PLEASE NOTE:
*
CCNet DIGEST, 14 July 1999
-------------------------
(1) NEAR-EARTH ASTEROID NO LONGER A COLLISION THREAT
SPACEVIEWS, 13 July 1999
(2) ANOTHER ASTEROID THREAT DEFUSED
MSNBC SPACE NEWS, 13 July 1999
(3) ASTEROID THREAT LOWERED
EXPLOREZONE, 13 July 1999
(4) PREDISCOVERY IMAGE OF 1999 AN10
Arno Gnädig <gnadig@mind.de>
(5) UPDATE ON ASTEROID 1999 AN10
Ron Baalke <baalke@ssd.jpl.nasa.gov>
(6) IRRESPONSIBLE AN10 STORY IN GERMANY
Daniel Fischer <dfischer@astro.uni-bonn.de>
==============
(1) NEAR-EARTH ASTEROID NO LONGER A COLLISION THREAT
from SPACEVIEWS, 13 July 1999
http://www.spaceviews.com/1999/07/13a.html
The discovery of a 44-year-old photo of a near-Earth asteroid has
all
but eliminated any possibility that the object could hit the
earth next
century, astronomers reported July 12.
Two German amateur astronomers, Arno Gnadig and Andreas Doppler,
located
a pre-discovery image of asteroid 1999 AN10 that dates back to
1955. The
image, taken as part of the first Palomar Sky Survey, dates back
to when
the asteroid was making a close approach to the Earth and visible
high
in northern skies.
Asteroid 1999 AN10 attracted attention earlier this year shortly
after
its discovery, when astronomers computed its orbit and discovered
a
billion-to-one chance that it could collide with Earth in 2039.
Later
analysis discovered another possible impact with 500,000-to-1 in
2044.
Those predictions, though, were based on only few months' worth
of
observations and thus had large uncertainties. The discovery of
the 1955
image allows astronomers to tie down the orbit with much greater
accuracy.
The refined orbit essentially eliminated any possibility of an
impact in
2039 and 2044. In fact, Brian Marsden and Gareth Williams of the
Minor
Planet Center note that in 2044, 1999 AN10 will be on the
opposite side
of the Sun, more than 320 million kilometers (200 million miles)
from
the Earth at the time of the previously-predicted impact.
The improved orbit also adjusted a close approach the asteroid
will make
to the Earth in 2027. Instead of passing as close as 32,600 km
(20,200
mi.), the asteroid will pass at around 390,000 km (242,000 mi.),
or
about the Moon's distance from the Earth. The asteroid will not
pass
close to the Earth until 2076, when it will come no closer than
1.2
million kilometers (745,000 mi.) to the Earth.
The revised orbit underscores the need to not only ramp up
current
searches for near-Earth objects, but to dig into archives to look
for
images that include the object prior to its discovery.
The discovery of the impact potential for 1999 AN10 was
publicized in
April by Benny Peiser, moderator of a mailing list used by the
near-Earth asteroid research community. Peiser generated some
criticism
for publicizing the earlier impact probabilities, but he notes
ironically now that the whole affair could have been avoided,
since the
pre-discovery image is included in the publicly-accessible
Digital Sky
Survey.
"It is quite astonishing that the teams involved in
calculating impact
probabilities for 1999 AN10 apparently failed to check this data
before
going public," he said in a message on his list July 13.
"After all,
they could have avoided announcing a short-term 'problem' right
from the
start."
"Unless we can improve this astronomical data base [of facts
and
observations] substantially," he added, "we will have
to rely on
short-lived and highly speculative probability statistics which
begin to
look like a game of pure gamble."v
Copyright 1999, SpaceViews
===========
(2) ANOTHER ASTEROID THREAT DEFUSED
From MSNBC SPACE NEWS, 13 July 1999
http://www.msnbc.com/news/272798.asp#BODY
Further analysis reduces risk of midcentury collision to zero
By Alan Boyle
MSNBC
July 13 — Yet another asteroid threat has been knocked down
at last,
thanks to a re-examination of 44-year-old images made by the
Palomar
Observatory. Astronomers had said there was more than a
1-in-a-million
chance that Asteroid 1999 AN10 could collide with Earth in the
middle
of the next century. But a review of the Palomar images provided
enough
information about the asteroid’s path to eliminate even that
chance ...
at least through 2076.
THE INITIAL ALARM over 1999 AN10 — and the subsequent
stand-down —
eerily echoed the controversy that erupted in March 1998 over
another
asteroid, known as 1997 XF11.
Back then, even the suggestion that an asteroid might hit Earth
in 2028
generated a media frenzy — until additional analysis of
images taken
years earlier showed that it would pass by safely.
“The problem there was that the press release preceded the
analysis,”
said Donald Yeomans, an astronomer at the Jet Propulsion
Laboratory who
heads NASA’s asteroid detection efforts, “whereas in
this case the
analysis was done as it should have been done.”
Asteroid 1999 AN10 was spotted in January by the Lincoln Near
Earth
Asteroid Research Project, also known as LINEAR. The asteroid’s
path
takes it relatively close to Earth several times over the next
few
decades, and astronomers focused on the very slight possibility
of a
collision, perhaps in 2039 or 2044.
Some calculations suggested that the chances of a direct hit in
2044
were as high as 1 in 500,000 [actually 1 in 100,000; BP] —
depending on
how close the asteroid came during a crucial pass in 2027.
Those odds are longer than the chance of an earth-shattering
object
coming out of the blue at any time, NASA scientists say. In any
given
year, they figure there’s a one-in-100,000 to
one-in-a-million chance
that an undetected object bigger than a kilometer across will
hit
Earth. Nevertheless, the prospect of a collision with 1999 AN10
was
enough to send astronomers hunting through decades’ worth
of
observations, hoping to find traces that could help them plot the
asteroid’s future path more precisely.
As anyone who has seen the movie “Deep Impact” or
“Armageddon” knows,
the stakes are, well, astronomical: Asteroid 1999 AN10 is thought
to be
on the order of a kilometer across — meaning it would cause
a
thermonuclear-scale explosion and a global catastrophe if it hit
Earth.
Scientists surmise that similar collisions have sparked mass
extinctions in the past, including the demise of the dinosaurs 65
million years ago.
FINDING THE TRAIL
After a painstaking search of old records, two German amateur
astronomers, Arno Gnadig and Andreas Doppler, reported that they
detected the extremely faint trail of 1999 AN10 on an image made
in
1955 and archived as part of the Palomar Sky Survey. The streak
hadn’t
even been recognized as the trail of an asteroid until Gnadig and
Doppler spotted it.
“There’s no way you would have just run across it by
accident,” said
Gareth Williams of the International Astronomical Union’s
Minor Planet
Center, which has headquarters in Cambridge, Mass.
The Minor Planet Center, which acts as a clearinghouse for
asteroid
observations, double-checked its own Palomar images and confirmed
that
the trail indeed belonged to 1999 AN10.
Cranking in the new numbers, astronomers found that in 2027 the
asteroid would swish by at a distance of about 240,000 miles
— about
the distance between the moon and Earth, which puts it No. 1 on
the
list of sizable asteroids due to make a close approach. At its
brightest, the asteroid would be a little dimmer than the planet
Neptune in the night sky, according to the Minor Planet Center.
Such an approach would be far wider than the earlier estimates,
and
completely eliminates the possibility of a collision during later
passes as far into the future as 2076, the Minor Planet Center
said in
a bulletin dated Monday. “By 2076, of course, this object
will have
been seen many times since now,” Williams said.
‘EERILY PARALLEL’
He said the latest case was “eerily parallel” to last
year’s asteroid
scare. In both cases, a review of previous observations —
which
recorded unnoticed traces of the asteroid in question —
reduced the
risk of collision to zero.
“In both cases, if those pre-discovery photographs had not
existed,
then we would have been worrying about these objects for several
years
to come,” he said. “So once again the old photography
has shown itself
to be absolutely vital for clarifying the situation with these
objects.”
Astronomers are still trying to figure out just what it would
take to
throw an asteroid or comet off a collision course. As part of its
effort to study such objects, NASA announced last week that it
would
move forward with a mission known as Deep Impact, aimed at
blasting a
crater in Comet P/Tempel 1 on the Fourth of July in 2005.
Copyright 1999, MSNBC
============
(3) ASTEROID THREAT LOWERED
From EXPLOREZONE, 13 July 1999
http://explorezone.com
07/13: In April, we reported to you that asteroid 1999 AN-10 had
a
chance, albeit a small one, of hitting Earth sometime early next
century. New calculations based on a 1955 photograph of the
object have
all but removed the threat, says Brian Marsden of the Minor
Planet Center. In
2044, a year when an impact had been thought possible, the object
will
pass through the inner solar system more than 200 million miles
away
from Earth, on the far side of the Sun, Marsden said yesterday.
There is
no chance of impact through at least 2076.
Robert Roy Britt
Editor
explorezone.com
rob@explorezone.com
http://explorezone.com
============
(4) PREDISCOVERY IMPAGE OF 1999 AN10
From Arno Gnädig <gnadig@mind.de>
Downloading of the 1999 AN10 prediscovery image from 1955
is possible via DSS_PLATE_FINDER:
http://faxafloi.stsci.edu:4547/cgi-bin/dss_plate_finder
Plate-Id: 07ID
RA : 08 38 00.0
DE : +72 40 00.0
Squuare : 10 arcmin * 10 arcmin
--- Arno Gnadig ----
===========
(5) UPDATE ON ASTEROID 1999 AN10
From Ron Baalke <baalke@ssd.jpl.nasa.gov>
Update On Asteroid 1999 AN10
JPL Near-Earth Object Program Office
July 13, 1999
http://neo.jpl.nasa.gov/news/news037.html
As announced in MPEC 1999-N21
(http://cfa-www.harvard.edu/mpec/J99/J99N21.html),
a trail of asteroid
1999 AN10 was discovered on plates taken in 1955 from the Palomar
Sky
Survey. The nominal and minimum-possible close-approach
distance for
the 2027 Earth encounter are now 0.00260 AU and 0.00258 AU
respectively
(about 389,000 km). Preliminary analyses indicate that the 2044
and
2046 impacting key-holes (http://neo.jpl.nasa.gov/news/news018.html)
are well outside the current 2027 impact-plane error ellipse.
This
implies that those previously highly unlikely impacts are now
virtually
impossible. The next Earth close-approach is in 2076 and will
likely be
between 0.046 and 0.009 AU (6,900,000 and 1,300,000 km).
============
(6) IRRESPONSIBLE AN10 STORY IN GERMANY
From Daniel Fischer <dfischer@astro.uni-bonn.de>
Dear Benny,
by a perverse coincidence the (formerly) respected German TV
politics
show "Report aus Muenchen" has broadcast a particularly
misleading story
on an "Asteroid Approaching: Will the Celestial Body bring
the End of
the World?" just an hour before the MPC came out that
declared 1999 AN10
no longer a danger. The text of the story can still be found at
http://www.br-online.de/politik/ard-report/0712asteroid.htm
(in German); it was illustrated mainly by the usual "Deep
Impact" and
"Armaggedon" clips - and some Leonids captured on video
during the
German expedition to Mongolia last year.
First of all the clueless reporter - who was neither aware of the
current open discussion on 1999 AN10 nor had bothered to ask an
expert
about it - said that an impact in 2027 was not ruled out (while
that
in fact had *never* been an issue) and that the orbit was
completely
unpredictable anyway. None of the pre-July-12th impact
probabilities
for other years in the 21st century, readily available on the
net, were
mentioned.
But much more disturbing were his repeated statements that only
"a giant
number of telescopes in orbit" would be able to catalog the
NEOs and
that such an early-warning system would be "unbelievably
expensive".
Apparently the discussion on search strategies and the current
wave of
success from LINEAR et al. has completely escaped large sections
of
the public...
This was followed by a statement from the equally clueless
presenter
(who couldn't even tell comets from asteroids) that it now would
be
time for politics to wake up. Certainly not from this kind of
irresponsible misinformation...
Daniel Fischer
http://www.astro.uni-bonn.de/~dfischer/mirror.html
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CCNet-ESSAY, 14 July 1999
-------------------------
DIARY OF A FIREBALL: OR HOW NOT TO DO
SCIENCE
By Ian Griffin (07/14/99) <iang@stardome.org.nz>