Friday, 6 April 2007

2007 March notes: 2007 EH, 2007 EK and 6R10DB9

March was an exceptional month for NEO close approaches, with ten objects observed moving faster than 25"/min, and two observed while inside the distance of the Moon.

In the table below "/min is the apparent speed of the object in arcsec/minute and LD = Lunar distance = 0.00257 AU

2007 DJ 01.9 30 0.021 8
2007 DX40 02.1 33 0.028 11
2007 EH 11.1 1,250 0.0011 0.4
2007 EK 13.2 382 0.0018 0.7
2007 EV 15.2 42 0.016 6
2007 EO88 18.8 288 0.0032 1.2
2007 FC3 20.8 142 0.0090 3.5
2007 FG1 22.0 25 0.025 10
2007 FY20 31.9 35 0.018 7
2006 VV2 31.9 57 0.024 9

2007 EH is the fastest natural object I have tracked and is currently the third closest observed approach of a designated minor planet ever (only 2004 FH and 2006 DD1 having had astrometry reported while closer).

It was discovered 44 hours before the close approach and put on the NEO Confirmation page during the afternoon of 9th March, but that evening, with it still unconfirmed I spent some time searching about +/- 0.5 degree around the predicted position but without success. Reviewing the discovery positions from the Catalina Sky Survey, one or two looked somewhat out of step with the others and so an orbit was calculated leaving these out. The resulting prediction was about 1 degree west of the NEOCP prediction and the object was indeed picked up close to that place, allowing the subsequent close approach prediction for the next night to be greatly refined.

The close approach itself was remarkable, to watch images appear on the monitor with the object racing across so fast... at it's fastest speed of 1,250"/min it was 15th mag and covering the field of view of my CCD in 53 seconds, or the diameter of the Moon in less than 1.5 minutes! When first picked up on the evening of the 10th at 19:16 UT it was at RA=11h 41m Dec=+30, reached RA=15h 50m Dec=+60 at 00:45UT on 11th and was last seen at 02:22UT at RA=19h 37m Dec=+50, over 80 degrees of sky covered in less than 7 hours!

Full details of the confirmation, animations from the close approach night and details of the techniques used to measure astrometry of such a fast moving object can be found at

2007 EK which passed at 0.7 Lunar Distances just two nights after 2007 EH would in a more average month have headlined itself. However, it was nearly two magnitudes fainter than 2007 EH and so was not quite the spectacle of the earlier NEO.

One other noteworthy object seen during the month was 6R10DB9, a Catalina Sky Survey temporary designation given to an object discovered last September which has since then been in geocentric orbit, originally expected to be a small piece of man-made space junk, but increasingly suspected of being natural. It was picked up at mag +19 moving at 24"/min in a dense starfield in Gemini, just 1.2 Lunar Distances from Earth, as it approached it's 2nd to last perigee. It will be perturbed out of the Earth's vicinity for the foreseeable future this coming summer. Attempts to obtain spectra with the 6.5-m MMT during the March perigee were unfortunately clouded out, but there will be one last opportunity in June to try and determine once and for all whether it is indeed a natural object. Some details of the story so far of this interesting object can be found at, but hopefully more to come in June and July.