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(meteorobs) Rob McNaught saves Earth, or Excerpts from "CCNet, 7 October 1999"


See Item (1). Bravo, Rob! :)

------- Forwarded Message

From: Benny J Peiser <b.j.peiser@livjm.acdot uk>
To: cambridge-conference@livjm.acdot uk
Subject: CCNet, 7 October 1999
Date: Thu, 7 Oct 1999 11:19:59 -0400 (EDT)

CCNet, 7 October 1999
------------------------


(1) NEW OBSERVATIONS BY AUSTRALIAN ASTRONOMER DISPEL IMPACT    
    THREAT
    Benny J Peiser <b.j.peiser@livjm.acdot uk>

(2) SOUTH AFRICAN CRATER IDENTIFIED AS WORLD'S LARGEST IMPACT   
    STRUCTURE
    SpaceDaily, 5 October 1999 

(3) PUZZLE OF COMETARY ORBITS HINTS AT LARGE UNDISCOVERED OBJECT 
    Jacqueline Mitton <jmitton@dial.pipex.com>

[...]

(6) ACCURATE PREDICTIONS OF LEONID METEOR STORMS
    Benny J Peiser <b.j.peiser@livjm.acdot uk>

[...]


=========
(1) NEW OBSERVATIONS BY AUSTRALIAN ASTRONOMER DISPEL IMPACT    
     THREAT
 
>From Benny J Peiser <b.j.peiser@livjm.acdot uk>
 
The history of public impact threat announcements repeats itself, or so 
it would seem. When a potential impact risk posed by asteroid 1997 XF11 
was announced 18 months ago, it took just 24 hours before new (or, to 
be precise, old) observational data were able to eliminate the threat 
completely. Now, a similar impact threat announcement (although on a 
much smaller scale than the initial 1:50,000 impact probability of 
XF11) has been annuled within two days.  
 
New observations of asteroid 1999 RM45 made by Australian astronomer 
Rob McNaught and published yesterday by the Minor Planet Center in 
Cambridge, Mass. (http://cfa-www.harvarddot edu/mpec/J99/J99T22.html) now 
provide a 21-day arc of orital data which practically rule out any 
impact risk for the next five decades. The effect of these new 
observations have reduced the orbital uncertainty by a factor of ten. 
It would thus appear that the small impact possibilities suggested for 
2042 and 2050 by Steve Chesley and his colleagues at Pisa University 
have now completely disappeared. 
  
I understand that the next possible close approach to the earth (based 
on the the 21-day arc) is in September 2012. Further observations 
during the next couple of months should clarify this situation. Unless 
the NEO search community will get use of a large telescope, there will 
be no chance of any further observations until the year 2008. 
 
Benny J Peiser

P.S. I note with some lack of understanding that the NeoDys impact risk 
page at http://newton.dm.unipidot it/neodys/1999RM45.risk.html, still 
features the 2042/2050 impact calculations from Monday although Rob 
McNaught's new observations have been known for almost two days. It be 
wiser and less confusing, I believe, to up-date such impact-threat 
announcemnets regularly. 

==================
(2) SOUTH AFRICAN CRATER IDENTIFIED AS WORLD'S LARGEST IMPACT   
    STRUCTURE

Fom SpaceDaily, 5 October 1999 
http://www.spacedaily.com/spacecast/news/spaceguard-99g.html

World's Largest Impact Found In South Africa

Johannesburg (AFP) October 5, 1999 - South African geologists have 
identified a crater in central Free State province to be the oldest and 
largest in the world caused by the impact of a comet or an asteroid, 
scientists said.

World renowned University of the Witwatersrand (Wits) 
paleo-anthropologist Philip Tobias told a public lecture on human 
evolution here that the Vredefort crater, which is between 250 and 300 
kilometers (150 and 190 miles) in diameter, was long thought to be of
volcanic origin.

However, geologists, led by Wits professor Uwe Reimold, had recently 
shown that the structure was caused by the impact of an 
extra-terrestrial object such as an asteroid or comet, Tobias said 
Wednesday.

"It is the largest impact structure that has yet been identified on 
planet Earth. It exceeds even the Sudbury crater in Ontario, Canada, 
which is about 200 kilometers (125 miles) in diameter," he said.

"Not only is the Vredefort crater the biggest so far identified on 
Earth, but it is the oldest. It has been dated to 2.1 billion years."

The town of Vredefort is situated at the centre of the crater, which is 
bigger than the Chicxulub depression made by an asteroid or comet at
Yucatan, in Mexico. The Chicxulub collision is thought to have caused the
extinction of most of the dinosaurs.

"Like Chicxulub, Vredefort may well have been a major catastrophe whose 
worldwide consequences had an enormous impact on the history of life on 
Earth," Tobias said.

Reimold told AFP that the way minerals in the crater had been deformed 
indicated the indentation could not have been caused by volcanic 
activity.

Initial estimates, he added, indicated that the crater could have been 
caused by a comet or asteroid five to 10 kilometers (three to six 
miles) in diameter, travelling at a speed of between 40,000 and 250,000
kilometers (25,000 and 150,000 miles) an hour.

According to Reimold, the impact on the Earth's atmosphere could well 
have caused a setback of a few million years in the evolution of life 
as it existed at the time.

The crater is so old and eroded, however, that it is difficult, except 
in a few places, to see the effect of the impact with the naked eye.

Scientists at both Wits and Potchefstroom, southwest of Johannesburg, 
who are working jointly on the project, say many studies remain to be 
undertaken at Vredefort.

The site has been known since the turn of the century, but only dated 
in 1996, and only in the past few years has it been suspected that it 
was caused by a collision.

Copyright 1999 AFP & SpaceDaily. All rights reserved

==================
(3) PUZZLE OF COMETARY ORBITS HINTS AT LARGE UNDISCOVERED OBJECT 

>From Jacqueline Mitton <jmitton@dial.pipex.com>

ROYAL ASTRONOMICAL SOCIETY
PRESS NOTICE

Date: 7 October 1999                                     
For immediate release

Ref. PN 99/32
Issued by: Dr Jacqueline Mitton
RAS Press Officer
Phone: Cambridge  ((0)1223) 564914
FAX: Cambridge ((0)1223) 572892
E-mail: jmitton@dial.pipex.com

RAS Web: http://www.ras.orgdot uk/ras/

* * * * * * * * * * * * * * * * * * * * * * * *

CONTACT FOR THIS RELEASE

Dr John B. Murray (j.b.murray@open.acdot uk)
Phone: 01908 652118

Dept. of Earth Sciences, The Open University,
Milton Keynes MK7 6AA

* * * * * * * * * * * * * * * * * * * * * * * * *


PUZZLE OF COMETARY ORBITS HINTS AT LARGE UNDISCOVERED OBJECT 

Intrigued by the fact that long-period comets observed from Earth seem 
to follow orbits that are not randomly oriented in space, a scientist 
at the Open University in the UK is arguing that these comets could be 
influenced by the gravity of a large undiscovered object in orbit 
around the Sun. Writing in the issue of the Monthly Notices of the 
Royal Astronomical Society published on 11th October, Dr John Murray 
sets out a case for an object orbiting the Sun 32,000 times farther 
away than Earth. It would, however, be extremely faint and slow moving, 
and so would have escaped detection by present and previous searches 
for distant planets.

Long-period comets are believed to originate in a vast 'reservoir' of 
potential comets, known as the Oort cloud, surrounding the solar system 
at distances between about 10,000 and 50,000 astronomical units from 
the Sun. (One astronomical unit is approximately the average distance 
between the Earth and the Sun.) They reach Earth's vicinity in the 
inner solar system when their usual, remote orbits are disturbed. Only 
when near to the Sun do these icy objects grow the coma and tails that 
give them the familiar form of a comet. Dr Murray notes that the comets 
reaching the inner solar system include a group coming from directions 
in space that are strung out along an arc across the sky. He argues 
that this could mark the wake of some large body moving through space 
in the outer part of the Oort cloud, giving gravitational kicks to 
comets as it goes.

The object would have to be at least as massive as Jupiter to create a 
gravitational disturbance large enough to give rise to the observed 
effect, but currently favoured theories of how the solar system formed 
cannot easily explain the presence of a large planet so far from the 
Sun. If it were ten times more massive than Jupiter, it would be more 
akin to a brown dwarf (the coolest kind of stellar object) than a 
planet, brighter, and more likely to have been detected already.

So Dr Murray speculates that such an object, if it exists, will be 
planetary in nature and will have been captured into its present orbit 
since the solar system formed, even though the probability of such an 
event seems low on the basis of current knowledge.

Though a large, distant planet is a fascinating possibility and the 
evidence is suggestive, Dr Murray nevertheless stresses that he is not 
ruling out other possible explanations for the observed clustering of 
the comet orbits.

==================
(6) ACCURATE PREDICTIONS OF LEONID METEOR STORMS

>From Benny J Peiser <b.j.peiser@livjm.acdot uk>

Talk by David Asher (Armagh Observatory):
Accurate predictions of Leonid meteor storms

Wednesday, 13 October, 4pm

Astrophysics Research Institute, Liverpool John Moores University,
Twelve Quays House, Egerton Wharf, Birkenhead, L41 1LD,
  
It has often been regarded as difficult to predict exactly when the 
most spectacular meteor storms occur.  But in fact, orbital 
integrations can be used to derive the timings to high accuracy. Here,  
such a technique is applied to the Leonids, which have produced many of 
the best storms in the past two centuries.  The Leonid parent, Comet 
55P/Tempel-Tuttle, returns to perihelion every 33 years or so and 
generates a trail of meteoroids and dust. The dynamical evolution of 
each trail is calculated, since these narrow trails represent the 
highest density regions of the stream, and storms occur when the Earth 
passes near the centre of a trail.

The Armagh Observatory's web page about the Leonids can be found at

   http://www.arm.acdot uk/leonid/

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