PLEASE NOTE:
*
CCNet DIGEST, 19 May 1999
-------------------------
(1) NASA INCREASES IMPACT PROBABILITY FOR ASTEROID 1999 AN10 BY
A FACTOR OF 100
Benny J Peiser <b.j.peiser@livjm.ac.uk>
(2) THE CONTINUING STORY OF ASTEROID 1999 AN10
Ron Baalke <baalke@ssd.jpl.nasa.gov>
(3) CONTROVERSIAL ASTEROID MAY MAKE CLOSE PASS IN 2027
EXPLOREZONE, 18 May 1999
(4) NEW ASTEROID DATA SHOULD NOT BE PUBLICIZED
Clark Chapman <cchapman@swri.edu>
(5) WERE SATELLITE OWNERS LUCKY LAST YEAR? MORE INTENSE LEONID
BOMBARDMENT
PREDICTED FOR 1999
Andrew Yee <ayee@nova.astro.utoronto.ca>
(6) US ASTRONOMER DISCOVERS 18TH MOON ORBITING URANUS
Andrew Yee <ayee@nova.astro.utoronto.ca>
=============
(1) NASA INCREASES IMPACT PROBABILITY FOR ASTEROID 1999 AN10 BY
A FACTOR OF 100
From Benny J Peiser <b.j.peiser@livjm.ac.uk>
In a press statement released yesterday (see below), Paul Chodas
of NASA's
Near Earth Object Program Office confirmed the latest MPC
calculations
regarding asteroid 1999 AN10. According to Chodas, the new
observational
data provides a "considerably improved orbit" which
shows that the
object might come as close as 37,000 km on August 7, 2027. Whilst
the
probability of a collision in that year is "essentially
zero", Paul Chodas
underlines that "the probability of collision in 2039 has
now increased
to about 1 chance in 10 million."
It is important to stress that NASA's revision by a factor of 100
does
not make AN10 much more likely to be an actual threat in fourty
years
time. A chance of 1 in 10 million is still extremely small. It
seems
more likely that additional observations of AN10 in the next few
months
will reduce rather than increase the overall impact risk.
In view of these new findings, Clark Chapman has again questioned
the
wisdom of making this impact risk data public. Although his
criticism
is clearly directed at the CCNet (see his statement below), it
applies
just as much to the much wider publicity NASA has decided to give
to
their own impact threat calculations.
Nevertheless, I hope this is the right place to answer Clark's
main
objection as to *why* I believe that there was and is a
legitimate
scientific argument for publicising the data in the first place.
When Andrea Milani, Steven Chesley and Giovanni Valsecchi, the
authors
of the original paper on 1999 AN10, explained to the reviewers of
their
paper why they did not wish to make their results public, they
were
under the impression that "the asteroid is now almost
impossible to
observe, and even if it were observed new astrometric positions
taken
now would not contribute significantly to the improvement of the
orbit"
(CCNet, 20 April 1999).
Richard Binzel (MIT) and David Morrison (NASA) simarly claimed
that
there "was no reason for this finding to be disseminated
publicly.
[...] the asteroid is already in a part of the sky where it
cannot
be observed for months, so there is no such urgency" (Boston
Globe, 14
April 1999).
In contrast to these assumptions, an amateur astronomer in
Australia has
had no problems whatsoever to observe 1999 AN10; what is more,
the new astrometric positions he provided have significantly
improved
the asteroid's orbit. It would thus appear that the original
assumption,
on which the decision not to publish the reviewed findings was
made,
was mistaken.
At this point I should like to add a correction to yesterday's
posting.
Frank Zoltowski, who made the observations, is not, as stated
yesterday,
an Australian, but an American amateur astronomer currently
working
in South Australia. His observations prove that 1999 AN10 can be
easily
tracked even with a small 30-cm telescope - it's not like one
needed
some huge professional telescope to solve this problem. However,
it is
more than likely that Frank Zoltowski would never have searched
for AN10
without the publicity surrounding the controversial web paper.
In fact, experience has shown that if one does not specifically
draw
attention to a particularly interesting asteroid, it might simply
not
get observed when visible in the sky (as in the classical example
of
asteroid 1997 XF11). In short, the worst that could have happened
in
the case of AN10 would be the lack of any additional observations
prior
to the publication of the web paper.
To postpone the publication of such relevant data until published
in a
peer reviewed journal could have meant the witholding of this
information
for up to six months. As a result, many observers might never
have known
that the current problem with AN10 could be solved by
observations this
summer. In this case, we might have had to wait until the object
becomes
observable again in 2004.
That's why I believe Andrea Milani, Steven Chesley and Giovanni
Valsecchi
should have informed the NEO search community and the general
public about
their findings once they were generally confirmed by independent
reviewers.
Benny J Peiser
==============
(2) THE CONTINUING STORY OF ASTEROID 1999 AN10
From Ron Baalke <baalke@ssd.jpl.nasa.gov>
The Continuing Story of Asteroid 1999 AN10
http://http://neo.jpl.nasa.gov/news/news017.html
New observations are now available for asteroid 1999 AN10, which
is
gradually moving away from the glare of the Sun. The new data
allow a
considerably improved orbit to be calculated for this potentially
hazardous object, and the revised predictions indicate that this
kilometer-size asteroid could pass particularly close to the
Earth on
August 7, 2027. The passage in 2027 could be as close as 37,000
km from
the Earth's center (just 19,000 miles above the Earth's surface),
but no
closer. The miss distance is still very uncertain, and the
asteroid
could easily pass well outside the Moon's orbit. The probability
of a
collision in 2027 is essentially zero.
The accompanying diagram (http://neo.jpl.nasa.gov/neo/an10.gif>
shows
the uncertainty in the predicted close approach in 2027.
The asteroid
must pass through the plane of the diagram somewhere within an
extremely elongated uncertainty ellipse, which appears simply as
a line
segment. (To be precise, the ellipse as drawn is a three-sigma
linear
confidence boundary.) The center of the ellipse is indicated by
the
plus sign, which is located at a nominal distance of 58,000 km
from the
center of the Earth. The minimum distance between the ellipse and
the
Earth center is 37,000 km.
There is still a very remote possibility that asteroid 1999 AN10
could
pass by Earth in 2027 in such a way as to return in the year 2039
on an
impacting trajectory. First identified by researchers
Andrea Milani,
Steven R. Chesley and Giovanni B. Valsecchi, this scenario is
still
exceedingly unlikely, but the probability of collision in 2039
has now
increased to about 1 chance in 10 million. The post-2027 (Monte
Carlo)
analysis of this object's motion will continue.
Paul W. Chodas
Research Scientist
Near Earth Object Program Office
Jet Propulsion Laboratory
May 18, 1999
==================
(3) CONTROVERSIAL ASTEROID MAY MAKE CLOSE PASS IN 2027
From EXPLOREZONE, 18 May 1999
http://www.explorezone.com/archives/99_05/18_asteroid_an10.htm
By Robert Roy Britt, explorezone.com
05/18/99: New observations and calculations show that an asteroid
scientists had previously warned had an extremely small chance of
hitting the Earth in 2039 may make a close pass in 2027.
Researchers say
a close pass could cause the asteroid's path to be altered by
Earth's
gravity, increasing the chances of an impact on some later orbit.
Asteroid 1999 AN10 first made news on April 13 of this year when
Dr.
Benny J. Peiser, a researcher who focuses on neo-catastrophism at
Liverpool John Moores University, wrote in his newsletter about a
scientific paper on the asteroid. Peiser's newsletter, along with
explorezone.com's subsequent story, contributed to significant
controversy and debate over the publication of the research
contained in
the paper, which was posted on a Web site but was not intended to
be
made public. [See the original story]
Today, Peiser tells of new observational data that shows the
asteroid,
which is a little less than a mile wide, may make a very close
approach
in 2027 -- a mere 23,600 miles. Or, researchers said, the
distance could
be much greater.
The fresh calculation for the possible close approach was made by
Brian
Marsden and Gareth Williams of the Minor Planet Center at the
Smithsonian Astrophysical Observatory. The new data was supplied
by
Australian astronomer F. Zoltowski.
"We already knew from the paper by Andrea Milani, Steven
Chesley and
Giovanni Valsecchi that an impact was not possible in
(2027)," Peiser
wrote in his newsletter today. "But the new calculations
confirm their
initial speculation that the asteroid might approach within the
Earth's
sphere of influence and thus could, theoretically, be perturbed
in such
a way that it might impact some years later."
Peiser said uncertainty in the new calculations make it
impossible to
know if the chances for an impact have increased. More
observational
data will be required, he said.
Marsden and Williams, in discussing the new calculations, said
"additional observations during the next several months will
be useful,
because (after that) there are no other reasonable observing
opportunities until at least 2004." ez
================
(4) NEW ASTEROID DATA SHOULD NOT BE PUBLICIZED
From Clark Chapman <cchapman@swri.edu>
Dear Benny,
Your continuing emphasis on 1999 AN10 is incompatible with the
facts
concerning that asteroid. As your recent
"Special" notes, there is no
chance of an impact in 2027 (or before) and there are plenty of
opportunities to observe it then, and long beforehand, to
ascertain
where it might go in the decades beyond. So *why* are you so
insistent
on the urgency of publicizing it. When any conceivable danger
from AN10
(and a rather minucule chance, at that) is decades from now, why
can't
the observers and orbit calculators take their time to reach the
right,
verified conclusions, outside of the glare of public hype?
Thanks to lessons learned last year from XF11, PHA cases like
AN10 are
now routinely having their future "near misses"
calculated and there
was never cause for alarm. There will be many future cases
of
mile-wide NEO's being discovered that will have rather close
passes to
the Earth during the next century, and even more cases of smaller
NEO's
making such passes. And quite a few of them will be
calculated to have
impact probabilities with Earth during the next century in the
range of
1 chance in a hundred thousand to 1 chance in a
million. After all,
the probability of impact of any one of the ensemble of
kilometer-sized
and larger NEO's striking Earth in the next century is something
like 1
in a thousand. As we discover an increasing fraction of these
bodies,
it is our duty to demonstrate that their probability of hitting
is, in
fact, zero rather than a chance in a million...and we should go
about
this task dispassionately. After all, there is thankfully only
that
small, 1-in-a-thousand chance that any of them will actually be
found to be on a collision course.
If we continue to generate alarms and headlines each time a body
is
found that, temporarily, has a 1-in-a-million chance of hitting,
we
will have so bored and saturated the public with false alarms
that we
might be in danger of having a *real* alarm discounted.
Clark R. Chapman
Southwest Research Inst., Boulder CO, USA
===============
(5) WERE SATELLITE OWNERS LUCKY LAST YEAR? MORE INTENSE LEONID
BOMBARDMENT
PREDICTED FOR 1999
From Andrew Yee <ayee@nova.astro.utoronto.ca>
Aerospace Corporation
El Segundo, California
News Release: May 16, 1999
Leonid Conference Participants Ask: "Were We Lucky Last
Year?"
"Were we lucky last year?"
That is a question asked at the second Leonid Meteoroid and
Satellite
Threat Conference held May 11-13 in Manhattan Beach, California.
The answer -- "maybe" -- was about as clear cut as
possible given the
unpredictability of meteor showers.
About 100 satellite owners and operators from the international
space
community attended the event, sponsored by The Aerospace
Corporation and
the American Institute for Aeronautics and Astronautics. These
included
civil, commercial and military participants.
None reported damage to their satellites from the Nov. 1998
Leonids
shower, though there were reports of impacts from the tiny but
zippy
particles that make their presence known every 33 years or so.
Because the Leonids, the fastest meteoroids that visit Earth,
normally
occur with strength in pairs of years, preparations are being
made for
the 1999 event.
And some scientists at the conference predicted a more intense
bombardment on Nov. 17/18 than was experienced last year at the
same
time.
This Year?
At least two conference presenters predicted a storm-level
concentration
of meteoroids for Nov. 1999. But even at storm-level, the
consensus was
that the 650 operational satellites on orbit will not be
significantly
threatened, though the uncertainty factor leaves open the
possibility.
Satellite controllers said they will be making plans for this
year's
event based on their experience in 1998 and on what they learned
at the
conference where a great deal of information was shared. Most
operators
said they will make adjustments and improvements to their plans.
The 1998 Leonid shower galvanized those in the satellite
community to
action and a new awareness about threats from the space
environment has
emerged. One scientist at the conference said the 1998 event was
"a
wakeup call" for satellite operators. This wakeup call and
the response
by the satellite community represented "the real
success" achieved,
another participant said.
Space Weather
Included in this year's conference was a session on solar
activities and
the significant threat posed by the solar maximum due in the
spring-to-summer period in 2000.
David K. Lynch, Ph.D., technical chair of the conference,
announced that
another Leonids conference will be held in 2000 with increased
emphasis
on the areas of space weather, space debris and satellite
operations.
Meanwhile, scientists who monitored the Leonids in 1998 from
Mongolia,
Australia, the air and other locations said they plan to repeat
their
exercises this year, once again employing sophisticated sensors
and
cameras.
Called For
Among actions called for at the conference were:
* establishment of an independent
"clearinghouse" for collection and
distribution of information on
meteoroids and other threats from the
space environment
* creation of better meteoroid prediction models
* more focus on the role of sporadic meteoroids
* a satellite-based meteor-watch capability
* new techniques to track meteoroids
Other information on the Leonids phenomenon is available at
http://www.aero.org/leonid/
==================
(6) US ASTRONOMER DISCOVERS 18TH MOON ORBITING URANUS
From Andrew Yee <ayee@nova.astro.utoronto.ca>
News Services
University of Arizona
Contact:
Erich Karkoschka Lunar and Planetary Lab
University of Arizona
Tucson, AZ 85721-0092
Phone: (520) 621-3994
Fax: (520) 621-4933
E-mail: erich@pirl.lpl.arizona.edu
May 18, 1999
UNIVERSITY OF ARIZONA RESEARCHER DISCOVERS 18TH MOON ORBITING
URANUS
An Arizona scientist has discovered an 18th moon orbiting the
planet
Uranus, the International Astronomical Union announced today.
Until
now, Saturn has been the only planet in our solar system known to
have
as many as 18 satellites.
Erich Karkoschka, a researcher at the Lunar and Planetary Lab of
The
University of Arizona in Tucson, made the discovery. The newly
found
moon is the first satellite of Uranus discovered in 1999 but will
still
be designated as Satellite 1986 U 10 (short S/1986 U 10).
"This discovery is very unusual," Karkoschka said.
"Typically,
satellites are found within days after the discovery image has
been
taken. In this case, the discovery image is more than 13 years
old."
The interplanetary spacecraft Voyager 2 took seven images of the
new
satellite when it flew by Uranus in late January, 1986. These
images
have been publicly available in digital format. However, nobody
recognized the satellite until Karkoschka investigated these
images
recently. He has studied the Uranian satellites based on images
taken
with the NASA/European Space Agency Hubble Space Telescope (HST)
and
found the new satellite when he compared his HST results with
images
taken by Voyager 2.
(The discovery image can be viewed from the links below. The
second
link is a high resolution version.)
The image shows Uranus with its ring system and the 10 innermost
satellites. All but S/1986 U 10 were known at the time the image
was
taken, based on Voyager images taken in January 1986. Arrows at
the
edge of the image point to the 10 satellites. The other dots of
light
are background stars of the constellation Sagittarius. (If you
know
enough astronomy to want to look this up on a star chart, the
bright
star next to Juliet is Kaus Borealis, Lambda Sagittarii.)
Belinda and S/1986 U 10, imaged near the upper right hand corner,
circle Uranus in almost identical orbits. They pass each other
once a
month. This is the first example of two satellites in nearby
orbits
passing each other so slowly.
Astronomers began discovering moons around other planets in our
solar
system in the 17th century. Throughout the approximately 60
satellite
discoveries made over the four centuries since, either Jupiter or
Saturn has had the most known satellites. Saturn is known to have
18
moons. Jupiter has 16 known satellites, not counting the Galileo
spacecraft, an artificial satellite around that planet. Many
scientists
had thought that these two largest planets in our solar system
would
have more moons than smaller planets. Smaller Uranus now dispells
that
belief.
The other known satellites orbit Neptune (8 satellites), Mars (2
satellites), and Earth, Pluto, and asteroids Ida and Eugenia (1
each).
Soon after England's William Herschel discovered Uranus in 1781,
he
found its two largest satellites, which are about half the size
of our
moon. In 1851, English astronomer William Lassell detected two
more
Uranian satellites. In 1951, Gerard Kuiper of the University of
Chicago
-- later founder of the UA Lunar and Planetary Lab -- discovered
Uranus' fifth satellite. The Voyager team found 10 more Uranian
satellites in 1985-86.
Two years ago, Philip Nicholson of Cornell University discovered
the
16th and 17th satellites. These two satellites are some 100 times
farther away from Uranus than are the satellites discovered by
the
Voyager team.
Nicholson and Karkoschka have been the only scientists to find
new
moons around a major planet in the 1990s. However, during this
decade,
the first two satellites of minor planets (Ida and Eugenia) were
imaged.
The new satellite is about 25 miles (40 km) in diameter, similar
in
size to comet Hale-Bopp, and it may also have similar composition
as
the comet, Karkoschka said.
"Hale-Bopp was a spectacular sight when it crossed the inner
part of
the solar system two years ago," he said. "On the other
hand, the new
satellite will never get spectacular since it will remain in the
dark,
frigid parts of the solar system. It will remain a tiny speck of
light."
Uranus may well have more than 18 satellites, Karkoschka noted:
Jupiter
and Saturn have satellites of about half the size of the new
Uranian
satellite. No such small satellite has yet been discovered around
Uranus since the dim sunlight at Uranus makes the detection of
such
small satellites very hard.
Based on the detection in seven images, Karkoschka concluded that
the
satellite orbits Uranus once every 15 hours and 18 minutes. This
is
similar to the rotation period of Uranus. The satellite hovers
32,000
miles (51,000 km) above the clouds of Uranus, or the same
distance as
the diameter of Uranus. The motions of satellites of Uranus can
be
viewed at the Space Telescope Science Institute from the link
below.
When Voyager 2 took the discovery image on January 23, 1986, it
was
650,000 miles (1 million km) from Uranus. This is 2,500 times
closer
than the Earth ever gets to Uranus. Nineteen hours later, Voyager
2
flew by Uranus.
The 10 satellites shown in the new discovery picture have been in
continuous sunlight during the last 25 years. Starting next year,
Cordelia, the satellite inside the ring system, will enter the
shadow
of Uranus during every orbit. The other satellites will follow.
By
2002, all 10 innermost moons will enter the shadow of Uranus
every
orbit. These eclipses occur during two intervals within the
84-year
long Uranus-year. Similarly, lunar eclipses on Earth occur twice
within
each Earth-year, currently in January and July.
The new discovery image is a mosaic of 10 exposures, Karkoschka
said.
The exposures of Uranus had shorter exposure times than the
exposures
of the surrounding area containing the rings and satellites.
Since
Uranus is a million times brighter than its satellites,
Karkoschka
retained the darker planet image so the satellites would be
visible.
"To an astronaut on board the Voyager spacecraft, the
satellites would
have appeared as faint stars while Uranus in the center would
have been
blazingly bright, as bright as the full moon on Earth,"
Karkoschka
said. "In visible light, Uranus seems to be a bland, quiet
place. Only
two faint little cloud features can be found upon close
examination of
the image. The true activity in the atmosphere of Uranus is only
revealed in infrared light." While the Voyager camera was
not sensitive
to infrared light, the Hubble Space Telescope has imaged
atmospheric
activity. The HST image can be viewed from the link below.
The colors in the image are close to realistic, he added. The
newly
discovered moon won't be stuck with the name
"S/1986U10" forever,
Karkoschka noted. The International Astronomical Union names
satellites
and asteroids a year or more after discovery. In the past, the
IAU has
often adopted a name suggested by the discoverer if that name
fits in
the context of the system's previously named satellites. However,
anyone can suggest what the new moon might be named, Karkoschka
added.
Brush up your Shakespeare. Uranus' other nine innermost moons are
Belinda, Bianca, Juliet, Rosalind, Ophelia, Cressida, Portia,
Cordelia
and Desdemona.
LINKS:
http://science.opi.arizona.edu/pics/disc1.jpg
http://science.opi.arizona.edu/pics/disc2.jpg
http://oposite.stsci.edu/pubinfo/pr/1999/11/animations.html
http://oposite.stsci.edu/pubinfo/pr/1998/35/index.html
----------------------------------------
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