2009 November notes: 2009 VX, 2009 VZ, 2009 WJ6, 2009 WV51 and 9U01FF6

Although many nights in November had interruptions from cloud, observing time was logged on 18 nights and there were plenty of Near Earth Objects to be followed that had been discovered during the month by the surveys.

Apollo 2009 VX had been discovered on Nov. 9th by the Catalina Sky Survey (CSS) as a 19th mag. object but had brightened to 17th mag. by the time it was picked up from Great Shefford early on the morning of Nov 12th, moving at 150"/min. It was then at 2.8 Lunar Distances (LD) and would pass at 2.59 LD at 13h UT the same day.

Another relatively bright new discovery was Apollo 2009 VZ and although it didn't get any closer than 15 LD it remained above 17th magnitude for 12 nights, I recorded it at 15th mag. on Nov. 12 & 14th. 2009 VZ was intrinsically about 5 magnitudes brighter than 2009 VX, which translates to 2009 VZ having a diameter about ten-times larger than 2009 VX (approx. 300 meters vs. 30 meters), assuming similar albedos for the two objects.
2009 WJ6 was another CSS discovery from Nov 19th and was followed from Great Shefford later that same day. By then it was already about mag. +17.0, at 2.1 LD and moving at 58"/min. It reached its closest to Earth at 11am UT the next day at 0.46 LD and was reported from the Westfield site of the Astronomical Research Observatory, Illinois three hours before perigee, at a distance of 0.82 LD.

One other close approach Apollo object was 2009 WV51. Discovered at 7am on Nov 23 by the CSS it was due to pass at just 0.39 LD the next day. I picked it up on the evening of Nov 23 at 17th magnitude when it was at a distance of 2.8 LD and moving at 'just' 22"/min. Watching individual images download it was easy to see it rising and falling in brightness by approximately 1 magnitude in just a few minutes, though the lightcurve has yet to be reduced. It was last reported from the Magdalena Ridge Observatory, New Mexico on Nov. 24 at 05:43 UT with the 2.4-m reflector, at a range of about 1.8 LD. It went unobserved from Great Shefford that night at its closest approach due to bad weather, but would have been 14th magnitude and moving at over 1,000"/min in the early evening of Nov. 24.

The probable artificial satellite 9U01FF6 mentioned last month was due back at perigee early on Nov. 28 after being followed for only 44 hours by 7 observatories at the end of October. I started searching for it on the evening of Nov 23 but given a likely positional uncertainty of up to 1°, the waxing Moon only about 30° to the south and the predicted mag. being +21.2 I was not expecting much success. However, it was picked up only 5' from the predicted position and ranging in magnitude from +20.5 up to +18.9, the standard asteroid magnitude formula obviously not providing a good fit for this object! Further positions obtained on three subsequent nights allowed the effect of Solar Radiation Pressure (SRP) to be determined using FindOrb using all the available observations (26 October - 27 November 2009). SRP effectively pushes an object away from the Sun and the smaller the mass and larger the surface area of the object exposed to the Sun, the larger the discrepancy from Newtonian motion may be observed. Without taking into account SRP the RMS residual for 78 positions over the two apparitions is a very unsatisfactory 16", but taking into account SRP this drops to 0.8". The value of SRP (or Area/Mass Ratio) determined was 0.011 m2/kg which is similar to those determined using FindOrb for other distant artificial satellites, e.g.

LCROSS (incl. Centaur) size 14.5m x 4.7m, mass ~3,200kg, SRP = 0.015 m2/kg
IMP8 size 1.4m x 1.6m, mass 371kg, SRP = 0.010 m2/kg
ASTRON (1983-020A) size 6m long, mass 3250kg, SRP = 0.008 m2/kg

and is 10 times larger than the 0.0011 m2/kg value derived for 2006 RH120 (=6R10DB9), the tiny (natural) minor planet that was temporarily trapped in Earth orbit during 2006-2007. All this points to 9U01FF6 being man-made and from a posting on the SeeSat-L (Visual Satellite Observers) mailing list here http://www.satobs.org/seesat/Oct-2009/0176.html it is suggested that 9U01FF6 is very likely to be from a lunar transfer mission of some kind, but the perturbations on the orbit make identification of the specific launch very difficult. It is noted that some of the Agena rockets for the Ranger missions of the 1960s were in very similar orbits.

2007 June notes: 6R10DB9's fourth and final perigee

As anyone in the UK will already know, the poor weather in May just got worse through June. I suffered the least number of hours observing since December 2002.

The unusual object with provisional designation 6R10DB9 made it's fourth and final perigee in June. Back during the March perigee it was observed with the 10-m SALT telescope and found to have a rotation period of only 2.75 minutes and an amplitude at that time of 1.2 magnitudes. This time it approached from the sunward side of the Earth, passed over the North pole and was picked up again a day after perigee on June 15th in Draco, about 1 degree from Theta Cep while only 0.80 Lunar Distances from Earth, magnitude +19 - +20 and moving at 47"/min. Never 'bright', it was recorded at mag +18.6 on June 18th and at about +19.5 on the 20th, fading again as it receded from both Sun and Earth. The only other observations reported at the time of writing are radar detections from Goldstone on June 12 & 14 and optical astrometry from the 1.5-m Mt Lemmon telescope on June 22. By the end of June it was below 20th mag and too far south to attempt from the UK.

The main indicator that this object is likely to be natural rather than a piece of artificial space junk come from determinations of solar radiation pressure (SRP) acting on it. Bill Gray's FindOrb freeware program includes routines to calculate SRP, given as the area-to-mass ratio or AMRAT in m^2/kg. With astrometry extending for 10 months now, it gives a value of 0.0011, with an RMS residual from 132 observations of 2.5". Not including SRP increases the RMS residual to an unsatisfactory 9.1". The JPL Horizons orbit solution which also includes the Goldstone Radar observations, gives an even smaller value of AMRAT of 0.0007. In comparison, various distant artificial satellites, such as IMP8, Geotail, J002E3 (the piece of old Apollo hardware discovered by Bill Yeung in 2003), WMAP etc have values between 10 and 50 times larger, indicating that 6R10DB9 is much more massive and much less prone to the perturbing effects of SRP than artificial satellites and is therefore likely to be a rocky body, probably about 4 metres in diameter. There is still a chance that time might be spent at some of the large observatories to get spectra and other measurements during July before it goes out of range completely.

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

Object	March UT	"/min	Distance AU	Distance LD
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 http://www.birtwhistle.org/Gallery2007EH.htm.

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 http://www.birtwhistle.org/Gallery6R10DB9.htm, but hopefully more to come in June and July.