PLEASE NOTE:
*
CCNet 75/2002 - 27 June 2002
----------------------------
"Asteroid impacts produce a number of environmental insults,
several
of which are implicated in subsequent global cooling episodes.
But the
formation of planetary rings by impacts is not a possible
contributor to our understanding of these events because it is
excluded by
the laws of dynamics and physics."
--Tom Van Flandern, Meta Research, 26 June 2002
"In case you didn't notice, an asteroid barely missed
hitting earth
last week. It's okay if you didn't see it, neither did the
thousands
of scientists monitoring the skies until the asteroid had already
gone
past the earth. It was only the largest asteroid to miss earth in
over
two decades."
--Bermuda Sun, 26 June 2002
Comet
Frozen volatiles that jet in enigmatic geysers
from black mass of unknown stuff -comet!
Eager probes from planet Earth speed past
kevlar wrapped, staring, sampling, smelling
the gases, particles, molecules that glow
in skies now free from fear of unknown omens.
What's in that tiny core that masks itself
with luminous coma, streaming tails?
Mystery we hope to open up by hurling down
a copper missile from our probe to scatter
debris and provoke an outburst to reveal whatever
lurked inside that planetisimal since creation!
Malcolm Miller
27.6.2002
(1) BON VOYAGE, CONTOUR, AND HAPPY COMET CHASING
European Space Agency, 27 June 2002
(2) CHASING A COMET'S TAIL
The Guardian, 27 June 2002
(3) ASTEROIDS AND SOCCER BALLS: NEAR MISS OR NOT, THEY ALL END UP
IN THE NET
Otago Daily Times, 26 June 2002
(4) 'NO ADDITIONAL NEO TELESCOPES NEEDED ONLY UNTIL 2008': DAVE
MORRISON'S
CLARIFICATION
David Morrison, 26 June 2002
(5) TWO RECENT ASTEROID "NEAR MISSES"
Asteroid and Comet Impact Hazard, 24 June 2002
(6) NEW NEO WEBSITE
Alessandro Morbidelli <morby@obs-nice.fr>
(7) IMPACT CRATERS ON EARTH
http://www.sciencemall-usa.com/impactposter.html
(8) RE: IMPACT-TRIGGERED ICE AGES?
Mark Boslough <mbboslo@sandia.gov>
(9) Re: IMPACT-TRIGGERED ICE AGES?
John Fleck <jfleck@abqjournal.com>
(10) PLANETARY RINGS NOT A FACTOR FOR ENVIRONMENTAL COOLING
Tom Van Flandern <tomvf@metaresearch.org>
(11) AND FINALLY: THE END IS NIGH, AGAIN
Reason Magazine, 26 June 2002
==============
(1) BON VOYAGE, CONTOUR, AND HAPPY COMET CHASING
http://sci.esa.int/content/news/index.cfm?aid=13&cid=36&oid=30185
Rosetta wishes CONTOUR luck chasing comets
27-Jun-2002 Comets are suddenly in vogue in space research. ESA
is getting
ready to send its comet chaser Rosetta in January 2003 to
rendezvous with
Comet Wirtanen and study it in immense detail. Rosetta aims to
physically
drop a lander on a comet for the first time. Before that,
however, on 1 July
2002, NASA will dispatch its CONTOUR spacecraft to fly past at
least two
comets, and it has two other small comet missions planned.
What makes comets special is that they contain raw materials left
over from
the birth of the Sun and the planets. Finding out what comets are
made of
gives scientists priceless clues to both the origin of the Earth
and the
origin of life. It is also important for planning possible
defences, if a
comet should threaten to collide with the Earth, as Comet
Shoemaker-Levy 9
did with the planet Jupiter in 1994.
Comets have always been attractive to scientists and to the
general public.
However, they are elusive objects and catching one is very
difficult. For
this reason, different space projects have different aims. In
1986, two
Japanese, two Soviet and one European spacecraft flew past
Halley's Comet.
ESA's Giotto went closest to the nucleus of the comet. It sent
back
wonderful pictures and data for scientists to analyse. Although
damaged by
Halley's dust, Giotto went on to fly even closer to Comet
Grigg-Skjellerup
in 1992.
In the follow-up, ESA has one major project, Rosetta, and NASA
three small
ones, Stardust, CONTOUR, and Deep Impact. Stardust is already on
its way to
gather dust from close to Comet Wild and return it to the Earth.
CONTOUR,
leaving shortly, will make fast but very close fly-bys of Comets
Encke and
Schwassmann-Wachmann 3, investigating why comets can be so
different from
one another. Deep Impact, due for launch in January 2004, will
shoot a large
copper ball into the nucleus of Comet Tempel 1. Its fireworks
show, on 4
July 2005, will scatter subsurface comet matter into space for
analysis by
telescopes back at the Earth.
ESA's Rosetta, however, is the one milestone mission that comet
scientists
have wanted since the Space Age began. It will fly past Comet
Wirtanen, go
into orbit around its nucleus, and drop an instrumented lander on
it. Named
after the famous stone with inscriptions that held the key to
understanding
ancient Egyptian civilisation, Rosetta will cruise alongside the
comet for
17 months while Wirtanen nears the Sun. Unlike previous brief
impressions,
Rosetta promises to give us the first complete picture of a
comet's
composition and behaviour.
Comet scientists on both sides of the Atlantic are already
cooperating
fully. For example, Jochen Kissel of Germany's
Max-Planck-Institut f|r
extraterrestrische Physik is responsible for the comet dust
analysers on
CONTOUR and Stardust, as well as on Rosetta. He is a veteran of
the Soviet
and Giotto missions to Halley's Comet. The CONTOUR science team
has Gerhard
Schwehm, who is also ESA's project scientist for Rosetta.
"We're all after the same knowledge," Schwehm comments
"What we learn from
the NASA missions will help us to be even better prepared for our
big task
at Comet Wirtanen. So all of us in ESA's Rosetta team say, 'Bon
voyage,
CONTOUR, and happy comet chasing!' "
===========
(2) CHASING A COMET'S TAIL
>From The Guardian, 27 June 2002
http://www.guardian.co.uk/science/story/0,3605,744221,00.html
As another comet probe launches, Duncan Steel wonders what the
future will
bring
On Monday morning, all being well, Nasa will launch another comet
probe.
Contour is the next step in an international programme to explore
these
celestial visitors that intrigue and worry us at the same time.
Last year, Deep Space 1 returned the best-ever pictures of a
cometary
nucleus, when it flew past the comet Borrelly. Already Nasa has
its Stardust
probe en route to the comet Wild 2, and should return a sample to
Earth for
analysis in 2006. Another US probe, Deep Impact, will slam a
projectile into
comet Tempel 1 in 2005, to create a crater large enough to show
what comets
hide beneath their sooty surfaces.
Next year, the European Space Agency (ESA) will launch perhaps
the most
ambitious mission, Rosetta. The mother craft will fly alongside
comet
Wirtanen for several years, monitoring how its behaviour alters
as it gets
closer to the sun, while a small lander takes a closer look at
the surface.
ESA sent its Giotto probe to Halley's comet in 1986, accompanied
by two
Soviet and two Japanese missions.
We've come a long way since Edmond Halley predicted, in the early
18th
century, the return of his famous comet. He was correct, although
Halley
knew he would not live to see it. For the first time, comets
became
predictable, marking their departure from superstition and their
arrival in
science.
In the master list of comets maintained by astronomers, Halley's
is number
one. For shorthand, we write it as 1P/Halley, where the P stands
for
"periodic." In this case, it is visible once every 76
years.
Most comets observed are not periodic in that they tend to be
seen once
only. These are icy bodies winging in from the Oort cloud, a
reservoir of
trillions of comets that stretches a good fraction of the way to
the nearest
stars. Every so often, something nudges one out of the cloud, and
it falls
in toward the planets on a voyage that takes millions of years
before we see
it. Then it is off again, most often never to return, at least
during the
next millennium.
Next on the master list is 2P/Encke. Encke's comet shares a
characteristic
with Halley's: it is named after the mathematician who
investigated its
orbital motion. Johann Encke was born five years after the comet
was
discovered in 1786, but he showed in 1822 that it returns with
the shortest
orbital period of all, just three years and four months.
This makes comet Encke unique, because its orbit is entirely
interior to
that of Jupiter. This was a long-term puzzle, since we think that
periodic
comets are captured from elongated orbits falling from the Oort
cloud
through close approaches to Jupiter, the most massive of the
planets. How
could a comet reach an orbit that does not even cross that of
Jupiter?
Six years ago, working with David Asher of the Armagh
Observatory, I found
the solution. It is complicated and involves the combined effects
of orbits
resonant against the time Jupiter takes to circuit the sun, and
the forces
imposed by the outward jetting of evaporating ices from the
cometary
nucleus. An analogy would be that in a random search for a radio
station,
you're more likely to sweep across a frequency, and so boost the
electrical
current in the radio circuit, if you give the knob large twists.
That aside, planetary scientists have recognised for a long time
that comet
Encke is important. On a random night you might see 10 or so
meteors (or
shooting stars) per hour. Up to 90% of these derive from comet
Encke. This
comet seems to power most of the interplanetary complex of
meteoroids and
dust. Much of the 100 tons per day of cosmic debris that cascades
into our
atmosphere started out from this comet, or one of its siblings.
Apart from the random arrivals, a dozen specific meteor showers
is linked to
this comet. Those occurring during the night are seen from
October to
January, peak in November, and arrive from the Taurus
constellation. In
consequence they are called the Taurids.
The broad stream of cometary debris also intersects the Earth
between May
and July, but on the daytime side of the planet. The most intense
meteor
shower of the year is active right now, although you will not
have noticed
it. Using suitable radars, we are able to count the meteors
burning up far
above our heads.
The last time our planet was struck by any sizeable object from
space was on
the last day of June in 1908, when a 60-metre space rock blew up
over
Tunguska in Siberia. The date fits in with the daytime Taurid
showers, and
the direction it came from also coincides with what we would
expect. It is
very likely, then, that comet Encke shares its orbit with a huge
number of
pea-sized meteoroids, and also myriad larger lumps.
Comet Encke is the Contour spacecraft's primary target, scheduled
for launch
on July 1. Contour - which stands for Comet Nucleus Tour - has a
launch
window lasting just 12 seconds on Monday morning, at about 7:56
UK time.
That is shortly before 3am at Cape Canaveral. If there are any
hitches,
there are other launch opportunities on most mornings throughout
July.
Contour will fly past Encke's comet in November 2003, having used
the
Earth's gravity to send it in to the required trajectory. Next on
the agenda
is a visit to Comet Schwassmann-Wachmann 3 in 2006. Again we have
a special
reason to be interested in this object. Shortly after its
discovery by two
German astronomers, this comet flew close by the Earth in 1930,
one of the
nearest passages ever observed.
What then? The original brief called for a fly-by of comet
d'Arrest in 2008,
but comets are now discovered so frequently that it is very
likely that a
target of opportunity - a newly found, non-periodic comet - will
appear on a
trajectory that makes a rendezvous by Contour possible.
Such a target would be of scientific interest, because it would
be
unaffected by the sun. Although comets share various basic
characteristics,
we also realise they show huge diversity, contrasting with each
other just
as the animals in a zoo are all different.
Contour, along with other space probe missions, will certainly
answer many
of our questions, but will doubtless throw up many new puzzles.
Who knows
what we'll be saying about comets in a decade's time?
Duncan Steel is reader in space technology at the University of
Salford
Copyright 2002, The Guardian
==============
(3) ASTEROIDS AND SOCCER BALLS: NEAR MISS OR NOT, THEY ALL END UP
IN THE NET
>From Otago Daily Times, 26 June 2002
http://www.odt.co.nz/
MOST browsers (not wowsers) lead to the Fifa World Cup these days
and there
is rarely a web site which fails to have some reference to it.
Keeping up with the soccer frenzy has been a full-time occupation
for many,
including e-mail correspondents who use OOARS (out of office
automated
replies). I wonder what prospective clients thought of this one
from a
business address in the United Kingdom: "Watching the
soccer. Back in two
hours." Tot all that up and think of the billions it is
costing the business
world when matches occur in office hours.
There have been many near misses on goal recently but none
matched the one
out in space. There was some irony in the fact that an asteroid,
said by
scientists to be the size of a football pitch, narrowly missed
earth (by
about 120,000 km, a third the distance to the Moon) while we were
all
watching the soccer. No-one on look out? Apparently not.
Astronomers say it
is very difficult to see these lumps of rock until after they
have passed,
which is the same problem soccer goalkeepers have.
According to Nature Science Update.com, British scientists have
been trying
to find a way to help keepers predict where the ball is likely to
go in
penalty shoot-outs, after England departed the 1998 World Cup.
They offer no
advice on where asteroids are likely to strike but news sources
say people
are working on the asteroids.
Now here is a striking coincidence. Scientists looking for
asteroids and
those studying soccer penalties are colleagues at Liverpool John
Moores
University. Where soccer balls go has to do with the stance and
posture of
the striker in the split-second before he kicks, according to
Mark Williams
in a research paper. His colleague Benny Peiser, an expert on
near earth
objects said that most asteroids do not come as close as the one
last week
but noted the latest "reminder" comes as Britain tests
telescopes on the
Spanish island of La Palma to search for the objects.
"Such near misses do highlight the importance of detecting
these objects,"
he said. And so say all of us!
... All we need now are sharp-eyed goalkeepers out in space. See
if you can
guess right in tonight's soccer semifinal. Any volunteers to
stand watch for
asteroids?
BOOKMARKS
www.nature.com/ for strikes
on goalkeepers.
www.universetoday.com/
for strikes on Earth.
==============
(4) 'NO ADDITIONAL NEO TELESCOPES NEEDED ONLY UNTIL 2008': DAVE
MORRISON'S
CLARIFICATION
As posted on MPML, 26 June 2002
Jay:
Thanks for noting that I must have been misquoted in the excerpts
from the
TV interview that Benny circulated on CCNet yesterday. I would
more
accurately say I was quoted out of context, but that amounts to
nearly the
same thing.
My position on "blind spots" and such was clearly
stated in NEO News
yesterday (which Benny chose not to print). It really does not
matter
(except for radar work) whether a NEO is discovered on the
incoming or
outbound leg of its flyby of Earth, as long as it is found. I am
surprised
that someone with your knowledge would think otherwise! Perhaps
you should
apply a "reality check" and tell me (or anyone) how we
would have been
better off if 2002MN, for example, had been found on 12 June
rather than 17
June.
It is also a fact that no additional telescopes are required to
complete the
Spaceguard Goal of 90% of the NEAs larger than 1 km by 2008. Even
if
construction were started on a new survey telescope today, it
would not
likely come on-line in time to contribute much before 2008.
The real issue is what we do next. Go for 95% at 1 km? Go for 300
m
diameters? This has not been decided either internationally or
within the
US, and it is an issue that needs discussion and planning.
It is also interesting to me that you decry "the US, with
its paltry $3.5
million per year expenditure." So far the only searches are
being done with
US funding. When the UK and other nations are actually willing to
spend real
money, then we can move toward the international Spaceguard
Survey that I
know we all want.
Dave [Morrison]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NOTICE: Material quoted or re-posted from the Minor Planet
Mailing List
should be proceeded
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FROM THE MINOR PLANET MAILING LIST [date]. For the full text or
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==============
(5) TWO RECENT ASTEROID "NEAR MISSES"
>From Asteroid and Comet Impact Hazard
http://impact.arc.nasa.gov/
On June 15, asteroid 2002 MN came within 120,000 km of the Earth,
while 2002
EM7 made a close flyby in March.
On June 17, the LINEAR Spaceguard system discovered Near Earth
Asteroid
(NEA) 2002 MN, which had passed the Earth on June 15 at a
distance of only
120,000 km, one of the closest asteroid fly-bys on record. Based
on its
brightness, 2002 MN has a nominal diameter of about 100 m, large
enough to
penetrate through the atmosphere to the surface if it struck the
Earth. In
March, another asteroid, 2002 EM7, passed within 463,000 km. This
asteroid
also was not found until after its flyby of Earth.
Considerable press interest in this objects has been evident, as
well it
might be. The June 15 approach of 2002 MN was among the closest
on record.
Unfortunately, however, some of the press coverage has been
sensationalistic. Some stories either decry that these NEAs were
found after
closest approach (rather than before) or express concern about
the "blind
spot" otherwise commonly known to astronomers as the daytime
sky. It is
quite true that an asteroid close to the Sun in the sky cannot be
seen.
However, if an NEA is approaching Earth from the daytime sky, it
is quite
likely to pass into the night sky, where it can be discovered, as
these two
asteroids were. Far from being a cause of concern, the discovery
of NEAs
2002 EM7 and 2002 MN is an example of the success of the
Spaceguard program;
there is no cause for "doom and gloom" in either of
these asteroids.
Presumably a part of the problem is that many people do not
understand the
Spaceguard Survey strategy to discover and catalog NEAs long in
advance of
any possible threat, providing decades (or more) of warning if
any NEA is
currently on a collision course. It makes no difference if a NEA
is
discovered on approach or departure from the vicinity of the
Earth. We don't
give extra points for an approaching NEA or demerits for one that
has
already passed the Earth at discovery. The only effect of
"blind spots",
whether they be due to sunlight or moonlight or bad weather or
lack of a
southern hemisphere survey telescope, is to slow down the
completion of the
NEA catalog. Objects in blind spots will be missed until they
move into a
more favorable geometry, sometimes within a few days, otherwise
usually
within a few years. Both of these asteroids were successfully
found,
although they are well below the 1-km diameter that is emphasized
by the
current Spaceguard effort.
To put the latest asteroid (2002 MN) in perspective, a 100-m
asteroid hits
the Earth at an average interval of several millennia. One passes
within the
orbit of the Moon, however, at least once per year. This has been
happening
throughout history. What is new is that we are now beginning to
discover
these objects, whereas previously they would have sped past
undetected and
unheralded.
David Morrison
=============
(6) NEW NEO WEBSITE
>From Alessandro Morbidelli <morby@obs-nice.fr>
Hi Benny
I would like to notify that we have prepaered a website on our
work on the
debiased orbital, magnitude and albedo distribution of NEOs, the
impact
hazards on Earth, the prospects to achieve the Spaceguard
goal.....
All this on http://www.obs-nice.fr/morby/ESA/esa.html
Cheers
A. Morbidelli
Alessandro Morbidelli
Observatoire de la Cote d'Azur
B.P. 4229 06304 Nice Cedex 4, France
TEL: (33) 492003126
FAX: (33) 492003033
EMAIL: morby@obs-nice.fr
http://www.obs-nice.fr/morby/
==========
(7) IMPACT CRATERS ON EARTH
http://www.sciencemall-usa.com/impactposter.html
A new poster featuring the contributions of noted impact
scientists Drs
Bevin French
Carolyn Shoemaker
V.L. Sharpton
R.R. Anderson
C. Koeberl, and more
Meteorite Impact Craters on the Earth is a new full-size color
poster that
provides a super introduction to the science of meteorite impacts
and impact
craters. The fact is, there is a new understanding of impacts as
a
fundamental geologic process in the solar system:
"In recent years, geoscientists have begun to realize the
important role
that hypervelocity impacts have played in the formation and
development of
the Earth and the many life forms that call it home. The Earth
itself
appears to be the product of the accretion of smaller bodies
through
countless impacts, and our Moon is probably the product of the
impact of a
Mars-size body. Early impacts facilitated the crustal out-gassing
that
produced our atmosphere, and the impacting bodies themselves may
even have
contributed volatiles to it. Large impacts have affected the
course of life
on the planet by altering the environment so dramatically that
many forms of
life were driven to extinction." (Dr. Raymond. R. Anderson /
Iowa Geological
Survey Bureau)
Meteorite Impact Craters on the Earth features a table with
information
about the size, location, and features of 160 verified craters so
far
discovered on Earth.
* See the world map, showing all 160 craters plotted
geographically (and
keyed to the data table). Is there one near your home? (The most
"visited"
crater in the world is under O'Hare Airport in Chicago, and
thousands of
Chicagolanders actually live within its diameter!)
* See pictures of, and read about, some of the amazing rock and
mineral
types that are created ONLY by hypervelocity impacts.
* Understand the way craters are formed when the meteorite hits
the ground,
and the way differences in impactor size affect the type of
crater produced.
* Learn about the way our Earth has been pounded throughout its
history, by
following the colorful "Timeline and Relative Size of Impact
Craters on
Earth".
* Discover the man called the "father of impact
science".
* Also includes a 6-page information sheet with MANY more photos
(meteorite
samples, too), and teachers' review questions and answers.
The 38.5 x 27 inch poster is printed in full color on heavyweight
stock, and
is given a protective UV gloss coating that will even resist
splashes of
water and alcohol!
Price (UV protective coated) $16.00
The wait is over....available NOW!
============================
* LETTERS TO THE MODERATOR *
============================
(8) RE: CCNet: IMPACT-TRIGGERED ICE AGES?
>From Mark Boslough <mbboslo@sandia.gov>
Hi Benny,
Is this URL (http://abob.libs.uga.edu/bobk/ccc/ce120799.html)
correct? I
couldn't find anything in Hoyle's essay about impact-induced ice
ages. Is
there a reference to a scientific paper by Hoyle on this subject?
Maybe you
were thinking of John A. O'Keefe or Peter Schultz, both of whom
suggested
the existence of a terrestrial ring system and its climatic
consequences,
but did not have the resources to model. We referenced O'Keefe
and Schultz
in our paper, but may have overlooked any contributions by Hoyle.
I hope you
can track down a reference so we can give proper credit next
time!
Regards,
Mark Boslough
MODERATOR'S NOTE: Hoyle and Wickramasinghe have suggested a
rather different
scenario in which cometary impacts into the oceans do the trick;
see F.
Hoyle & C. Wickramasinghe: Cometary impacts and ice-ages,
ASTROPHYSICS AND
SPACE SCIENCE, 275 (4): 367-376 MAR 2001; F. Hoyle, On the Causes
of
Ice-Ages, EARTH MOON AND PLANETS, 31 (3): 229-248 1984. For an
alternative
theory of ice ages due to cosmic dust-loading by giant comets,
see: Bill
Napier, Temporal variation of the zodiacal dust cloud, MONTHLY
NOTICES OF
THE ROYAL ASTRONOMICAL SOCIETY, 321 (3): 463-470 MAR 2001.
================
(9) Re: CCNet: IMPACT-TRIGGERED ICE AGES?
>From John Fleck <jfleck@abqjournal.com>
Benny -
Just a note to let you know that the Associated Press rewrite
rather mangled
my original story on this. I noted in my story that Boslough is
the one who
suggested to Fawcett that they try doing a ringworld climate
simulation.
That became the above quote "The idea came from
Boslough" line. Sigh.
In any case, I didn't want you or your readers to think Boslough
is so
arrogant as to think he came up with the idea of impacts causing
ice ages.
:-)
Unfortunately, for reasons obscure, my original story isn't on
the web.
Cheers,
John
--
John Fleck, science writer
Albuquerque Journal, PO Drawer J, Albuquerque NM, 87110
(505) 823-3916
jfleck@abqjournal.com
(w), jfleck@inkstain.net
(h)
http://www.abqjournal.com/scitech/,
http://www.inkstain.net/fleck/
================
(10) PLANETARY RINGS NOT A FACTOR FOR ENVIRONMENTAL COOLING
>From Tom Van Flandern <tomvf@metaresearch.org>
Benny,
>From Tom Van Flandern, Meta Research <tomvf@metaresearch.org>
In CCNet for 2002/06/26, your first article cites an AP story
announcing
that Peter Fawcett and Mark Boslough are trying to explain a
100,000-year
cold spell during the Eocene epoch 35 million years ago with
planetary rings
formed during an asteroid impact event. However, one of the basic
rules of
celestial mechanics is that "A single impulse from the
surface of a body
can't inject anything into a stable orbit." So the idea that
planetary rings
were responsible for the Eocene cooling is not credible.
The reason for this rule of dynamics is that the point where an
impulse is
applied must remain a point on the resulting orbit. For example,
if the
impulse results from an impact, every non-escaping bit of debris
ejected
from the impact follows a trajectory that is an ellipse with the
center of
the Earth at one focus. And the point of ejection, a point on the
Earth's
surface, remains a point on the new elliptical trajectory. So any
bit of
debris that survives an impact has only two possible fates: (1)
escape to
interplanetary space if its speed exceeds escape velocity from
the Earth, 11
km/s; or (2) entering an elliptical orbit that intersects the
Earth's
surface, destined to collide with the ground again in less than
one
revolution.
So achieving a stable orbit with a single impulse is dynamically
impossible.
That is why nothing can be placed into Earth orbit by firing it
from a canon
on the ground. It is also why the first stage (or two) of a
satellite-carrying rocket works to get the satellite up to some
altitude
well above the Earth's atmosphere, and the final stage provides a
new,
horizontal impulse that lifts the rest of the elliptical orbit
above the
atmosphere. This is known as the "two-burn" problem in
rocketry. You can't
reach stable orbit with a single thrust, however large.
There is a second problem with the planetary ring hypothesis as
well. To
achieve a stable orbit, a satellite must have a speed of at least
7 km/s.
However, small bodies ejected from rest by a single impulse
cannot be given
a speed of more than 3 km/s without totally vaporizing them from
the energy
of the shock wave. [B.J. Gladman, J.A. Burns et al. (1996),
"The exchange of
impact ejecta between terrestrial planets", Science, v. 271,
pp. 1387-1392.]
This has long been known as a constraint on meteorites from the
Moon (escape
speed 2.4 km/s), and is a problem often not addressed by
scenarios that
hypothesize "SNAC meteorites" are from Mars (escape
speed 5 km/s), as we
reported to CCNet for 2001/07/11 last year. So getting ring
material into
Earth orbit without vaporizing it is also an insurmountable
difficulty with
this new planetary-rings theory. The greatest distance to which
ordinary
ejecta can be thrown by a terrestrial impact is roughly 1000 km,
as we
mentioned in connection with our discussion of the K/T boundary
event in
CCNet for 2002/02/01.
In conclusion, asteroid impacts produce a number of environmental
insults,
several of which are implicated in subsequent global cooling
episodes. But
the formation of planetary rings by impacts is not a possible
contributor to
our understanding of these events because it is excluded by the
laws of
dynamics and physics.
Best wishes. -|Tom|-
[response from Mark Boslough below]
==========
(11) AND FINALLY: THE END IS NIGH, AGAIN
>From Reason Magazine, 26 June 2002
http://reason.com/rb/rb062602.shtml
Environmentalists insist that humanity really has overshot the
earth's
carrying capacity this time.
By Ronald Bailey
The United Nations Summit on Sustainable Development is coming up
at the end
of August, so expect to see a spate of news stories warning that
humanity is
on an unsustainable economic path. To bolster this notion,
environmentalists
are positioning their views to make it easy for the press to echo
them.
In an article published this week by the prestigious journal
Proceedings of
the National Academy of Sciences (http://www.pnas.org/),
a group of
environmentalists led by Mathis Wackernagel of Redefining
Progress claim
that human consumption and waste production have overshot the
earth's
capacity to create new resources and absorb waste. They calculate
that
"humanity's load corresponded to 70% of the biosphere's
capacity in 1961,"
and "this percentage grew to 120% in 1999." They
explain that "20% overshoot
means that it would require 1.2 earths, or one earth 1.2 years,
to
regenerate what humanity used in 1999."
Such worries about overpopulation and resource scarcity have a
long history.
The Roman writer Tertullian warned in 200 A.D. that "we men
have actually
become a burden to the earth" and that "the fruits of
nature hardly suffice
to support us." In 1798 the Rev. Thomas Robert Malthus
published An Essay on
the Principle of Population, in which he claimed that population
growth
would always outstrip food supplies, inevitably resulting in
famine,
pestilence, and war. Biologist Paul Ehrlich notoriously updated
Malthus'
gloomy predictions in his 1968 book The Population Bomb, which
predicted
that hundreds of millions of people would die of famine in the
1970s.
Well, are the alarmists right this time around? Is the end
finally nigh? No.
Wackernagel et al. focus their analysis of how humanity uses the
biosphere
on six areas: growing crops, grazing animals, harvesting timber,
fishing,
building infrastructure, and getting energy from fossil fuels and
nuclear
power. According to their own calculations, humanity has not
exceeded the
biosphere's capacity in the first five of these areas, although
they say we
are close to the limits for growing crops and fishing. This
leaves fossil
fuels and nuclear energy, which they claim account for fully half
of
humanity's biosphere use. By their account, then, humanity would
be using
only 60 percent of the biosphere's capacity if energy use weren't
a problem.
To estimate our impact on the biosphere, Wackernagel et al.
calculate an
average of how many hectares it takes to support each person. The
reason
energy use figures so prominently in their calculations is that
they are
looking at how many hectares it would take to absorb the carbon
dioxide
produced by burning fossil fuels. Their concern is that burning
fossil fuels
adds carbon dioxide to the atmosphere, which traps heat, which
leads to
global warming.
These calculations embody an ideal of stasis, both ecological and
economic.
What the authors miss is that for every one of the six areas they
are
looking at humanity's ecological footprint probably is going to
become
smaller, not larger, during this century.
Jesse Ausubel, director of the Program for the Human Environment
at
Rockefeller University, believes the 21st century will see the
beginning of
a "Great Restoration" as humanity's productive
activities increasingly
withdraw from the natural world. For example, Ausubel and his
colleagues
calculate, "If the world farmer reaches the average yield of
today's US corn
grower during the next 70 years, ten billion people eating as
people now on
average do will need only half of today's cropland. The land
spared exceeds
Amazonia." If 10 billion people choose meat-rich diets in
2070, then farmers
will need only 75 percent of today's cropland. In other words,
through
technologically improved farming, millions of acres will revert
to nature.
With regard to grazing animals, many environmentalists
paradoxically oppose
intensive meat production that can spare millions of acres.
"If you very
efficiently produce grain to feed chickens rather than allowing
free range
cattle," explains Ausubel, "it's hard to see how you
have a problem with
increased meat consumption."
Ausubel also notes that "forest regrowth appears part of
modernity." He
points out that U.N. Food and Agriculture Organization studies
"of forest
biomass for the decade of the 1990s in the boreal and temperate
region in
more than 50 countries show the forests expanding in every one of
them." As
global cropland and grazing area shrink, forests will continue to
expand.
Ausubel estimates that humanity will need to use 20 percent or
less of the
world's 3 billion hectares of forest to sustainably supply all of
our wood
needs in the 21st century.
"The fish situation is much more difficult," Ausubel
cautions. Many
fisheries are being harvested at or over their sustainable
limits. Ausubel
notes that humanity consumes about 800 million tons of animal
products--meat
and milk--produced on land, compared to 80 million tons caught
wild in the
oceans. His solution to overfishing? "The ancient sparing of
land animals by
farming shows us how to spare fish in the sea," he says.
"We need to raise
the share we farm and lower the share we catch."
Already, 20 percent of seafood is produced by aquaculture that
can be
expanded in sustainable ways, relieving pressure on wild species
such as cod
and rockfish. In addition, as Iceland's and New Zealand's
fisheries show,
privatizing fisheries dramatically increases the incentives to
conserve and
protect wild stocks.
As for infrastructure, Ausubel calculates that if an additional 4
billion
people (who are unlikely to materialize, according to the latest
U.N.
population projections) chose to occupy as much land as the
average
Californian does today, they would cover 240 million hectares of
land, about
2.5 percent of the earth's terrestrial surface.
So we come to Wackernagel et al.'s chief concern: energy use.
"Some people
try to use the climate change issue as a trump card," says
Ausubel. "It
sounds like they're doing that." Keep in mind that despite
Wackernagel et
al.'s certitude, there are still serious questions about whether
adding
cabon dioxide to the atmosphere is really causing significant
problems for
humanity or the biosphere.
Assuming that man-made global warming is a real problem, there
are plenty of
ways to handle it. One is to deploy technologies we already have
to mitigate
its effects on humanity: heating, air conditioning, seawalls,
irrigation of
farmland, crop switching, and so forth. We could also choose to
sequester
extra carbon dioxide by pumping it back into the ground whence it
came,
fertilizing the tropic ocean deserts so that they bloom with
phytoplankton
that absorbs it from the air, or planting more trees.
In any case, Ausubel doesn't think that carbon dioxide is a
long-term
problem because the world's energy system has been inexorably
decarbonizing
for the past two centuries. His research traces humanity's steady
progress
from wood to coal to oil to natural gas and, eventually, to
hydrogen. At
each stage, consumers, without being commanded to do so by
regulators, have
chosen fuels containing more hydrogen over fuels containing more
carbon.
Ausubel sees that trend continuing until carbon-based fuels are
eliminated
by the end of the century. He expects that carbon dioxide
concentrations,
now about 360 parts per million (ppm), will peak at 450 ppm. That
is 100 ppm
less than the U.N.'s sometimes stated goal of
"stabilizing" carbon dioxide
at 550 ppm, and it would happen without draconian increases in
energy prices
or the creation of global bureaucracies aimed at regulating the
atmosphere.
So Wackernagel et al. are wrong on every measure they chose to
analyze with
regard to the future sustainability of the human enterprise. How
could they
get it so wrong?
"Biologists and ecologists tend to overlook the power of
technical progress
compounded over the years," says Ausubel. "If you're
trained in ecology and
botany, you think of technology as a bulldozer, but what it
really is, is
efficiency, using less to do more."
Technological progress has already dramatically expanded the
carrying
capacity of the earth. In the 21st century it will so outpace the
increasing
demands of a growing and wealthier population that more and more
land will
revert to nature.
"It looks like over the next 100 years, for most
environmental concerns, we
will do better," concludes Ausubel. "You get smarter as
you get richer."
Ausubel's own article in the June 11 issue of the Proceedings of
the
National Academy of Sciences concludes, "An annual 2-3%
progress in
consumption and technology over many decades and sectors provides
a
benchmark for sustainability." In other words, economic
growth and
technological progress are sustainable in the long run and make
it less and
less likely that humanity will overshoot any limits the biosphere
may have.
Let the Great Restoration begin!
Ronald Bailey, Reason's science correspondent, is the editor of
Global
Warming and Other Eco Myths (Prima Publishing) and Earth Report
2000:
Revisiting the True State of the Planet(McGraw-Hill).
Copyright 2002, Reason Magazine
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*
NOTHING IN PHYSICS PROHIBITS IMPACT-PRODUCED RINGS
>From Mark Boslough <mbboslo@sandia.gov>
Tom,
Thanks for your detailed explanation of 2-body celestial
mechanics. If
that had been the mechanism we had suggested for generating a
planetary
ring system, I can assure you that the editors of JGR would have
been
smart enough not to accept our paper! I realize that you do not
have a
copy of our paper and could not have known what we suggested, but
it is
based on the experimental work of Schultz and Gault (GSA Special
Paper
247, 1990).
Quoting from our paper:
"At low impact angles (30 degrees from the horizontal), the
original
impactor disrupts and ricochets downrange at a significant
fraction of
its incoming velocity. The ricochet component becomes embedded in
and
accelerated by an expanding vapor cloud. Continued
interaction between
the solid debris and the turbulent expanding vapor cloud can
potentially
provide the non-ballistic force that allows some fraction of the
debris
to be inserted into orbit." For a simulation of such
an impact on a
planetary scale, see Dave Crawford's movies:
http://sherpa.sandia.gov/planet-impact/asteroid/.
According to Schultz & Gault (1990): "In general,
conditions favoring
injection of significant quantities of projectile and target into
orbit
appear to be a 10 to 20 degree impact between 15 and 20 km/s into
an
ocean or into carbonate sediments... such an event for
10-km-diameter
body would be likely over a time interval of 300 m.y."
In my opinion,
our planet has had an impact-produced ring system many times in
its
history. One does not need to run a fancy GCM to recognize that
such a
ring would have had climatological consequences, but the GCM lets
us get
a handle on second-order effects (first-order being the obvious
cooling
from reduced insolation).
It is noteworthy also that the "giant impact"
hypothesis for the
formation of the moon involves the formation of a ring system by
impact,
albeit at a much greater scale. This is dynamically possible
because,
again, it is not a simple 2-body celestial mechanics problem;
there are
hydrodynamic forces as well as distributed body forces.
There are similar assumptions built into your second objection.
Melosh
(Icarus 59, 234, 1984) showed how material can be ejected from a
planet
to high velocity by shock-wave interference and non-uniaxial
loading
effects without strong shock effects (let alone melting or
vaporization).
Likewise, O'Keefe and Ahrens (Science 234, 346, 1986) modeled
vapor-plume
entrainment as a way of getting weakly shocked rocks off a
planet,
similar to what Schultz and Gault observed experimentally and
what we
invoked. The Gladman et al. article you site does not question
the
possibility of getting SNCs off Mars, as you implied.
Just in case you think these are contrived, egg-headed
theoretical tricks
that could not ever really work, have a look at the proceedings
of the
1992 Hypervelocity Impact Symposium. My colleague, Lalit
Chhabildas,
cleverly applied similar ideas to enable the launching of an
unmelted
projectile at speeds exceeding 12 km/s (Chhabildas et al., Int.
J. Impact
Eng., 14, 1993). See Boslough et al. (Int. J. Impact Eng., 14,
1993) for
a flash x-ray radiograph of an unmelted, intact plate being
launched to
10 km/sec by a single impulse!
The lesson is that when you do real-world physics, the
idealizations you
were taught as an undergraduate do not always apply. Real life is
messier, and it is the messiness that is the most interesting!
Regards,
Mark Boslough
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