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2004 AS1 (When initial predictions go wrong...)

This animation was put together from 15 separate images taken on the first night that 2004 AS1was accessible from Great Shefford after discovery, having been north of +68 before that time. It was travelling at 4"/minute.

This object was originally added to the NEO Confirmation Page at 22:50 UT on 13th Jan 2004 with the temporary designation of AL00667, having been discovered by LINEAR some 15 hours beforehand on 4 images taken over a period of about 1 hour.

The original MPC ephemeris was more than interesting - it showed that in 27 hours time the object was predicted to impact the Earth. At a declination of +72 and still heading North the area could not be imaged from Great Shefford that night and all that could be done was to image the other objects posted that night on the NEOCP and follow the unfolding story being posted on the Minor Planet Mailing List (see Reiner Stoss's first posting on AL00667 and the subsequent 100 or so follow-up messages)

AL00667 evaded detection by the few observatories with clear skies and that could get to the area that night, but was picked up again 24 hours after discovery by LINEAR and then 8 hours after that observations from Ondrejov (557) by Peter Kusnirak allowed the publication of MPEC 2004-A56 that gave it the provisional designation 2004 AS1.

The very first LINEAR position was shown to be over 3" out (about 3% of the movement recorded in the first hour's observations) and probably contributed to the incorrect initial assessment of the orbit.

The orbit actually placed the object much further from the Earth than originally predicted (though it would approach the Earth to 0.085 AU on 16 Feb 2004 by which time it brightened to mag +17.2) and would actually stay within 1 AU of the Earth for nearly 2 years! It is an Apollo asteroid, with perihelion at 0.88AU, a relatively small eccentricity of 0.17, an inclination of 17 and a period of just 1.11 years.

For those that like a good ephemeris(!) the original (incorrect) predictions are reproduced below, calculated for Great Shefford showing what an impact trajectory would look like. Even if this original trajectory had been broadly correct, the uncertainties by the time of closest approach would have been so large that this ephemeris can be regarded as no more than an interesting indication of what might have been.


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