PLEASE NOTE:
*
CCNet SPECIAL, 13 July 1999: ASTEROID 1999 AN10 PROBLEM SOLVED
--------------------------------------------------------------
(1) ASTRONOMERS SOLVE ASTEROID 1999 AN10 IMPACT PROBLEM
- AT LEAST FOR SOME CONSIDERABLE TIME
Benny J Peiser <b.j.peiser@livjm.ac.uk>
(2) "IT PAYS TO SAVE OLD PHOTOGRAPHS"
Brian G. Marsden <bmarsden@cfa.harvard.edu>
and
Gareth V. Williams <gwilliams@cfa.harvard.edu>
(3) 1999 AN10
MINOR PLANET CENTER, 12 July 1999
===============
(1) ASTRONOMERS SOLVE ASTEROID 1999 AN10 IMPACT PROBLEM
- AT LEAST FOR SOME CONSIDERABLE TIME
From Benny J Peiser <b.j.peiser@livjm.ac.uk>
It is exactly half a year ago that asteroid 1999 AN10 was
discovered -
and three month to the day that the its potential threat became
widely known. The story about 1999 AN10 made headlines around the
world after I drew attention to the web-paper by Andrea Milani,
Steven Chesley and Giovanni Valsecchi on the potential risk of
asteroid 1999 AN10 hitting the Earth in 2039 (CCNet Special, 13
April
1999). Two weeks ago, the team based at Pisa University even
claimed
that the impact risk had significantly increased to a probability
of
1:100,000.
Now, two amateur and two professional astronomers have dispelled
the
concerns about potentially hazardous asteroid 1999 AN10 colliding
with planet Earth in 40 years time. The discovery of 44-year-old
photographic images of the asteroid by Arno Gnadig and Andreas
Doppler,
two German amateur astronomers, and orbital computations by Brian
Marsden and Gareth Williams of the Minor Planet Center in
Cambridge
(Mass.), show that there is no longer any risk of asteroid 1999
AN10
colliding with Earth at least for most of the twenty-first
century.
Marsden and Williams cannot say what will happen after 2076, but
they
don't expect anything immediately precipitous. The important
result of
Marsden's and William's calculations is that the impact
probability in
the 2040s is now essentially zero.
Interestingly, Arno Gnadig and Andreas Doppler found the 1955
image of
the asteroid in the Digital Sky Survey (DSS) which is generally
available to the scientific community. It is quite astonishing
that the
teams involved in calculating impact probabilities for 1999 AN10
apparently failed to check this data before going public. After
all,
they could have avoided announcing a short-term
"problem" right from
the start.
The main lesson to come out of this latest asteroid scare
underscores
what Brian Marsden, the Director of the Minor Planet Center, has
stressed ever since the similar 1997 XF11 affair errupted: More
important (and much more reliable) than inherently erratic
probability
calculations are hard facts and real observational data. Unless
we can
improve this astronomical data base substantially, we will have
to rely
on short-lived and highly speculative probability statistics
which
begin to look like a game of pure gamble.
Benny J Peiser
=======================
(2) "IT PAYS TO SAVE OLD PHOTOGRAPHS"
From Brian G. Marsden <bmarsden@cfa.harvard.edu>
and
Gareth V. Williams <gwilliams@cfa.harvard.edu>
So wrote Malcolm Browne in The New York Times on March 14 last
year
with reference to some eight-year old photographs of 1997
XF11. It was
of course the identification and measurement by Eleanor Helin and
Ken
Lawrence of images of 1997 XF11 on films obtained with the
18-inch
Schmidt telescope at Palomar on two consecutive nights in March
1990,
and the resulting orbital computations by us and others, that
removed
any possibility that the infamous object could impact the earth
during
the foreseeable future. Now it seems that the recognition of
44-year-old Palomar images and the resulting orbital computations
show
that the earth is also quite safe from impact by the almost
equally
infamous 1999 AN10, at least through most of the twenty-first
century.
Beginning this past April, attention has often been drawn to the
possibility that 1999 AN10, a presumed half-mile object
discovered by
the LINEAR project in January, could hit the earth at some time
during
the next six centuries or so, conceivably even only 40-50 years
from
now. Any specific impact probability was initially very
small indeed,
largely because it required the object first to make a very close
approach to the earth in 2027, and it was initially not at all
clear
that this would happen. Interest in 1999 AN10 was therefore
considerably augmented, in the scientific community, at any rate,
when
the post-conjunction recovery observations in May showed the
inevitability of the 2027 close approach, after which the impact
probabilities for the 2040s were substantially increased, perhaps
even
just to the point where one might want to take notice. This
situation
was very comparable to that of the possibility of impact in the
2040s
by 1997 XF11 on the basis of the observations available before
the 1990
observations were discovered, the day after 1997 XF11 made the
headlines.
The similarity between the two situations is now even more
complete.
Despite a widespread feeling that pre-1999 images of 1999 AN10
did not
exist, the German amateur astronomers Arno Gnadig and Andreas
Doppler
have now found one, from 1955 Jan. 26, when, as at its 1999
discovery,
the object was located above north declination 70 degrees.
Furthermore, Gnadig and Doppler found the image in a resource
that is
readily available, namely, the Digital Sky Survey. The long trail
on
the digitization of the 45-minute red-sensitive exposure from the
Palomar Sky Survey is very weak, but it was located well within a
moon's diameter of the expected position. Furthermore, the length
of
the trail matches what would have been expected of 1999 AN10,
then some
20 million miles away. But in a case like this it is better to
utilize
hard copies of the Survey exposures, which are also available at
most
professional observatories. For one thing, there were two
separate
images, a 12-minute blue-sensitive exposure having been begun
shortly
after the red-sensitive one was completed. Not only does the
paper copy
of the red plate show the image somewhat more clearly than does
the
digitized image, but that of the blue plate shows a very much
clearer
image. Measurement of the ends of the 1955 trails is not
easy, the
result in any case being compromised by the fact that the
beginnings
and ends of the exposures are timed only to the nearest minute.
Nevertheless, despite these shortcomings, the 130-fold increase
in the
arclength permits a very dramatic improvement in the orbit
determination of 1999 AN10. The miss distance on 2027 Aug. 7 will
be
0.0026 AU, just the distance of the moon, and therefore now the
closest
confirmed approach of a sizeable minor planet. For a few hours it
should become as bright as eighth magnitude. Its subsequent
revolution
period of slightly more than 1.74 years completely eliminates the
possibility of close approaches in 2044, 2046--and even 2034,
when the
minimum distance will be comparable to that at the time of the
1955
observations. At the time of the purported 2044 encounter
the object
will be more than 200 million miles away, on the far side of the
sun!
The next significant approach after 2027 will not be until Feb.
2076,
when the distance is likely to become less than 0.05 AU, although
a
miss distance as small as 0.008 AU would not be possible.
Computations
into the past show miss distances of 0.0062 AU on 1946 Aug. 7 and
0.025
AU on 1990 Aug. 8.
=====================
(3) 1999 AN10
From the MINOR PLANET CENTER, 12 July 1999
http://cfa-www.harvard.edu/mpec/J99/J99N21.html
M.P.E.C.
1999-N21
Issued 1999 July 12, 21:23 UT
The Minor Planet Electronic Circulars
contain information on unusual
minor planets
and routine data on comets. They are published
on behalf of Commission 20 of the International
Astronomical Union by the
Minor
Planet Center, Smithsonian Astrophysical Observatory,
Cambridge, MA 02138, U.S.A.
BMARSDEN@CFA.HARVARD.EDU
or GWILLIAMS@CFA.HARVARD.EDU
URL http://cfa-www.harvard.edu/iau/mpc.html
ISSN 1523-6714
1999 AN10
Revision to MPEC 1999-K07
Observations:
J99A10N 5 1955 01 26.40208 08 38 25.08
+72 39
45.7
675
J99A10N 5 1955 01 26.43333 08 37 35.21
+72 40
05.4
675
J99A10N 5 1955 01 26.43750 08 37 26.05
+72 40
07.3
675
J99A10N 5 1955 01 26.44583 08 37 13.24
+72 40
11.7
675
Observer details:
675 Palomar Mountain. Earlier trail located and measured by
A. Gnadig and
A. Doppler. Later trail measured (and
earlier trail remeasured) by
G. V. Williams. 1.2-m Oschin Schmidt.
Orbital elements:
1999
AN10
PHA 0.015A
Epoch 1999 Aug. 10.0 TT = JDT
2451400.5
Williams
M
70.04961
(2000.0)
P
Q
n 0.55941450 Peri.
268.25229
-0.56757144 +0.68457751
a 1.4587479
Node 314.55304
-0.21820270 -0.66076120
e 0.5621418
Incl. 39.93185
-0.79388302 -0.30781206
P
1.76
H
18.0
G
0.15
U 2
Residuals in seconds of arc
550126 675 3.1- 0.3+ 990123
071 0.1+ 0.0 990214 587
0.9- 0.2-
550126 675 6.5+ 2.0+ 990124
046 0.4+ 0.0 990214 587
0.3+ 0.2+
550126 675 3.4- 1.7+ 990124
046 0.4+ 0.1- 990215 046
0.5- 0.3-
550126 675 1.4+ 1.7+ 990124
046 0.0 0.3- 990215 046
0.3+ 0.6+
990113 704 1.2+ 0.8+ 990124
046 0.8+ 0.3- 990215 046
0.1+ 0.6+
990113 704 (0.1+ 2.5-) 990124 658
0.3+ 0.6- 990215 046 0.3+
0.5+
990113 704 0.6- 0.5- 990124
658 0.1- 0.3- 990218 104
0.1+ 1.0-
990113 704 0.4+ 0.4+ 990124
658 0.3+ 0.6- 990218 587
0.0 1.0+
990113 704 1.9- 0.1- 990126
071 0.4+ 0.4+ 990218 587
0.8- 0.2-
990114 557 0.2- 0.5- 990126 071
(0.2- 2.8+) 990218 587 0.6+ 0.7+
990114 557 0.0 0.0
990126 402 0.5+ 0.7+ 990218
587 1.0+ 0.7-
990115 046 0.1+ 0.0 990126
402 0.2- 0.3+ 990220 428
0.8+ 0.7-
990115 046 0.0 0.2+ 990126
402 0.5+ 0.7+ 990220 428
1.0+ 1.4-
990115 046 0.3- 0.5- 990126
360 0.4+ 0.3+ 990515 426
0.7- 0.2+
990115 046 0.1- 0.2- 990126
360 0.1- 0.6+ 990515 426
0.2- 0.4-
990115 046 0.3- 0.1+ 990126
360 0.4+ 0.4+ 990515 426
0.5- 0.2+
990115 587 0.8+ 0.7+ 990127
587 0.4- 0.0 990516 426
0.8- 0.2-
990115 587 0.0 1.0+ 990127
587 0.2- 0.4- 990516 426
1.3- 0.1-
990116 704 0.6+ 0.4- 990130
402 0.8+ 0.6+ 990516 426
0.8- 0.7+
990116 704 0.2+ 0.0 990130
402 0.1+ 0.2- 990523 426
1.7- 0.2-
990116 704 0.7- 0.3+ 990130
402 0.2+ 0.3- 990523 426
1.6- 0.5+
990116 704 0.3+ 0.6+ 990204
402 0.3+ 0.1- 990526 950
0.3- 0.6+
990117 046 0.0 0.0
990204 402 0.1+ 0.1- 990526
950 0.5+ 0.1+
990117 046 0.2+ 0.3- 990207
587 0.5+ 0.1- 990526 950
0.8- 0.2-
990117 046 0.0 0.1+ 990207
587 0.8+ 0.3+ 990527 950
0.3+ 1.3+
990117 046 0.1+ 0.0 990207
587 0.6+ 0.5- 990527 950
0.0 1.2+
990117 402 0.4- 0.1+ 990208 704
(0.9+ 2.8+) 990609 675 0.3+ 0.6+
990117 402 0.1- 0.1- 990208
704 0.6+ 0.3+ 990609 675
0.1+ 0.6+
990117 402 0.4- 0.1+ 990208
704 0.4- 0.8+ 990609 675
0.1+ 0.7+
990117 540 0.6- 0.3+ 990208
704 0.2- 0.0 990609 675
0.1+ 0.6+
990117 540 0.5- 0.1+ 990208
704 0.6- 0.7+ 990609 675
0.1+ 0.6+
990117 540 2.0- 0.1+ 990208
900 0.2- 0.0 990609 675
0.1+ 0.6+
990119 151 0.8- 0.3- 990208
900 0.4+ 0.4- 990620 046
0.9- 1.9-
990119 151 0.6+ 0.1+ 990208
402 0.0 0.4- 990702 413
0.4+ 1.1+
990119 151 3.3- 1.4+ 990208
402 0.1+ 0.8- 990708 587
0.4- 1.4-
990119 587 0.1+ 0.1- 990208
402 0.4+ 0.8- 990708 658
0.1- 0.8-
990119 587 0.2- 0.1+ 990209
360 0.5+ 0.0 990708 658
0.2+ 0.1-
990121 046 0.0 0.3- 990209
360 0.7+ 0.3+ 990708 658
0.7+ 0.2+
990121 046 0.5+ 0.2- 990209
360 0.4+ 0.2+ 990709 658
0.1- 0.5+
990121 046 0.1+ 0.1- 990212
587 0.0 0.8+ 990709 658
0.7- 0.7+
990121 587 0.2- 0.5- 990212
587 0.1+ 0.8- 990709 658
0.6+ 0.4+
990121 587 0.1- 0.3- 990212
587 0.1+ 0.2-
990123 071 0.0 0.1+ 990214
587 0.4- 0.1+
Ephemeris:
1999
AN10
a,e,i = 1.46, 0.56,
40
q = 0.6387
Date TT R. A. (2000)
Decl. Delta
r Elong.
Phase V
1999 07 11 01 00.58 +31
25.4 1.096
1.393 82.4
46.4 20.7
1999 07 21 00 57.23 +37
29.3 1.082
1.474 89.2
43.6 20.7
1999 07 31 00 48.15 +43
13.5 1.070
1.551 96.1
40.6 20.7
1999 08 10 00 31.51 +48
22.8 1.064 1.624
102.8 37.5 20.7
1999 08 20 00 05.90 +52
32.2 1.066 1.692
109.0 34.4 20.7
1999 08 30 23 32.06 +55
13.2 1.080 1.756
114.3 31.6 20.7
1999 09 09 22 54.25 +56
05.3 1.107 1.816
118.3 29.2 20.8
1999 09 19 22 19.32 +55
11.0 1.150 1.872
120.5 27.6 20.9
1999 09 29 21 52.54 +52
58.1 1.208 1.924
120.8 26.6 21.0
1999 10 09 21 35.38 +50
02.4 1.280 1.972
119.3 26.2 21.2
1999 10 19 21 26.86 +46
54.5 1.366 2.016
116.3 26.3 21.4
1999 10 29 21 25.15 +43
55.2 1.462 2.057
112.4 26.5 21.6
1999 11 08 21 28.54 +41
15.8 1.567 2.094
107.7 26.8 21.8
1999 11 18 21 35.77 +39
01.9 1.679 2.127
102.7 27.0 22.0
A trail of 1999 AN10 was located and
measured by A. Gnadig and A. Doppler
on the Digital Sky Survey (DSS) copy of a 45-min red-exposure
Palomar Sky
Survey I (PSS) plate. Gnadig and Doppler remarked on the
difficulty of their
trail measurement. Examination of the DSS shows an
extremely weak image. In
view of this, it was decided to remeasure the trail from the PSS
prints, as
well as measuring the corresponding trail from the 12-min
blue-exposure plate.
Extracts from the two prints were scanned and the resulting
images were
measured. The r.m.s. of the fit of 25-30 USNO-A2.0
comparison stars was 0".22.
As examination of the residual block above shows, the trail-end
measures are
clearly not consistent at the subarcsecond level, partly because
of the poor
definition of the trail ends and partly because the times of
exposure of the
PSS plates were recorded only to the nearest minute. The
apparent better
agreement of the start of the first trail with the second-trail
measures
is presumably fortuitous.
Computations by B. G. Marsden and G. V.
Williams show that the miss
distance on 2027 Aug. 7.3 UT will be 0.0026 AU. The
subsequent revolution
period of a little over 1.74 years precludes the possibility of
any further
significant approach to the earth until Feb. 2076, when the miss
distance
can be expected to be less than 0.05 AU (although it cannot be as
small
as 0.008 AU).
Gareth V.
Williams
(C) Copyright 1999
MPC
M.P.E.C. 1999-N21
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