PLEASE NOTE:


*

CCNet 56/2003 - 15 July 2003
----------------------------


"The warming may have allowed a final flourishing of some species that were already on the path to extinction... There's no scientific agreement on what caused this climatic instability, but it's quite likely that current studies are over-estimating the effect of the asteroid impact."
    --Chris Hollis, Geological and Nuclear Sciences (GNS), 14 July 2003


"One day, inevitably, there will be a NEO on a collision course with Earth. With luck, it will be small and won't cause much damage. If it is spotted years or decades in advance, there might be time to intervene. "This is one threat we can do something about," he declares. Various defensive strategies have been proposed, including nudging an approaching asteroid with a nuclear blast or darkening part of the object's surface so that the thrust produced by radiated heat changes its orbit. Marsden is not sure how much money should be spent exploring these options but insists that "we have to do more than the dinosaurs."
     --Steve Nadis, Scientific American, August 2003


"It was only because of [Lembit Opik] the MP for Montgomeryshire's tireless campaign to increase asteroid awareness that the government agreed to set up a task force to investigate the risk of giant rocks crashing into the earth and wiping us all out. Even though these "global killers" (his words, not mine) usually only strike every 30m years, it has been about 65m years since the last one, and that one got rid of the dinosaurs. In other words, the end of the world is looking decidedly nigh. But there's no need to panic. Thanks to Lembit, scientists are hard at work designing a giant "cosmic condom" (again, his words) to catch asteroids before they turn us into crostini. If only the dinosaurs had had their own Lembit, they might still be here today."
     --The Guardian, 8 July 2003


(1) DINOS DOOMED BY CLIMATE CHANGE: "CURRENT STUDIES OVER-ESTIMATE EFFECT OF K/T ASTEROID IMPACT"

(2) "FRESH," RAYED IMPACT CRATER SEEN ON MARS

(3) KEEPER OF THE OBJECTS: BRIAN MARSDEN 

(4) CATCHING A COMET'S TAIL IN THE EARTH'S UPPER ATMOSPHERE

(5) METEOROIDS 2004

(6) A LUNAR KLONDIKE?

(7) RE-MYSTIFYING THE TUNGUSKA EVENT

(8) RE: IMPACT HAZARD SUMMARY BY ANDREA MILANI

(9) AND FINALLY: "WHY I LOVE LEMBIT OPIK MP"

===========
(1) DINOS DOOMED BY CLIMATE CHANGE: "CURRENT STUDIES OVER-ESTIMATE EFFECT OF K/T ASTEROID IMPACT"

From Agence France Press, 14 July 2003
http://www.itechnology.co.za/index.php?click_id=31&art_id=qw1058175900797B252&set_id=1

Auckland - The dinosaurs were probably heading for extinction even before an asteroid strike wiped them out 65 million years ago, New Zealand scientists said on Monday.

Palaeontologist Chris Hollis and a team of scientists from the government-owned Geological and Nuclear Sciences (GNS) have uncovered evidence of significant global climate change even before the meteor strike.

"An unknown number of species may have been in sharp decline when the asteroid struck and the impact winter probably finished them off quite quickly," Hollis said in a statement.

He added: "There's no scientific agreement on what caused this climatic instability, but it's quite likely that current studies are over-estimating the effect of the asteroid impact."

By studying fossils and sediments at six sites in New Zealand, the research team found a centimetre thick layer of meteorite dust formed precisely at the time of major environmental change 65 million years ago.

They also found abrupt changes in microscopic plants and animal fossils in marine sediments.

This supports the idea that the main effect of the asteroid was to throw up a global dust cloud that blocked out the sun for months or even years.

But the cool climate that prevailed in New Zealand for millions of years after the strike might not be, as some had supposed, evidence of a prolonged "impact winter".

"Instead, it may represent a return to normality following unusual warming at the end of the Mesozoic," Hollis said.

At around the time of the impact, toward the end of the Mesozoic period, the planet's climate was changing rapidly with a period of long-term cooling.

But the scientists believe there had been unusually warm conditions just before the impact.

"The warming may have allowed a final flourishing of some species that were already on the path to extinction."

The reappearance of several survivor species after the impact shows that, even though the effects were global, the survival rate of species in New Zealand was higher than in the northern hemisphere.

Because New Zealand was about 1 500km closer to Antarctica at the time, the local flora and fauna were probably adapted to cold and darkness and therefore better able to withstand an impact winter.

GNS earlier said its study of evidence in New Zealand suggests that the destruction of forests because of the impact winter was largely confined to the American continent, within a radius of several thousand kilometres of the suspected site on the Yucatan Peninsula in Mexico. 

Copyright 2003, Sapa-AFP

=============
(2) "FRESH," RAYED IMPACT CRATER SEEN ON MARS

Spaceflight Now, 14 July 2003
http://spaceflightnow.com/news/n0307/14marscrater/

This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a fresh, young meteor impact crater on the martian surface. It is less than 400 meters (less than 400 yards) across. While there is no way to know the exact age of this or any other martian surface feature, the rays are very well preserved.

On a planet where wind can modify surface features at the present time, a crater with rayed ejecta patterns must be very young indeed. Despite its apparent youth, the crater could still be many hundreds of thousands, if not several million, of years old.

This impact scar is located within the much larger Crommelin Crater, near 5.6 deg N, 10.0 deg W. Sunlight illuminates the scene from the left.

Malin Space Science Systems and the California Institute of Technology built the MOC using spare hardware from the Mars Observer mission. MSSS operates the camera from its facilities in San Diego, California. The Jet Propulsion Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor spacecraft with its industrial partner, Lockheed Martin Astronautics, from facilities in Pasadena, California and Denver, Colorado.

Copyright 2003, Spaceflight Now

=============
(3) KEEPER OF THE OBJECTS: BRIAN MARSDEN 

Scientific American, August 2003
http://www.sciam.com/article.cfm?colID=30&articleID=000C14F2-565A-1F03-BA6A80A84189EEDF

With a shoestring budget, asteroid and comet watcher Brian Marsden looks out for Armageddon from the skies--and not without controversy

By Steve Nadis
 
Every day our neighborhood appears a bit more crowded--and dangerous. The band between Earth and Mars hosts swarms of swift-moving asteroids, some of which might eventually threaten our planet. The inner solar system is home to an estimated 1,000 to 1,500 asteroids a kilometer or greater in width, with perhaps a million rocks 50 meters and larger. Asteroid observations pour in at the rate of 15,000 or more a day.

The burden of keeping track of near-Earth objects (NEOs)--asteroids and the occasional comets that pass through our vicinity--falls on Brian Marsden. Since 1978 he has directed the Minor Planet Center (MPC) at the Smithsonian Astrophysical Observatory in Cambridge, Mass. Sky watchers from all over the world send putative sightings to the MPC, which operates on behalf of the International Astronomical Union (IAU). The MPC processes and organizes data, identifies objects, computes orbits, assigns tentative names and disseminates information on a daily basis. For objects of special interest, the center solicits follow-up observations and requests archival data searches. "We are the focal point," Marsden says. "All the observations come here."

Marsden has served as the referee for all NEO sightings over the past 25 years--a period in which the total search effort has grown from a fledgling survey or two into a productive and efficient international network. At times this role has put him in the middle of controversy. Perhaps the most notorious incident occurred on March 11, 1998, when Marsden indicated on the MPC Web site that an asteroid discovered in December 1997 (then named 1997 XF11 and now called asteroid 35396) would make a close approach in 30 years. "The chance of an actual collision is small," he wrote, "but one is not entirely out of the question." That phrase set off a media circus that ranked among the 20 top science debacles of the century, according to Discover magazine.

Marsden admits that his word choice was "ill advised" but insists the calculation was correct at the time. He emphasized its uncertainty in the original notice and asked for more data. When the computations were redone a day later, incorporating orbital information from an old photograph, the threat vanished.

COLLISIONS with even small NEOs pose a threat: an object only 100 meters wide flattened these trees in Siberia in 1908.

"Much as the incident was bad for my own reputation, we needed a scare like that to bring attention to this problem," Marsden remarks. "Many wondered whether I'd survive, but I'm still here." More important, he says, the field itself has prospered. In the wake of XF11 publicity, NASA increased funding for asteroid searches from $1 million to $3.5 million annually. In addition, groups at the University of Pisa in Italy and the Jet Propulsion Laboratory in Pasadena, Calif., began doing routine risk evaluations of potentially menacing objects. To date, the confirmed NEO total includes about 2,250 asteroids, a dozen comets that complete their orbits in less than 200 years, and 1,000 long-period comets (on orbits 200 years or longer) that pose no immediate concern.

It's a far cry from the early 1960s, when Marsden started adding to the list of some two dozen known NEOs with detections he made as a Yale University graduate student. After earning his Ph.D. in astronomy in 1965, he took a job at the Smithsonian, where he has worked ever since.

When Marsden began studying minor planets, "nobody cared about asteroids. They were dismissed as 'vermin of the sky.'" Now the study is a bona fide field, thanks to automated search programs such as the Lincoln Near-Earth Asteroid Research (LINEAR), run by the Massachusetts Institute of Technology Lincoln Laboratory, and NASA's Near-Earth Asteroid Tracking (NEAT), which collectively account for 90 percent of all NEO detections. The MPC is hard-pressed to keep up with the tide of incoming data, especially with a volume of main-belt asteroid observations 100 times as great as that for NEOs.

Despite the workload, the MPC staff consists of only 2.5 people, including Marsden, who would like to keep the center running 24 hours a day. But that is not feasible: MPC gets just $130,000 a year from NASA, despite the agency's increased spending on NEO surveys. Other income, from subscriptions and donations, is not enough to cover the 80- to 100-hour workweeks. "Here we are saving the world, and they expect us to do it on our own time," Marsden quips.

More draining than the task at hand, however, is the time wasted on arguments. "There's a lot of infighting in this business. Not everybody likes everybody," he says. Besides the XF11 affair, which soured his relationships with several colleagues, Marsden has taken heat over access to information. He would rather not release data for tentative, single-night asteroid sightings--"one-night stands," as he calls them--both to ensure the data's reliability and to conform to the policies of leading programs such as LINEAR, NEAT and Spacewatch, which do not want unsubstantiated data made public. Astronomers who are anxious to see everything blame Marsden for impeding the information flow. "Brian follows the rules [set by the IAU], but the rules are flawed," Lowell Observatory astronomer Ted Bowell complains. He states that Marsden and others "often post orbital predictions without sharing the data that led to the calculations. I find that scientifically unacceptable."

Despite such criticism, the IAU recently extended the Smithsonian's contract for running the MPC through 2006. As for beyond that, rumors swirl about "hostile takeovers," in Marsden's words. Grant Stokes, who heads the LINEAR program, thinks that moving the MPC to a new home would be a mistake. "Brian and his center service the observing community wonderfully," Stokes says. "It's hard for me to believe this effort could be duplicated elsewhere."

Marsden tries to ignore the squabbles as he looks to the future. One day, inevitably, there will be a NEO on a collision course with Earth. With luck, it will be small and won't cause much damage. If it is spotted years or decades in advance, there might be time to intervene. "This is one threat we can do something about," he declares. Various defensive strategies have been proposed, including nudging an approaching asteroid with a nuclear blast or darkening part of the object's surface so that the thrust produced by radiated heat changes its orbit. Marsden is not sure how much money should be spent exploring these options but insists that "we have to do more than the dinosaurs."

Until now, the focus has been on large asteroids, a kilometer or bigger. The goal of the Spaceguard Survey, funded mainly by NASA, is to find 90 percent of these objects by 2008. More than 650 asteroids have been identified so far, perhaps half the total. (Astronomers estimate the total based on discovery rates from previous surveys.) Still, Marsden remarks, "we should begin planning the next step." Looking for 200- to 300-meter-wide objects is often proposed as a sensible target, but that would require new telescopes and roughly 10 times as much money.

Marsden turns 66 this month and would eventually like to hand the reins over to MPC's associate director, Gareth Williams, his partner since 1990. There's no timetable for a transition, says Williams, who admits he has "very big shoes to fill. Brian has been preeminent in the field since the 1960s." NASA Ames astronomer David Morrison, chair of the IAU's NEO working group, also lauds Marsden's efforts. Given Marsden's long tenure in the NEO field--starting out as he did when there was no "field" to speak of--Morrison is skeptical about talk of his impending retirement: "I think he'll do it forever." That is, of course, if the world doesn't end first.

--------------------------------------------------------------------------------
Steve Nadis is a science writer based in Cambridge, Mass.

Copyright 2003, Scientific American

===========
(4) CATCHING A COMET'S TAIL IN THE EARTH'S UPPER ATMOSPHERE

Andrew Yee <ayee@nova.astro.utoronto.ca>

[ http://www.jsc.nasa.gov/news/releases/2003/J03-80.html ]

Catherine E. Watson
Johnson Space Center, Houston, Texas July 10, 2003
Phone: 281/483-5111

Release No.: J03-80

CATCHING A COMET'S TAIL IN THE EARTH'S UPPER ATMOSPHERE

For more than 20 years, NASA has flown high-altitude research aircraft to collect cosmic dust -- debris of comets and asteroids that fills the inner solar system. In late April though, they made the first attempt to collect dust particles from a very specific target -- comet Grigg-Skjellerup.

Until that flight, scientists had no way of knowing the cosmic origin of the dust particles they collected. Using a computer model developed by Dr. Scott Messenger, a researcher in the Office of Astromaterials Research and Exploration Science at NASA's Johnson Space Center in Houston, they were able to determine exactly when to fly in order to catch a piece of the comet they wanted to examine.

"In effect, NASA is exploring the solar system with airplanes," Messenger said.

Messenger predicted that the week of April 22 was the best opportunity for collecting Grigg-Skjellerup particles, as the Earth passed through the dust stream created by the comet as it flew around the Sun.

Dust streams from comets are similar to those that produce meteor showers, but are different in several important ways. First, the particles are much smaller than meteor particles, which are about the size of a grain of sand. Second, the dust streams hit the Earth's atmosphere at much lower speeds, enabling the dust to survive entry into the atmosphere without melting. Third, these streams are very young, produced as recently as 30 years ago, while many meteor streams are hundreds of years old.

This last aspect is what makes the comet dust particles possible to identify in the dust collections, even among a very abundant background of interplanetary dust. The fresher cometary dust particles can be identified by their lack of solar flare damage tracks and implanted gas from the solar wind. Dust particles from comet Grigg-Sjkellerup will be identified by a detailed examination of the collected samples, a process that could take years.

"The key measurements will be performed by transmission electron microscopy, a technique that gives compositional information on an atomic scale," Messenger said.

Comet samples are a good place to look for the ingredients of the early solar system, which themselves came from the remnants of early stars in the universe.

"Identifying cometary dust particles will allow us to study the most distant parts of the solar system on a microscopic scale," Messenger said.

===========
(5) METEOROIDS 2004

Peter Brown <pbrown@uwo.ca>

First Announcement

METEOROIDS 2004

A conference to be held at the University of Western Ontario, London, Ontario, CANADA 16-20 August 2004

This conference will be the fifth in a series of meteoroid meetings which have been held every few years since 1992, the last in Kiruna, Sweden in 2001. It will accommodate a broad range of meteoroid research ranging from the dynamics, sources and distribution of these bodies, their chemistry and their physical processes in the interplanetary medium and the Earths atmosphere to their impact on space weather and their hazard to space technology, and laboratory studies of meteorites, micrometeorites and interplanetary dust. The high activity of the Leonid stream and the appearance of the very bright comet, Hale-Bopp  provided  new data related to meteoroids in recent years. Furthermore, the accurate measurement of orbits for several recent meteorite falls and detailed observations and modeling of their behaviour is providing a bridge between meteoritic material studied on Earth and composition of Near Earth Asteroids. The discovery of  solid particles entering the solar system from interstellar space and improved dust measuring capabilities on interplanetary spacecraft broaden the range of experimental data. Current research further benefits from the use of large aperture radar facilities to detect fainter meteors and the general availability of high powered computing facilities to support dynamical model calculations. Special emphasis of the discussion will be on the observational sensitivities and biases that arise from the recent application of different observation methods. With this theme we wish to address both the dynamics of small bodies in the solar system as well as the evolution of solid matter which provides a bridge to include aspect of astrobiology and astromineralogy that currently is enabled through IR astronomical obersvations. The meeting will be of interest to researchers from astronomy, astrophysics, cosmochemistry, mineralogy and space physics.


TOPICS

Scientific areas:
* Dynamics, sources, and spatial distribution of meteoroids including
sporadic, shower, and interstellar meteoroids
* Physics and chemistry of meteoroids and their interaction processes in the
atmosphere including ablation studies and radar head echo and trail effects
* Fireball and bolide phenomenology from modeling and observational studies
and in connection with meteorite falls
* Mineralogy, chemistry and physical properties of extraterrestrial materials (meteorites, micrometeorites, IDPs)
*  Influence of meteoric constituents on atmospheres
* Hypervelocity impacts on spacecraft
* Space debris and meteoroid models and flux - defining the natural particulate environment in space.
* Interelation of meteoroids, meteorites, IDP's, asteroids and comets
Experimental and observational methods:
* Optical observations of meteors including ground-based visual,
photographic, video, and telescopic techniques
* Satellite observations of meteors in various passbands
* Measurements of meteoric atoms in the atmosphere by lidars and other techniques
* Acoustic measurements using infrasound and seismic detection techniques
* Radio detection of meteors (VLF, ELF - relation to electrophonic sounds)
* Meteor- and large aperture radar observations
* Observations, in-situ satellite and laboratory measurements of dust and meteorite material

SCIENTIFIC ORGANIZING COMMITTEE
**************************************

Jack Baggaley, University of Canterbury, New Zealand
Martin Beech, Campion College, Regina, Canada
Addi Bischoff, Institute of Planetology, University of Muenster, Germany
Jiri Borovicka, Astronomical Institute ASCR, Ondrejov Observatory, Czech Republic
Peter Brown, University of Western Ontario, London, Canada
Eberhard Gruen, Max-Planck-Institut fuer Kernphysik, Germany
Robert Hawkes, Mount Allison University, Canada
Peter Jenniskens, NASA Ames Research Center, United States
Ingrid Mann, Institute of Planetology, University of Muenster, Germany, (Chair)
Tadashi Mukai, Kobe University, Japan
Asta Pellinen-Wannberg, Space Research Institute Kiruna, Sweden
Olga Popova, Inst. for Dynamics of Geospheres RAS, Russia
Vladimir Porubcan, Astronomical Institute SAV, Bratislava, Slovakia
Douglas O. ReVelle, Los Alamos National Laboratory, United States
Frans Rietmeijer, University of New Mexico, United States
Junichi Watanabe, National Astronomical Observatory of Japan, Japan
Iwan Williams, University of London, UK

LOCAL ORGANIZING COMMITTEE
***********************************

Peter Brown, Margaret Campbell-Brown, Peter Jedicke, Alan Webster (University of Western Ontario)
Robert Hawkes (Mount Allison University) (co-chairs)

==============OPINION==============

(6) A LUNAR KLONDIKE?

Tech Central Station, 9 July 2003
http://www.techcentralstation.com/1051/techwrapper.jsp?PID=1051-250&CID=1051-070903A

By Glenn Harlan Reynolds
 
It's happening again. With commercial interest in space exploration beginning to pick up steam, scientists are complaining that someone is stepping on their turf, as an article (sadly, not available on the Web) from last week's Financial Times makes clear:

But one man's science fantasy looks considerably less attractive to others. Richard Steiner, a professor and conservation specialist at the University of Alaska, is deeply concerned at the prospect of any country granting licenses for lunar exploitation without proper international consultation.

"The moon is owned by everyone," he says. "A farmer in Zimbabwe should also have a say. This has huge historic importance." While this first commercial launch seemed "relatively innocuous", Mr Steiner says it sets a dangerous precedent for more intrusive projects, such as strip-mining.

Calling for clearer international rules, he is also campaigning for the moon to be named a World Heritage Site. When asked about the prospect, to some incredulity, the UN said that was legally impossible.

Yes. You see, the Moon is a different, er, World. And, as earlier critics also failed to note, the grant of licenses to private companies to commercially exploit the Moon isn't lawless. Instead, it's governed by the Commercial Space Launch Act and specifically involves the regulators ensuring that international obligations are complied with. The 1979 Moon Treaty represented an effort to enact Steiner's views into law, but it failed miserably and was not joined by any space power.

But the complaints of people like Steiner -- like those of so many critics of U.S. action -- don't really have much to do with law, as the U.N.'s incredulous reaction makes clear. (It's revealing, too, that Steiner, like most such critics, seems to regard international law as a potent wish-fulfillment tool without bothering to see what it actually requires.) Rather they seem to stem from a fear of change, and a visceral opposition to doing something. (Forget the Zimbabwean farmer -- nobody's offering him a veto on the European Union's restrictive policies regarding genetically modified foods, after all, despite its far more significant impact on his life. He's just there to provide a bit of multi-culti camouflage. And what's wrong with "strip mining" on the Moon? The complaint about strip mining on Earth is that it leaves the landscape "looking like the Moon." The Moon already looks like the Moon.)

I think that this sort of opposition -- like the anti-American sentiment with which it is often, though not always, coupled -- stems from a visceral dislike of human progress, and the notion that humans are some sort of cancer on the Universe, that that the Universe would be better off without. As I wrote here a while back:

It is always a surprise to me that people who view humanity as a cancer somehow continue to live, and even to raise children, rather than committing the honorable suicide that self-diagnosis as a cancer cell would seem to call for, but the human mind is entirely capable of holding contradictory views as it operates. And this view does describe a certain part of the environmental movement: the part that seems to be motivated more by a view of human works as evil than by a desire to preserve nature.

I believe that it is this aspect of the environmental movement that will play the biggest role in opposing terraforming efforts, and that -- by speaking out against the terraforming of a dead Mars, or even a Mars inhabited by bacteria and lichens -- those people will be forced to show their true colors. After all, one may be motivated to protect a sequoia forest either by hatred of loggers or by love of trees. But when one opposes development of rocks and sand, it is pretty obviously not action in the cause of life. So pay attention to who denounces proposals for Martian terraforming as they begin to appear more frequently in mainstream discourse. It will not only be of interest in itself, but will tell you something about how you ought to view the denouncers' other positions.

I don't regard human works as evil. I rather doubt that farmers in Zimbabwe do, either. Those views seem to be held largely by pampered Westerners more interested in striking moral poses than in helping humanity. The good news is that their influence is steadily declining. The bad news is that their complaints are growing steadily more tiresome. At least, I'm certainly tired of hearing them

Copyright 2003, Tech Central Station

============LETTERS=============

(7) RE-MYSTIFYING THE TUNGUSKA EVENT

Daniel Fischer <dfischer@astro.uni-bonn.de>

Dear Benny,

I'm noting a disturbing trend in the (not only German) mass media in re-mystifying the Tunguska event, and I fear that this tendency will only increase with the 100-year anniversary creeping closer. Just in the last few weeks there were big radio and TV features in some of the supposedly-leading science programmes here in Germany in which the standard view of the Tunguska explosion, i.e. the airburst of a stony asteroid, was attacked. A lack of clearcut evidence for extraterrestrial material was given as an argument against this model as well as an apparently too complicated pattern of the fallen trees - but the alternative offered were certainly not more
convincing, namely a highly complicated scenario with an exploding column of volcanic gas which nonetheless seems to be particularly attractive for a certain brand of science popularizers.

Until that recent wave of anything-goes-but-the-accepted-view shows (plus numerous newspaper and magazine articles with the same slant) I had the impression, which most on this forum seem to share, that the case for the stony meteorite impact is pretty solid, with perhaps the three most important and influential papers being

Sekanina, The Tunguska event - No cometary signature in evidence,
   Astron. J. 88, 1382 [1983],

Chyba & Zahnle, The 1908 Tunguska Explosion: Atmospheric Disruption of a Stony Asteroid,
   Nature 361, 40 [1993] and

Farinella et al., Probable asteroidal origin of the Tunguska Cosmic Body,
   Astron. & Astrophys. 377, 1081 [2001].

Now either the scientific debate has moved beyond those and many similar papers without anyone in the impact community noticing, and the doubts voiced about the asteroidal model are justified and severe - or the outspoken 'skeptics' faction is just more appealing to the media than the mainstream researchers. When a model is established enough (like for 10...20 years) time might just be right to attack if, regardless of its merits? One way or another, I consider the 'bad press' the Tunguska standard view is getting these days increasingly disturbing.

Interestingly, at the same time there seems to be increasing criticism of the impact model for the K/TB mass extinction (also 20+ years old), again mainly in the media. Just the other day, a respected science show on German TV (based on the Discovery channel, I think), was most vigorously pushing the volcanic alternative and even dared to claim that (paraphrasing) 't is only the mass media who still believe in the asteroid.' While it is true that there are new doubts among some geologists about the Chicxulub structure really being the 'killer crater', again I'm not aware that the impact view is quickly losing out to the Deccan volcanism
view in the wider community. So, what's going on here?

Regards,

Daniel Fischer

===============
(8) RE: IMPACT HAZARD SUMMARY BY ANDREA MILANI

Jens Kieffer-Olsen <dstdba@post4.tele.dk>


Dear Benny Peiser,

It is a pleasure to read Andrea Milani's lucid contribution 'IMPACT HAZARD SUMMARY' from Science, 20 June 2003 and included in CCNet 55/2003 - 10 July 2003.

It's a demanding task to combine the scientific expertise with the necessary political flair, and AM has surely done a remarkable job in that area, making several points which should be standard tools in our inventory of arguments. My comments below are therefore no more than just that -
comments. 
 
> A recent reassessment of the Tunguska-class impacts
> suggests that the average frequency for impacts of this
> size is only one in about 1,000 years (1).

Considering that it makes an important difference to the urgency of predicting/obviating smaller impacts, whether the frequency is once every 150 years or a full one magnitude lower, I'm puzzled why the pressure is on the NEO community to swear allegiance to that recent reassessment, which I presume is bound to be followed by more reliable future reassessments? 
 
[snip]

> The choice of targeting the surveys to objects above
> 1 km is optimal, provided that this coincides with the
> critical size for global effects. This can be shown by
> a probabilistic computation of the expected damage,
> in human lives lost per year (5). The onset of global
> effects is believed to increase the number of casualties
> by as much as an order of magnitude. If this is true,
> then the expected casualty rate is approximately the
> number of casualties just above the global effect
> threshold times the frequency of such an impact (6).
> Thus, if the casualties are 1 billion and this happens
> once in a million years, the expected damage is ~1,000
> deaths per year (7). The contribution of the more
> frequent Tunguska-class impacts is minor: the expected
> damage is a few tens of thousands casualties divided
> 1,000 years, or a few tens per year.  Thus to target for
> discovery the objects just above the global effects
> threshold is the most "cost effective" way to decrease
> the risk.
>
> This "insurance approach" to the problem of impact
> risk appears questionable to many, including myself.
> Two other rational arguments can be used. We could
> agree on a level of damage we consider unacceptable:
> an impact by a 1 km asteroid, with energy comparable
> to a global thermonuclear war, could be considered
> unacceptable even if it might not trigger global effects.
> The other argument is the technological limit: there is
> no point in setting a goal we cannot achieve in the
> foreseeable future.

There is a third approach, since we could attempt to anticipate the public reaction to a minor impact killing and maiming thousands of people.  The lift in public awareness AFTER such an event does not come without a price - that is a loss in confidence in those astronomers supposed to have warned us beforehand.

[snip]

> Observations and computations to date have not
> discovered a likely impactor. It is unlikely that a
> serious threat is discovered in our lifetime (20).
> But what should be done if such an impactor is
> identified? We cannot justify the effort to discover
> it unless we can safeguard of our planet even in this
> worst case.
>
> The effort necessary to deflect an asteroid to avoid
> a collision goes well beyond the level of resources
> available to the scientific community and cannot be
> prepared before the need arises.  On the contrary,
> the know how necessary for such a task should be
> gathered in advance. The space agencies, such as
> NASA and ESA, have the necessary capabilities and
> are interested in including this goal in their mission.

Especially in the case of smaller impactors a warning is enough to save people's lives through evacuation. That is justification enough for the detection effort, and moreover that effort is open for all countries to contribute to.
 
Deflection is not to be demanded by anyone in a cavalier manner, since we are effectively talking big-time spending by the American taxpayer.  The issue will be handled by the US congress when the time is right, and they will not be paying all that much attention to idealized views on the matter - even if presented by an expert such as AM.
 
Yours sincerely
Jens Kieffer-Olsen, M.Sc.(Elec.Eng.)
Slagelse, Denmark

=========
(9) AND FINALLY: "WHY I LOVE LEMBIT OPIK MP"

The Guardian, 8 July 2003
 
I'm terribly worried about Charles Kennedy. One minute he was standing in the House of Commons objecting to the imminent invasion of Iraq at the top of his whisky-loving lungs, and the next he was gone. Has someone kidnapped him? Has he run away? Charles, if you're reading this, you're not in any trouble; I just want to know you're OK.

Still, one great side effect of Charles's disappearance is that it increases the chances of my favourite MP, Lembit Opik, taking over as head of the Lib Dems. There is almost no reason not to love Lembit. He's tall, he's Welsh and he looks a bit like an enthusiastic Labrador. He can play the harmonica (but doesn't). He's going out with Sian Lloyd. His name was invented during a drunken game of Boggle. But, most importantly of all, while the rest of the honourable members are lying in the gutter, Lembit is looking to the stars.

It was only because of the MP for Montgomeryshire's tireless campaign to increase asteroid awareness that the government agreed to set up a task force to investigate the risk of giant rocks crashing into the earth and wiping us all out. Even though these "global killers" (his words, not mine) usually only strike every 30m years, it has been about 65m years since the last one, and that one got rid of the dinosaurs. In other words, the end of the world is looking decidedly nigh. But there's no need to panic. Thanks to Lembit, scientists are hard at work designing a giant "cosmic condom" (again, his words) to catch asteroids before they turn us into crostini. If only the dinosaurs had had their own Lembit, they might still be here today. Although what they'd make of I'm a Celebrity - Get Me Out of Here! I don't know. Perhaps they'd eat Phil Tufnell.

Copyright 2003, The Guardian

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