An object with temporary designation AO60675 was posted on
the NEO Confirmation page on 2004 July 17th, listed at 18th
magnitude and moving relatively slowly at 0.5"/minute. It was observed
at Great Shefford early on July 20th and was given the provisional
designation 2004 NN31 by the Minor Planet
Center later that same day. It turned out to have a
perihelion distance just larger than 1.3 AU (the upper limit for
Amor type objects) and so was not categorised as a Near Earth Object.
The chart above shows a ~ 4° x 6°
area of the vicinity in western Aquarius, about 1° south west of
Uranus where 2004 NN31 was at discovery,
together with a number of nearby minor planets observed in the
following weeks.
While exposures were still being taken that night, the images already
available were being stacked to make sure the new object was
visible. It was found in the stacked images, but also another
brighter minor planet could also be seen moving at about the same
speed, moving north to south, fast approaching a field star. At
that time this object did not show up on the Minor Planet Checker
(it did by the next day, with designation 2004 NX21) and so,
thinking it may be a new, previously unknown minor planet, further
exposures were taken.
Eventually, after 2004 NX21 had moved past
the field star, all the exposures were stacked and examined. As
well as the two minor planets already noted, three fainter ones were
found, none of which showed up on the Minor Planet Checker. Each
of these was measured and the astrometry sent off to the Minor
Planet Center.
Soon afterwards the Minor Planet Center identified one as 2001
TN218. This object had been followed for 10 weeks
between October and December 2001 and had not been seen
since, by the time it was picked up in the field of 2004
NN31 it was about 0.5° off track. Two cloudy
nights followed before confirmation positions could be obtained
for the other two objects and sent off to the Minor Planet Center.
Designations came back indicating that they were new objects 2004
OH9 and 2004 OJ9, credited to
Great Shefford Observatory. Väisälä orbits were calculated for
the two by the Minor planet Center (some simplifying assumptions
being made because of insufficient positions being available to
allow a general elliptical orbit to be determined).
Bad weather continued, further positions for 2004 OH9 were
obtained on July 24.0 in poor conditions (2004 OJ9
could not be recorded) and positions for 2004 OJ9
on July 28.0. The next opportunity on Aug 7.0 was used to get
further positions for 2004 OJ9 but these images
showed another moving object that could not be identified using
the Minor Planet Checker. A second night of positions were
obtained the next night on Aug 8.0 and sent off to the Minor
Planet Center. This object was eventually designated 2004 PN2
and again credited as a discovery to Great Shefford.
By this time, both 2004 OH9 and 2004 OJ9
had enough observations (including some from the surveys LINEAR,
NEAT and LONEOS) for reasonably good orbits to be calculated, so
attention was switched to getting at least three nights for 2004
PN2. The next opportunity was Aug 13.0 and
positions were obtained. Remarkably, another moving object was
found on the stacked images and once again did not match any
object on the MPC's Minor Planet Checker. The following night was
cloudy, but a second night was made on Aug 15.0 and the
measurements sent off to the Minor Planet Center. The designation
for the new object was returned as 2004 PO95 and
again credited to Great Shefford.
So, in a period of four weeks, two minor planets were
discovered in a single field while following up a NEO Confirmation
Page object and two further minor planets were found while
following up on previous discoveries.
By August 16th the Minor Planet Center had managed to link
observations of 2004 OJ9 to a single night of
positions reported by Spacewatch in February 1997 and from single
nights reported by Spacewatch, LINEAR and NEAT surveys in February
& March 2002.
Update March 2006: 2004 OJ9
was recovered at its next opposition from Great Shefford on 05
Nov 2005 and was last observed in Feb 2006. It received permanent
number (128465) in March 2006 from the Minor Planet Center and
becomes the first minor planet discovery from Great Shefford to be
numbered.
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