PLEASE NOTE:
*
CCNet 58/2003 - 22 July 2003
----------------------------
"A stated goal of finding 90 percent of all large Near Earth
Asteroids (NEAs) by 2008 is more or less on target, leading
experts said last week at the General Assembly of the
International Astronomy Union (IAU) in Sydney, Australia... When
the current goal is reached, there will still be many unfound
smaller objects that are easily capable of destroying a large
city. Yet present technology is somewhat limited in its ability
to find the thousands and perhaps millions of smaller asteroids
that could potentially threaten the planet."
--Michael Paine, Space.com, 21 July 2003
(1) SEARCH FOR LARGE ASTEROIDS NEARS COMPLETION, EXPERTS PONDER
GAPS IN PROGRAM
(2) SMALL ASTEROIDS = SMALL THREAT?
(3) "400 ASTEROIDS, 30 COMETS THREATEN EARTH - RUSSIAN
SCIENTISTS"
(4) CONFRONTING CATASTROPHE IN THE ANCIENT WORLD
(5) THREAT FROM SMALL ASTEROIDS
(6) Re: SPIN ON NEO IMPACT RATES
(7) SIRENTE CRATER FESTIVAL
(8) REALITY OF MANTLE PLUMES LOOKS LESS LIKELY
=============
(1) SEARCH FOR LARGE ASTEROIDS NEARS COMPLETION, EXPERTS PONDER
GAPS IN PROGRAM
Space.com, 21 July 2003
http://space.com/scienceastronomy/asteroid_report_030721.html
By Michael Paine
Special to SPACE.com
SYDNEY, Australia -- A stated goal of finding 90 percent of all
large Near Earth Asteroids (NEAs) by 2008 is more or less on
target, leading experts said last week at the General Assembly of
the
International Astronomy Union (IAU) in Sydney, Australia. The
goal, originally outlined by NASA and mandated by the U.S.
Congress, is designed to insure that space rocks in the vicinity
of
Earth's orbit, and larger than 1 kilometer (0.62 miles), are
found and tracked. An object of this size could cause
global destruction if one were to hit Earth.
An international affiliation of groups, collectively called
Spaceguard, carries out the search and follow-up observations
needed to purse the targets. NASA funds much of the work.
No asteroids are presently known to be heading toward the planet.
The global experts gathered here reiterated a common concern
among asteroid scientists: When the current goal is reached,
there will still be many unfound smaller objects that are easily
capable of destroying a large city. Yet present technology is
somewhat limited in its ability to find the thousands and perhaps
millions of smaller asteroids that could potentially threaten the
planet.
The search for Earth-threatening asteroids was described by three
international experts at a public forum Thursday: David Morrison
from NASA's Ames Research Center; Alan Harris of the Space
Science Institute in Colorado, and Andrea Milani from the
University Pisa, Italy. Bigger, better telescopes are on the
drawing board for finding these smaller asteroids, the scientists
said. Meanwhile, images of the sky taken by current programs
could be crucial to future attempts to find and track small
asteroids using the new telescopes. Determining an asteroids
exact trajectory and potential future danger requires
observations across time, so the object's movement can be
plotted.
Importantly, there are no large telescopes devoted to the task of
hunting asteroids from the Southern Hemisphere. A major search
program down under would help in this task, the panelists said.
The forum, "The danger from space: Are Near Earth Objects a
catastrophe waiting to happen?" was moderated by Australian
science celebrity Karl Kruszelnicki.
NASA's Morrison described the consequences of an asteroid
colliding with Earth. The larger NEAs, bigger than a half mile (1
km), would cause global environmental disaster, he said. Smaller
objects are still a danger to cities and regions and Spaceguard
will eventually be expanded
to cover these smaller objects.
Harris, from the Space Science Institute, showed the progress
made with Spaceguard and described new telescopes that, within
the next decade, could be used for detecting and tracking NEAs.
He cautioned, however, that these new telescopes would have
competing demands and most would be devoted to Spaceguard on a
part-time basis.
Harris said the lack of a major asteroid search program in the
Southern Hemisphere was limiting the pace of new discoveries. A
specialized Schmidt 1.2-meter (4-foot) telescope at Siding Spring
in Australia is under-utilized and could be upgraded to search
for near-Earth asteroids, he said. This would involve replacing a
large photographic plate holder with a modern CCD camera (like
those in video cameras).
With new technology involving multiple CCDs, the Siding Spring
telescope could be better at searching for asteroids than any
current Spaceguard telescopes, Harris said. Australian astronomer
Duncan Steel pointed this out in a science paper written in 1995,
shortly before the Australian Spaceguard program was terminated
as government funding was dropped.
Milani, from the University Pisa, described the computations
necessary to establish an asteroid's orbit around the Sun and to
calculate whether it would hit the Earth in the future. He
suggested that it was not very useful searching for new
near-Earth asteroids if the extra work was not also done to check
whether there was a risk of a collision. This usually involves
alerting astronomers around the world to conduct follow-up
observations. Much of the asteroid tracking effort involves
amateurs who volunteer their time.
Asteroids are sometimes initially found to have remote risks of
hitting Earth. The additional observations are included in
revised computations that, so far, have resulted in an impact
risk being downgraded to zero in all cases that have been studied
over time. Milani and his colleagues
recently developed computer programs to generate numerous
possible paths for a newly discovered asteroid. If any of these
"virtual impactors" is found, by computation, to be on
a collision course, then mathematicians can describe its
predicted orbit and astronomers can carefully check whether the
actual asteroid is on the same path.
Just as important in this process is the checking of old sky
images. The mathematicians can run a predicted orbit back in time
and old images can be checked for signs of the object. Harris
explained that not finding an object in old images could be used
to eliminate the possibility an impact. The approach illustrates
the importance of archiving astronomical observations -- a blank
area on a picture could be just as important as a small white
dot.
It is also a good reason to immediately start taking images of
southern skies, researchers say.
After the public forum a discussion ensued about ways to deflect
an incoming asteroid.
The work by Milani and others has demonstrated that, if an
asteroid is determined to be on a collision course, the most
likely scenario is that over several decades it will perform
multiple close approaches to the Earth before the impact. During
these close encounters the asteroid must pass through a window,
or "keyhole" in space if it is to continue on its
collision course.
In these cases it only takes a deflection of a few hundred
kilometers (miles) to force a rock to miss the keyhole and
therefore avoid Earth impact in a subsequent orbit.
This compares with an object heading directly for an impact that
must be deflected by thousands of kilometres (miles) so that it
misses the Earth. Because they pass close to the planet on
several occasions before impact, it should be possible to detect
quite small keyhole asteroids
with current telescope technology -- but only if scientists are
effectively looking for them.
A keyhole deflection is only possible if the threatening asteroid
can be detected decades ahead of the impact and if sufficient
sightings have been made to pin down its orbit. This was cited as
another good reason for stepping up the Spaceguard effort and
adding a southern sky search.
On July 25, the Australian Minor Planet Workshop will take up
discussion of how to jump-start asteroid searches in Australia
and New Zealand.
c2003 Space.com
=================
(2) SMALL ASTEROIDS = SMALL THREAT?
Sky & Telescope, 16 July 2003
http://skyandtelescope.com/news/article_1005_1.asp
By J. Kelly Beatty
July 16, 2003 | Every time a rocky body whizzes past Earth,
asteroid specialists brace themselves for a frenzied burst of
"what-if" doomsday questions from the news media. But
while the risk of the interloper striking our planet is usually
vanishingly small, the longer-term prospects for all such
near-Earth asteroids are poorly known. Current thinking holds
that objects 50 to 75 meters across, comparable to the one whose
airburst devastated the Tunguska region of Siberia in 1908,
probably come crashing down every 1,000 years on average. Most
researchers think that objects twice that size, even though they
arrive less often, probably strike the ground intact - wreaking
havoc locally if one should hit land and triggering an
ocean-spanning tsunami if it makes a splash.
But Philip A. Bland (Imperial College London) and Natalya A.
Artemieva (Institute for Dynamics of Geospheres, Moscow) argue
that the threat from small asteroids has been greatly
exaggerated. Writing in July 17th's Nature, they conclude that
stony asteroids up to several hundred meters across rarely make
it to the ground but instead almost always break up high in the
atmosphere.
Their finding is based more than 1,000 computer-simulated
collisions with bodies up to 1 kilometer in diameter. In the
past, most theorists have treated cosmic projectiles as giant
blobs of liquid racing downward through Earth's atmosphere. But
Bland and Artemieva believe that even sizable stony objects
should break into successively smaller pieces while still very
high up. This fragmentation model, first introduced in 1980 and
refined recently by Artemieva and others, implies that a stony
impactor will be reduced to rubble long before it reaches ground
level.
"Our simulations predict atmospheric fragmentation for much
larger objects than previously thought," the two researchers
conclude. They predict that a 220-meter-wide asteroid, the size
considered most likely to create a tsunami at least 5 meters high
when it strikes the open ocean, actually makes it all the way to
the ground only once in 170,000 years on average - an interval 50
times longer than previously estimated. Bodies 3 to 5 meters
across, big enough to create a 100-meter crater, should strikes
Earth every 200 to 400 years.
Artemieva points out that their "separated fragment"
model doesn't apply to comets or loosely bound piles of rocky
material, which behave more like fluids as they disintegrate in
the atmosphere. But it's a particularly good fit to iron
meteoroids, which will remain intact longer but should still
break apart if no more than about 50 meters across. "I think
the most intersting advantage of this model is the possibility to
predict strewnfields," she says, which are clusters of
meteorites dropped during a single event like the 1947
Sikhote-Alin fall in eastern Siberia.
Dynamicist Erik Asphaug (University of California at Santa Cruz)
comments that if Bland and Artemieva are right, "certainly
the tsunami hazard becomes trivial in comparison with other
natural catastrophes." But Clark R. Chapman (Southwest
Research Institute) warns that we shouldn't lose sight of the
potential damage from Tunguska-like airbursts. "Atmospheric
breakup and explosion in the lower atmosphere may be even more
damaging than if the object hit the ground intact," he
points out.
If the threat from small asteroids were truly reduced so
dramatically, astronomers would probably rethink their plans to
build telescopes capable of detecting hundreds of thousands of
Earth-threatening asteroids in the 100- to 500-meter size range.
One such effort, dubbed the Panoramic Survey Telescope and Rapid
Response System (Pan-STARRS), got the U.S. Air Force's go-ahead
for development last October. "A 200-meter body carries
roughly 1,000 megatons of kinetic energy," observes David C.
Jewitt (University of Hawaii), a Pan-STARRS participant.
"Personally, I want to know as much as possible about any
1,000-megaton explosion on Earth - no matter where it might
occur!"
Copyright 2003 Sky Publishing Corp.
=========
(3) "400 ASTEROIDS, 30 COMETS THREATEN EARTH - RUSSIAN
SCIENTISTS"
ITAR-TASS 20th July 2003
ST. PETERSBURG, July 20 (Itar-Tass) -- Russian scientists named
about 400 asteroids and 30 comets in the Universe that probably
may collide with the Earth in the future.
The orbits, physical parameters and energy of these celestial
bodies are included in a scientific monograph "Asteroids and
comets approaching the Earth" prepared by the Institute of
applied astronomy of the Russian Academy of Sciences. Its
director corresponding member of the Russian Academy of Sciences
Andrei Finkelshtein told Itar-Tass on Saturday that the
International astronomic union adopted resolutions that called on
the world scientific community to thoroughly study a problem of
an asteroid threat. The corresponding state programmes were
adopted in the United States, Great Britain and Japan. The orbits
of not less than 90 percent of asteroids with a kilometre and
more in diameter that may approach the Earth should be defined by
2008. The scientist is confident that the collision of the Earth
with such a celestial body will result in a catastrophe and the
inevitable death of the human civilisation (sic).
Copyright (c) 2003 Itar-Tass. All Rights Reserved.
=================
(4) CONFRONTING CATASTROPHE IN THE ANCIENT WORLD
ANCIEN-L@LISTSERV.LOUISVILLE.EDU
Dear Colleagues,
We wish to draw your attention to the following scientific
workshop that will be held at Osmangazi University, Eskesehir, in
western Turkey, on 20-22 June 2004.
CONFRONTING CATASTROPHE IN THE ANCIENT WORLD
Human development over the last 11,500 years (the Holocene) is
set against an environmental backdrop of climatic and geological
instability. The natural actions of sudden and dramatic climatic
shifts and of extreme geophysical events ensure that nature in
the ancient world was in flux, not balance. But what are the
cultural resonances of rapid environmental change? How did past
human communities adapt to and recover from a constantly moving
and frequently harmful natural world? And, most critically, how
can we disentangle the cultural consequences of natural change
from those of human action?
This 3-day workshop seeks to bring together an interdisciplinary
forum of geologists, archaeologists, historians, anthropologists,
climate scientists, and ecologists to critically examine human
responses to past rapid environmental change. The convenors
encourage submission of
research presentations that are seeking to elucidate the cultural
history of major environmental downturns or reconstruct the
environmental history of dramatic cultural transitions.
Contributions with an emphasis on establishing high-resolution
chronologies of cultural and environmental change are
particularly welcome.
Abstract deadline: 15 January 2004
The workshop is the joint initiative of two current international
research projects: (1) International Council for Science (ICSU) -
'Dark Nature - Rapid Natural Change And Human Responses', and (2)
International Geological Correlation Programme Project 490 - 'The
Role Of Holocene Environmental Catastrophes In Human History'.
An associated fieldtrip around key cultural and geological sites
in western Turkey will take place immediately following the
workshop (24-30 June 2004).
A first circular with further details of the scientific
programme, the fieldtrip and the local and international
scientific committee is currently in preparation. However, those
interested in participating are encouraged to contact the main
lead convenors as early as possible:
Dr Erhan Altunel,
Osmangazi University, Eskesehir,
ealtunel@ogu.edu.tr
Dr Iain Stewart
University of Glasgow,
Glasgow G12 8QQ,
UK.
E-mail: istewart@geog.gla.ac.uk
=======LETTERS==========
(5) THREAT FROM SMALL ASTEROIDS
Michael Paine <mpaine@tpg.com.au>
to: editor of Sky & Telescope
Kelly
I am glad that you included the comments from Clark Chapman and
David Jewitt in your article about the threat from small
asteroids. Airbursts above land are, indeed, more destructive
than surface blasts. In his book Rain of Iron and Ice, John Lewis
gives an optimum height of
10km for a 100Mt explosion (~100m diameter asteroid). At this
height the 3psi blast wave (sufficient to topple conventional
buildings) reaches 50% further than a surface blast (that is,
about twice the area of destruction). Radiant energy effects
(firestorms) are also magnified by
airbursts.
Most attempts at estimating human casualties have assumed already
that many stony asteroids under 200m in diameter will explode
above the ground. Also the estimates of tsunami risk set out by
Ward and Asphaug in Icarus (2000) have been regarded as too
pessimistic by some researchers in the tsunami field.
Given the random nature of impacts, the increased destruction
from airbursts over land (compared with surface impacts) and the
overwhelming influence of large impacts, it is likely that the
overall risk to mankind is not greatly affected by the new
research. In any case, there are still very good reasons
for finding NEOs between 200m and 1km.
regards
Michael Paine
The Planetary Society Australian Volunteers
=============
(6) Re: SPIN ON NEO IMPACT RATES
Jens Kieffer-Olsen <dstdba@post4.tele.dk>
Dear Benny Peiser,
Duncan Steel's below remark invites a follow-up.
> Finally, the later discussion in today's CCNet about the
> probability of Tunguska-type events is somewhat misguided.
> The 1908 event occurred, so that a posteriori its
probability
> was unity. On its own, it tells us nothing about the a
priori
> probability of such occurrences. The statement that Al
Harris
> made about it - "The fact that one such event occurred
just a
> century ago argues for a population closer to the former
value"
> - really is about the most that can be made of it.
The Tunguska event is in no way a precondition for us debating
the frequency of impacts in its range, rather the argument works
the other way round, since we had not been in a position to
discuss impacts at all, if an even larger event had taken place
recently and impeded the progress of Western civilization.
So, Tunguska does indeed give us input to a probabilistic
estimate of mean interarrival time for impacts. And surprise or
no surprise, assuming three centuries of observation time and a
50% chance of detection, the result is once per 150 years.
I shall not attempt to quantify the confidence level of this
estimate or set bounds for that of an estimate based on a mean
interarrival time of 1000 years, even if it would be infinitely
more meaningful to do so than to assign values to the parameters
of the Drake equation, in order to assess how close to Earth the
nearest lot of aliens might be.
The fact that Alan Harris' simulation comes along with the
uncertainty specified as a factor 3, bears witness to a low
confidence interval for it as well. It's therefore more
than interesting that a mean interarrival time of 300 years fits
reasonably well with both the length of period over which we have
observed one actual event, and with the simulation based on 30 or
so NEAs detected by LINEAR in the course of looking for much
larger objects.
A final question, the earlier suggested estimate of 10,000 years
between impacts mentioned by Harris is presumably history now
thanks to his simulation?
Yours sincerely
Jens Kieffer-Olsen, M.Sc.(Elec.Eng.)
Slagelse, Denmark
============
(7) SIRENTE CRATER FESTIVAL
Duncan Steel <D.I.Steel@salford.ac.uk>
Dear Benny,
I am appending some information about an exhibition and series of
public talks to be held in August in Italy concerning the
recently recognised Sirente impact crater, about 100 km east of
Rome. This crater has been discussed in previous issues of CCNet,
along with its implications (e.g. some people believe it could be
connected with Constantine's vision).
Anyone who wants further information might contact Laura Borgione
as
laura.borgione@regione.abruzzo.it
Ciao,
Duncan Steel
====================================================================
UN SEGNO DEL CIELO : A SIGN IN THE SKY
Exhibition promoted by the town of Secinaro in collaboration with
APTR, The Abruzzo Region, Province of L'Aquila, Sirente-Velino
Regional Park, Sirentina Mountain Community and the
MPRAT-Astronomers Group
Thursday, 07 August
9:00
Meeting place: village streets, Secinaro
The event begins with a contemporary painting exhibition :
artists who create their works on the spot finding inspiration in
the meteoroid, historical events and legends relating to it.
(Vision of the Emperor Constantine "In hoc signo
vinces"; the legend of the "goddess Sicinna"; the
legend of the "Madonna della Consolazione").
17:30
Meeting place: Council Hall of the Municipal Administration
Scientific Convention: the first impact crater in Italy and
theories related to space objects impact.
Introduction: Gian Gabriele Ori - "University of
D'Annunzio" in Pescara (Abruzzo, Italy)
Participants : Angelo Pio Rossi and Goro Komatsu, responsible for
conducting the crater research group together with its
discoverer, the Swedish geologist Jens Ormo, and others.
Friday, 09 August
17:30
Meeting place: Council Hall of the Municipal
Administration
Presentation of the book written by Evandro Ricci "Il
Meteorite del Sirente, nella visione di Costantino, nella
tradizione e nella leggenda della Madonna della
Consolazione"
21:00
Meeting place: Council Hall of the Sirentina Mountain Community
Exhibition opening of digital panels about the Sirente crater
Saturday, 09 August
17:30
Meeting place: Council Hall of the Sirentina Mountain Community
Meeting on the topic "Preservation and valorisation of the
Sirente crater field"
21:00
Images of the most important terrestrial impact craters
(presented by the International Research School of Planetary
Sciences).
Sunday, 10 August
17:30
Meeting place: Council Hall of the municipal government
Meeting on the topic: "Christianity, from Constantine The
Great to the New Europe"
Introduction by Mark Lewis (Director of the Historical Institute
of the Society of Jesus)
Monday, 11 August
21:00
Meeting place:Stairs of the San Nicola Church
Theatre performance "Costantino, in hoc signo
vinces" - Milo Vallone Theatre Company
23:00
Sky-watching with telescopes of the astronomers group of Abruzzo
24:00 Refreshments: pizza and watermelon
From 07 to 11 August
9:00 - 12:00 a.m, 18:00 - 22:00 p.m.
In the rooms of the Elementary School
Exhibition of astronomical photos - by the astronomers
group of Abruzzo
These events are open to the general public and participation is
free of charge
Information: Comune: 0864.79302.
=============
(8) REALITY OF MANTLE PLUMES LOOKS LESS LIKELY
Hermann Burchard <burchar@math.okstate.edu>
Dear Benny,
here is the paper, where it is shown that the Yellowstone hotspot
does not penetrate deep into the mantle:
Christiansen, R.L., G.R. Foulger and J.R.
Evans, Upper-mantle origin
of the Yellowstone hotspot, Bull. Geol. Soc.
Am., 114, 1245-1256,
2002.
The paper amounts to an impressive refutation of the "mantle
plume" hypothesis. It is listed among publications of
the 2nd named author, Gillian Foulger, Department of Geological
Sciences, University of Durham.
http://www.dur.ac.uk/g.r.foulger/
<g.r.foulger@durham.ac.uk>
Best regards,
Hermann Burchard
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