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First radar echo from asteroid 2004 MN4 |
0.000242 +/- 0.000058 AU
36200 +/- 8700 km
0.094 +/- 0.023 Earth-Moon distances
5.7 +/- 1.4 Earth radii
This is 28,000 km closer than predicted by the pre-radar
(optical-only) orbit and closer than geosynchronous satellites. The asteroid's 2029 flyby is closer than any known past or future approach by natural objects larger than about 10 meters (other than objects that have entered Earth's atmosphere).
2004 MN4 is expected to reach 3rd magnitude for observers in Europe, Africa, and western Asia, where it will be visible to the unaided eye.
Approaches as close as the 2029 event, by objects as large as 2004 MN4, are very rare, occuring on average at intervals longer than a thousand years.
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Click here to enlarge this sketch of the asteroid's most likely
trajectory during its 2029 close approach as predicted using the Jan. 2005 radar
astrometry. Since the asteroid's
position in space is not perfectly known at that time, the white dots
at right angles to the blue line are possible alternative positions of
the asteroid. Neither the nominal position nor any of its possible
alternative positions touches the Earth, effectively ruling out an
Earth impact in 2029.
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<----Arecibo----> <---Goldstone--->
Year Month SNR/Date SNR/Run SNR/Date SNR/run
---- ----- -------- ------- -------- -------
2005 Jan 14 5 8 1
2005 Aug 6 2 0 0
2006 May 5 2 1 0
2013 Jan 33 10 11 1
2020 Oct 7 3 1 0
2021 Mar 110 26 8 1
2028 Sep 7 2 0 0
Click here to go to a University of Michigan press release on how the 2029 encounter will alter the asteroid's spin state. For a better version of that site's animation showing what such spin-state alteration might look like, click here.i
Circular No. 8477
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
CBAT@CFA.HARVARD.EDU (science)
URL http://cfa-www.harvard.edu/iau/cbat.html ISSN 0081-0304
2004 MN_4
On 2004 Dec. 20, K. E. Smalley (cf. MPEC 2004-Y25) identified
an object placed on the 'NEO Confirmation Page' on Dec. 18
(following its discovery by G. J. Garradd via the Siding Spring
Survey) with 2004 MN_4 (which had been recorded at Kitt Peak on
June 19 and 20; cf. MPS 109613). Although the recognition of
further prediscovery observations by Spacewatch on Mar. 15 (MPEC
2004-Y70) precluded the possible 2029 Apr. 13 earth impact
discussed extensively in the WWW during 2004 Dec. 23-27 [notably on
the Jet Propulsion Laboratory (JPL) and Pisa NEODys "risk pages"],
it was clear that the object would then make an unusually close
approach. L. A. M. Benner, JPL; M. C. Nolan, National Astronomy
and Ionosphere Center, Arecibo Observatory; J. D. Giorgini, S. R.
Chesley, and S. J. Ostro, JPL; and D. J. Scheeres, University of
Michigan, report: "Arecibo delay-Doppler radar astrometry obtained
on 2005 Jan. 27, 29, and 30 significantly refines the 2004 MN_4
orbit. On Jan. 29.0 UT, the range was 294 km closer to the earth
than the pre-radar orbit solution predicted. This correction
results in a 2029 approach to the geocenter of only 0.000245 +/-
0.000060 AU (36700 +/- 9000 km or 5.7 +/- 1.4 earth radii, 3-sigma
uncertainties), which is just below geosynchronous orbit and 28000
km closer than predicted by the pre-radar ephemeris. During its
close approach, it is likely that tidal torques will significantly
alter the object's spin state."
(C) Copyright 2005 CBAT
2005 February 4 (8477) Daniel W. E. Green
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Circular No. 8593
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
CBAT@CFA.HARVARD.EDU (science)
URL http://cfa-www.harvard.edu/iau/cbat.html ISSN 0081-0304
(99942) APOPHIS
J. D. Giorgini, L. A. M. Benner, S. J. Ostro, Jet Propulsion
Laboratory; M. C. Nolan, Arecibo Observatory; and M. W. Busch,
California Institute of Technology, report: "Arecibo (2380-MHz,
12.6-cm) radar observations of (99942) Apophis = 2004 MN_4 (cf.
IAUC 8477) made during Aug. 7.655-7.769 UTC produced a CW detection
and a Doppler measurement of 8186.8 Hz at Aug. 7.713, a correction
of +0.3 +/- 0.2 Hz (+18.9 +/- 12.6 mm/s) relative to nominal
prediction. Including this Doppler correction in a new orbit
estimate and n-body gravitational propagation increases the 2029
April 13.9 Earth-center miss-distance from 5.77 +/- 0.39 to 5.86
+/- 0.12 Earth radii, reducing the along-track position uncertainty
at closest approach from +/- 1957 to +/- 757 km; the volume of the
spatial uncertainty region decreases from 173000 to 39800 km**3.
The new Doppler measurement increases the predicted nominal Earth
close approach in 2036 from 0.005 to 0.14 AU. However, we have
found that computational noise intrinsic to 64-bit representations
of real numbers used in arithmetical operations, exacerbated by the
close Earth encounter in 2029, can accumulate trajectory-prediction
error exceeding the radius of the earth by 2036. Using more
precise 128-bit representations, the specified local error
tolerance was reduced from 10**-14 to 10**-19 and the maximum
predictor/corrector order (used for step-size and error-control
decisions) increased from 14/15 to 21/22. This approach reduces
error growth in the integration due to the finite representation of
real numbers and permits examination of those specific orbit
variations in 2036 for which trajectory offsets comparable to the
size of the earth are significant."
...
(C) Copyright 2005 CBAT
2005 September 2 (8593) Daniel W. E. Green
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Circular No. 8711
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
CBAT@CFA.HARVARD.EDU (science)
URL http://cfa-www.harvard.edu/iau/cbat.html ISSN 0081-0304
...
(99942) APOPHIS
L. A. M. Benner, J. D. Giorgini, and S. J. Ostro, Jet
Propulsion Laboratory; M. C. Nolan, Arecibo Observatory; and M. W.
Busch, California Institute of Technology, report that Arecibo
(2380-MHz, 12.6-cm) radar observations of minor planet (99942) =
2004 MN_4 during May 6.497-6.562 UTC yielded a 5.5-sigma
continuous-wave detection and a Doppler measurement of -118256.8 Hz
at May 6.534, for a correction of +0.1 +/- 0.1 Hz (+6 +/- 6 mm/s)
relative to the nominal prediction. An orbit estimation
incorporating the new Doppler measurement with 779 optical
measurements spanning 2004 Mar. 15-2006 Mar. 26, along with the
four Doppler and two range measurements from observations in 2005,
increases the 2029 Apr. 13.9 earth-center miss-distance by 450 km,
from 5.86 +/- 0.11 to 5.93 +/- 0.09 earth radii, and reduces the
along-track-position uncertainty at closest approach from +/- 730
to +/- 570 km (cf. IAUC 8593). The volume of the one-standard-
deviation spatial uncertainty region decreases by 23 percent, from
261000 to 201000 km**3, and the nominal predicted earth-close-
approach distance in 2036 increases from 0.168 to 0.276 AU, moving
the statistical earth encounter to a lower-probability region
within the distribution of possible orbits.
(C) Copyright 2006 CBAT
2006 May 17 (8711) Daniel W. E. Green