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2003 RU11 (small Aten making close approach to Earth)

Discovered by LINEAR on 2003 Sep 14 on four images taken between 4:16 - 5:07 UT, it was added to the NEO confirmation page by the Minor Planet Center (MPC) later that day with a temporary designation of AH79759.

When darkness was falling in the UK, just 16 hours after LINEAR's last observation it was +18th magnitude and moving at over 30"/minute and the uncertainty region indicated by the MPC was already about 2 long. The star field was quite rich, in Draco near the border with Cygnus.

A search was made of the uncertainty area, the diagram below showing the uncertainty region as the range of possible positions calculated by the Minor Planet Center.

An initial run was made covering the whole uncertainty region quickly in case it was going to be easily recognised. This was a set of five images of each field. However, AH79759 was not identified on these images on an initial scan and a further set of images of the uncertainty region were taken, each field being imaged nine times, so that stacking could be done to enhance the image of the object. Again it was not picked up on this search. Details of the unsuccessful search were e-mailed to the MPC.

The next night, having sent some astrometry to the MPC on another object, the MPC e-mailed back that AH79759 had now been confirmed (by LINEAR) and requested I re-check my images from 14 September. With a good ephemeris the object was located in two of the search fields:

A stack of two sets of two images each shows the asteroid faintly on the images taken during the initial run. The field shown here is 6'x6' or about 1/4 of the whole frame. As can be seen, there was plenty of noise in the image that caused it to not be detected that first night:

Two pairs of two images stacked to reveal the motion of 2003 RU11 in the initial run taken to search for the asteroid. Each frame is a 20 second exposure binned 2x2, this image enlarged by a factor of x2.

Unfortunately, having located it on the images from the previous night the object was not able to be imaged that night 15 September, but it was located the next night, 16 September (see animation at top of page), just four hours before closest approach.

The next night 17th Sep 2003 was also clear and the asteroid was again registered, moving at over 38"/minute, but this time very faintly at mag +20. The positions obtained at 19:38 and 19:54 UT that night were the last optical observations reported of the asteroid. Coincidentally it was being observed by radar at Arecibo at 19:51 and 20:28 UT the same night.

2003 RU11 passed 3.7 lunar distances from the Earth at 00:17 UT on 17 Sep 2003. Its perihelion distance is 0.726 AU and aphelion 1.052 AU and is thought to be between 20 and 50 metres in diameter.


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