CCNet SPECIAL: 13 April 1999
ASTEROID 1999 AN10 ON POTENTIAL COLLISION COURSE WITH EARTH IN 2039 -
AND NOBODY SEEMS WILLING TO INFORM THE PUBLIC
THE CHANCE OF AN ACTUAL COLLISION IS SMALL, BUT ONE IS NOT ENTIRELY OUT
OF THE QUESTION
From Benny J Peiser <email@example.com>
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
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
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
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.
To underline this point and to make all list members aware of the
potential impact hazard posed by asteroid 1999 AN10, I have attached
excerpts of the paper in question below. The full version (including
the references) can be accessed at
Benny J Peiser
CLOSE EARTH APPROACHES OF ASTEROID 1999 AN10: RESONANT AND NON-RESONANT
Andrea Milani, Steven R. Chesley
Dipartimento di Matematica, UniversitÓ di Pisa
Via Buonarroti 2
56127 PISA, ITALY
E-mail: firstname.lastname@example.org, email@example.com
Giovanni B. Valsecchi
Area di ricerca CNR
Via Fosso del Cavaliere
00133 ROMA, ITALY
March 26, 1999
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 2027 encounter with 1999 AN10
The asteroid 1999 AN10 was discovered by the LINEAR telescope on 13
January 1999. The discovery was somewhat unusual in that the declination
was +70'. We checked for possible prediscovery observations in the
archives made available by the Minor Planet Center, and found
none; this is not surprising, given that this asteroid is
typically visible in a portion of the sky which has been very
little surveyed in the past. The asteroid was observed until 20
February: afterwards the angular distance from the sun became
Whenever the asteroid and the Earth are in phase at each node, close
approaches are possible. Indeed a close approach is possible in August
2027. [ ...] The occurrence of a very close approach [in 2027] is not
very likely: the true orbit could be anywhere along a very long line,
including long stretches corresponding to very shallow encounters.
In conclusion, the August 2027 encounter could be a very shallow
approach, or could be, with a low, non-negligible probability, very
close, but in any case cannot result in an impact. The case for a
possible dangerous encounter, however, is not closed after 2027; indeed,
it is just opened. [...]
2 Resonant returns
The possibility of a resonant return of an asteroid involved in a close
approach was proposed by B. Marsden. This idea did not receive the
attention it deserved. Marsden applied this idea only to a hypothetical
case, namely the asteroid 1997 XF11 in the assumption that the 1990
precovery observations had not been discovered. In that hypothetical
case there are indeed more than 20 different solutions leading to a
return after injection by the 2028 close approach into a resonance with
the Earth. The real 1997 XF11, with the orbit determined by using all
the available observations, is only mildly perturbed by the 2028
encounter, and cannot have a resonant return. [...]
The other element to be taken into account is the so called Minimum
Orbital Intersection Distance (MOID), the minimum distance between the
two osculating ellipses representing the orbit of the Earth and of the
asteroid. Even if the asteroid were exactly on time at the rendezvous
with the Earth, the unperturbed close approach distance cannot be less
than the MOID. In the case of 1997 XF11, within a few decades after the
2028 encounter the MOID becomes large enough to make the most dangerous
encounters impossible. Thus in the hypothetical case without 1990
precovery only 11 resonances have to be taken into account to assess the
risk of resonant return; [...]
What is the evolution in time of the local MOID's of 1999 AN10? It is
not enough to compute the evolution of the MOID's along the nominal
solution, because the close approaches can change them: in particular,
an encounter near the ascending node (in August) can reduce the distance
at the descending node, and make possible a closer approach at the
descending node (in February). [...] The answer is that 1999 AN10 will
continue to have a very low distance at both nodes, until the crossing
at the descending node, which should take place `on average' in 2633,
and for a few decades later. Thus it is simply not possible to perform
close approach analysis [...] for all possible resonant returns: there
are hundreds of them.
3 Non-resonant returns
Among these secondary returns there is one in August 2039 for which the
interpolated MOID is less than the radius of the Earth. Since the
stretching is extreme, we have checked by performing close approach
analysis [...], and verified that a collision solution actually exists.
The high stretching, however, appears as divisor in the formula for the
probability, and this results in an estimate of the probability for
this impact of the order of 10^9. The possibility of such an impact
could be frightening, but if we assume that the probability of an
impact by an undiscovered 1 km asteroid is of the order of 10^5 per
year, the probability of an impact by 1999 AN10 in 2039 is less than
the probability of being hit by an unknown asteroid within the next few
Asteroid 1999 AN10 will be again at >60' from the Sun after the
beginning of June; by that time the uncertainty of its position on the
sky will grow to ~1.5 arc minutes [...], that is any new observation
will significantly contribute to an improvement of the orbit. It is
very likely that the observations made in the second half of this year
will allow to determine the orbit well enough to predict accurately the
2027 encounter. This implies that some of the returns of the Table will
be discarded as incompatible with the observations; if the 2027
encounter is not very deep, most of the close approaches in the Table
would not be possible any more.
The problem, however, will not go away, because all along the variations
line there are possible encounters occurring later, almost every six
months. E.g., we have analysed with our global method the same 1000
multiple solutions discussed above over a time span of 50 years after
2027, and found 165 possible returns, out of which 117 in the moderate
to low stretching region. This situation is qualitatively stable:
whatever the actual orbit is, it will not be possible to predict with
certainty the returns after the next close approach for a time span
longer than a few decades.
Since at least one node of 1999 AN10 will remain close to the orbit of
the Earth for centuries, this implies that this asteroid shall have to
be monitored, by observations and computations, for a very long time.
It is conceivable that at some time in the future a decision could be
made to deflect and/or destroy it. However, a deflection decreasing the
depth of some specific close approach could increase the impact risk at
a later date. Thus before such a decision can even be contemplated we
need to better understand the theory of resonant and non-resonant
returns, which has only been outlined in this paper.
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CCNet SPECIAL: ASTEROID 1999 AN10
PUBLISHED THREAT OF POSSIBLE ASTEROID IMPACT STIRS CONTROVERSY
By Robert Roy Britt, explorezone.com
04/13/99: Bypassing conventional scientific review, a group of Italian
researchers has posted an article on their own Web site detailing the
possible impact of an asteroid with Earth in 2039.
The threat, though muted by an obscure method of publication, is
reminiscent of a similar one issued in 1998 about Asteroid 1997 XF11.
In that instance, however, normal scientific channels of publication
were followed and, ultimately, the threat was retracted.
The newly discovered asteroid, named 1999 AN10, was spotted by the
LINEAR telescope on 13 January. It orbits the Sun on a plane that is
highly inclined to the ecliptic, the plane in which Earth orbits.
Twice each year, Earth passes close to Asteroid 1999 AN10. The closest
approaches are due to occur in August 2027, but no impacts are possible
then, say Andrea Milani and Steven R. Chesley of the University of Pisa
and Giovanni B. Valsecchi in the research they posted on the Web.
The researchers go on to say that there is a chance that the asteroid's
path could be perturbed in such a way that it could hit Earth in 2039.
"We have developed a theory which successfully predicts the 25 possible
such returns up to 2040," the researchers report. "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.
"The possibility of such an impact could be frightening, but if we
assume that the probability of an impact by an undiscovered 1 km
asteroid is of the order of [10^9] per year, the probability of an
impact by 1999 AN in 2039 is less than the probability of being hit by
an unknown asteroid within the next few hours."
Further, the researchers say, the asteroid's chaotic behavior means
that close encounters could be possible for the next 600 years, and
that there's simply no way to predict the possible paths more than a
few decades in advance.
"This implies that this asteroid shall have to be monitored, by
observations and computations, for a very long time," the report
Benny J. Peiser, a researcher who focuses on neo-catastrophism at
Liverpool John Moores University, wondered allowed in a newsletter
today why the information was published on an obscure Web site before
going through normal scientific review procedures.
"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,"
Peiser said. "If, however, no such independent assessment has taken
place, the data should not be in the public domain in the first place."
Peiser offered one possible reason for the unusual posting: The authors
may have reacted to NASA guidelines on the reporting of impact
probabilities of individual asteroids.
"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," Peiser said.
About the danger of an actual impact, Peiser noted that the statistical
chances are very small. "Nobody needs to lose any sleep due to this
object," he said.
The authors of the report have not yet responded to questions from
Copyright 1999, Explorezone
CCCMENU CCC for 1999
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