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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