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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