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2003 XJ7 (Apollo caught on its approach to 0.4 lunar distances of Earth)

2003 XJ7 was posted on the Near Earth Object Confirmation Page (NEOCP) with temporary designation AK00118 a few minutes after midnight early on Dec 6th 2003. The preliminary ephemeris had it listed at that time as being bright at mag +16.4 and moving at over 20"/minute and was due to double that speed and double in brightness in the following five hours! It was obviously already very close to Earth and still approaching rapidly.

Another NEOCP fast mover was being imaged at Great Shefford when the details for AK00118 came through (this one was eventually designated 2003 XH10), so the initial search for AK00118 was delayed for about 20 minutes. The first run of 10 x 10 second exposures on AK00118, centred on the nominal ephemeris position was started at 00:33 UT and an initial inspection of the images immediately revealed the object only about 7' from the ephemeris (see a full frame image showing how close it was to the expected position). The initial orbit calculated by the MPC must have been very close to reality and the indicated close approach was on.

The 10 exposures were immediately processed using Astrometrica to produce three precise positions, but while these were being prepared and mailed to the MPC to allow them to improve the orbit the MPC had posted a revised ephemeris for the object, using a different set of assumptions from the original LINEAR astrometry. This revision had the new object travelling at only about 5"/minute and was obviously wrong. A hurried e-mail was dispatched to the MPC indicating that their original orbit was good and with the three positions in hand the MPC revised the ephemeris again minutes later.

The revision showed the NEO would be a mag +13 object travelling at nearly 1/2 per minute 18 hours later, passing just 92,000 miles from the Earth (or 40% of the distance to the Moon, less than 12 Earth diameters away).

It was last reported by the Ageo Observatory (349) about 15 miles from Tokyo at 12:05 UT on 6th Dec 2003 when it was moving at about 150"/minute, 7 hours before closest approach.

At discovery this object was the 6th closest recorded fly-by of the Earth ever (2003 SQ222 being the closest). See the MPC's closest approaches list here.


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