY DEFENSE AGAINST ASTEROID IMPACT *WAS* INVENTED IN 1916!
    Ron Miller <rmiller@crosslink.net>

(2) MORE ON THE MOON MAKER
    Bob Kobres <bkobres@uga.edu>

(3) DOES NASA HQ REALLY UNDERSTAND THE IMPACT HAZARD?
    David J. Johnson <starman@mail.fwi.com>

(4) THE PASSIONATE ASTRONOMER
    Malcolm Miller <stellar2@actonline.com.au>

(5) THE NEAR-EARTH ASTEROID TRACKING (NEAT) PROGRAMME
    S.H. Pravdo et al., CALTECH,JET PROP LAB

(6) OBSERVATIONS OF PHOBOS & DEIMOS
    N. Thomas et al., MAX PLANCK INST AERON

(7) SPECTRAL MEASUREMENTS OF PHOBOS AND DEIMOS
    S. Murchie et al., JOHNS HOPKINS UNIVERSITY

(8) WHEN A COMET MEETS A PLANET
    V. Batllo, CNRS

========================
(1) PLANETARY DEFENSE AGAINST ASTEROID IMPACT *WAS* INVENTED IN 1916!

From Ron Miller <rmiller@crosslink.net>

Benny J Peiser wrote:
> BTW: Are you sure the book was published as early as 1917?

Oh, yes indeed! It was originally published as a serial in
"Cosmopolitan" magazine, beginning in the October 1916 issue. It was  a
sequel to the novel, "The Man Who Rocked the Earth" (Doubleday, Page &
Co., NY: 1915), which, while not a space travel story, introduced  the
"Flying Ring", the vehicle used as a spacecraft in the succeeding
story.  So far as I know, "The Moon Maker" (the terminal "s" was a typo
in my letter to Sir Arthur) did not appear in book form until 1958
(Kreuger, NY).

The "Flying Ring" was an aluminum torus about 75 feet in diameter,
surmounted by a tripod carrying the propulsion unit at its apex. (A
detailed description, along with a schematic drawing, can be found in
my book, "The Dream Machines", a copy of which Sir Arthur possesses).
Propulsion was obtained by the energy released by disintegrating an
uranium cylinder. The spacecraft flew on a jet of superheated
helium. The motor assembly was in an electrically-controlled gimbal
mount for steering.

The descriptions of the details of the spacecraft and of the conditions
encountered during its flight through space are almost flawlessly
accurate (there is no sensation of weight, for example, except when the
engine is firing).

The same energy that is used to disintegrate the uranium fuel is used
to set up a nuclear reaction on the surface of the asteroid Medusa. The
jet reaction of this is enough to deflect the asteroid from its
projected impact on the earth (it eventually goes into orbit as a
small second moon).

Arthur Train was lawyer-turned-author who had written a long series of
highly-successful mystery novels and short stories. Robert Williams
Wood was a professor at Johns Hopkins--and was evidently the source for
the excellent science and mathematics in both books.

Best--
Ron Miller

================
(2) MORE ON THE MOON MAKER

From Bob Kobres <bkobres@uga.edu>

From THE MOON MAKER, pp 69-70, 1958 Krueger edition:

Through their glasses, they could see that on one side the surface of the
asteroid was pitted with holes and craters similar to those upon the moon,
while the other, which had been subjected to the fierce erosion of the dense
gases of the comet [which, as in Armageddon, altered the asteroid's orbit],
was worn almost smooth and plowed into furrows. The Ring was now moving on a
course parallel to that of Medusa, which floated apparently motionless in
space at a distance which Bennie estimated to be less than five hundred
miles.  Both, drawn by the combined attraction of the sun and earth, were in
reality rushing on toward the latter. The three men were busy with their
preparations for the projection of the great ray, and Rhoda drew herself
over to the side deadlight, through which streamed the pale yellow beams
from the runaway planet. Now that they were running alongside, but one-half
of the illuminated hemisphere was visible, and Medusa appeared like the moon
at the half-phase, but fifty rimes as big.

Monstrous and sinister it looked to her, and she shuddered involuntarily as
she thought of its distant target, peopled with millions of helpless human
beings, doomed to be wiped out of existence in a blinding flash of fire.
Could they do aught to prevent it-four insects in a flying pellet of metal,
aspiring to stop a runaway world? Had not perhaps the thing been put in
motion by some Supreme intelligence which controlled the universe, and might
not the destruction of the world be a part of the Great Plan, a cog in the
great wheel of destiny? If so, what could they hope to do to alter the plan?
And then she thought of the taming of the thunderbolt by the lightning-rod,
and drew a long breath and clenched her hands. Man had, from the beginning,
devised ways and means of averting impending disasters due to the forces of
nature. The present case differed in no respect from the others except in
magnitude. The evolution of defense against nature had been steady and
progressive, from the stone age, when prehistoric man sought shelter in
caves from the pelting hailstones, to the present one in which they were
about to whip out of its course a planet that was running wild through the
solar system.

There in front of her, just outside the deadlight through which she was
gazing, and silhouetted against the shining disk of the asteroid, was that
terrible weapon, the generator of the disintegrating ray. In a few minutes,
it would be hurling its mysterious. beam across the void of space. She would
be present, and would see what happened. Already, the Ring was reverberating
with the noise of the machinery for generating the electric current that fed
the coils of the inductor.  Both dynamos were running at full-speed, and the
scream of the radio-turbines filled the air. Through the din, she heard
Bennie's voice-"Clear for action!" .
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

As far as I've been able to learn, THE MOON MAKER, by Arthur Train and
Robert W. Wood, was first published in a book format by Krueger in 1958
(only 500 copies).  As this edition is partitioned into five parts, I
suspect that the original publication was in serial form; possibly in
Harpers, Century or some similar periodical.  The story's event is placed
ten years after the uneventful passage through Comet Halley's tail and The
World War has been halted, so an original publication date of around 1917 is
reasonable.  If I obtain a copy of the story published in that time
period--pre 1923--it will be in the public domain and I'll put it on my
web-site.  It's quite a fun read.

bobk

A bit more from earlier in the book (pp 22-25):

There was soon no doubt regarding Thornton's prediction. Careful
observation, supplemented by independent calculations, demonstrated beyond
peradventure that the asteroid Medusa would certainly pass through the head
of the comet, which now blazed nightly in the sky like the beam of a huge
search-light. Never had such a meteor been known before, for it surpassed in
brilliancy and size the famous comet of 1811.  All night long the streets of
every American city were filled with crowds of people watching the huge
fire-ball, the diameter of which appeared to the terrestrial observer to be
nearly half that of the moon itself.  From the dawn of time these dragons of
the sky have caused consternation in the hearts, not only of the ignorant
savage but in those of the half-civilized as well, and even among the
educated classes there still lingers some echo of that fear, inherited
through millions of generations of men, who, from the birth of the race,
have sought to read upon the scroll of the heavens the tracings of the hand
of Fate. And so the boulevards of the capital swarmed with thousands of
people, who gazed in silence at this monster of the sky. Unlike the Chinese,
who endeavor to scare away such celestial demons by exploding firecrackers
and making all the noise humanly possible, these Occidental multitudes
viewed the comet in solemn if not religious awe, realizing poignantly, for
the first time, that our universe is not protected from attack by wandering
celestial bodies. Had a hostile Zeppelin appeared upon the horizon, a fleet
of aeroplanes would have instantly arisen to meet and destroy it. But no
known human agency existed which could go forth to challenge and possibly
vanquish a fire-monster appearing thus malevolently out of the infinity of
space. The man in the street walked with his nose pointing to the midnight
zenith, and next morning complained at breakfast of having a most
unaccountable "crick" in his neck; but the crowd was still save for the
newsboys, who ran hither and thither shouting shrilly: "Extree! Extree! All
about the comic!"

Consumptive old men, gray-bearded and withered survivors of antebellum days,
wastrails of the vissitudes of fortune came crawling out of garrets to set
up small, battered brass telescopes on weather-beaten mahogany tripods. And
about these collected knots of people, who eagerly paid small sums to get a
nearer view of this astonishing phenomenon which portended no one knew what..
In the "black-and-tan" quarters of the city, the impassioned tones of the
exhorters, mingled with the groans and wailings of converts and the chant of
salvation-hymns, filled the air, for there, at least, the conviction
prevailed that the day of Judgment was at hand, and that the sheep were at
last to be definitely separated from the goats.

Four days after the meeting of comet and asteroid, which was duly reported
by observing astronomers, newsboys were again crying, "Extra!" in the
streets of Washington. An evening paper had been made the recipient of the
following, the result of calculation on the part of Thornton:


EARTH TO BE ANNIHILATED!
ASTEROID "MEDUSA" WILL TORPEDO OUR PLANET ON APRIL 22.
CATACLYSM NOW ABSOLUTELY CERTAIN

It is announced positively by the officials of the National Observatory that
the asteroid Medusa, having been arrested in its orbit by its collision with
the comet, is now plunging toward the sun with an increasing hourly
acceleration and will undoubtedly hit the earth in less than five months
from today. Calculations have shown that the point of impact will he in
Mexico on the line of latitude passing through Tampico, though it is
possible that the body may fall in the Pacific if the time of arrival is a
little later than that predicted, or in the gulf of Mexico, if earlier. The
opinions held by the leading scientific men of the country as to the
immediate effects of the collision differ in the extreme. Some consider
that, a-side from earthquakes, tidal waves and considerable atmospheric
disturbances, the destructive effects will be confined to an area of not
more than three or four hundred miles radius. Others believe, however, that
the concussion will destroy all life over the greater part of two Americas,
and that the "splash" of the asteroid will bury the United States under a
layer of fused rock, broken stones, dust, and mud to a depth varying from
several miles in Texas to several feet in Maine and Oregon. All agree,
however, in the belief that every building in the United States will he
razed to the ground by the shock, and that the atmospheric disturbances will
be such as to render the loss of life enormous over the entire continent.

The most extreme view is that taken by Professor Katz, of Columbia, who
asserts that the impact will reduce our globe to powder. His colleague,
Professor Smithers, claims that that part of the earth's surface subjected
to the blow will be entirely fused and vaporized, while other scientists
believe that the concurrent earthquake shock will travel completely around
the earth and destroy all life upon both hemispheres. All agree that, if
nothing worse occurs, the vast bulk of the asteroid will penetrate the film
of the earth's surface for several hundred miles, the globe's diurnal
rotation will be affected, the shape will be changed, and its orbit around
the sun will be altered. Ultimate consequences cannot be predicted but THE
END OF THE WORLD IS AT HAND.


The civilized world received the astounding news of the pending annihilation
of the earth, first, with the amused silence of incredulity, and then with a
gasp of horror that swept over the entire surface of the globe.  The
immediate reaction of the human brain to this inconceivable catastrophe was
that of sublime disbelief in its possibility. The finite mind, incapable, as
it is, of grasping the infinities, resolutely declined to accept any
proposition outside the history of man's experience. Since that moment when
the human race in the course of evolution, had appeared upon the face of our
planet, the latter's orbit through space had never been attacked or even
affected by any other celestial body, and since the earth had spun for
countless millions of years in its regular course about the center of the
solar system, and summer had inevitably followed winter, and men had been
born, made love, fought, and died, no one was ready at first to accept the
simple scientific truth that, if a meteorite weighing perhaps only a single
ton could fall flaming earthward to bury itself in some farmer's plowed
field, there was no reason, in the nature of things, why a meteorite a
million times larger should not do the same thing, or why another planet
several times larger than the earth should not shatter it to atoms.

Kings, emperors, presidents, sultans, and rajahs, with their courts,
Cabinets, and wise men, treated the preliminary announcement of the
observatories of Washington, Moscow, and Greenwich much as they had in the
past treated the prophecies of clairvoyants and others that the day of
Judgment was positively going to occur on certain specified dates.  The
newspapers carefully refrained from any editorial comment.  Somebody,
evidently, had made a big mistake which would presently be discovered, and
then everybody would breathe easily again.  But, unfortunately, the supposed
mistake obstinately continued to remain undetected, and further observations
merely served to corroborate those already made and to substantiate, not
only the probability but the absolute certainty of what Thornton had
prophesied.

Then, with a shriek of astonishment and despair the news-papers of all the
nations gave themselves over to this, the greatest sensation in the history
of the planet, and the combined energies of astronomers throughout the
entire globe were concentrated upon determining, so far as possible, the
size and weight of the falling asteroid, and the point upon the surface of
the earth which would receive its momentous impact.

It was soon authoritatively announced that its diameter was not less than
ninety or more than one hundred and sixty miles, and that, unless it was
deflected from its course by the attraction of the moon or of some planet,
it would strike the earth in the neighborhood of Galveston, Texas, with a
velocity of nearly nineteen miles a second. What the precise result of this
terrific concussion would be upon the earth and its movement, it was, of
course, impossible for anybody to predict accurately or even imagine.

Would the earth be shattered, or would it resist the titanic blow of this
monster from out of space? Would both bodies retain their integrity so that,
one embedded in the other in a strange and horrible association, they would
gyrate through eternity?  What would the effect be upon the earth's orbit,
its climatic conditions, and its life? What might happen at the worst, the
mind of man refused to conjecture. But it was admitted that, beyond
peradventure, the best that could be hoped for would be that the asteroid
itself might suffer annihilation - in which event, its shattered carcass
would lie smothering a thousand miles of the earth's surface, changing the
latter's axis and sending it staggering a-long a new orbit under conditions
which might render human life upon the globe impossible. And the blow
itself: Could life continue after such a shock, which would be greater by
ten thousand times than that of the most violent earthquake known in the
history of man?

And in the midst of all this rumpus, Professor Benjamin Hooker suddenly
stated that he purposed going out in the Flying Ring to meet the asteroid in
its fall through space, attack it with the famous lavender ray that had
disrupted the Atlas mountains, and either deflect it from its course so that
it should not strike the earth at all or blow Medusa into smithereens! Yet
his announcement that he intended to sally forth and slay the celestial
monster - like a little scientific David - did not tend to assuage the
universal terror in the slightest.
~~~~~~~~~~~~~~~~~~

Bob Kobres
Main Library
University of Georgia
Athens, GA  30602
bkobres@uga.edu
706-542-0583
http://abob.libs.uga.edu/bobk

================
(3) DOES NASA HQ REALLY UNDERSTAND THE IMPACT HAZARD?

From David J. Johnson <starman@mail.fwi.com>

Dear Benny,

In February this year I had sent some querries to the White House and to
NASA to which I recieved this response. You will notice their is NO
mention of Spaceguard. I get the feeling that NASA and the USAF
believe they are now the Front Line Defense, and can take care of all
our NEA-NEO woes.

Though the programs Mr. Riegler talks about will provide a range of data
needed in our research, I do not think that NASA should be the
centeral control. We are all aware of the paradox of putting all our
eggs in one basket...

NASA has no intention of funding anything like Spaceguard.

Regards,

David Johnson

------
NASA Letter Dated May 10, 1999


Dear Dr. Johnson:

Thank you for your e-mail dated February 28,1999, to President Clinton
concerning Asteroids.

NASA is currently funding 5 Near Earth Object (NEO) search programs.
NASA's goal is to inventory the population of NEO's larger than 1KM
and to characterize a sample of them. If we are able to inventory the
NEO population and obtain good orbits for these NEOs, we will not need
to monitor them further.

NASA is currently funding the operations of the Lincoln Near Earth
Asteroid research effort which you mentioned in your e-mail. We have,
in addition, provided some capital funds to the Lincoln Laboratory to
allow them to add a second 1M telescope to their search effort. The
Lincoln Laboratory program is but one example of our active, ongoing
cooperative efforts with the Air Force Space Command to search for
NEO's.  Our total funding for all aspects of NEO observational work is
3.58 Million this year.

In addition, we have an active program of space exploration of
asteroids and comets. These missions were selected on the basis of
their intrinsic merit as science missions, but all provide data
crucial to us if we are required to respond to an asteroid or comet
with any likelihood of Earth impact. Next year, the NEAR mission, will
encounter the NEA Eros and go into orbit around Eros. The mission will
provide a wealth of physical and chemical data on this NEA 1992 KD in
July of this year. Another approved mission CONTOUR will fly by three
comets giving us a data set which will allow us to compare
short-period and long-period comets. NASA is providing instruments for
the ROSETTA orbiter, a mission operated by ESA, and a Rover for the
Japanese mission to a NEA. The recently launched STARDUST mission will
fly through the coma of Comet Wild II and return samples of the comet
dust.

Within the resources available to us, we believe that NASA is moving
expeditiously to inventory the NEO population and provide the physical
data necessary to respond to any likely deflection requirement.

Thank you for your interest in the Space program.

Sincerely,

Guenter Riegler
Director
Research Program Management Division
Office of Space Science
NASA HQ
Washington, D.C.  20546-0001

================
(4) THE PASSIONATE ASTRONOMER

From Malcolm Miller <stellar2@actonline.com.au>

Dear Benny,

I am a retired astronomer who has only recently found out about
your newsletter from my friend Andrew Glikson.

You may not know that both Andrew and I are published poets. We
have both published books of poems with astronomical references.

For your amusement, I attach a poem from my book 'The Passionate
Astronomer' launched on Thursday May 13.


Mathilde exposed

Lifelessly orbiting the sun, stark shadows
outlining a crater's edge.  Dead asteroid, near-black,
doomed to circle forever, pummelled with impacts
long ago when all the worlds were young.
A target now, probed by a shiny, juvenile device,
tourist from a younger,  larger world,  with lenses,
cameras, antennas cocked like ears to hear the whispers
out of time and space, beaming back its espionage.
Merciless interrogation  of a lonely planetoid,
stripped now of all mystery, revealed as a naked
pile of coal-black rubble, sticky with tars, colder than ice.
Poor little Mathilde, unchanged now for four billion years.
How much longer will you have to wait,
and what could you be waiting for?  We know you now;
you are no further use to us, your dossier can be closed.

24.7.98

===============
(5) THE NEAR-EARTH ASTEROID TRACKING (NEAT) PROGRAMME

S.H. Pravdo*), D.L. Rabinowitz, E.F. Helin, K.J. Lawrence, R.J.
Bambery, C.C. Clark, S.L. Groom, S. Levin, J. Lorre, S.B. Shaklan, P.
Kervin, J.A. Africano, P. Sydney, V. Soohoo: The Near-Earth Asteroid
Tracking (NEAT) Program: An automated system for telescope control,
wide-field imaging, and object detection. ASTRONOMICAL JOURNAL, 1999,
Vol.117, No.3, pp.1616-1633

*) CALTECH,JET PROP LAB,4800 OAK GROVE DR,PASADENA,CA,91109

The Near-Earth Asteroid Tracking (NEAT) system operates autonomously at
the Maul Space Surveillance Site on the summit of the extinct Haleakala
Volcano Crater, Hawaii. The program began in 1995 December and
continues with an observing run every month. Its astrometric
observations result in discoveries of near-Earth objects (NEOs), both
asteroids (NEAs) and comets, and other unusual minor planets. Each
six-night run NEAT covers about 10% of the accessible sky, detects
thousands of asteroids, and detects two to five NEAs. NEAT has also
contributed more than 1500 preliminary designations of minor planets
and 26,000 detections of main-belt asteroids. This paper presents a
description of the NEAT system and discusses its capabilities,
including sky coverage, limiting magnitude, and detection efficiency.
NEAT is an effective discoverer of NEAs larger than 1 km and is a major
contributor to NASA's goal of identifying all NEAs of this size. An
expansion of NEAT into a network of three similar systems would be
capable of discovering 90% of the 1 km and larger NEAs within the next
10-40 yr, while serving the additional role of satellite detection and
tracking for the US Air Force. Daily updates of NEAT results during
operational periods can be found at JPL's Web site
(http://huey.jpl.nasa.gov/ similar to spravdo/neat.html). The images
and information about the detected objects, including times of
observation, positions, and magnitudes are made available via NASA's
SkyMorph program. Copyright 1999, Institute for Scientific Information
Inc.

============
(6) OBSERVATIONS OF PHOBOS & DEIMOS

N. Thomas*), D.T. Britt, K.E. Herkenhoff, S.L. Murchie, B. Semenov,
H.U. Keller, P.H. Smith: Observations of Phobos, Deimos, and bright
stars with the Imager for Mars Pathfinder. JOURNAL OF GEOPHYSICAL
RESEARCH-PLANETS, 1999, Vol.104, No.E4, pp.9055-9068

*) MAX PLANCK INST AERON,MAX PLANCK STR 2,D-37191 KATLENBURG
   DUHM,GERMANY

The Imager for Mars Pathfinder (IMP) was used to observe several
objects during the Martian night. The satellites, Phobos and Deimos,
were observed on two occasions each, through the IMP geological filters
covering the wavelength range 440 nm to 1 mu m. The observations were
converted to geometric albedo using triaxial ellipsoid models of the
satellites and phase functions derived from Viking Orbiter images. The
spectral slopes over the full wavelength range were 7.9(+/-0.5)% (100
nm)(-1) and 9.6(+/-0.6)% (100 nm)(-1), respectively referenced to 600
nm. In the Deimos spectra, some evidence for decreased reddening toward
the trailing hemisphere was found. The geometric albedoes of Phobos and
Deimos were found to be 0.065 (+/-0.010) and 0.068 (+/-0.009),
respectively, averaged over 440 and 600 nm, in good agreement with
previous measurements. The nighttime optical depth was investigated
using observations of stars. A mean value of 0.56 (+/-0.09) was
determined from measurements at different airmass. A possible maximum
in the optical depth near 0200 local time was found, which may result
from condensation during the night. A measurement of the egress of
Phobos from eclipse was made. Modeling of the light curve gave a scale
height for the scatterers of 10-15 km. The exact time of the eclipse
reappearance over the limb could be reconstructed from the measurements
and was in reasonable accord with predictions, although a small
modification to the predicted position of Phobos of 6.8 (+/-6.0) km
would have produced better agreement. Copyright 1999, Institute for
Scientific Information Inc.

=============
(7) SPECTRAL MEASUREMENTS OF PHOBOS AND DEIMOS

S. Murchie*), N. Thomas, D. Britt, K. Herkenhoff, J.F. Bell:
Mars Pathfinder spectral measurements of Phobos and Deimos:
Comparison with previous data. JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS,
1999, Vol.104, No.E4, pp.9069-9079

*) JOHNS HOPKINS UNIV,APPL PHYS LAB,JOHNS HOPKINS RD,LAUREL,MD,20723

The Imager for Mars Pathfinder (IMP) acquired four spectra of parts of
the sub-Mars hemispheres of Phobos and Deimos. The measured region of
Phobos is expected to be a mixture of the two spectral units identified
on that satellite from Phobos 2 data, and the IMP spectra of Phobos are
intermediate to the two units as expected. The derived geometric albedo
is consistent with the value for that part of Phobos determined from
Viking imagery. The IMP spectrum of Deimos is generally consistent
with previous measurements acquired from the ground and from the Hubble
Space Telescope (HST), but the signal-to-noise ratio is lower than that
of the Phobos data. The spectral contrast between the two moons is
similar to that seen in HST and Phobos 2 data. Mars Pathfinder
measurements therefore substantiate recent results which indicate that
Phobos and Deimos are not, as previously believed, analogous to C-type
asteroids. They also provide some indications for an absorption near
700 nn, perhaps like that seen in other low-albedo asteroids. Both
Martian moons are redder than most asteroids, and most closely resemble
two analog materials believed to have undergone very dissimilar
histories: primitive D-like asteroids, and highly space-weathered,
mafic-rich assemblages, such as are present in lunar mare soils.
Copyright 1999, Institute for Scientific Information Inc.

===========
(8) WHEN A COMET MEETS A PLANET

V. Batllo: Study of a particular model of encounter between a comet and
a planet. CELESTIAL MECHANICS & DYNAMICAL ASTRONOMY, 1998, Vol.71,
No.3, pp..191-201

CNRS,BUR LONGITUDES,77 AVE DENFERT ROCHEREAU,F-75014 PARIS,FRANCE

The objective of this paper is to develop a simple model of an
encounter between a comet and a planet, with a subsequent capture or an
escape, and to study the potential consequences. The hypothetical
scenario is as follows: a comet with a conic orbit meets close to one
of its vertices (located near the ecliptic plane), a jovian planet, and
transforms its orbit. There are two hypotheses which are made for the
shock: this vertex becomes one of the final vertices and the orbital
plane of the comet is unchanged during the encounter as it was the
case for Brooks 2 in 1886. In this model, it was able to find an
equation which was then used to obtain the pre- and post-encounter
orbits elements and the kind of orbit (ellipse, hyperbola, parabola)
with respect to the initial inclination. The numerical experiments with
the observed comets often provide pre-encounter orbits with an aphelion
point located near another jovian planet farther from the Sun, and so
on with sometimes several planets, or with an aphelion point located
beyond the Pluto orbit. Copyright 1999, Institute for Scientific
Information Inc.

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