Sunday 6 December 2009

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 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.