PLEASE NOTE:
*
CCNet 134/2001 - 18 December 2001
=================================
"As it took with the terrorism business, it takes a nasty
event to
bring people to their senses. One of these days we'll get another
Tunguska, and then people will think about putting some money
into
this."
--Brian Marsden, The Independent, 14 December 2001
Ann Keen: To ask the Secretary of State for Trade and Industry if
she will make a statement on the Government's response on 24
February
to the recommendations contained in the report of the Near Earth
Object
Task Force.
Ms Hewitt: An updated response is nearing completion and will be
published shortly.
-- House of Commons, 13 December 2001
(1) NEAR EARTH OBJECTS IN THE HOUSE OF COMMONS: UK GOVERNMENT
RESPONSE
EXPECTED SOON
House of Commons, 13 December 2001
(2) ONE ASTEROID CAN RUIN YOUR DAY
Wired News, 14 December 2001
(3) THEY COME FROM OUTER SPACE
The Independent, 14 December 2001
(4) WAS LIFE ON EARLY EARTH NEARLY WIPED OUT BY MASSIVE IMPACTS?
Andrew Yee <ayee@nova.astro.utoronto.ca>
(5) LEONID METEOR HIGH-SPEED IMAGING
Andrew Yee <ayee@nova.astro.utoronto.ca>
(6) NASA BIDS FAREWELL TO THE SUCCESSFUL DEEP SPACE 1 MISSION
NASANews@hq.nasa.gov
(7) DEEP SPACE 1 SOWS COMET SENSE
Ron Baalke <baalke@jpl.nasa.gov>
(8) DID ANCIENT CIVILISATIONS COLLAPSE DUE TO LARGE EARTHQUAKES?
Andrew Yee <ayee@nova.astro.utoronto.ca>
(9) HYPERVELOCITY IMPACT SYMPOSIUM
Ron Baalke <baalke@zagami.jpl.nasa.gov>
(10) SEASONS GREETINGS & UPDATE
Andy Smith <astrosafe@yahoo.com>
(11) THE DATE OF GERVASE'S EVENT OF JUNE 1178
Peter Nockolds, LONDON, UK <ASTROLIT@aol.com>
(12) REPLY TO PAUL WITHERS
Peter Nockolds, LONDON, UK <ASTROLIT@aol.com>
(13) MOON OR CAPTURED ASTEROID?
Tom Van Flandern <tomvf@metaresearch.org>
==========
(1) NEAR EARTH OBJECTS IN THE HOUSE OF COMMONS: UK GOVERNMENT
RESPONSE
EXPECTED SOON
>From House of Commons, 13 December 2001
http://www.parliament.the-stationery-office.co.uk/pa/cm200102/cmhansrd/cm011213/text/11213w01.htm#11213w01.html_sbhd5
Near Earth Object Task Force
Ann Keen: To ask the Secretary of State for Trade and Industry if
she will
make a statement on the Government's response on 24 February to
the
recommendations contained in the report of the Near Earth Object
Task Force.
Ms Hewitt: An updated response is nearing completion and will be
published
shortly. Copies will be put with the report and the Government
response
which were placed in the Libraries of both Houses. A copy of this
response
and press release will also be found at www.nearearthobjects.co.uk
==============
(2) ONE ASTEROID CAN RUIN YOUR DAY
>From Wired News, 14 December 2001
http://www.wired.com/news/print/0,1294,49124,00.html
By Mark K. Anderson
Robert Duvall, Bruce Willis and Sean Connery have all had
cinematic bouts
with "planet killer" asteroids, but the actual hazard
such interplanetary
cannonballs pose is both more gradational and more uncertain than
Hollywood
portrays.
The more likely threat from collisions with asteroids and comets
comes not
from chunks of space rock the size of Texas, as in the movie
Armageddon, but
rather from objects mere tenths of a mile across, which are
harder to find
and track.
This is one of the subjects to be covered Friday when Britain's
Royal
Astronomical Society hosts a symposium in London in an attempt to
jump start
the U.K.'s involvement in the search for Near Earth Objects.
The last planet killer came 65 million years ago and wiped out
the
dinosaurs. Yet these objects -- roughly the size of a small city
-- are now
thought to collide with Earth only once every hundred million
years.
When they do, of course, they are what Grant Stokes of MIT's
Lincoln Lab
euphemistically calls an "evolutionary reboot."
On the other hand, it was less than a hundred years ago that a
football
field-sized asteroid or comet exploded into the atmosphere over
Tunguska,
Siberia, yielding a blast many times more powerful than the
atomic bomb that
flattened Hiroshima.
Since the region was unpopulated, the casualties of the Tunguska
event were
mostly trees and forest wildlife. The chance of a Tunguska-like
impact
happening again during any given year is now estimated at one in
250.
"A hundred-meter sized object could kill a city," said
Mark Bailey of the
Armargh Observatory in Northern Ireland. "When you look at
the actuarial
risk, it would pay you to seek out asteroids as small as one or
two hundred
meters across."
The U.S. now leads the worldwide hunt for Near Earth Objects,
spending a
million dollars a year on telescopes in New Mexico, Arizona,
California and
Hawaii. This program has to date found more than 700 asteroids or
comets
whose orbits brush close to the Earth's.
But these new discoveries are heavily weighted toward the planet
killer end
of the spectrum. It's still unknown how many nearby chunks of
space rock or
stray comet fragments there are that, if they fell to Earth,
could cause a
"sub global event."
"If anything, getting hit in the ocean is worse than getting
hit on land,
especially for the smaller objects," said Duncan Steel of
the University of
Salford, U.K. "Something two or three hundred yards across
would generate a
tsunami which would really be fatal for the cities on the
coastline around
it."
According to a recent British government report (PDF), the
telescopes now
hunting and tracking Near Earth Objects work well in studying
potential
planet killers. But to find and follow the smaller and more
populous sub
global event objects, larger telescopes would be required.
"As it took with the terrorism business, it takes a nasty
event to bring
people to their senses," said Brian Marsden of Harvard's
Minor Planet
Center. "One of these days we'll get another Tunguska, and
then people will
think about putting some money into this."
Stokes of MIT, the principal scientist behind the most successful
Near Earth
Object hunter to date -- a NASA/Air Force telescope called Linear
--said the
Near Earth Object programs are good science as well as good
insurance.
"It's worthwhile doing," he said. "But if you
asked me about the dangers to
the life of me and my children, I'm much more likely to perish
driving on
Route 128 than I am in an asteroid hit.
"I do not expect us to find a large object on a collision
course with Earth.
That would be against the odds. But if there is one, by some
chance, you
really want to know."
Copyright © 1994-2001 Wired Digital Inc. All rights reserved.
=============
(3) THEY COME FROM OUTER SPACE
>From The Independent, 14 December 2001
http://news.independent.co.uk/uk/science/story.jsp?story=109928
Worried about an asteroid strike destroying our planet? Well, you
should be,
says Ian Brown. Scientists believe the danger is all too real
Humanity could one day be caught between a rock and a hard place
- and it
just could be a very large fast-moving rock. The potentially
catastrophic
threat posed to humanity by an asteroid colliding with the Earth
is to be
discussed at a meeting today of the Royal Astronomical Society in
London.
This is not the stuff of purely academic debate or Hollywood
science
fiction. Last year, the Government set up a Task Force on
Potentially
Hazardous Near Earth Objects to consider the threat. This made 14
recommendations for action, including some thoughts on what are
the options
for deflecting any object on a collision course with Earth.
Meanwhile, both Europe and America aim to take a much closer look
at the
problem. Among today's speakers, Marcello Coradini of the
European Space
Agency will explain Europe's plans to study the physical nature
of asteroids
and comets. The American National Aeronautics and Space
Administration
(Nasa) has several spacecraft either already in space or planned
for launch
within the next few years.
Europe's Rosetta mission, the first probe aiming to orbit a
comet, is
scheduled for launch in 2003. GAIA, a space telescope due for
launch around
2010, will be able to detect asteroids as small as 500 metres
wide. Another
probe, called BepiColombo, will also be able to search for
unknown asteroids
between the Sun and Earth although its main destination is
Mercury. These
Near Earth Objects (NEOs) are particularly dangerous, since they
can
approach the Earth from the direction of the Sun, and so be
masked by its
glare.
Today's meeting will also discuss how British astronomers and
researchers
will work with the international Spaceguard programme, and how
the asteroid
hazard ranks against other large-scale potential disasters (such
as nuclear
power station accidents).
One of the meeting's organisers, Duncan Steel, a physicist from
Salford
University, says that this is astronomy close to home. "Only
recently has
the importance of comets and asteroids to our own planet been
recognised,"
Steel says. "But quite apart from potential impact
catastrophes, NEOs are
worlds in their own right. Studying them is becoming a central
feature of
solar system exploration. The next few years promise a wealth of
interesting
information on asteroids and comets."
Steel is urging governments around the world to take the issue
more
seriously. "The UK has the expertise in astronomy. We have
the telescope
facilities in the Canaries, Hawaii and elsewhere that would be
ideal in
making a contribution to a wider international effort. This is
something to
be taken very seriously, but nothing has been done," he
says.
Millions of asteroids and comets orbit our Sun, but only a tiny
fraction
approach the Earth. Don't breath a sigh of relief yet, though.
These objects
range in size from pebbles to mountains. And because they travel
at very
high speed even the medium-sized objects pose a potential danger.
At
present, 291 potentially hazardous asteroids have been firmly
detected. But
astronomers estimate that there are between 750 and 1,100
near-Earth
asteroids bigger than one kilometre, the minimum size thought to
pose
catastrophic risk.
Such objects, of course, have collided with Earth since its
formation. Some
brought the carbon and water which made life possible. Others
caused
widespread changes in the Earth's surface and climate. It is now
generally
accepted that a 10-kilometre asteroid killed the dinosaurs 65
million years
ago.
In 1994, astronomers were treated to a rare - and sobering -
direct glimpse
of the devastation caused by such impacts. Thankfully it wasn't
here on
Earth. They were watching fragments of Comet Shoemaker-Levy 9
bombard
Jupiter in a cataclysmic display of cosmic violence.
The amount of damage caused by a NEO's impact with Earth would
depend on its
size. In 1908, an asteroid or comet 50 metres across exploded
above Siberia,
devastating a vast but uninhabited forest. Such an impact over a
city would
have instantly levelled it. An asteroid over one kilometre would
release
energy equivalent to 10 million times the power of the Hiroshima
atomic bomb
and wreak global catastrophe. The report of the UK's Task Force
questions
how prepared we are to address the risk. "The threat from
Near Earth Objects
raises major issues," it says, "among them the
inadequacy of current
knowledge, confirmation of hazard after initial observation,
disaster
management (if the worst came to the worst), methods of
mitigation including
deflection, and reliable communication with the public."
The Task Force, led by Harry Atkinson, a former chairman of the
European
Space Agency council, was specifically asked to confirm the
nature of the
hazard; the potential level of risk; and advise on what further
action
should be taken.
His report concludes: "Discussions of this global problem
with the US
Department of Defence, Nasa, ESA and the UK Defence Evaluation
and Research
Agency have thus far provided no clear position on what should be
done,
although it is clear that the highest priority lies in the
provision of
improved observation to provide the maximum possible warning
time."
There are two main options for deflecting NEOs, the Task Force
says. Launch
one or more small spacecraft many years in advance of the
predicted
impact-date to rendezvous with and gently "nudge" the
NEO away from its
collision course. Or last-minute deflection using high energy
explosive
devices - "the use of which would need to be very carefully
considered," it
adds, with very British understatement. "Mitigating any
impact by deflection
would appear to be a more attractive option than break-up, since
the latter
might well result in a greater number of smaller NEOs to cope
with
worldwide," it adds.
The risk from comets is estimated to be between 10 and 30 per
cent of that
from asteroids - but the advance warning period for a potential
impact from
a long-period comet may be as short as a year compared to decades
or
centuries for asteroids.
At present, the British National Space Centre is to take the lead
in
Whitehall policy on the threat posed by NEOs. But the Government
is also
looking into the options for a dedicated British Centre for Near
Earth
Objects. The successful applicant is expected to be announced any
day now.
Duncan Steel, however, is not impressed: "The only remit of
this centre is
to give information, not do any research," he said. "We
have to stop talking
and start taking action."
Copyright 2001, The Independent
============
(4) WAS LIFE ON EARLY EARTH NEARLY WIPED OUT BY MASSIVE IMPACTS?
>From Andrew Yee <ayee@nova.astro.utoronto.ca>
News Service
Stanford University
Stanford, California
Contact:
Mark Shwartz, News Service
(650) 723-9296; e-mail: mshwartz@stanford.edu
12/14/01
Geophysicist studies life in the early solar system
By Etienne Benson
Between the cataclysmic impact that created the Moon around 4.5
billion
years ago and the first evidence of life 3.8 billion years ago,
there may
have been long periods during which life repeatedly spread across
the globe,
only to be nearly annihilated by the impact of large
asteroids.
The early Earth, in other words, may have been an interrupted
Eden -- a
planet where life repeatedly evolved and diversified, only to be
sent back
to square one by asteroids 10 or 20 times wider than the one that
hastened
the dinosaurs' demise. When the surface of the Earth finally
became
inhabitable again, thousands of years after each asteroid impact,
the
survivors would have emerged from their hiding places and spread
across the
planet -- until another asteroid struck and the whole cycle was
repeated.
"We know that large asteroid impacts can sterilize or
partially sterilize
planets," says Norman Sleep, a professor of geophysics at
Stanford who will
present the theory at the fall meeting of the American
Geophysical Union in
San Francisco on Friday, Dec. 14.
"An asteroid a few hundred kilometers in diameter will boil
off much of the
ocean and leave the rest of the ocean very hot, so all that will
survive
will be high-temperature organisms living deep in the
subsurface," he says.
Rock vapor and water would fill the atmosphere, killing off any
life on the
surface with temperatures upwards of 1,000 C (1,800 F).
The only organisms that could survive such an impact are
thermophiles --
heat-loving microbes -- buried half a mile or more below the
Earth's
surface, where the effects of the burning atmosphere would have
been muted
to a survivable 100 C (212 F). Those organisms may have given
rise to much
of the life on today's Earth.
Sleep calls the region where those organisms would have lived the
"Goldilocks Zone" -- deep enough for microbes to avoid
the heat of the
burning atmosphere, but not so deep that they ran afoul of the
Earth's
internal heat.
Since there are no records of life before 3.8 billion years ago,
there is no
direct proof that Sleep's theory is correct. But several strands
of evidence
are highly suggestive.
The first is that two of the three major branches of life that
exist on
Earth today -- Archaea, Bacteria and Eukarya -- began with
organisms that
were designed to live in extremely hot environments, the kinds
that would
have existed for millions of years after the impact of a large
asteroid.
A glance at the names of modern members of the Archaea and
Bacteria branches
turns up an overwhelming number of "thermos" --
Thermococcus, Thermotoga,
Thermoproteus and others. All of them thrive at temperatures
above 80 C (176
F), with some managing to eke out an existence in conditions that
would
literally boil most organisms alive. (The current record-holder
can survive
in environments above 115 C [239 F], says Sleep.)
"The roots of these two branches of the tree are clearly
thermophile, which
is exactly what's going to survive in a large impact," says
Sleep.
Where Eukarya -- the branch that includes yeast, worms, corn and
humans --
fits into the story is less certain. "It's unclear whether
Eukarya, which we
are, has a thermophile root or not," says Sleep. "We
may never have had a
high-temperature-organism ancestor. But clearly two of the three
branches
look like asteroid survivors: very complex, highly-evolved
organisms that
are thermophile."
The second strand of evidence is geophysical. Although it has
long been
thought that early Earth would have been rendered lifeless by
continual
asteroid bombardment, there are now good reasons to believe that
our planet
was struck by fewer than 20 large asteroids between the time of
the
Moon-forming impact and the first fossil signs of life. That
would leave
hundreds of millions of years between each asteroid strike,
during which
complex organisms -- and life itself -- would be free to evolve.
When asteroids did strike, only those organisms that could find
some kind of
shelter would have survived. The most obvious refuge is deep
within the
Earth itself, but Sleep believes there may have been another,
more exotic
way for early organisms to survive such Earth-shattering
catastrophes.
Martian invaders
Perhaps, says Sleep, some of the asteroids that struck the early
Earth were
large enough to destroy all life on the planet, even those
organisms hidden
deep within the crust. There was still at least one other place
where life
could have survived, even flourished, before
returning to Earth: Mars. Although Mars is now a frigid desert,
four billion
years ago it may have been a warm, water-filled oasis as friendly
to life as
early Earth.
But could a microorganism really have survived the trip from
Earth to
Mars? To successfully complete the interplanetary journey, a
microbe
first would have to survive an asteroid impact powerful enough to
free a
chunk of rock from the grip of gravity. Once in space, the
traveler would be
faced with conditions harsher than anything found on Mars or
Earth: total
vacuum, subzero temperatures, harmful radiation and the passage
of perhaps
thousands of years before the interplanetary dart hit its target.
Even then,
the colonizing microbe would have to hope that some of its
descendants were
buried deep enough in the rock to avoid burning up in Earth's
atmosphere.
Sleep says these factors make the trip difficult, but not
impossible. Models
have shown that the initial shock of ejection from a planet isn't
necessarily deadly, especially for the hardiest microbes, and
especially
from a small planet like Mars where the atmosphere is thin and
gravity is
relatively weak. "You don't sterilize a milk bottle by
throwing it off your
roof," he explains.
And laboratory experiments have shown that earthly microbes,
especially if
hidden in cracks deep within a meteorite, can survive the harsh
conditions
of space at least for a few years. Of course, no one has tested
whether they
can survive for thousands of years, but there's no reason to
think they
can't, notes Sleep. "Conditions are not good for
microorganisms, but they're
not bad," he adds.
So it is possible that life came from another planet -- but did
it really
happen? So far there is no direct evidence of life on other
planets or
asteroids, although it is becoming clear that conditions exist,
at least on
Mars and Europa -- one of Jupiter's inner moons -- where microbes
that live
comfortably in Earth's harsher climates would have felt at home.
As Sleep
put its, Mars "is no more uninhabitable than
Antarctica" -- uncomfortable
for humans, but perfect for some microbes.
Conclusive evidence for or against the theory only will come when
scientists
can examine samples from other planets and asteroids, something
that is
still a long way off. But Sleep says he's not frustrated by the
sometimes
slow pace of studying early life.
"The origin of life is one of the fundamental problems of
science, and it
always has been. Living at a time when you can do that, it's not
something
I'm going to pass up," he says.
###
COMMENT:
Norman Sleep, Geophysics, (650) 723-0882, norm@pangea.stanford.edu
EDITORS: This press release was written by science writing intern
Etienne
Benson. The American Geophysical Union will hold its annual fall
meeting
Dec. 10 to 14 at the Moscone Convention Center, 747 Howard
Street, San
Francisco, CA 94103. Prof. Norman Sleep will give the opening
talk at AGU
Session U51A, "Origin and Early Evolution of the Earth
I," on Fri., Dec. 14,
8:30 a.m. PT in Room 134. For more information, visit the AGU
website at
http://www.agu.org .
Relevant Web URLs: http://geo.stanford.edu/GP/sleep.html
==============
(5) LEONID METEOR HIGH-SPEED IMAGING
>From Andrew Yee <ayee@nova.astro.utoronto.ca>
[Extracted from Leonid Multi-Instrument Aircraft Campaign (MAC)
website,
http://leonid.arc.nasa.gov/recent_updates6.html]
December 11, 2001
METEOR HIGH-SPEED IMAGING
High speed imaging has now for the first time shown details in
the head of a
meteor that reveil the dimensions and shape of the sources of
light that
make a shooting star. In a series of unique images obtained by
Leonid MAC
participant Prof. Hans Stenbaek-Nielsen of the University of
Alaska, a
meteor is seen to develop from a ball of light into a an object
with a bow
shock and a tail. These results were unveiled in a standing-room
only
special session "The 2001/2002 Leonid meteor storms" at
the Fall Meeting of
the American Geophysical Union in San Francisco on December 11,
2001.
Prof. Nielsen used an unusual intensified high frame-rate camera,
specially
designed for sprite observations. This camera records video
images at a rate
of 1000 frames per second. Nielsen, a Danish national, observed
from a site
at Pokers Flat, Alaska, and had to continually watch a video
screen to catch
the meteor in flight. The images shown above are frames #200, 300
and 400
from a 463 millisecond sequence of a bright Leonid meteor at
10:48:59 UT,
November 18. These are false-color images. The originals are in
black-and-white
only. The red color is chosen arbitrarily to highlight contrast.
The frames are cropped in
horizontal direction. The vertical field of view is about 6
degrees.
The meteor starts as a very localized ball. Then it brightens and
develops a
tail, and one can clearly see the shock set up around the front.
"Our images for the first time confirm that most meteor
light comes from a
bright plasma just behind the meteoroid," says Leonid MAC PI
Dr. Peter
Jenniskens of the SETI Institute at NASA Ames Research Center.
This confirms
conclusions made indirectly from spectroscopic studies in prior
Leonid MAC
missions. "The images now provide dimensions of the gas
cloud behind the
meteoroid", says Jenniskens, "and tell us how long
organic molecules have to
endure a hot plasma before cooling down". Just behind the
gas cloud, a wake develops
that is thought to be due to green forbidden line emission of OI
at 557.2 nm.
Jenniskens believes that the bow shock may be a consequence of
the vapor
cloud of ablated material surrounding the meteoroid growing to
sizes larger
than the mean-free path in air at altitude. "This emission
may be
responsible for some of the ionised emissions of Mg+ and Ca+ that
are
observed in bright Leonids", he says, "more so when the
meteoroids are
larger". The pictures for the first time show the meteor's
bow shock.
The special Leonid storm session was organised by Jenniskens in
collaboration with Prof. Chet Gardner of the University of
Illinois.
Presentations included this and other first results of the 2001
Leonid
campaign, new modeling of meteor physical processes, studies of
the erosion
of organic matter in meteoric plasma, the expected mass
distribution of
Leonid meteoroid fragments, and the announcement that tiny 1 nm
sized dust
grains of recondensed vapor may now have been detected in the
upper
atmosphere.
[NOTE: Images supporting this release are available at
http://leonid.arc.nasa.gov/recent_updates6.html]
==========
(6) NASA BIDS FAREWELL TO THE SUCCESSFUL DEEP SPACE 1 MISSION
>From NASANews@hq.nasa.gov
Donald Savage
Headquarters,
Washington
Dec. 17, 2001
(Phone: 202/358-1727)
Martha J. Heil
Jet Propulsion Laboratory Pasadena, Calif.
(Phone: 818/354-0850)
RELEASE: 01-246
NASA BIDS FAREWELL TO THE SUCCESSFUL DEEP SPACE 1 MISSION
NASA's adventurous Deep Space 1 mission, which successfully
tested 12
high-risk, advanced space technologies and captured the best
images ever
taken of a comet, will come to an end Dec. 18, 2001.
"American taxpayers can truly be proud of Deep Space
1," said Dr. Colleen
Hartman, Director of NASA's Solar System Exploration Division,
Washington.
"It was originally designed to be an 11-month mission, but
things were going
so well that we kept it going for a few more years to continue
testing its
remarkable ion engine and, as a bonus, to get close-up images of
a comet. By
the time we turn its engines off tomorrow, Deep Space 1 will have
earned an
honored place in space exploration history."
Shortly after 3 p.m. EST Tuesday, engineers will send a final
command
turning off the ion engine, which has used up 90 percent of its
xenon fuel.
After Earth's final goodbye, the spacecraft will remain in orbit
around the
Sun, operating on its own. Its radio receiver will be left turned
on, in
case future generations want to contact the spacecraft.
"Deep Space 1 is a true success story," said Dr.
Charles Elachi, director of
NASA's Jet Propulsion Laboratory (JPL), Pasadena, Calif. "We
are proud that
future generations of spacecraft will benefit from its
accomplishments."
Deep Space 1 leaves the technologies it flight-tested as legacies
for future
missions, which would have been impossible without its
trailblazing
technology tests. Enabling spacecraft to travel faster and
farther than ever
before, Deep Space 1's ion engine was once a science fiction
dream. Now this
ion engine has accumulated over 670 days of operating time.
Future Mars
missions may use this technology to return samples from the Red
Planet.
Deep Space 1's successful test of autonomous navigation software
was a major
step in the path of artificial intelligence for spacecraft. Using
images of
asteroids and stars collected by the onboard camera, the
spacecraft was able
to compute and correct its course without relying on human
controllers on
Earth. NASA's Deep Impact mission will use a system based on
autonomous
navigation to reach the nucleus of comet Tempel 1.
Within nine months after launch, Deep Space 1 had successfully
tested all 12
new technologies. As a bonus, near the end of the primary
mission, Deep
Space 1 flew by asteroid Braille. In late 1999, its primary
mission
complete, Deep Space 1's star tracker failed to operate. So in
early 2000,
engineers successfully reconfigured the spacecraft from 185
million miles
(300 million kilometers) away to rescue it for a daring extended
mission to
encounter comet Borrelly.
In September 2001, Deep Space 1 passed just 1,349 miles (2,171
kilometers)
from the inner icy nucleus of comet Borrelly, snapping the
highest-resolution pictures ever of a comet. The daring flyby
yielded new
data and movies of the comet's nucleus that will revolutionize
the study of
comets.
Launched on October 24, 1998, Deep Space 1 was designed and built
in just
three years, the shortest development time for any interplanetary
spacecraft
NASA has flown in the modern age. It was the first mission in
NASA's New
Millennium program. In addition to its technical achievements,
Deep Space 1
is an ambassador of Earthlings' goodwill, carrying with it a
compact disc of
children's drawings and engineers' thoughts.
"I'm not sad it's ending, I'm happy it accomplished so
much," said Dr. Marc
Rayman, Deep Space 1 project manager at NASA's Jet Propulsion
Laboratory,
Pasadena, Calif. "I think it inspired many people who saw
the mission as
NASA and JPL at our best -- bold, exciting, resourceful and
productive."
JPL, a division of the California Institute of Technology,
Pasadena, manages
the mission for NASA's Office of Space Science, Washington.
Spectrum Astro
Inc., Gilbert, Ariz., was JPL's primary industrial partner in
spacecraft
development.
Additional information on Deep Space 1 is available at:
http://nmp.jpl.nasa.gov
=============
(7) DEEP SPACE 1 SOWS COMET SENSE
>From Ron Baalke <baalke@jpl.nasa.gov>
http://www.nature.com/nsu/011220/011220-5.html
Space probe shows comet sense
Deep Space 1 reveals Borrelly's dark secrets.
TOM CLARKE
Nature Science Update
December 14, 2001
A state-of-the-art space probe has shed new light on what may be
the darkest
object in the Solar System.
The potato-shaped comet Borrelly, although less showy than its
better-known
cousin Halley, is turning out to be something of an enigma,
researchers told
this week's meeting of the American Geophysical Union in San
Francisco.
Bad behaviour
As if Borrelly's blackness wasn't enough, other DS-1 data suggest
that it is
also behaving very strangely for a comet.
The Sun's heat boils off ice, other chemicals and dust trapped in
comets. On
bodies such as Halley, these emissions occur evenly. But jets of
material
spew out from patches in Borrelly's narrow middle section.
"They look just
like nozzles," says Laurence Soderblom of the US Geological
Survey in
Flagstaff, Arizona.
Full story here:
http://www.nature.com/nsu/011220/011220-5.html
================
(8) DID ANCIENT CIVILISATIONS COLLAPSE DUE TO LARGE EARTHQUAKES?
>From Andrew Yee <ayee@nova.astro.utoronto.ca>
News Service
Stanford University
Stanford, California
Contact:
Mark Shwartz, News Service
(650) 723-9296; e-mail: mshwartz@stanford.edu
12/13/01
Ancient civilizations shaken by quakes, say Stanford scientists
By Etienne Benson
Archaeology sometimes raises more questions than it answers. How
do you
explain a city that bustled with activity one day only to be
buried under
feet of silt the next? Or walls that collapsed in an instant,
crushing the
people standing next to them? Or rows of heavy stone columns, all
toppled in
the same direction?
Until recently, most researchers trying to explain these
enigmatic disasters
pointed to wars, fires or flash floods -- or simply shrugged
their shoulders
and kept digging.
But new research by geophysicists at Stanford and elsewhere is
painting a
picture of an ancient world in which earthquakes destroyed
fortified
buildings, changed the course of rivers and made elite rulers
vulnerable to
attack.
One of the proponents of that picture is Amos Nur, the Wayne Loel
Professor
of Earth Sciences at Stanford, who will moderate a session on the
impact of
natural disasters on ancient civilizations at the fall meeting of
the
American Geophysical Union on Dec. 14. Robert Kovach, a professor
of
geophysics at Stanford, will co-moderate the session.
Ancient quakes
The idea that ancient civilizations were shaped by earthquakes is
still
controversial, but a growing number of archaeologists and
geophysicists
believe that earthquakes might have intervened at crucial moments
in
history.
Nur's research on the ancient city of Megiddo, also known as
Armageddon,
provides one example. By studying ancient texts and
archaeological evidence,
Nur demonstrated that earthquakes, and not repeated conquests,
could have
been responsible for the city's sandwich-like layers of ruined
buildings.
Other research suggests that earthquakes -- caused when fault
lines release
built-up tension -- could have done more than just level cities;
they may
have brought down civilizations as well. According to Nur, storms
of
earthquakes raging over periods of 50 to 100 years might have
helped bring
the Bronze Age to an end.
In hierarchical societies where wealth was concentrated in the
hands of a
few well-fortified elites, says Nur, earthquakes that toppled
columns and
cracked walls could have instantly changed the balance of power.
That would
have been especially true during times of war or revolt.
The Harappan enigma
Manika Prasad, a research associate in the Rock Physics
Laboratory at
Stanford, has helped expand the study of ancient earthquakes
beyond the
Eastern Mediterranean. Together with Nur, Prasad is
studying the contribution of eartquakes to the collapse of the
Harappan
civilization in South Asia.
The Harappan civilization mysteriously disappeared in 1900 BC,
after almost
2,000 years of continuous existence. Some researchers have argued
that the
civilization slowly declined because of changing trade patterns;
others, now
mostly discredited, blamed Aryan invaders from the north.
Prasad and Nur blame earthquakes. Last January, a catastrophic
earthquake
struck the southern edge of the former Harappan territory, a
coastal area
near the border between India and Pakistan. In 1819, a similar
earthquake
raised an 80 to 100-kilometer (50 to 62 mile) ridge of earth
about 20 feet
(6 meters), creating an artificial dam known as the "Allah
Bund" (God's
Dam). Both earthquakes are evidence that the Harappan region,
though not
near a traditional fault zone, is seismically active.
The evidence of seismic activity in the region, combined with the
recent
discovery of an ancient riverbed at the center of the former
Harappan
region, offers a possible explanation for the
civilization's decline.
Four millennia ago, one or more quakes could have blocked or
diverted the
water that flowed through the riverbed, say Prasad and Nur. That
would have
helped turn the part of the Harappan region into the desert it is
today --
and destroyed the Harappan civilization in the
process.
The collapse of the Mayan Classic Period
While Nur has focused on the Mediterranean and, more recently,
Harappan
civilizations, Stanford Professor of Geophysics Robert Kovach has
been
studying the role of earthquakes in the Mayan
civilization of Central America.
When the Mayan Classic Period ended in the late 9th century A.D.,
the cities
of Quirigua and Benque Viejo (Xunantunich), now located in
Guatemala and
Belize, were suddenly abandoned. According to Kovach, the cities
could have
been destroyed by a single earthquake centered on the
Chixoy-Polochic and
Motagua fault zones.
But evidence for earthquake damage in Mesoamerica is harder to
come by than
in the Mediterranean. Documents that can be mined for hints about
ancient
catastrophes are rare, and tropical vegetation quickly overwhelms
any
archaeological evidence that might point to a major temblor.
With the help of Bernabe Garcia, a former graduate student at the
Stanford
Center for Latin American Studies, Kovach was able to piece
together
evidence of past quakes by looking at the effects of recent
quakes on
structures at archaeological digs. The evidence suggested that an
earthquake
struck the Mesoamerican region in the late 9th century, just as
the Mayan
Classic Period was collapsing. Like Nur, Kovach thinks the
Mayans' rigidly
hierarchical society could have made the quake especially
damaging.
Other research
Despite growing evidence of the effects of ancient earthquakes,
some
researchers remain skeptical. Iain Stewart, a geologist at Brunel
University
in England, will argue at Friday's AGU session that earthquake
damage is
hard to distinguish from the effects of poor construction, ground
instability or human intervention.
Other researchers, however, have warmed to the idea that
earthquakes may be
a missing piece of the archaeological puzzle. At the AGU session,
Italian
geologist Luigi Piccardi will present research linking
earthquakes to
ancient Mediterranean sanctuaries such as the temple at Delphi.
Erhan
Altunel of Osmangazi University in Turkey will propose that
massive
earthquakes may have helped destroy several ancient Turkish
cities. And
Italian researcher Emanuela Guidoboni
will present a case study of two ancient earthquakes that led to
the
collapse of temples in Sicily.
According to Prasad, the spread of geographical information
systems
technology, which allows different types of data to be integrated
into a
single map, should make the study of ancient earthquakes
increasingly easy.
"A lot of information is out there," she says.
"It's just a matter of
piecing it together."
###
COMMENT:
Amos Nur, Geophysics (650) 723-9526, nur@pangea.stanford.edu
Robert Kovach, Geophysics (650) 723-4827, kov@pangea.stanford.edu
EDITORS: This press release was written by science writing intern
Etienne
Benson. The American Geophysical Union will hold its annual fall
meeting
Dec. 10 to 14 at the Moscone Convention Center, 747 Howard
Street, San
Francisco, CA 94103. Prof. Amos Nur and Prof. Robert Kovach will
moderate
AGU Session U52B, "Archaeological Evidence for Historic and
Prehistoric
Earthquakes and Volcanic Eruptions and Their Impact on Human
Settlements,"
on Fri., Dec. 14, 1:30 p.m. PT in Room 134. The media are invited
to attend
an advance press briefing with Prof. Nur and Prof. Kovach on
Thurs., Dec.
13, 3:00 p.m. in Room 112. For more information, visit the AGU
website at
http://www.agu.org .
Relevant Web URLs:
* http://srb.stanford.edu/nur/
* http://pangea.stanford.edu/~kov/kovach-home-page.html
* http://www.agu.org/
===========
(9) HYPERVELOCITY IMPACT SYMPOSIUM
>From Ron Baalke <baalke@zagami.jpl.nasa.gov>
http://www.estec.esa.nl/conferences/hvis2003/index.html
HVIS 2003
Hosted by the European Space Agency's Research &
Technology Centre (ESTEC)
7-10 April 2003
Grand Hotel Huis ter Duin
Noordwijk, The Netherlands
The Hypervelocity Impact Symposium is a regular event that is
dedicated to
enabling and promoting an understanding of the basic physics of
high
velocity impact and related technical areas. This international
event
provides a forum for researchers to share and exchange a wealth
of knowledge
through oral and poster presentations and technical exhibits.
HVIS 2003 will be the eighth symposium in a series. It will be
hosted by
ESTEC and held in Noordwijk, The Netherlands. The dates of the
conference
coincide with the tourist season in the bulb district and
Noordwijk is
located in this district.
The technical sessions will be held at the Grand Hotel Huis ter
Duin,
Noordwijk during April 7-10, 2003.
All papers presented at the Symposium will be published in a
refereed volume
of the International Journal of Impact Engineering.
Symposium topics
* Hypervelocity phenomenology studies
* High-velocity launchers and diagnostics
* Spacecraft meteoroid and debris shielding and
failure analysis
* Material behaviour under high velocity impacts
* Fracture and fragmentation
* High velocity penetration mechanics and target
response
* Analytical and numerical simulation techniques
* Asteroid impact and planetary defence technology
* Penetration mechanics of shaped charges and
explosively formed
penetrators
* Planetary impacts
Call for papers
Abstract of proposed papers are solicited from those actively
interested and
involved in hypervelocity impact. The preferred method of
submitting
abstracts is using the form on this web site.
If it is not possible to submit your abstract through the web
site, it may
be submitted by e-mail as an attachment or by mailing a printed
copy, along
with a diskette copy to the following address:
HVIS 2003
ESTEC Conference Bureau
Postbus 299
NL-2200 AG Noordwijk
The Netherlands
Tel: +31-71-565-5005
Fax: +31-71-565-5658
E-mail: confburo@esa.int
Abstract must be received no later than May 15, 2002
Authors will be notified in June 2002 of the review decision for
their
proposed paper. An author's packet will be mailed to authors
whose abstracts
are accepted.
Acceptance of an abstract indicates preliminary acceptance of a
paper for
publication in the International Journal of Impact Engineering,
subject to a
technical peer review with final recommendation on the basis of
such review.
Abstract Guidelines
* Abstracts should be at least 500 words plus
figures and references.
* The official language is English.
* Abstracts must be cleared for public release with
unlimited
distribution. An abstract booklet of
accepted papers will be
distributed at the symposium.
* Include name, address, affiliation, phone number,
fax number and e-mail
address of the primary author.
* Indicate author's preference for oral or poster
presentation
* Indicate appropriate topic.
Commercial Exhibits
Commercial Exhibits will be on display during the entire
symposium giving
attendees ample opportunity to meet with company representatives.
Companies
interested in exhibiting should contact the ESTEC Conference
Bureau, P.O.Box
299, 2200 AG Noordwijk, NL. Tel.. +31 71 5655005, Fax: +31 71
5655658,
e-mail: confburo@esa.int
Schedule
August 2001 Abstract 1st call
January 2002 Abstract 2nd call
May 2002 Abstracts due
June 2002 Notification to
authors
September 2002 Papers due for review
October 2002 Preliminary Programme and
Registration details
February 2003 Deadline for Hotel Reservation
March 2003 Final papers due
April 2003 HVIS Symposium
HVIS Web site http://www.hvis.org/
============================
* LETTERS TO THE MODERATOR *
============================
(10) SEASONS GREETINGS & UPDATE
>From Andy Smith <astrosafe@yahoo.com>
Hello Benny and CCNet,
We want to wish all of you (who share the great enlightenment) a
very merry
christmas and a happy and impact-free new year.
The Watch
We have passed the 400 NEO discovery-point. This year's hunt has
already
established another record. 1998 was our first 3-digit year (204)
and each
following year has shown a significant increase. Our next goal is
the 1,000
point and we can reach that with the 6 existing search
facilities....if they
are able to operate near full-time.
The ultimate goal....which will require help from the larger
telescopes, the
construction of a special terrestrial survey system (like the 8
meter
Dark-Matter Telescope) and a few orbiting spotters....is 10,000
NEO per year
and the completion of most of this vital hunt in a decade.
LINEAR found about 61% of the new discoveries and we are all very
grateful
to the dedicated MIT and U.S. Air Force operating and management
staff folks
for their skills and dedication. The NASA/JPL NEAT team found
about 22% and
we are equally grateful to them and to the Lowell LONEOS team
(11%) and the
pioneering SPACEWATCH team (4%), for their valuable
contributions.
There are about 70 potentially hazardous asteroids (PHA) in the
total and
about 100 (25%) are wider than a kilometer.
Thanks to the CCNet Family
We have almost made it safely through another orbital
cycle....and this
network (CCN)is uniquely qualified to appreciate the significance
of that
fact. We thank all of you for your efforts and contributions.
To us, in the International Planeatry Protection Alliance (IPPA),
the age of
asteroid/comet emergency awareness and enlightenment started in
about 1990
and we see this Century as probably the most critical one in
history. We now
have both the knowledge and the equipment needed to protect
ourselves and we
are truly in a race with that rock. We are still moving much too
slowly and we still have very little political and monetary
support.
We have divided the Century into 4 phases. Phase 1 is from 1990
to 2015 and
the risk of a hit (Tunguska or larger), in this phase, is about 1
in 4 (1 in
100 per year)...a truly alarming risk, in the light of the
possible
consequences (which might include the destruction of several
major coastal
cities).
We, in the global enlightened community (EC), increased our
discovery rate,
significantly, and made some progress in the other areas
(planetary defense
and civil preparedness). Much of this progress is due to the
efforts of
volunteers from many disciplines... and we thank them all, again
and again.
Salute to Fred Whipple
David Levy wrote an excellent article about our distinguished
colleague, Dr.
Fred Lawrence Whipple, for the January issue of Sky and Telescope
magazine.
Dr. Whipple started, at the Harvard College Observatory, in 1931;
built the
organizational foundation for the Minor Planet Center; developed
the
dirty-snowball comet theory and has made many other contribitions
to the
important specialty of space surveillance. We want to thank Dr.
Comet (the
deserved name used in the Levy article) for all that he has done
and
continues to do, at a spry 95 years of age.
NASA Comet/Asteroid Protection Study (CAPS)
Leonard David wrote an excellent article, in the 12 December
issue of the
SPACE.com newsletter, about the subject study, which is being
conducted at
the NASA Langley Research Center, Hampton, Virginia (on the edge
of the
Chesapeake crater). We will be watching, with great interest, as
this
program develops. We hope they will take full-advantage of all of
the
excellent
work which has been done by our Russian and other colleagues and
that a
global team-effort will be associated with this activity.
Mayan Committee
We have formed a new working group of representatives of the
Mayan culture,
to discuss and study the events leading to the great exodus and
we will
report on our progress.
Coastal City Emergency Preparedness (CCEP)
Finally, we encourage all CCNet participants, who live in coastal
areas, to
contact the emergency
preparedness (EP) offices in their areas and to urge them to
develop rapid
tsunami evacuation plans, similar to the ones in Hawaii, Japan
and
elsewhere, on the Pacific. We will soon provide the CCNet a draft
of the
preliminary public guidelines (which we plan to submit to the EP
community).
Perhaps we can collectively sponsor an EP information service.
Public
information, community preparedness (the marking of routes, etc.)
and
evacuation training will be essential, for the saving of life in
an
asteroid/comet emergency (ACE). Please let us know, if you are
able to find
receptive EP contacts. So many of the offices we have contacted
have no
appreciation of the problem.
Double Cheers,
Andy Smith
===============
(11) THE DATE OF GERVASE'S EVENT OF JUNE 1178
>From Peter Nockolds, LONDON, UK <ASTROLIT@aol.com>
Graeme Waddington has questioned the usual reading of 'dies
Dominica"
Here we note that Hathorn has followed Stubbs in the usual
assumption that
"die Dominica" refers to a Sunday, whereas in mediaeval
(not medieval!)
monastic tradition the phrase should more correctly be rendered
as the
Lord's day and as such may refer either specifically to a Sunday
or,
generically, to any ecclesiastical feast day (which included all
sundays) in
a monastry's liturgical calendar.
His argument does not seem impossible, and indeed would resolve
the
difficulty of the Moon having been invisible if Gervase had been
referring
to a Sunday. Unfortunately although Waddington expresses his
challenge to
the 'usual assumption' regarding 'die Dominca' with some
confidence he does
not support this by citing texts other than Gervase. If he
can cite other
texts it would be helpful if he would.
Peter Nockolds
33 Vicarage Road
LONDON
SW14 8RU
===========
(12) REPLY TO PAUL WITHERS
>From Peter Nockolds, LONDON, UK <ASTROLIT@aol.com>
Reply to Paul Withers, Meteor storm evidence against the recent
formation of
lunar crater Giordano Bruno. [MAPS 36, 525-529 (2001)]
Whilst rejecting Hartung's lunar impact hypothesis Withers admits
the
possibility that the event may have been real, perhaps fitting
Nininger and
Huss's meteor transit hypothesis. In view of the problems
relating to the
date of the phenomenon he also admits the possibility of
unreliability in
the source, the medieval chronicle of Gervase. There are in fact
substantial
historical reasons for questioning the reliability of the source.
A wider reading of the chronicle might lead the modern reader to
suspect
that Gervase does not meet all the criteria of scientific
reliability. He
reports several instances of miracles [e.g. AD 1171, 1181] and
visions
[1186] and reports what is apparently an aurora borealis as three
people in
the sky, two of whom wear bishops' mitres [Oct 12
1188]. He describes
atmospheric phenomena visible across England on 29th November
1177 and links
these to the victory of Christians over Moslems at Ramleh in
Palestine which
took place four days earlier. Although many real
events may have been
reported and interpreted as omens, the concern with affirming
victories over
Islam raises the question that the whole event could have been
invented by
Gervase or others, and inserted into the chronicle.
Withers acknowledges that the Moon was not visible on the
particular night
with which he is concerned. However it would have been
visible both
Palestine and through most of the Arab world. This new Moon
marked the
beginning of the Moslem year AH 574. The supposed event took
place during
the time of the Crusades. The Moon is a well-known symbol
of Islam. The
Qu'ran contains a reference to the splitting of the Moon. The
phenomenon
described by Gervase could be interpreted as portending the
defeat of Islam.
The day in question was also the 23rd anniversary of the
coronation of
Frederick Barbarossa as Holy Roman Emperor. Accession days of
monarchs are
widely celebrated as a 'feast-day' for the monarch in question.
As Frederick
was elected to this office the coronation marks the beginning of
his reign.
At that time the Christian kingdom of Jerusalem was under threat.
Ambassadors from the kingdom were seeking help from Christian
rulers in
Europe. Frederick had fought in the unsuccessful Second
Crusade of 1145-9
and according to Runciman 'longed to do battle again with the
infidel'.
Gervase's interests were cosmopolitan: he describes European
events such as
the treaty between the Pope and Barbarossa in 1177 in some
detail. Gervase
has already related atmospheric phenomena of the previous year to
the defeat
of Moslem armies. The lunar phenomenon described for June 18th
1178 could
then be a piece of propaganda, holding the prospect of the defeat
of Islam
if Barbarossa would intervene.
Stubbs, who edited the most recent edition of the chronicle
considers that
Gervase began to assemble his chronicle in 1188. The report would
certainly
be apposite at this time. Jerusalem fell to the Moslems in 1187
and in the
following year Barbarossa set out at the head of a fresh crusade.
If this is propaganda it is not clear whether Gervase knowingly
played a
part in inventing it or whether he passed on the reports of
others in good
faith. Likewise it might not be clear if it was fabricated in
1179 or
subsequently. However there is certainly good reason to believe
that it may
be propaganda.
If this is propaganda then no astronomical explanations of this
report are
required. Astronomers who use historical chronicles as
sources of
scientific data may wish to consider such possibilities of
distortion.
Peter Nockolds
===========
(13) MOON OR CAPTURED ASTEROID?
>From Tom Van Flandern <tomvf@metaresearch.org>
Comment on CCNet 2001 December 7: (2) MOON OR CAPTURED ASTEROID?
Alan
Gilmore describes the theory that Triton is an asteroid captured
from the
"Kuiper belt". But that theory creates more mysteries
than it answers.
Two-body capture under gravitation alone is impossible under the
laws of
dynamics. Tidal capture and collision are extremely
low-probability
phenomena that require excessive fine-tuning to achieve.
Frictional capture
by a nebula around Neptune works too well: The friction continues
until
Triton crashes into Neptune unless something makes the nebula
disappear
immediately after capture. Moreover, given the similarities
between Neptune
and the other gas giant planets, why should Neptune alone have
started with
no natural, regular moons of its own when the others have four or
more?
The following article offers a more viable alternative. It is
updated from
that published in "Worlds apart", a Focal Point debate
between W.B. McKinnon
and T. Van Flandern over the origins of Pluto, Charon, and
Neptune's moons,
Sky&Tel. 82, 340-341 (1991). It is based extensively on
research reported in
"The satellites of Neptune and the origin of Pluto",
R.S. Harrington and
T.C. Van Flandern, Icarus 39, 131-136 (1979).
On the Origin of Pluto and Triton
By Tom Van Flandern <tomvf@metaresearch.org>
[Meta Research <http://metaresearch.org>]
Background
Three of the four gas giant planets in the outer solar system,
Jupiter,
Saturn, and Uranus, all have natural satellite systems which
resemble
miniature planetary systems. Ignoring captured asteroids, these
planets each
have four or more large moons revolving in roughly circular
orbits in the
plane of their planet's equator, and in the same direction as
their planet's
spin. Especially for Jupiter and Uranus, the spacing of these
moons is
regular as well because the orbital periods are synchronous, with
ratios of
roughly 1:2:4:8.
However the orbit of the ninth planet, Pluto, crosses the orbit
of the
eighth planet, Neptune. And Neptune's two outer moons have
uniquely
irregular orbits. These two anomalies in the outer solar system
stand out,
because no other major planet or satellite crosses the orbit of
another; and
because Triton is the only major (non-asteroidal) moon in the
solar system
which revolves in the opposite direction from its planet's spin.
Neptune's
other classical moon, Nereid, has an orbit so elongated that it
is close to
the threshold of escape from Neptune into its own solar orbit.
Moreover the tilt of Triton's orbital plane to Neptune's equator,
20 degrees
(ignoring the retrograde motion), is greater than for any natural
moon of
any other planet. And Nereid's orbit is not only tilted by 27
degrees, but
so elongated that it is close to the threshold of escape.
Interestingly, Pluto's orbit also has an anomalously high
inclination at 17
degrees. Another anomaly is that Pluto has a moon, Charon, with a
diameter
half as big as its own. Such a relatively large moon of a planet
is also
unique in the solar system.
An unusual origin for these bodies is suggested by these odd
facts. Since
Pluto, Triton, and Charon are similar to each other, but
different from most
other moons in size, density, and composition, their formation
seems likely
to have something in common. Two schools of thought have arisen
about this.
The first holds that, after forming as planetesimals in solar
orbit, Triton
was captured by Neptune, and Charon was captured in a grazing
impact event
with Pluto. The second holds that, after all forming as moons of
Neptune,
something caused Pluto and Charon to escape and Triton to remain
behind in
an irregular orbit.
Scenario without improbable events
We begin our reasoning with the frequently heard conjecture that
the solar
system was originally formed with one or more additional major
planets
beyond Neptune. Occasionally over billions of years, a passing
star may
approach the Sun close enough to disrupt the orbital motion of
the Sun's
most distant and loosely bound planets. Strongly disrupted planet
orbits
will escape the solar system. Less strongly disrupted planet
orbits are
likely to cross the orbit of a planet further in. Sooner or
later, two
planets with non-resonant, crossing orbits will have a close
approach. This
remains true even if initially the orbits are inclined, because
such orbits
must precess until they eventually intersect. If the two planets
are
comparable in mass, the most probable result of a close encounter
is that
one of them gets ejected from the solar system, while the orbit
of the other
will become elongated, and cross the orbit of the next planet
further in.
This "chaos" induced in the outermost planet orbits by
passing stars must
evolve until most such planets have escaped the system.
The situation is different when any remaining outermost planet
with a
chaotic orbit is not sufficiently massive to seriously disrupt
the orbits of
regular planets further in. But it will still be massive enough
to disrupt
the satellite system of a regular planet on the occasion of any
close
approach. In our solar system, the outermost regular planet
remaining today
is Neptune.
At the US Naval Observatory in 1978, my late colleague Bob
Harrington and I
did some calculations to determine what would happen next. We
started
Neptune with a set of four regular moons in synchronous, circular
orbits in
the plane of Neptune's equator, modeled on the regular moon
systems of
Jupiter and Uranus. We then allowed hypothetical "Planet
X" candidates to
make close approaches to Neptune, and observed what happened in
the computer
to Neptune's moons.
In these trials, we learned that if the disrupting body, which we
call
"Planet X", was more massive than about 5 Earth masses,
Neptune's moons
usually escaped, and Neptune's own orbit was changed in the
process. If
Planet X was smaller than about 2 Earth masses, the disruption of
Neptune's
moons was too slight to resemble what we observe. But for
disrupter masses
between those limits, and especially near 3 Earth masses, the
hypothetical
Neptune moons were often disrupted in ways similar to what we
observe at
Neptune today: escaped moons and moons with reversed motion.
In particular, we found encounter conditions in which one of
Neptune's
regular moons was reversed in direction (as for Triton); another
was left
near the threshold of escape (as for Nereid); and yet another was
forced to
escape Neptune completely and enter a solar orbit which crossed
the orbit of
Neptune (as for Pluto). Tidal forces from Neptune would
subsequently
partially melt Triton, increasing its density, causing loss of
volatile
elements, and circularizing its orbit, just as observed.
The orbit of the escaped Neptunian moon often resembled that of
Pluto's
present-day orbit, even with its roughly 3:2 resonance of orbital
periods,
which turns out to be moderately insensitive to initial
conditions.
Interestingly, in these trials it was easily possible to get two
Neptunian
moons to escape. When that happened, the escapes were in the same
general
direction and with similar velocities. But once Pluto recedes far
from
Neptune, its own gravitational sphere of influence (within which
it can hold
moons of its own) expands to about 10 million kilometers. This
means that
any body closer than that to Pluto and roughly co-moving with it
will become
permanently trapped as a moon of Pluto. Tidal forces would then
circularize
the orbit of such a moon, bringing it closer to Pluto, and
melting and
increasing the density of Pluto and its moon in the process.
The final state would be just like what we observe: Charon is
just such an
unusually large moon of Pluto with quite high angular energy, as
if its
orbit around Pluto were once quite a bit larger than it is today.
Our
scenario predicts that both bodies were former, independent moons
of
Neptune, stripped away by Planet X; and that Charon passed from
Neptune's
sphere of influence directly into Pluto's, without ever being in
a solar
orbit of its own.
Given our starting premise of additional original planets beyond
Neptune,
there is nothing improbable about any of the subsequent events.
It seems
altogether natural that planetary systems of other stars will
have this same
characteristic, that the satellite system of their outermost
regular major
planet will have been disrupted (like Neptune and Triton), and
with some
former moons now in planet-crossing orbits (like Pluto and
Charon).
Scenarios with low-probability events
By contrast, the competing theory that Triton was captured does
require some
event of low probability to have occurred. A purely gravitational
capture,
even aided by tidal friction, is extremely improbable. If drag
through a
nebula surrounding Neptune aided in the capture of Triton, that
same nebula
would cause Triton's decay into Neptune in short order. A
collision between
Triton and a Neptunian moon is not only a low probability event,
but rather
destructive as well.
Similar remarks apply to the formation of Charon by a collision
with Pluto.
If the previous hypothetical solar orbits of these objects were
similar,
they would be forced to librate and avoid collisions; but if
dissimilar,
then collisions are of extremely low probability. Moreover
collisions
generally result in either accretion, or else destruction of the
target
body. Splitting of the target body into two stable, orbiting
bodies is
another extremely low-probability event.
In the scenario with no events of low probability we outlined
above, a
single, coherent theory provides plausible explanations for the
odd and
unique orbital characteristics of Neptune's existing moons,
Triton and
Nereid; why Neptune no longer has a normal satellite system;
where Pluto and
Charon came from; why there are virtually a "double
planet" with high
angular energy; why their orbits cross the orbit of Neptune; and
why Pluto
and Triton have high orbital inclinations and
larger-than-expected
densities.
[This paragraph was written in 1992:] Moreover the theory points
to the
intervention of a "Planet X" at some past epoch.
Unexplained perturbations
in the outer planet orbits have also suggested to some
astronomers that
another planet remains yet to be discovered. If such a body was
found, and
it had a Neptune-crossing orbit and a mass near 3 Earth-masses,
we would
consider that a virtual proof for our scenario that Pluto and
Charon are
escaped moons of Neptune.
[This paragraph was added in 2001:] Since 1992, astronomers have
discovered
a whole new asteroid belt in the trans-Neptune region, with many
of these
asteroids on Neptune-crossing orbits. Recent work on theoretical
mechanisms
in connection with the exploded planet hypothesis indicates that
disruption
of planetary interiors by a close approach to another planet is a
possible
explosion trigger mechanism. So a trans-Neptunian asteroid belt
seems
consistent with the entire scenario described here. The
hypothetical Planet
X may once have existed and disrupted Neptune's moons, been
rendered
unstable by the close approach to Neptune, and subsequently
exploded into
thousands of trans-Neptunian asteroids in solar orbits.
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