AUSTRALIAN SPACEGUARD SURVEY - COMMENTS

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Contents

• Duncan Steel - threat from small objects
• Tony Beresford - Australian politicians
• Nature article - Southern Ocean impact
• Clark Chapman's testimony to the US government
• David Morrison - How are we doing?
• Big Splash - more on the Southern Ocean impact
• Kinetic energy of impacts
• Uncertainty about impact frequency and energy
• A crude estimate of tsunami height from hydrostatics
• Lunar impacts detected by Apollo instruments and the very fresh lunar crater Giordano Bruno
• Cretaceous-Paleogene disaster: How many satellites did the Earth have in the Late Mesozoic
• Tsunami warning lines 'broken down'
• Australian Science Festival - 1998
• Giant impact on Venus 800 million years ago?
• Dealing with the impact hazard
•  Press release 27 May 1999
• Coordination Committee on Science and Technology activities 1998/99
• Abstract of Icarus paper Asteroids: Shattered but Not Dispersed
• Transcript of 60 Minutes item
• Chinese meteorite disaster in 1490AD
• Spaceguard supporter Congressman George Brown dies
• Press release 8 Oct 1999
• Crater ages and geological boundaries
• Press release 1 Dec 1999.
• Book Review - Comet and asteroid impact hazard on a populated Earth.
• How often do NEOs come "close" to Earth - David Morrison.
• Rob McNaught describes NEO follow up (March 2001).
• Spotting extra-solar impacts
  

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Duncan Steel 20 November 1997

One thing I would note is that the letter from Edward Teller for which you provide a link (headed 'Correspondence with UK politicians!') was sent not only to John Major (then UK PM) but also to John Howard. I do not know how the Australian government replied to Teller; one would hope in a more respectful manner than did the UK government.

Another thing is that back in March the Minister for Science etc. put out a press release saying that Howard had asked the ministers for Science (i.e., him), for Defence, and for Education, Employment, Training & Youth Affairs, to look into how they might refund the Spaceguard programme. Media articles appeared on April 1st (maybe a joke?) in Australia, and a few days later in many places around the world. In fact at the time I was in the US and I only became aware of this later when various people, in Australia and elsewhere, asked me about it: they were under the impression that the media release implied that the program had re-started. In fact I have never heard anything official from the government on this matter, so I don't know what was done (or not done). Having waited for six months, a few weeks back I wrote to Howard to enquire as to whether anything was happening. As of yet I have not received a reply, but these things take time.

One problem with all of this is that people (the public, and public servants) tend to think that we are talking about only cataclysmic events which have very low probabilities (actually, the way they tend to think is that if massive impacts only occur once every 100,000 years then we must be safe for another 50,000...). In reality, the basis of the whole thing is that there is a paradigm shift under way in science which is leading to the realization that the Earth is not an isolated system, and that now, in the Space Age, we need to think about the things in 'space' which can affect us. A short-term example is this. Comet Tempel-Tuttle passes perihelion next February. It happens to have an orbit which passes very close by that of the Earth. Although the comet itself will not hit the Earth (at least, not 'soon', meaning many millennia), bits of it DO strike the Earth every year: the Leonids meteor shower, around November 17. Last Monday night there was a fine display visible especially from the eastern Pacific region. The rates have been climbing in recent years as the comet has been coming back on its 33-year period orbit. Indeed about every 33 years since AD 902 there has been a Leonids meteor storm. Those in 1799, 1833 and 1866 caused great panics (e.g., for a century after the 1833 storm, the Seventh Day Adventist Church interpreted the storm as being a sign of the Second Coming of Christ and the approach of the Apocalypse). In 1966 there was a major storm, but at the time there were no astronauts in orbit, and just four comsats, total area ten square metres. If one does the sums, there seems IN THEORY to be a small hazard to satellites (of the order of 1% that one satellite from the total population will be taken out of action). But it seems that there is something we don't understand: in 1993, an outburst of the Perseids meteor shower (much weaker than the Leonids storms) appears to have taken out two satellites (ESA's Olympus, and Telstar-4), whereas really zero damage would have been expected. Thus various people are worried about what may happen on 17 November 1998 and 1999, when Leonids storms are anticipated. For example, NASA does not plan any Space Shuttle flights, so far as I am aware, and of course there is concern that surveillance or GPS satellites may be lost. My point is that in the Space Age we MUST understand what is going on in space, and although comets seem remote, they can affect us even without an unlikely massive impact on Earth occurring.


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Tony Beresford, 22 November 1997

Duncan Steel passed on your letter , and his reply to me, probably because I am a member of the SpaceGuard foundation. I had two personal meetings with Gene & Carolyn Shoemaker, A Comet hunter's lunch ( with Bill Bradfield) in October 1993, and a restaurant dinner in Sept 1996.

Just been looking at your Web page. I have been involved in lobbying support for Spaceguard Australia for 4 years now. Our politicians just arent interested. Just last Sunday I was talking to a person, who had written to John Moore. His reply managed to simultaneously admit that only 10% of NEO's had been found, and be satisfied with the statement ( true of course) that no KNOWN object was on an impact trajectory. Didn't seem to care about the unkown ones. A reply from the Space Policy officer, maintained that support was "still under consideration", Seems to me we are in the middle of an extra script for "Yes Minister". The reply from my local MP [ Trish Worth of Adelaide], just echoed earlier bureaucrats comments that Duncan Steel should ask for ARC funding. Of course ARC funding is not supposed to be given to routine work, which the NEO search is of course.

Tony Beresford Ph.D., FRAS, FBIS
Technical Information Officer, Astro Soc. of South Australia
Ph (08) 8338 1231, Fax (08) 8379 4145
e-mail starman@camtech.net.au


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Abstract from 27 Nov 97 issue of Nature

Geological record and reconstruction of the late Pliocene impact of the Eltanin asteroid in the Southern Ocean "

In 1995, an expedition on board the research vessel FS Polarstern explored the impact site of the Eltanin asteroid in the Southern Ocean, the only known asteroid impact into a deep ocean basin. Analyses of the geological record of the impact region place the event in the late Pliocene (~2.15Myr) and constrain the size of the asteroid to be >1km. The explosive force inferred for this event places it at the threshold of impacts believed to have global consequences, and its study should therefore provide a baseline for the reconstruction and modelling of similar events, which are common on geological timescales.

R Gersonde, F T Kyte, U Bleil, B Diekmann, J A Flores, K Gohl, G Grahl, R Hagen, G Kuhn, F J Sierro, D V”lker, A Abelmann & J A Bostwick

(Abstract duplicated here because it only appears on the Nature site for a limited time)

See also this CNN News Item


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Experts Say Asteroid Danger Is Real

c The Associated Press AP-NY-05-21-98 1809EDT

By PAUL RECER

WASHINGTON (AP) - A mile-wide asteroid could smash the Earth, causing widespread death and destruction, and ``we wouldn't even know it was coming,'' an expert told a congressional panel Thursday.

Such an asteroid, striking the planet at thousands of miles an hour, would ``threaten the future of modern civilization'' by darkening the sky for a year, causing widespread starvation by destroying food crops and directly or indirectly killing millions of people, said Clark R. Chapman, an asteroid expert with the Southwest Research Institute in San Antonio.

Testifying at a hearing of the House Science Committee's panel on space and aeronautics, Chapman said a mile-wide asteroid would gouge a crater bigger than Washington, D.C., and deeper than 20 Washington Monuments piled on top of each other.

Chapman said the chances of such an asteroid striking the Earth next year are one in a few hundred thousand, but this ``is more likely to happen than that the next poker hand you are dealt will be a royal flush.'' The odds for a such a poker hand are about 649,000 to one, he said.

A person's lifetime chances of being killed by an asteroid, of any size, are about one in 20,000, said Chapman. He noted the odds of being killed by an asteroid are about the same as the risk of dying in a passenger aircraft crash, but more likely than being killed by a tornado or a flood.

The scientist said that an asteroid much smaller than a mile wide exploded over Tunguska, Siberia, in 1908 and the shock wave flattened trees across an area larger than New York City. Such a burst over a major city, he said, could kill millions instantly.

Chapman and other experts said that the Earth's only protection from such a space bombardment is to search the skies, find asteroids apt to hit the Earth and then rocket out bombs that would divert the space rocks away from the planet.

With a 10-year warning, ``we could probably save ourselves,'' said Chapman. ``At the very least, we could evacuate ground-zero and save up food supplies to weather a global environmental catastrophe.''

But he said that little effort is being put out to find Earth-threatening asteroids and only about 10 percent of an expected 2,000 near-Earth objects have been identified and tracked.

Rep. Dana Rohrabacher, R-Calif., the committee chairman, pressed Chapman on his statement that a killer asteroid could hit without warning.

``Yes,'' said Chapman. ``A mile-wide asteroid could hit tomorrow and we wouldn't even know it was coming.''

Rohrabacher said that a committee led by the late asteroid expert Eugene Shoemaker recommended five years ago that the National Aeronautics and Space Administration start a systematic effort to search out, identify and plot all asteroids that pose a threat to the Earth. The report said the effort would cost about $5 million a year, but the congressman said the space agency has done little to follow up on that recommendation.

Also, he said, an Air Force asteroid mission was canceled last year after President Clinton used his line-item veto against the project.

In response, Carl Pilcher, NASA's science director for solar system exploration, told the panel that his agency a year ago recognized it was not spending enough to complete a comprehensive survey of Earth-threatening asteroids. Pilcher said, however, that NASA has six missions either planned or under way to explore, land on and sample asteroids. He said this work is essential for science to understand how best to divert threatening asteroids.

AP-NY-05-21-98 1809EDT

Copyright 1998 The Associated Press. The information contained in the AP news report may not be published, broadcast, rewritten or otherwise distributed without prior written authority of The Associated Press. 

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SPACEGUARD ASTEROID SURVEY: HOW ARE WE DOING?

For the January 1999 update see this NASA site.

From David Morrison, NASA (via Cambridge Conference) , August 1998

The goal of the Spacewatch Survey is to find 90% or more of the Near Earth Asteroids (NEAs) within a decade. It is also a goal of NASA, stated in the NASA Office of Space Science Strategic Plan, to discover 90% of the NEAs within the next decade. This is a summary, prepared in collaboration with Alan Harris of JPL, to see where we stand today (mid-1998) in this effort. We will try to make further updates at 6-month intervals and post them on the NASA Impact Hazard website.

For purposes of this discussion, NEAs with Diameter (D) > 1 km are equated to asteroids with absolute H magnitude less than or equal to 18.5, with perihelion distances less than 1.3 AU. There are approximately 2000 NEAs estimated to exist that fit this definition. Other definitions of NEAs (or ECAs, Earth-Crossing Asteroids, or PHAs, Potentially Hazardous Asteroids) are more restrictive and also require more detailed analysis of their orbits. The present definition of an NEA, however, together with the estimate of 2000 total NEAs, is sufficient to assess the current performance of the survey.

Note that many of the NEAs discovered are smaller than 1 km (H > 18.5). Any survey system will discover as many or more small asteroids as large ones. But we will consider only asteroids larger than 1 km, since these are the most dangerous, and the metric for success of the survey is defined in terms of objects with D > 1 km.

The three most successful searches during the past year have been LINEAR (the Lincoln Laboratory NEA survey of the US Air Force), NEAT (the NEA survey carried out jointly by JPL and the USAF), and Spacewatch (the search carried for more than a decade at the University of Arizona). Together they accounted for more than 85% of the discoveries. LINEAR has dominated the recent growth, going from 0 to 4 to 16 NEAs (D > 1 km) in the last three 6-month periods.

The table below shows 38 NEAs larger than 1 km discovered from July 1997 through June 1998. There was a marked increase in discovery rate over this period, from 11 NEAs discovered in the first 6 months to 27 in the most recent 6 months.

In a ten-year survey expected to detect 90% of this NEA population, we must discover just over 20% in the first year, with the rate declining exponentially thereafter as greater completion is reached and more of the objects found are rediscoveries. Therefore, to achieve the stated Spaceguard goal of finding 90% of the 2000 NEAs in a decade, we must increase the discovery rate by approximately a factor of 12 over the average for the past 12 months, or a factor of 9 over the average of the past 6 months. Searchers have just now pulled within an order of magnitude of the required discovery rate, with another factor of 10 needed to implement the Spaceguard Survey.

David Morrison

NEA DISCOVERY SUMMARY (Diameter > 1 km)
FOR JULY 97 THRU JUNE 98

Discoverer	12 month	1997:July-Dec	1998:Jan-Jun
LINEAR	20	4	16
NEAT	9	4	5
Spacewatch	4	1	3
Other	5	2	3
Total	38*	11	27

*Total required to implement the Spaceguard Survey: >400 discoveries/year 

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Big splash: Scientists describe asteroid's ancient ocean plunge

From the CNN News Website (reproduced here because it is no longer accessible at CNN but is highly relevant to the issue of tsunami and asteroids)

November 26,1997 Web posted at: 5:39 p.m. EST (2239 GMT)

SYDNEY, Australia (AP) -- An asteroid that tumbled through space for eons blasted into the sea off Antarctica more than 2 million years ago with the force of "a cosmic bomb," a multinational team of scientists said in a research paper published Wednesday.

Striking the Bellingshausen Sea with the explosive power of 100 billion tons of TNT, the asteroid Eltanin blew a column of water 5 kilometers (3 miles) high and punched a temporary "oceanic crater" in the sea, according to the paper, which appeared in the British science journal Nature.

The researchers estimate the asteroid was at least 1 kilometer (six-tenths of a mile) and possibly up to 4 kilometers (2.5 miles) in diameter. The blast in the ocean did not leave a crater on the seabed, but a similar strike on land would have left a hole 15 to 40 kilometers (9 to 25 miles) across.

'Devastating mega-tsunamis'

Eltanin, the only asteroid ever known to have hit water, triggered waves 20 to 40 meters (65 to 130 feet) high, "devastating mega-tsunamis" that swamped the coasts of South America and Antarctica.

"The tsunami ... destroys enormous, large areas. ... In the Pacific Rim there are signs of such things," one of the lead researchers, Rainer Gersonde of the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, Germany, told The Associated Press in a telephone interview Wednesday.

Sediment spread up to 4,000 kilometers (2,500 miles) away and dust, vapor and salts wafted around the world. Enough debris and hot vapors were emitted to possibly damage the Earth's ozone layer, the researchers said.

"The dust and vapor probably caused a major change in climate, but whether that persisted or was for just a few years, we just don't know," said Karsten Gohl, a geologist from Macquarie University in Sydney who worked on the project.

There is no evidence that the climatic change caused the extinction of any species.

New seismic and deep-sea surveys conducted in 1995 by the German research ship Polarstem enabled the scientists to accurately date the blast to the late Pliocene period, 2.15 million years ago, and to gauge its effects.

An enigma solved?

The blast was well after the Northern Hemisphere's Ice Age began but "close to one of the strongest cooling events in this time period," the researchers'paper said.

"It might be that this strong cooling was related to the impact," Gersonde told AP. The fallout from the blast may explain the "Sirius enigma," the puzzle of why marine fossils are found high above sea level in the Transantarctic Mountains.

The researchers believe fallout from the stearn and vapor cloud dropped micro-fossils directly on the mountains, an idea that geologist Peter Barrett at Victoria University of Wellington, New Zealand, called "reasonably plausible."

David Harwood at the University of Nebraska, an expert on the Sirius fossils, conceded that the fallout theory "has potential" but said some Sirius deposits do not fit the model. He is among those who feel moving ice sheets may have scoured fossil deposits and redeposited them in unexpected sites.

The Eltanin impact was a medium blast, as asteroids go.

About 65 million years ago, an asteroid about IO kilometers (6 miles) in diameter struck off Mexico's Yucatan Peninsula and is widely believed to have killed off the dinosaurs by blotting out the sun with the dust it kicked up.

But rocks far smaller than Eltanin can cause massive damage: A meteorite only 45 meters (150 feet) across created Arizona's Meteor Crater, 1,220 meters (4,000 feet) across and 180 meters (600 feet) deep.

First known ocean strike

Eltanin is the only asteroid known to have struck the ocean, compared with about 140 known to have hit land -- even though the Earth's surface is 70 percent water, Jan Smits of the Research School of Sedimentary Geology at Amsterdams Vrije University noted in a commentary on the research in Nature.

Besides Gersonde, in Germany, researchers on the project included Frank Kyte at the Institute of Geophysics and Planetary Physics at UCLA and scientists from the Department of Geology at the University of Salamanca in Spain; Macquarie University's School of Earth Sciences in Sydney; and the U.S. Naval Research Lab in Washington.

Eltanin is named for the U.S. research ship that brought up deep sea samples in 1965 that later were fomd to contain iridiurn, an element in asteroids.

Copyright 1997 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.


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Kinetic Energy of an Asteroid Impact

Michael Paine

The Kinetic Energy (KE) of an asteroid of typical density (around 3 grams per cubic centimetre) can be approximated by:
KE = 600 x (diameter/200)^3 x (speed/20)^2    Megatons of TNT
The following graph shows KE for a range of asteroid diameters and speeds (the vertical scale is logarithmic). There are numerous other factors which determine the amount of destructive energy reaching the ground - particularly the proportion of blast energy which is converted to tsunami wave energy if the asteroid explodes above a deep ocean.

For comparison, the Hiroshima atomic bomb had a yield of about 20 kilotons of TNT, the first H-bomb had a yield of about 5 Megatons (it "obliterated an island, leaving a hole 175ft deep and a mile in diameter") and the largest H-bomb built probably has a yield of about 100 Megatons. A major tsunami can be generated by an earthquake which is equivalent to 2 Mt of TNT. The lowest point on the graph is about 2Mt!

(tip: To expand the graph in Netscape, right click on the graph and select View Image)

 

Uncertainty about impact frequency and energy

The following graph illustrates the uncertainty about the frequency and kinetic energy of  impacts for a range of asteroid diameters (50m to 1 km).
The horizontal range - variation in impact energy - is based on impact speed ranging from 12km/s to 45km/s. Although speeds of up to 70km/s are possible (retrograde "head-on" collision) they are very unlikely. The chosen speed range probably represents more than 95% of impacts. The vertical lines represent a "typical"  impact speed of 20km/s.
The vertical range - variation in average* interval between impacts -  is mainly due to the uncertainty about the number of objects of each size that are in Earth-crossing orbits (mainly based on Ducan Steel's book "Rogue asteroids and doomsday comets"). This uncertainty can be reduced through a Spaceguard survey although, with current technology, we can only detect a very small proportion of objects under 200m diameter and therefore considerable uncertainty will remain.

* Impacts are probably randomly distributed in time - see Poisson Distribution.

(tip: To expand the graph in Netscape, right click on the graph and select View Image)


Not illustrated here is the uncertainty about asteroid diameter. These object are generally so small and so far away that their diameter has to be inferred from their absolute magnitude. Brightness, in turn, depends on the object's albedo (amount of light reflected from the surface). An object of magnitude 23 might have a diameter between 65m and 108m. Kinetic energy is proportional to mass which, in turn, is proportional to the cube of diameter therefore the uncertainty about diameter can lead to substantial uncertainty about impact energy. Finally, with limited observations, the absolute magnitude range +/-0.5 so, combined with the uncertainty about albedo, the estimated diameter can range from 50m to 190m.


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A crude estimate of tsunami height from hydrostatics

Important note: Sandia National Laboratories will soon be releasing the results of a comprehensive study of tsunami produced by small asteroids. These latest simulations reveal that the tsunamis generated by such impacts are considerably smaller (by orders of magnitude) than indicated on this web page. The researchers conclude that only large impactors pose a significant threat for an entire ocean basin (something greater than 1-2km) and that small atmosphere-exploding impacts will produce only local effects and negligible tsunami. If this is the case then the following calculations are likely to be invalid - but it was fun deriving them and science is supposed to be self-correcting! In hindsight, the reasonable agreement between the following calculations and earlier work is probably a fluke since it is reasonable to expect the tsunami height to be proportional to the square root of the "wave" energy.

This section gives an alternative method of estimating tsunami height from an "airburst" event, such as an asteroid exploding several kilometres above a deep ocean, using a calculator rather than a super-computer. The method involves estimating the energy reaching a square metre of ocean surface and equating this to the work required to depress that surface against hydrostatic pressure which, like a spring, increases in proportion to distance. From this a hydrostatic "head" can be derived:
            Head = SQRT(2 * work_done / (water density * g))
Now the energy reaching a square metre of ocean will be the blast energy divided by the surface area of  sphere centred on the explosion. For an explosion 8km above the ocean the surface area of the sphere  is approximately 8E8 sq m. An explosion equivalent to 10Mt of TNT is 4.2E16 Joules therefore the energy flux at the surface of an 8km sphere is 5.2E7 J/sq m. Assume 50% is this is converted to work in depressing the surface of the ocean (this is a guess but may not be too bad - see papers by Hills and Mader and Nemtchinov et al) (update:  the actual value may be just a few %). The resulting "head" from the above equation is 73 metres. In other words, we can expect the average depth of depression of the ocean surface under the blast to be 73m (update: this implies a dynamic pressure of about 7 atmospheres, which seems unlikely). The next major assumption is the surface area of ocean affected by the blast (although, it turns out that this does not greatly affect the height of the tsunami at a distance). If we project a cone from the centre of the explosion with an angle A=45 degrees then the resulting area of ocean will have a radius of about 8km. 
The tsunami height at a given distance from "ground zero" (hypocentre) will be inversely proportional to the ratio of distances therefore at 1,000 km we can expect a deep water wave height of 73*8/1000 = 0.6 metres. A "typical" airblast from a 50m stony asteroid is about 10Mt of TNT therefore this method is in reasonable agreement with the value provided by Gerritt Verschuur in the book "Impact!". The following table sets out a range of values for this method.
 

Approximate NEO diameter (m)	Kinetic Energy  (Mt of TNT)	Derived head of water (m)	Deep water tsunami height @ 1,000km  (m)  [Impact!]  {Hills & Mader}
50	10	73	0.6  [0.8]
-	20	103	0.8
-	50	163	1.3
100	75	200	1.6  [2.0]
200	600	565	4.5 {3.8*}

* The Hills & Mader value is for a surface explosion - see their equation (3) - for asteroid diameter D=200m or more, V=20km/s and density=3g/cu cm

deepwater tsunami height h=0.019 * D  (metres, at a distance of 1,000km)
As the tsunami approaches a shoreline its height can increase dramatically because the wave slows in shallow water and the energy becomes more concentrated. The final "run-up" size of the wave depends on the profile of the sea floor and other physical factors but it can reach 40 times the deepwater wave height. Therefore a 0.6m tsunami in the deep ocean can produce a 24m tsunami at a shoreline 1,000km from the impact. However, a more typical "run-up" factor is 10 and the resulting wave in this case would be 6m high.
See Tsunami from asteroid/comet impacts for more information.

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Lunar impacts detected by Apollo instruments

Michael Paine

Between 1969 and 1972 there were 6 Apollo Moon landings. The seismometers left on the Moon recorded a total of 114 impact events between 1969 and December 1975. The following graph shows the results - note the clustering of events. The impacts in July 1972 and September 1973 are described as "large".
There seems to be a case for permanent seismometer stations located on the Moon - after all, it is a excellent target surface for meteoroids, asteroids and comets - most "moonquakes" are probably due to impacts. The magnitude and frequency of small impacts could therefore be established.
Thanks to Peter Grego from Britain's Society for Popular Astronomy for the impact statistics.
 


 

NASA image of Crater Bruno (35.9N, 102.8E)



Lunar crater Giordano Bruno

The Apollo missions also revealed another interesting impact possibility, as speculated by Carl Sagan in "Cosmos". On 25 June, 1178 AD some monks in Canterbury , England witnessed what may have been a large impact on the far side of the Moon. The 22km crater Bruno is a prime candidate for this 800 year old impact (see also this NASA FAQ and here plus images from Clementine ("Giordano Bruno") and this Planet-B). The Apollo astronauts took photographs of this region of the moon and laser ranging equipment left on the Moon revealed that the Moon may still be "ringing" from this impact (a 3 metre, 3 year oscillation). On Earth a 1 kilometre* or larger object would be needed to create such a crater (although other reports suggest a 120Mt event - much smaller than the typical energy of a 1km NEO). If Bruno is 800 years old  then it will be a very recent example of a NEO impact sufficient to cause global catastrophe, should it have hit the Earth.
 
• Update Nov 1999: LPL's Crater Calculator gives a predicted impactor diameter of 850m, assuming a stony asteroid).
• Update 17 Mar 2001 Sky & Telescope: AN EYEWITNESS IMPACT DEBUNKED - Lunar Crater Bruno not associated with 1178AD event. Also it would have created a spectatular meteor show on Earth but none was recorded.

Links

• NASA's catalogue of lunar events.
For further information see the book "Rogue asteroids and doomsday comets" by Duncan Steel. See also "Rain of Iron and Ice" by John Lewis and "Possible relationship between the Farmington meteorite and a seismically detected swarm of meteoroids impacting the Moon" by J Oberst, (Meteoritics, 24, 23-28 1989 - copy on NASA's abstract database) for a detailed description of lunar impacts detected by Apollo and the relationship with the Taurid Meteor Complex (incl Tunguska) and crater Giordano Bruno (the latter is an unlikely link since, in 1178AD, the Taurids would have peaked around Apri or May).
Update: February 1999, The Japanese Lunar-A mission plans to land a seismometer station on the Moon.


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Cretaceous-Paleogene disaster: How many satellites did the Earth have in the Late Mesozoic

A.E.Rosaev, Roskomnedra, GNPP "Nedra", Yaroslavl, Russia

Reference: Rosaev A.E. Cretaceous - Paleogene disaster: how many
satellites did the Earth have in the Late Mesozoic // "30-Int.  Geolog.
Congr.  Abstr., Vol 3 of 3, Beijing, China, 4-14 aug 1996" p.508.

Now a hypothesis which explains a biological disaster occured between the
Mesozoic and Cenozoic eras by the fall of a large cosmic body onto Earth
has become well known. Below there is proposed a new interpretation of
available geological data on collection of craters at the boundary between
the Cretaceous and Psleogene periods. It has been proved that in case of
really simultaneous origin of Livian, Dniper and Kars groups of craters
the body which generated them could not move along a heliocentric orbit bu
t had been an Earth's satellite.
Due to a considerable inclination the orbit (68o) such satellite had a
short living time and consequently the disastrous event between the
Cretaceous and Paleogene was preceded by another no less dramaric event in
the past - capture or collision.
Within the proposed hypothesis it is possible to explain some detailes of
the catastroph on the boundary between the Mesozoic and Paleogene eras -
the cause of global fires and a final duration of extiction of biological
types.
A character of distribution of known craters by age and spatial position
within an interval of 0-100 mln. years leads to assumption that at least
once, 40 mln. years ago the Earth temporarily acquired a satellite in a
near polar orbit. Popigai,Beyechime-Salaatin, Wanaptei,Mistastin and
possibly Shunak craters are the consequence of its destruction. In this
case  the most probable parameters of the orbit were i=74o, W=96oW. It is
also impossible to exclude such interpretation of available data at which
38 mln years ago the last pieces of the Cretaceous-Paleogene bolide fell
onto the Earth.

Your’s sincerely,   Alexey E. Rosaev
Yaroslavl Astronomical Society, Russia


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Tsunami warning lines 'broken down'

                   Wednesday 11 November, 1998 (8:41am AEDT)

                   The Australian Geological Survey Organisation (AGSO) says
                   normal lines of communication for the National Tsunami Warning
                   System appear to have broken down for the Northern Territory.

                   On Monday, two earthquakes seven minutes apart, with an
                   epicentre in the Banda Sea, 600 kilometres north of Darwin,
                   started a tsunami.

                   The survey organisation's Kevin McCue says Emergency
                   Management Australia and the Australian Bureau Of Meteorology
                   were notified the wave might reach Darwin but the information
                   was not passed on effectively.

                   Mr McCue says he hopes the matter will be addressed at a
                   national meeting in Adelaide next week.

                   "Hopefully, we'll do it better next time but I'm [sure] that will be
                   a topic of discussion of great interest at the meeting," he said.

                   "I suppose what it does show looking on the positive side of
                   things is that there is a need for this to happen - that there is a
                   need for it to happen properly and appropriately and in a very
                   timely fashion and we'll try and get it right next time."

                   Territory Emergency Services director Iain Raye says it is
                   fortunate the tsunami was no more than a ripple by the time it
                   reached the Darwin coastline.

                   "We need to speed up the lines of communication between
                   AGSO and the Northern Territory and what will be
                   recommended is that we get advised the same time as Perth, even
                   though it may not affect Northern Territory waters," Mr Raye
                   said.


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1998 Australian Science Festival

by  Matthew James

As part of the 1998 Australian Science Festival  TPS arranged a free public lecture on planetary space exploration by Dr Miriam Blatuck, NASA Senior
Representative on 5 May: A capacity crowd of 300+ braved the rain to hear NASA's Senior Representative in Australia, Dr Miriam Baltuck provide a polished
overview of where we are at in the art and science of planetary
exploration. She particularly enthralled the audience with some insights
into the big questions of life and the Universe, while also catering to
the younger aspirations present.
Thanks are due to the Australian Science Festival staff, Dr Lawrie Brown
and "Sky and Space" magazine for assisting with the promotion of yet
another very successful annual lecture. Perhaps next year with
millennium fever rising, a presentation on the asteriod and comet
collision threat would be timely.


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Giant impact on Venus 800 million years ago?

To: The Editor, Scientific American

"Global climate change on Venus" by Mark A. Bullock and David H. Grinspoon [Scientific American, March 1999] describes evidence of "a geological event of global proportions [that] wiped out all the old craters some 800 million years ago". The article notes that "the idea of paving over an entire planet is unpalatable to many geologists" and explanations such as planet-wide volcanism are discussed. There is, however, an event that could result in the entire surface of a planet being "repaved" - an impact by a comet hundreds of kilometres in diameter. I understand that this would not necessarily cause a recognizable impact "crater" but could severely disrupt the crust and trigger volcanism. Research into this possibility would need to explain how Venus subsequently acquired its very dense atmosphere, since the original atmosphere would have been stripped away, and what happened to the impact debris in space - why didn't a small moon or ring form? Perhaps 800 million years is sufficient time for Venus to "recover".
Michael Paine
The Planetary Society Australian Volunteers

Dear Michael,
Thanks very much for your note (which we may or may not publish - it
depends on the other mail we've received).  Below is the authors' response.
Best wishes,
George Musser
 

Mr. Paine makes an excellent point about the potential for a large impactor on Venus to have altered the planetary climate.  David Grinspoon and I have calculated that the largest comet that one would expect to
have impacted Venus in the last billion years (from statistical arguments) would have increased the atmospheric water inventory 10 - 100 fold.  Such a comet would have been smaller than 100's of km in diameter -- perhaps 40 km or so, but could certainly have caused some kind of lithospheric disruption.  A 40 km comet would not have put a pre-lunar like ring around Venus, but would certainly have been capable of precipitating volcanic events and climate change.

Investigating the effects of impact-induced climate change on the terrestrial planets is currently a major subject of research at NASA's Astrobiology Institute.

Mark Bullock


---

Dealing with the impact hazard

by Michael Paine (posted on CCNet 20 April 1999 as a follow-up to the item in Explorezone)

I have given some thought to the chance of the (proposed) Spaceguard
program actually detecting an object that will impact the Earth in the
next fifty years.

I have used 50 years because this seems to be an upper limit to the
ability to predict an orbit (recent events suggest this might be highly
optimistic). I know that many of the following numbers are subject to
debate but let's just consider them a ballpark estimate. The table
shows the estimated chance of an impact by a NEO of given diameter over
the next 50 years. The smaller NEOs have a much higher impact frequency
than the larger NEOs but they are also much more difficult to detect. I
have used a graph from the Spaceguard report which shows "fraction
completeness after 10 years (of observing)". The following values for
50m and 100m objects are, however, a guess.

Chance of detecting a NEO that will impact
in the next 50 years




Asteroid Diameter (m)	Av.Impact Interval (yr)	Chance in  50 yrs   1 in...	Completeness  after 10yrs	Chance of detected object impacting in 50yrs   1 in...
50	100	2	0.5%	400
100	1,000	20	2%	1,000
200	5,000	100	20%	500
500	40,000	800	50%	1,600
1km	100,000	2,000	90%	2,222
All				152

This is for a full Spaceguard Survey, designed to detect 90% of NEOs 1km
diameter or greater over a 10 years observing program. The chance of
this Survey detecting a 1km+ NEO that will impact the Earth in the next
50 years is about 1 in 2,222.

Although the detection rates (completeness) are lower for
smaller objects their sheer numbers mean that the chances of detecting
an Earth-impactor are actually higher than for 1km+ NEOs. Combining the
probabilities suggests that the Survey has about 1 chance in 150 of
detecting an object that will impact in the next 50 years. Applying this
to some of the 1999AN10 orbital parameters (crosses Earth's orbit every 4 years then 6 months later; close encounter every 20 years):

Chance of a detected object (of any size)  hitting within
6 months: 1 in 15,000
4 years: 1 in 1,875
20 years: 1 in 375

This is with a full Spaceguard Survey. The chances with current search
efforts are about 10 times less (that is, 1 in 1,500 for an impact by
any detected NEO within 50 years).

This rough analysis tends to confirm the view that there is no need to
have an urgent mechanism for assessing the threat from newly discovered
NEOs and notifying the public - we are much more likely to have decades
of warning rather than a few months. Also note that a great many
smaller NEOs will "slip through the net" and there is a high risk of
another Tunguska event occurring without warning over the next 50 years
- this risk should be clearly expressed to the public in any "selling"
of the Spaceguard proposal because an undetected impact could be even
more detrimental to the program than a "false alarm" (update May 1999: and could result in around 1 million fatalities!).


---


THE PLANETARY SOCIETY AUSTRALIAN VOLUNTEERS
Media Release  27 May 1999
G.P.O.Box 2086, Canberra 2601

US Congress triples NASA's budget for Near Earth Object Survey - what
about Australia?

Australian members of The Planetary Society have called on the
Australian Government to re-commence the search for Earth-threatening
asteroids and comets. Society member Michael Paine said that Australia
should follow the example of the US Congress which has just tripled
NASA's allocation for the detection of Near Earth Objects (asteroids and
comets). In May 1998 a congressional committee heard testimony from
scientists about the hazard of asteroids and comets colliding with the
Earth. This was a factor in the decision by Congress to increase funding
from US$3.5 million per year to US$10.5 million per year. Although this
one of the first steps in a complicated US budget process this
authorization is a clear statement of interest from Congress in pursuing
the Spaceguard Survey.

Between 1990 and 1996 Australia was involved in a highly successful
search for Earth-threatening asteroids and comets. In 1996  Australian
Government funds were cut and the project closed down. The cessation of
the Australian component of "Spaceguard" has caused a major deficiency
in the ability to identify and predict these threats. Much of the
increasing Northern Hemisphere effort could be wasted if an
object is no longer able to be tracked because it moves into southern
skies. This criticism was raised in the US Congressional hearing:
"Australia, has actually backed away from its fledgling telescopic
program, which -- until the past couple of years -- played a fundamental
role by following-up on NEO's discovered elsewhere from its special
location in the southern hemisphere. International attempts to encourage
the Australian government to bring the telescopic program back into
operation have been to no avail." (Testimony of Clark Chapman)

The importance of Southern Hemisphere observations was recently
demonstrated. In January 1999 US observers detected a new "earth
crossing" asteroid - 1999 AN10. Subsequent observations by
Australian-based amateur NEO searcher Frank Zoltowski caused the Minor
Planet Centre to review the predicted orbit of the asteroid. On 7 August
2027 the 1km diameter asteroid could miss the Earth by as little as
37,000km or 3 Earth diameters.  Its orbit cannot be reliably predicted
after such a close approach but, in an interview with MSNBC, Don
Yeomans, head of NASA's Near-Earth Object Program Office at JPL, said
that asteroid 1999 AN10 has a 1-in-500,000 chance of hitting the Earth
in 2044 (for comparison, there is an estimated a 1-in-100,000 chance
that an undiscovered asteroid one kilometer or larger in diameter will
strike the Earth in a given year). Due to its unusual orbit around the
Sun it is likely to remain a threat for hundreds of years.

END
Contact:
Michael Paine,
New South Wales Coordinator,
The Planetary Society Australian Volunteers
Phone Sydney  02 9451 4870   Fax 02 9975 3966 Mobile 04-1816-5741
For numerous links, including NASA's budget see
http://www1.tpgi.com.au/users/tps-seti/spacegd.html


---

(Australian) Coordination Committee on Science and Technology

http://www.science.gov.au/ccst/activities.html
 

            Current Activities (Financial Year 1998-99)

            The Committee's major role as a forum for exchange of information
            among Commonwealth agencies with and interest in or responsibility
            for scientific and technological matters continued. Matters receiving
            attention in the current financial year include:

                 The role and terms of reference for CCST and its forward
                 work plan
                 Interactions between industry and universities - its extent and
                 ways of enhancing it
                 Coordination of Commonwealth policy and funding for major
                 research facilities
                 Developments in the proposed World Intellectual Property
                 Organisation database treaty
                 OECD Megascience projects - in particular the Square
                 Kilometre Array (SKA) radio telescope and the Global
                 Biodiversity Information Facility (GBIF)
                 Biotechnology opportunities and the role of government
                 Matters arising from multilateral international forums for
                 science and technology (APEC, OECD, UNESCO)
           Near Earth Asteroids
                 Possible topics for PMSEIC agendas

1998/99 Membership:

                 Deputy Chief Executive Officer, Department of Industry,
                 Science and Resources (Chairman)
                 Chief Scientist
                 Chief Medical Officer, Department of Health and Aged Care
                 Chief Defence Scientist, Defence Science and Technology
                 Organisation, Department of Defence
                 Chair, Australian Research Council
                 Chief Science Adviser, Environment Australia
                 Deputy Secretary, Department of Foreign Affairs and Trade
                 Executive Director, Australian Nuclear Science and Technology
                 Organisation
                 Deputy Secretary, Department of Education, Training and Youth
                 Affairs
                 First Assistant Secretary (Communications), Department of
                 Communications, Information Technology and the Arts
                 Chair of Chairs, R&D Corporations
                 Executive Director, Australian Geological Survey Organisation
                 Executive Director, Competitiveness & Sustainability Group,
                 Department of Agriculture, Fisheries and Forestry - Australia
                 Executive Coordinator, Economic and Industry Policy,
                 Department of the Prime Minister and Cabinet
                 Chair, Industry Research and Development Board
                 Chair, National Health and Medical Research Council
                 Chief Executive, CSIRO
                 Chief Executive, Australian Institute of Marine Science
                 First Assistant Secretary, Program and Policy Analysis Group,
                 Department of Finance and Administration
                 Chair, Research Committee of NHMRC
                 Director, Bureau of Meteorology
                 Executive Director, Bureau of Rural Sciences
                 Chair, Cooperative Research Centres Committee, Cooperative
                 Research Centres

---

Asteroids: Shattered but Not Dispersed

H. J. Melosh, E. V. Ryan

We use a combination of scaling laws and direct hydrocode computations that include material strength to show that the impact energy needed to disperse an asteroid is greater than that to thoroughly shatter it for asteroids larger than about 400 m in radius. Thus, asteroids larger than this size should probably be considered to be gravitationally bound, but otherwise strengthless, rubble piles.

Icarus, v 129, n 2, October 1997, p562-564 (ID IS975797)
Copyright © 1997 Academic Press. Available by subscription from IDEAL


---

Transcript of (Australian TV) 60 Minutes item, 30 May 1999

Have you noticed how asteroids seem to have been overlooked in the tax
debate?

Well let me assure you they have.  Indeed I'll bet that neither John Howard
nor Meg Lees have mentioned the subject since they began their
negotiations.

Income tax scales, diesel fuels, food-free-GST ... all that, but not a word
about asteroids.

Which is odd, given that an asteroid called 1999 AN10 - a kilometre long
chunk of rock, is heading towards us right now at a speed of 45 kilometres
per second.

When it arrives, in 28 years, a direct hit would mean a global catastrophe
with major climatic and taxation effects plus a billion fatalities -
including, of course, many taxpayers, accountants and Australian Democrats.

Fortunately, however, it's expected to miss us by an interplanetary
whisker, a mere 39-thousand kilometres.  This time.

So since Meg Lees is such a powerful political star right now, how can she
save the day?  Well, if she can get the GST off food it should be easy for
her to convince her new friend, John Howard, to revive the Australian
component of the Spaceguard Survey, which was abandoned in 96 when the
government scrapped its funding.  Spaceguard is an international effort to
detect and monitor near earth asteroids.  Labor's Martyn Evans has tried,
in vain, to alert a Parliament preoccupied by tax.

Martyn Evans
"If we do not know where these objects are, we will never know what is
going to happen nor will we be able to take any mitigating action in defence of
the planet."

And with no planet left so much for John Howard's beloved GST.  Thankfully,
though, the Americans have recently trebled their funding for Spaceguard
and, as we saw in the movie Armageddon, they can always call on Bruce
Willis and his team to save us all.  Remember that fiscally infamous line when
Willis was telling the top brass of his mens' demands for the job?

Bruce Willis "None of them want to pay taxes again.  Ever."

Who does Bruce?  Mind you, with a GST we Aussies won't have any choice.
Unless, of course, the flying Ayres Rock gets us first.

Paul Lyneham Channel Nine


---

Chinese meteorite disaster in 1490AD

Here is an email that I received from Dr Jin Zhu at Bejing Astronomical
Observatory
email: zj@bac.pku.edu.cn or jinzhu@sun.ihep.ac.cn
WWW Home Page: http://vega.bac.pku.edu.cn/~zj
 
 

Hello Mr. Michael Paine,

Sorry for my late response. I checked with the Chinese book I have, and
they do have some items on the 1490 AD event of meteorites.

There are 10 different descriptions in 10 books. The year (1490) and
place (Qingyang, Shaanxi) are quite fixed. All said 'stone from sky
like rain' or 'stone rain countlessly'.

1) date: 2 said Feb. 19 - Mar. 20; 1 said Apr. 4; 5 said Mar. 21 - Apr.
19.

2) 3 said 'bigger ones in about 2-2.5 Kg, smaller ones about 1-1.5 Kg,
kill tens of thousand people'.

3) 4 said 'bigger ones like cobblestone, smaller ones like Gordon
Euryale, and they can speak like man'.

With best regards, Jin

My email request:
> Hello from Australia
> I am searching for more information about a meteorite fall that
> apparently occurred in central China in 1490 AD. In his book "Rain of
> iron and ice" John Lewis states that the fall occurred at Ch'ing Yang,
> Shasi Province and over 10,000 people were killed.
> regards
> Michael Paine

Incidentally, John Lewis documents numerous other probable
meteorite-related fatalities in "Rain of iron and ice". I don't know
where the notion that "nobody has ever been killed by a meteorite" came
from. John rephrases this to "No one in recorded history has ever been
killed by a meteorite in the presence of a meteoritist and a medical
doctor"!


---

Congressman George Brown

NEO News (7/17/99) George Brown

Dear friends and students of NEOs:

It is with sadness that I report the death of George E. Brown of the U.S.
House of Representatives, the strongest supporter of Spaceguard within the
Congress. Representative Brown died in Washington on July 15 of
complications following heart surgery.

George Brown was first elected to the Congress in 1962. For many years he
chaired the Committee on Science and Technology in the House, and at the
time of his death he was the ranking Democrat on the Committee. He held a
degree in physics from the University of California at Los Angeles, and he
often described himself as a scientist (one of very few in the Congress).

In addition to his broad support over many years of scientific research and
space exploration, George Brown took a very real personal interest in the
NEO impact hazard. Under his leadership, the Congress first asked NASA to
study this issue in 1991, leading to the Spaceguard Report of 1992. After
the 1994 impact of Comet Shoemaker-Levy 9 into Jupiter, his Committee
challenged NASA to accelerarate plans for Spaceguard and to develop a
program plan to find 90% of NEOs larger than 1 km within a decade. We will
all miss his support and friendship.

Following are the remarks made by Mr. Brown at the 1993 Congressional
hearings on the NEO impact hazard, as well as the key language from his
Committee that defined the program that we now call Spaceguard.

David Morrison

----------------------------------------------------------------

Congressional Hearings, March 24 1993

Introductory statement by Mr. Brown:

For Members [of Congress] who are hearing about this subject [the impact
threat] for the first time, I know that the tendency is to be somewhat
skeptical. And, one could certainly ask why this subject should be of
interest to the Congress? None of our friends, relatives, or constituents
have ever been killed by an asteroid. It has probably been hundreds of
thousands of years since the last time a really big asteroid hit the Earth.

I think it is the duty of the Congress to provide periodic oversight of all
matters that relate to the health and welfare of the citizens of this
country. This is particularly true for issues where Congressional oversight
might spur the Administration forward to taking some appropriate action. I
believe that the topic of Earth-threatening asteroids is just such an issue.

I hope that [these hearings] will help create increasing awareness of this
issue within the international astronomical community. Indeed, the problem
of a potential large asteroid strike is not just a U.S.problem; it is a
worldwide problem. I believe that all industrialized nations of the Earth
should cooperate on a program to discover and track the large asteroids
that can pose a serious threat to our home planet.

[Today] the emerging scientific consensus seems to be that it is no longer
a question "If the Earth will again be hit with a large asteroid?"; the
question is now "When will the Earth again be hit by a large asteroid?"

If we invest the time and resources to find these things, we can remove the
guesswork. We will know ahead of time when we are at risk, so that we can
take appropriate actions to deflect the threatening asteroids years in
advance.

I believe that the initiatives we are now getting underway to deal with
this issue in a thorough and scientific manner have the potential for being
one of the most important things that mankind has ever done.

If some day in the future we discover well in advance that an asteroid that
is big enough to cause a mass extinction is going to hit the Earth, and
then we alter the course of that asteroid so that it does not hit us, it
will be one of the most important accomplishments in all of human history.

--------------------------------------------------------------------

1991 statement from the House Committee on Science and Technology as
enacted in the NASA Authorization Bill:

The chances of the Earth being struck by a large asteroid are extremely
small, but since the consequences of such a collision are extremely large,
the Committee believes it is only prudent to assess the nature of the
threat and prepare to deal with it. We have the technology to detect such
asteroids and to prevent their collision with the Earth.

The Committee therefore directs that NASA undertake two workshop studies.
The first would define a program for dramatically increasing the detection
rate of Earth-orbit-crossing asteroids; this study would address the costs,
schedule, technology, and equipment required for precise definition of the
orbits of such bodies. The second study would define systems and
technologies to alter the orbits of such asteroids or to destroy them if
they should pose a danger to life on Earth. The Committee recommends
international participation in these studies and suggests that they be
conducted within a year of the passage of this legislation.

--------------------------------------------------------------

1994 statement from the House Committee on Science and Technology passed as
an amendment to the House version of the NASA Authorization bill:

Catalogue of Earth-Threatening Comets and Asteroids

(a) Requirement -- To the extent practicable, the National Aeronautics and
Space Administration, in coordination with the Department of Defense and
the space agencies of other countries, shall identify and catalogue within
10 years the orbital characteristics of all comets and asteroids that are
greater than 1 km in diameter and are in an orbit around the sun that
crosses the orbit of the Earth.


---

NEW OBSERVATIONS BY AUSTRALIAN ASTRONOMER DISPEL IMPACT THREAT

>From Michael Paine  8 October 1999
mpaine@tpgi.com.au  Phone Sydney 94514870
The Planetary Society Australian Volunteers
http://www1.tpgi.com.au/users/tps-seti/

The importance of having an effective asteroid search system in
Australia has once again been demonstrated. Rob McNaught from the Anglo
Australian Observatory has conducted a successful "follow-up"
observation of a potentially  threatening asteroid. The new observations
show there is no possibility of a collision with Earth in the next 50
years.
The asteroid was found a few days ago by northern hemisphere astronomers
and calculations indicated a slight chance of a collision in 2042 or
2050. Further observations were needed to pin down the orbit and
fortunately Rob McNaught was able to track the object from Australia.
If this had not been achieved the next opportunity for observing the
asteroid (its next close approach to the Earth) would have been in 2012.
If, at that time, it was found that a collision was likely then Mankind
would have lost more than a decade in making plans to deflect the
asteroid away from the Earth.
Due to Australian government indifference to the asteroid threat, Rob
McNaught's asteroid search program in Australia is partly funded from
the USA. There is an urgent need to upgrade the equipment in use in
Australia.

[Thanks to Benny J Peiser for advice on this item. see
http://abob.libs.uga.edu/bobk/ccc/cc100799.html ]

Further comments from Rob McNaught

Michael,
It is most fulfilling to have these possibilities of impacts suggested and
to go out and actually observe these objects to refine the risk.  There is
no longer the need to rely on others to do this work.  Thankfully this is
another object from which we are safe, in the short term.

Just a couple of points regarding my new position.  I am employed by the
ANU (not the Anglo-Australian Observatory) on a contract for the Uni. of
Arizona.  The current program of observational follow up is fully funded
by the Uni. of Arizona through a NASA grant.  Note also that I am doing a
small amount of searching using the UK Schmidt plates (taken for other
purposes) and have found one Amor (1999 RM28), a distant comet (C/1999 S2
McNaught-Watson) and two other unusual asteroids (1999 QJ and 1999 RJ45).
This average of one interesting object per month so far is trivial
compared with the output of LINEAR and the other northern hemisphere
programmes, but at least *something*, no matter how insignificant, has
started up again in the southern hemisphere!  However there is so much
more to be done, we have barely started to scratch the surface in the
southern hemisphere.

Cheers, Rob

---

Craters, Geological Boundaries and Eruptions

Moved to a new page (getting too large!) - sorry for the inconvenience

---


THE PLANETARY SOCIETY AUSTRALIAN VOLUNTEERS

Media Release  1 Dec 1999

G.P.O.Box 2086, Canberra 2601

UK Government gets serious about Spaceguard - what about Australia?

Australian members of The Planetary Society have called on the
Australian Government to follow the lead of the UK government and look
at establishing a centre to search for and deal with asteroids or comets
that threaten the Earth. Society coordinator Michael Paine said that the
UK government had recognised that a Spaceguard program was highly
cost-effective. In Britain alone billions of dollars are spent on
preventing disasters such as nuclear accidents and airliner crashes. A
200 metre diameter asteroid striking a populated region of the Earth
would explode with the energy of 30 H-bombs, causing millions of deaths
and yet programs to search for these objects receive meager funding from
just a few governments.

Australia is strategically very important for this search effort but
government funds for a highly successful Australian program were cut
and the project closed down in 1996. Efforts by the Planetary Society
and other groups to get the Australian government to re-establish the
program have been unsuccessful.

Some Australian politicians have dismissed the issue as unimportant and
have erroneously claimed that nothing can be done if an object is found
to be on a collision course. The whole idea of Spaceguard is to detect
these objects decades before they collide with the Earth so that there
is adequate time to evacuate the impact area or send spacecraft to nudge
to object into a safe orbit. It is only if we don't look for these
objects that they will hit without warning and cause millions of
fatalities.

To the embarrassment of many Australians, a scaled-down professional
search recommenced this year in Australia with some funding from the
University of Arizona and NASA. The Americans were concerned that there was no major search in southern skies and their increasing effort in the northern hemisphere could be in vain if a threatening object moved south and was lost. The issue was even raised in US Congressional hearings.

The US and Japanese governments have now committed funds to
the worldwide Spaceguard program and the UK looks set to follow. How will
Australia respond?
 

END
Contact:
Michael Paine,
New South Wales Coordinator,
The Planetary Society Australian Volunteers


---

Book Review

Comet and asteroid impact hazard on a populated Earth.

by Dr John Lewis, Lunar and Planetary Laboratory, University of Arizona.

Dr Lewis has developed a computer program to run simulations of asteroid and comet impacts with
the Earth or other selected planets. This works as a Monte Carlo simulation, where events occur randomly over time and various parameters such as the size, composition, speed and trajectory of the impactor and the human population density of the target area are also randomly generated. In this way the impact hazard can be assessed by looking at the odds over many runs or extended time periods (hence the Monte Carlo gambling reference).

Lewis points out that hazard estimates based on "typical" events tend to overlook unusual phenomena that can be quite destructive. For example the Monte Carlo simulation shows that, over thousands of years, airburst events like Tunguska turn out to be important sources of fatalities. These types of events are very localized and may leave little or no physical evidence so information about the hazard is unlikely to be reliably passed on from generation to generation. Another significant source of localized fatalities is the impact of iron asteroids/meteoroids. Because they comprise just a few percent of all Near Earth Objects (NEOs) they tend to be ignored in "typical" hazard assessment and yet they are much more destructive than "stony" NEOs of the same size.

Although basically a handbook for the software, the book contains a wide range of physical information about NEOs, impacts with planets, effects on the human population, detection techniques and mitigation. It is an excellent scientific resource covering physics, chemistry and the environment perturbation and has 8 pages of bibliography. It is therefore an important reference for anyone studying the possible influence of impacts on the biosphere and human civilisation.

The book includes a diskette with the Monte Carlo program. It requires GW-BASIC to run (if all else fails a copy of BASIC.EXE (GW-BASIC) can be downloaded from http://www2.tpgi.com.au/users/aoaugh/basic.exe). To run the program in a higher version of BASIC such as Quick Basic you will need to convert it from binary to ASCII format from within GW-BASIC. To do this load the program in GW-BASIC (F3"path/filename.BAS") then save it with the ASCII option set  (F4 "path/new_filename.BAS" , A ). This is all subject to the copyright conditions of course.

The book and program include estimates of fatalities from tsunami generated by impacts. My own investigations have  revealed a wide difference in estimates of the size and range of tsunami generated by asteroid impacts (see http://www1.tpgi.com.au/users/tps-seti/spacegd7.html). Lewis uses the most pessimistic of these estimates. Even with these high estimates the proportion of all fatalities caused by tsunami only begins to approach that of direct effects (such as firestorms and blast waves) on timescales of millions of years so the assumptions about tsunami should not make a huge difference to outcomes over centuries. In any case, BASIC programmers could quite easily edit the couple of lines of code that cover tsunami in order to try out more optimistic parameters.

The final paragraph is an excellent summary of the impact hazard situation and (continuing the gambling theme) suggests that our society is taking a grave gamble if it ignores the NEO threat:

"Of all the natural hazards facing Earth, impacts are the most dangerous. Unlike native hazards of the Earth's surface, impacts know no size limit. Their effects can be devastating over the entire surface of the planet. They are the only credible natural threat to human civilisation. But impacts, especially those of large bodies, are both predictable and avoidable. The Near Earth Object (NEO) population constitutes both an unprecedented hazard and an unparalleled opportunity*. It is sometimes said that there is a fine line that separates a threat from an opportunity. The near-Earth asteroids present us with just this dilemma. They present us with an intelligence test of the highest order, with the highest possible stakes for the human race."

* see Mining the Sky, also by John Lewis - mining resource-rich asteroids that are more accessible than the Moon.

Michael Paine, 7 Dec 1999,


---

How often do NEOs come "close" to Earth - David Morrison, NASA, 29 Sep 2000.

...Those who commented with surprise on the fact that these two NEAs
were not discovered until close to the Earth presumably are thinking
in terms of a search program designed to pick up collision-bound NEAs
on their final approach to Earth. But this has never been the plan.
The Spaceguard strategy is to carry out a reasonably complete
inventory of NEAs, allowing a forward projection of their orbits;
such an approach would likely provide at least decades, and perhaps
centuries, of warning of any future impact.

However, there were others who simply expressed surprise that any
NEAs were coming as close as 12 times the distance to the Moon, let
alone two in one month. Just how remarkable was September 2000 in
this respect?

It is easy to calculate how often, on average, a NEA of a given size
comes within any particular distance of the Earth. We use the known
average impact rates on the Earth and Moon and correct for the larger
cross-section of a target with radius 5 million km (12 times the
Earth-Moon distance). The answer is that a 300-500 m diameter NEA,
such as 2000 QW7 and 2000 RD53, passes this close to Earth about once
every 2 months on average. Finding two within a month is therefore
not so unusual. Tunguska-size NEAs come this close at a rate of one
every few hours, and even 1 km NEAs come this close nearly once per
year. I would therefore suggest that we tighten the definition of a
"near miss" -- perhaps using this phrase only for NEAs that come
inside the orbit of the Moon.

David Morrison


---

Rob McNaught describes NEO followup observations.

Astronomer Rob McNaught from the Anglo Australian Observatory  provided the following advice to a student enquiring about NEO followup observations.

Immediately following a discovery of an asteroid, there is insufficient information to determine a meaningful orbit.  Until the unique orbitis calculated, it is important to engage in follow-up observations toaccurately determine the position of the asteroid in RA and Dec (or celestial longitude and latitude).  Only once the object has been accurately observed over several days, can any realistic idea of the potential for a collision be determined.  Often, these observations clearly indicate that no collision is possible (as with the bulk of known asteroids which reside in the asteroid belt between Mars and Jupiter).  In the small number of cases where a collision cannot be ruled out, additional observations are crucial for a more accurate assessment.

There are two ways in which I get involved in these additional observations. Firstly, I use the 1.0-m (40 inch) f/8 reflecting telescope at Siding Spring to make additional observations.  It uses a 2x2K thinned CCD, but I use it with 2x2 binning of the pixels to give a used size of 1x1K.  The pixels are then 1.2 arcseconds across, well matched to the average seeing (blurring due to the atmosphere).  The field of view is 20 arcmins square (The Moon is 30 arcmins across).  These new observations are often enough to improve the orbit sufficiently to say if a collision is possible (and in every case I've been involved in, these observations have discounted any possibility of a collision).

The other way I get involved is in extrapolating the initial orbit backwards and checking if the asteroid might be present on photographs of the sky taken in years past.  Here at Siding Spring, is one of the world's best photographic telescopes, the 1.2-m U. K. Schmidt.  It has taken many tens of  thousands of wide field (6 degrees across) photographs since 1973.  Quite often an asteroid can be found on the archived plates taken many years before it was discovered.  Just last week I found an image of a comet, P/2000 WT168 I think, on a photo taken in 1986!  Then another image was found from 1976!  These additional pre-discovery observations make a dramatic improvement in the orbit.  Thus only 3 months after discovery, the observed period has become 25 years!!!  No need to wait until 2026 to get a 25 year observed arc with the corresponding orbital accuracy.
 

Robert H. McNaught, March 2001

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Spotting extra-solar impacts

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Last update 8 December 1999

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