We can now announce that we have found a solution to the problem raised by 1998 OX4; the same method could be applied to other similar cases of lost potential impactors which might be discovered in the future. In short, the idea is to replace a full recovery campaign, requiring an inordinate amount of observational resources, with a targeted search for only those, among the possible orbital solutions for 1998 OX4, which lead to impacts; we call these the Virtual Impactors (VIs). We have shown that it is practical to launch a campaign of negative observations to show that the VIs do not actually exist, and that this can be accomplished using a very limited amount of telescope and observer time. Thus the impact risk could be eliminated, even without actually recovering the lost asteroid.
This result is announced in a paper now submitted for publication, with the title "Virtual Impactors: Search and Destroy," by Milani, Chesley, Boattini and Valsecchi. The preprint is available online from
http://copernico.dm.unipi.it/~milani/virimp/ (HTML version for WWW browsers)
http://copernico.dm.unipi.it/~milani/preprints/virimp.ps (PostScript version for laser printers).
Yours
Andrea Milani, Steven Chesley, Andrea Boattini, Giovanni Valsecchi
June 10, 1999
In May 1999, Frank Zoltowski, an amateur sky observer who received a
Planetary Society Gene Shoemaker Near-Earth Object (NEO) Grant in late 1998.
He demonstrated the value of amateur asteroid and comet tracking programs,
many of which, like Zoltowski's, are single-person operations conducted
using rudimentary telescopes set up in a back yard.
Zoltowski's follow-up observations of asteroid 1999 AN10 from his home in
Woomera, Australia, have enabled researchers at the Minor Planet Center
(MPC) to develop more precise future orbital calculations for the object,
which is expected to pass within 39,000 kilometers (about 24,000 miles) of
Earth in 2027, with the potential for even closer Earth approaches in 2044
and 2046.
The MPC is the clearinghouse for data about minor planets -- asteroids and
comets that travel through our solar system. As part of the International
Astronomical Union's Commission 20, the MPC oversees a network of
professional search programs and amateur sky observers who discover and
track these objects. In the case of 1999 AN10, which is considered a
near-Earth asteroid, particular follow-up tracking is significant in order
to determine if the object poses any future threat to Earth.
Both the MPC and NASA's NEO office at the Jet Propulsion Laboratory (JPL) in
Pasadena, California contend that, while Zoltowski's observations have been
integral to establishing more precise initial orbit predictions, AN10
currently poses a very small threat of colliding with Earth.
The near-Earth asteroid was first discovered by the Lincoln Near Earth
Asteroid Research (LINEAR) program, which conducts sky searches using an Air
Force telescope at the White Sands Missile Range in New Mexico. The objects
initial orbital calculations were established by researchers Andrea Milani,
Steven Chesley and Giovanni Valsecchi in Italy. Prior to publication, these
researchers had the MPC confirm their calculations, which set off a series
of alarmist articles that 1999 AN10 was a potential doomsday asteroid.
In fact, researchers still maintain that the chances of the object striking
Earth are extremely low. The MPC announced, "Additional observations during
the next several months will be useful, because there are no other
reasonable observing opportunities until at least 2004."
Paul Chodas at JPL, says on the NEO office website, "We have developed a
theory which successfully predicts the 25 possible [near-Earth] returns [of
1999 AN10] up to 2040. We have also identified six more close approaches
resulting from the cascade of successive returns. Because of this extremely
chaotic behavior, there is no way to predict all possible approaches for
more than a few decades after any close encounter, but the orbit will remain
dangerously close to the orbit of the Earth for about 600 years."
"The object is very faint--with a magnitude of about 20 [the lower the
number the brighter the object]--and it's moving fairly fast," Zoltowski
says. "These two considerations combined make it a very difficult target for
even many professional setups to find. Thanks to the new CCD camera I
obtained with the the Planetary Society Gene Shoemaker grant, along with
observational techniques I've fine-tuned over that last two years, I am able
to routinely get targets this faint."
Zoltowski was one of three recipients of a 1998 Gene Shoemaker NEO grant, a
program established by the Planetary Society in 1997 to help fund amateur
and underfunded professional efforts in discovery and follow-up tracking.
The grant money, which totalled $27,000 (US) in 1998 and went two other NEO
follow-up programs, is made possible by Planetary Society members, whose
voluntary dues and donations help support targeted research and development
programs in a number of areas.
Zoltowski "recovered" 1999 AN10 during two evenings after heated discussion
about the object began hitting the mainstream press in April 1999. Over the
course of two nights, Zoltowski was able to obtain good images of the
object's movement. After taking two frames of the sky where he believed 1999
AN10 to be moving, Zoltowski thought he had found it.
"The third frame confirmed my assumptions of the image on the second frame,
and I got another image to get three observations that first night," he
says. Following the MPCs recommendations that follow-up observations be
attempted on a second night, Zoltowski set up his equipment the following
evening and obtained a second set of observations.
"I guess what makes my recovery of 1999 AN10 interesting is that I had
obtained observations at all, considering the equipment that I have," he
says. "The performance of my new CCD is spectacular. With it I have been
able to get many objects--1999 AN10 included--that I wouldn't have had a
chance of imaging with my old CCD."
SpaceViews
June 9, 1999
Italian astronomer Andrea Milani and
colleagues reported the impact
probability at the end of the IMPACT
conference in Torino, Italy, earlier this
month. They found that 1998 OX4,
discovered last year at the Spacewatch
telescope in Arizona, has a 1-in-10
million chance of hitting the Earth in
January 2046.
From: David Morrison (dmorrison@arc.nasa.gov)
NEO News (4/19/99)
On 26 March 1999, these authors requested several colleagues to look at
their manuscript and check the general validity of their calculations of
the orbit of this asteroid. They wrote, in part: "The subject of this
paper is such that we consider essential that its content be reviewed by
the most qualified experts before it is made public. This paper has been
submitted to a scientific journal. We do not want the content of this paper
to reach the non-scientific media until it has been carefully reviewed.
Note that it would be unwise to hurry with a public announcement for
three good reasons. First, we have established that there is no risk of
impact until 2039, and even then the probability of impact is well below
the background level. Second, 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. Third,
the issues raised by this case are indeed very complex.
Please note that we had no obligation to submit our paper to this highly
unusual refereeing procedure: we felt this as a moral obligation. We are asking you
to carefully examine our paper looking for every possible fault in our
arguments, but with respect for our work and for our scientific priority...
We intend to make the paper available on our web server on April 6
unless some of you can point out to some reason not to. Thus you should
send us your comments, criticisms, and whatever queries you have, as soon
as possible. In particular if there is some fundamental flaw in our
arguments we would like to know before making any information publicly
available."
Several of the colleagues they addressed responded with detailed technical
commentary, but none disagreed with the basic conclusion that this asteroid
poses no significant threat of Earth impact for at least the next 40
years. Thus, Milani and his co-authors posted the manuscript on their
website early on 6 April, as they had indicated they would do. About a
week later the manuscript was circulated to a larger group of experts at
the request of the International Astronomical Union. These informal
technical referees also agreed with the conclusions concerning the
exceedingly low probability of an impact with Earth.
Subsequently to this Web posting, the case of asteroid 1999 AN10 became
widely known and has stimulated considerable discussion on the Internet and
in the international press. The remainder of this message reproduces some
of the commentary related to this asteroid and the mode of release of
information. Everything that appears here has already been made public on
other websites. The material is drawn together here as a reference on a
subject of general public interest dealing with the probability of asteroid
impact and of the best way such information should be made available to the
public.
David Morrison
Giovanni B. Valsecchi
March 26, 1999
Abstract:
The Earth passes very close to the orbit of the asteroid 1999 AN10 twice
per year, but whether or not this asteroid can have a close approach
depends upon the timing of its passage across the ecliptic plane. The
uncertainty of this timing grows with time: by 2027 it is +/- 12 days.
Among the possible orbital solutions there are some that undergo a close
approach in August 2027, but no impact is possible. However, the period of
the asteroid may be perturbed in such a way that it returns to an approach
to the Earth at either of the possible encounter points. We have developed
a theory which successfully predicts the 25 possible such returns up to
2040. We have also identified 6 more close approaches resulting from the
cascade of successive returns. None of these encounters can result in an
impact, except one in August 2039: the probability that the true asteroid
actually follows a collision course for that date is less than the
probability of being hit by an undiscovered asteroid within any given day.
Because of this extremely chaotic behaviour there is no way to predict all
possible approaches for more than a few decades after any close encounter,
but the orbit will remain dangerously close to the orbit of the Earth for
about 600 years.
The International Astronomical Union Working Group on Near Earth Objects
(WG NEO) provides, as a service to the international astronomical
community, voluntary expert review of reports that might have implications
for possible future Earth impacts. The review process was first used in
April 1999 in the case of newly discovered mile-wide asteroid 1999 AN10.
NEOs with orbits that permit close encounters or even collisions with the
Earth are of considerable interest to scientists who compute asteroid
orbits. As a consequence of their frequent close encounters with the Earth
or other planets, it is difficult to predict their orbits with high
precision for more than a century or so into the future. One such object is
1999 AN10, discovered by the MIT-USAF LINEAR search program on 13 January
1999.
A detailed analysis of the orbit of 1999 AN10 was completed by researchers
Andrea Milani, Steven R. Chesley and Giovanni B. Valsecchi in March 1999.
Their paper, which has been submitted for publication in a technical
journal, includes an examination of the potential risk of 1999 AN10 hitting
the Earth in the next several decades. They conclude that, while there is
some uncertainty in the exact orbit of this NEO following its next close
planetary encounter in August 2027, the chances of its actually hitting the
Earth in the next 40 years are minuscule -- the authors estimate that the
chance of impact is of order 1 in a billion (1 in a thousand million),
which they indicate is 10,000 times less than the chance that the Earth
will be struck by some as-yet-undiscovered similar-sized NEO in any one
year.
The IAU's Working Group on Near-Earth Objects has formed an ad hoc
committee, with widely international expert membership, whose members are
available to review predictions of impact hazards if so requested. This
committee functions similarly to the referees of most technical journal
articles in reviewing the predictions, and it also keeps the appropriate
IAU officials completely informed about any such predictions.
The technical paper by Milani and colleagues has been subject to such
informal review during the first two weeks of April 1999, and it is the
consensus of the reviewers that the work is accurate and of the highest
scientific quality. The IAU reviewers also note that the chances of impact
by NEO 1999 AN10 during the time-span considered in this paper are
negligible compared to the risks we run continuously of being struck by one
of man similar size NEOs that have not yet been discovered. Like asteroid
1997 XF11, which was widely discussed in the press in March 1998, this
asteroid does not pose any significant danger to the Earth on the time
scale of the next several decades.
Astronomers will continue to search for new NEOs and to track the orbits of
those already discovered, especially when, like 1999 AN10, their orbits
bring them close to the Earth. But this object, as demonstrated in the
technical paper by Milani and his colleagues, should not evoke any
particular public concern. Thus, the reviewers from the WG NEO agree with
the authors in ruling out any danger to Earth from 1999 AN10 in the next
forty years. The object will be followed closely over the next several
years in order to define the longer-term properties of its orbit more
accurately, as will be the case with numerous other, similar objects that
will be continue to be discovered over the next several years as NEO
searches intensify and orbital computation methods improve.
By pure coincidence, I have come across a research paper by Andrea Milani,
Steven R. Chesley and Giovanni B. Valsecchi on the potential risk of 1999
AN10 hitting the Earth in forty years time. Yet instead of informing the
interested public about their potentially explosive findings, the authors
have hidden away their results on an obscure web page.
The asteroid, known as 1999 AN10, was discovered by LINEAR on 13 January
1999. According to the Italian researchers, the object will come
particularly close to Earth in August 2027. No impact is possible in that
year, but there is a small chance that the asteroid will be perturbed in
such a way that it might impact the Earth in 2039. While
the chance of an actual collision is small, one is not entirely out of the
question.
Moreover, the extremely chaotic behaviour of this asteroid makes it
impossible to predict all possible approaches for more than a few decades
after any close encounter, but the orbit will remain dangerously close to
the orbit of the Earth for about 600 years.
If this information reminds you of the 1997 XF11 affair, you are spot on.
It is in fact only the second time in history that a major impact in the
near future cannot be ruled out altogether. And yet there is at one major
difference: At least we were informed about 1997 XF11 once a potential
hazard became clear. In the case of 1999 AN10, however, it is pure accident
that you hear about the information via the CCNet rather than through an
official press release.
Now, what is really worrying about 1999 AN10 is not the statistically very
small impact risk. Nobody needs to lose any sleep due to this object. What
is really disturbing, however, is the unnecessary and detrimental secrecy
that surrounds this object.
There is no reason whatsoever why the findings about 1999 AN10 should not
be made available to the general public - unless the findings haven't been
checked for general accuracy by other NEO researchers. If, however, no such
independent assessment has taken place, the data should not be in the
public domain in the first place.
Of course, one reason why the authors may have decided to hide their data
could be due to the current NASA guidelines on the reporting of impact
probabilities by individual NEOs. After all, NASA is threatening
researchers with the withdrawal of funding if they dare to publish such
sensitive information in any other form than in a peer reviewed medium.
Obviously, one's own web site can hardly be considered a peer reviewed
journal. One therefore has to wonder why such relevant information is put
into the public domain in such a wired and secretive way.
The 1999 AN10 'affair', in my view, should be seen as a rather damaging
consequence of the over-reaction regarding asteroid 1997 XF11. Moreover, I
would argue that the unclear and intimidating NASA guidelines on NEO
reporting should be dropped in their present form since they have become
part of the problem. Instead, international procedures (which would
acknowledge a certain level of scientific uncertainty regarding some
particular PHAs) should replace those ill-considered NASA guidelines which
were imposed in a rash last year.
In order not to repeat last year's mistakes, the discussion should be
focused on an international procedure of how future impact risk
calculations (and their inherent uncertainties!) should be reported in a
satisfactory way.
Dear Benny,
We strenuously object to your characterization of our actions regarding
this paper, and to your attempts to sensationalize our work. This whole
thing could have been explained easily if you had contacted one of us, but
that apparently does not suit your purposes. Instead you released a uninformed
report filled with speculation and innuendo.
We have submitted the paper in question to a journal, so it is undergoing
the usual peer review process even now. It is customary for researchers to
make available, through a variety of means, papers which are at all stages
of the publication and review process, even work still in preparation. This
fosters discussion among the community, and is an essential component of
the modern scientific method. In addition to submitting to a journal we
have voluntarily sent the paper to more than a dozen international experts
and officials for comment and criticism before we made the article
available on the Internet. This review has been going on for more than two
weeks now, and in fact some technical issues that we raise are still under
discussion, but, fundamentally, the content of our report has been well
received. (We posted the information to the Internet on April 6, about one
week after selectively releasing the paper.) This additional level of
review was done voluntarily on our part as we did not want to make
available erroneous or misleading information, which many perceive was done
in the 1997 XF11 scare. We also wanted to be in a position to issue a
controlled release to the public after all issues have been confirmed by
our independently convened panel of experts, should that be deemed
necessary. In the end a consensus among the experts was quickly reached
that this object does not fit any realistic criteria of imminent danger, so
we decided to follow normal channels with the paper. This entails
submitting the article to a journal and posting to the Internet as a
preprint.
More than likely, you stumbled upon the paper via Andrea's preprint page
(hardly an "obscure web page"):
http://virmap.unipi.it/~milani/preprints/preprint.html
You should note that some of the other papers listed there are also
currently under review for publication by scientific journals. Indeed the
paper in question is specified as "submitted." It is not our custom to
contact the media every time we write a paper, nor is it customary to treat
papers undergoing the peer review process as secret.
Your opening paragraph (above) clearly indicates that you are trying to
spark fear and controversy where none is warranted. You later call our
results potentially explosive, but then go on to say that the risk of
collision is small enough to be considered negligible.
So which is it? This is the fundamental flaw in your claim that we had some
obligation to broadcast this work as widely as possible to the general
public. Either it is of urgent concern, or it is not. Your claim that
"unnecessary and detrimental secrecy" surrounds this object is based on an
assumption that this paper presents time critical information which morally
obligates us to notify the public, the press, the United Nations, and the
commander of the Enterprise. This is clearly not the case here, and so your
argument is invalid, even paradoxical. If the important thing is the lack
of a press release rather than the risk of collision, as you stated, then
there was nothing to release outside of normal scientific channels.
You make the point that this case has been handled differently from the
XF11 affair, and you are right. In the XF11 scare, a possibility of
collision in 2028 was announced, when such possibility did not exist, even
based on the then available information. 1999 AN10 is qualitatively similar
except that in the cases where there is a non-negligible chance of a very
deep encounter (2027 and 2034), we have explicitly stated that collision is
not possible. The risk in 2039 is, of course, negligible.
Your speculation that we have decided to hide this report for fear of
losing our NASA funding is demonstrably false for two reasons. First we
have no financial support from NASA, and second, if we were hiding our
results you certainly would not have found them published on the Internet.
=46urthermore, to our knowledge, this proposal was only a proposal, and it
was never implemented.
We have scrupulously followed normal conventions for the release of
scientific data. Aware that this report could be sensationalized, we
submitted it to review by the panel of experts. This was done voluntarily,
but we also hope to set a precedent with this action. As a result of this
case the IAU is moving rapidly to formally establish voluntary guidelines
and procedures to be followed in future cases. Their plans are closely
modeled on our approach. Under this policy, researchers would submit their
results to an ad hoc committee of experts for comment and criticism before
going public. How long this delay should last is unclear, but probably
would depend on the urgency of the situation, anywhere from 2-5 days. After
that period the author could release the information in any manner deemed
appropriate, and the officials and agencies first confronted by the press
will be able to respond with an informed discussion of the threat. This
responsibility to seek confirmation before going public becomes even more
critical for more threatening situations.
You may object to this policy, but we expect that in the future virtually
all researchers in the Earth hazard community will be following it. We are
sorry to report that the reason these voluntary guidelines are necessary is
to thwart those in the press who would
seek to sensationalize reports of potential impact, no matter how carefully
we word them. In that sense you are part of the problem, Benny, and a
careful and deliberate release of information is only a response to
irresponsible actions such as yours.
1999 AN10 itself holds very little relevance to the general public. If our
research does have any relevance for the public at large, it is because we
have developed a general theory that can rule out impact for some finite
period of time, yet it also shows that we can say very little about the
possibility of collision for times beyond that point, because each
encounter predicted by our theory can spawn more close encounters, a
cascade too complex to be analyzed. The good news is that the further down
the cascade we go, the lower the probability of impact should a collision
solution exist. The essential point is that we feel that this paper should
not be used to confuse the general public, and we strenuously object to
your accusations that the information was handled irresponsibly. You will
have a very hard time to find a scientist who will accuse us of a lack of
openness in our research.
An important point: We want to avoid the perception of crying wolf when we
say in April that a collision is possible, while in July, after more
observations become available, we will almost certainly report that a
collision is no longer possible. We have verified that the object cannot
hit the Earth in the next 40 years, far longer than any threat mitigation
would require. And in a few months, when there is less uncertainty in the
orbit, the picture will be very different from the one we have now.
The timescales involved require no immediate action, hence the weeks (or
even months) required for the scientific review process to proceed is of no
consequence. Furthermore, there is no reason why this object should merit
any extraordinary public attention as the probability falls below that for
"undiscovered" objects out there.
Richard P. Binzel
Milani estimates that the chance of impact by 1999 AN10 is of order 1 in a
billion (1 in a thousand million), a factor of a million smaller than the
mistaken estimate of 1997 XF11's impact probability. He estimates the
impact probability as 10,000 times less than the chance that the Earth will
be struck by some as-yet-undiscovered kilometer
sized object NEXT YEAR! That makes 1999 AN10 a matter of scientific
interest, but of no practical interest and hardly meriting the "official
press release" you call for. (Unless, of course, you are the sort of person
who worries about being killed by snakes while you drive around town
chain-smoking and not wearing a seat-belt.)
Use of the same wording to describe probabilities that differ by a factor
of a million can only serve to confuse a literate, rational understanding
of risk. You obviously used this wording in an ironic, argumentative way,
rather than as an attempt to confuse. But the point needs to be made, if
society is to address risks in a rational way, that the quantitative
difference of a factor of a million makes for an *enormous* qualitative
difference. That is why the XF11 announcement would have *deserved* the
world-wide headlines, had it been true, while the AN10 matter has no
relevance to the "man-on-the-street" whatsoever.
Andrea Milani has been very responsible in having other experts check his
work before posting his results on his public web site. There is no
rational reason, however, for Milani to have called a press conference, or
offered his results to CCNet, and risked an unwarranted sensation (like you
seem to be trying to provoke) from a misunderstanding of his result, which
is irrelevant in the larger scheme of things. Such an announcement would
attach undue importance to an arcane result. People like yourself, who are
interested in the impact hazard, have long been aware of Milani's website,
so his work was hardly "hidden" away.
NASA is holding no gun to the head of a researcher at an Italian
university, so your remarks about NASA intimidation seem to be off-track.
There is room, of course, for legitimate debate about how to handle matters
of potential practical interest in a responsible way, so that the public
isn't misled by faulty, premature results but yet *is*
told about potentially important matters in a timely fashion. This is a
dilemma long-faced by emergency preparedness officials in communities and
nations around the world who have tried to establish responsible protocols,
but there are no easy answers. Your apparent belief, Benny, that every
infinitesimal threat needs to be announced in a press release seems to me
to be a step in the wrong direction.
Clark R. Chapman
Firstly, I believe the common goal is to protect the Earth from the
consequences of impacts by asteroids and comets. This involves:
Items (a) to (d) are relatively low-cost, "routine" activities that are
well described in the Spaceguard Proposal on NASA's Web site. The entire
cost of a ten year, worldwide Spaceguard Survey is about US$100 million --
apparently equivalent to US military expenditure for just two days in the
Balkan Conflict! Despite the low cost of this "insurance for mankind,"
efforts to introduce a worldwide Spaceguard Survey appear to
have stalled -- advisors to government don't seem to take the issue
seriously (in fact, I have questioned whether Spaceguard is too cheap for
its own good). Several groups around the world have been working on this by
lobbying politicians and key scientists. "False alarms" don't help this
effort and also unfairly undermine the credibility of
scientists working in the field.
It turns out that the authors of the paper describing the potential hazard
of Asteroid 1999 AN10 had submitted it for peer review prior to making a
"preprint" available on the Internet. This is entirely appropriate -- the
difficulty is deciding at what stage the media
should be informed and how such information should be worded in order to
not raise undue alarm. Brian Marsden from the Minor Planet Centre has
pointed out that 1999 AN10 was added to the list of "Potentially Hazardous
Asteroids" on February 16, well before the Italian paper was posted on the
Internet.
There are media relations precedents in other fields such as the release of
economic indicators -- everyone knows that the statistics are analysed by
competent people over several weeks but that public release of the results
will take place on a certain day. Another (perhaps more relevant) analogy
is where a medical doctor detects a potentially cancerous growth on a
patient and sends a sample away for pathology tests. The patient is told
that it will take a certain time (usually days) before the results of the
tests are available.
My suggestion is that there be a similar "official" delay in the
announcement of the results of NEO impact assessments. People would know
that sufficient information had been gathered to enable orbit calculations
to be undertaken, that one or more groups were performing these
calculations and that an announcement of the results be issued (probably by
MPC) on a certain day (say two months after its inclusion on the PHA list).
As several people in the NEO field have pointed out, there really is no
need for urgency in the release of these results.
A related issue is the need for consistency in terminology amongst
spokesperson scientists when dealing with the press. Terms such as
"potentially hazardous", "especially dangerous" (Brian Marsden's
suggestion), "possible impact" and expressions of probability need to be
clearly defined and some poorly understood terms need to be avoided
altogether. Richard Binzel's suggestion for a scale of impact
hazards, similar to the Richter Scale for earthquakes, has merit. Of
course, anyone commenting on an impact hazard issue should bear in mind the
likelihood that some sections of the media will sensationalise the story.
By Michael Paine, News South Wales Coordinator,
In a discovery eerily reminiscent of one made just a year ago, astronomers
have found an asteroid that will come quite close to Earth in a few
decades, and that even has a real but minuscule possibility of an impact.
Last year, astronomers made a similar discovery of an asteroid that they
said had a slight possibility of hitting Earth in about 40 years. In that
case, it was quickly determined that the Earth was safe after all, and
astronomers have been arguing ever since about the way the original report
was disseminated.
The latest asteroid, called 1999 AN10, was described in a detailed
scientific paper posted on a Web site by three astronomers. But unlike last
year's case, no information has been sent directly to the public and the
press.
The asteroid is thought to be about a mile in diameter - similar to the one
last year - and could possibly come very close to Earth in 2039. There is
about a one-in-a-billion chance that it could strike the Earth that year,
with devastating consequences.
That is less than the risk that an unknown asteroid or comet might hit
Earth on any given day, and therefore is not anything to be too concerned
about. What might be more worrisome, scientists said, is its long-term
potential.
For the next 600 years, according to astronomers Andrea Milani, Steven
Chesley, and Giovanni Valsecchi, the asteroid could remain very close to
Earth, and if it comes close enough to be affected by Earth's gravity its
orbit could become chaotic and impossible to predict for more than a decade
or two ahead. In that case, the asteroid would require constant, careful
monitoring for centuries to guard against a possible impact.
This is only the second time in history - or perhaps the first time,
depending on whose analysis of last year's discovery you believe - that an
asteroid has been discovered that has a small but non-zero possibility of
striking the Earth within a few decades. Even though the likelihood is
quite small, that makes it an interesting find. Some people have questioned
the wisdom of the changes in the way such information is disseminated as a
result of what many astronomers considered a serious public embarrassment
last year.
British anthropologist Benny Peiser, who has written extensively about the
effects of past impacts on the Earth, yesterday circulated an e-mail
message questioning why this discovery, unlike last year's, has not been
announced publicly or shared with news organizations. While acknowledging
that the risk of the asteroid hitting the Earth is tiny
and not something that anyone should lose any sleep over, Peiser said that
he found the lack of public notice disturbing, suggesting that it reflects
an overreaction to astronomers' embarrassment about last year's
announcement followed by a swift reversal.
But astronomers contacted yesterday said that they see this latest case as
a perfect example of how such information should be handled. The
astronomers who made the calculations of impact probabilities have
circulated their unpublished paper to several colleagues around the world
who specialize in such calculations, in order to make sure their
conclusions are correct. Some astronomers contacted yesterday said that all
the comments so far from such specialists have been positive.
"I commend them for the process of being careful," said Richard Binzel, an
astronomer at Massachusetts Institute of Technology who specializes in
asteroids.
David Morrison, NASA Ames Research Center
website: http://space.arc.nasa.goc
April 16, 1999
NEO Grant Recipient Puts New CCD Camera to Good Use
The Planetary SocietyNEO Grant Recipient Plays an Integral Role in Tracking
While lost to the LINEAR program and other professional programs in the
Northern Hemisphere, Frank Zoltowski was asked to track the object's passage
through Southern Hemisphere skies because of his reliable follow-up imaging
record since he began tracking asteroids and comets for the MPC in 1997.Another Asteroid with Earth Impact Probability Discovered
For the third time in a little over a
year, astronomers have found an asteroid
that has a very small, but non-zero,
probability of impacting the Earth next
century.THE CASE OF NEO 1999 AN10
Following is a file of information on the near-Earth asteroid called 1999
AN10, discovered by the MIT-USAF LINEAR telescope on 13 January 1999.
Dynamicists Andrea Milani, Steven Chesley, and Giovanni Valsecchi carried
out an analysis of its orbit, which involves resonances with the Earth and
permits close encounters with the Earth over the next several hundred
years. This research is of general interest because there is a very small
chance of a collision of this asteroid with the Earth.1) ABSTRACT OF THE TECHNICAL PAPER
CLOSE EARTH APPROACHES OF ASTEROID 1999 AN10: RESONANT AND NON-RESONANT RETURNS
Andrea Milani, Steven R. Chesley
Dipartimento di Matematica, Università di Pisa
Via Buonarroti 2
56127 PISA, ITALY
IAS-Planetologia
Area di ricerca CNR
Via Fosso del Cavaliere
00133 ROMA, ITALY2) OFFICIAL COMMENTS FROM THE INTERNATIONAL ASTRONOMICAL UNION
From the IAU website3) COMMENTS FROM BENNY PEISER TO THE CCNET NEWSGROUP (13 APRIL)
ASTEROID 1999 AN10 ON POTENTIAL COLLISION COURSE WITH EARTH IN 2039 -
AND NOBODY SEEMS WILLING TO INFORM THE PUBLIC
Imagine a newly discovered asteroid, some one mile in diameter, is on a
potential collision course with Earth in just 40 years - and no one is
telling you about it. This is exactly what is happening with asteroid 1999
AN10.4) THE AUTHORS RESPOND TO THE CCNET (14 APRIL)
Andrea Milani, Steven R. Chesley, Giovanni B. Valsecchi
> Imagine a newly discovered asteroid, some one mile in diameter, is on a
> potential collision course with Earth in just 40 years - and no one is
> telling you about it. This is exactly what is happening with asteroid
> 1999 AN10.
5) COMMENT TO CCNET FROM RICHARD BINZEL (14 APRIL)
THE TIMESCALE INVOLVED REQUIRED NO IMMEDIATE ACTION
The "1999 AN10 Affair" is nothing more than the scientific peer review
process at work. The authors have asked scientific colleagues to examine
and verify their results prior to issuing any IAU Circular or Press
Information Sheet. Better still, the authors intend to publish their
results in the refereed literature. The authors are to be applauded for
doing it right, that is, they are making sure their results are correct
before making any public announcement, and they will provide their full
analysis for scrutiny within the professional literature.
Professor of Planetary Science
Massachusetts Institute of Technology6) COMMENT TO CCNET FROM CLARK CHAPMAN (14 APRIL)
NASA IS HOLDING NO GUN TO THE HEAD OF ITALIAN RESEARCHERS
I regret the misleading wording you have chosen to use (both in your
heading and in your text) in announcing the Milani study of 1999 AN10 to
CCNet subscribers. You have written that "the chance of an actual
collision is small, but one is not entirely out of the question." In the
context of the impact hazard, those were the words used 13 months ago to
describe a very different situation. When used about 1997 XF11 in an
official IAU statement, they implied -- to both the writer, who had a
mistaken concept of the distribution of errors (see IAU Circular 6879), and
to scientifically literate readers (see Stuart Goldman's sidebar on pg. 33,
June 1998 SKY & TELESCOPE) -- a probability of impact of order 1 in 1000.
Southwest Research Institute7) COMMENT TO CCNET FROM THOMAS PAINE (15 APRIL)
MANAGING THE KNOWLEGE OF HAZARDOUS ASTEROIDS
The current debate about Asteroid 1999 AN10 amongst astronomers and others
in the scientific community is mainly concerned with the manner in which
information about potentially hazardous asteroids is released to the
public. This issue has received considerable attention since April 1998
when a "false alarm" was raised about another asteroid (1997 XF11). A
working group of the International Astronomical Union is
apparently preparing guidelines for announcement of possible impacts and
the 1999 AN10 "incident" should help that group review its work. As a
nonscientist who is trying, on a voluntary basis, to get a major NEO search
effort re-established in Australia, I would like to offer some comments on
this issue.
The Planetary Society Australian VolunteersNEWSPAPER COVERAGE IN THE BOSTON GLOBE (14 APRIL)
SCIENTISTS SAY ASTEROID MAY TANGO WITH EARTH
By David L. Chandler, Globe Staff, 04/14/99
+++++++++++++++++++++++++++++++++++++++++++
Tel 650 604 5094; Fax 650 604 1165
david.morrison@arc.nasa.gov or dmorrison@mail.arc.nasa.gov
website: http://astrobiology.arc.nasa.gov
website: http://impact.arc.nasa.govTHREAT OF POSSIBLE ASTEROID IMPACT IN 2039
Andrea
Milani and Steven Chesley
of the University of Pisa and Giovanni B. Valsecchi of IAS-Planetologia (Roma)
discuss Close
Earth Approaches of Asteroid 1999 AN10. The Earth
passes very close to the orbit of this Near
Earth Object (NEO) twice a year. A "collision solution" is found for
August 2039. But the probability that the true asteroid actually collides with Earth
is "less than the probability of being hit by an undiscovered asteroid
within any given day", it is carefully stated. Due to perturbations of the asteroid's
orbit there is no way to predict all possible approaches for more than a few
decades after any close encounter. But the orbit will remain dangerously close to
the orbit of the Earth for about 600 years.
One should be very careful with the interpretation of possible collisions by NEO's. Last year a false alarm was sounded for asteroid 1997 XF11. Therefore on April 15, 1999 an official statement by the International Astronomical Union was issued on the IAU Near Earth Objects homepage.
Mentioned below are some links to secondary sources of information, communicated by Ron Baalke of the Jet Propulsion Laboratory.
Carl Koppeschaar
BBC News: Earth Set For Close Asteroid Encounter
ABC News: Asteroid Warning: Scientists Say Rock Could Pass Near Earth
Albuquerque Journal: Asteroid's Path May Be Distastrous
Boston Globe: Scientists Say Asteroid May Tango With Earth
explorezone.com:
Published Threat Of Possible Asteroid Impact Stirs Controversy
KIJK, juni 1998: The End (Dutch)
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