Tuesday, 4 December 2007

2007 November notes: 2007 VA85 and 2007 VW266

The first half of November was reasonable, with at least some clear sky on 11 nights, but just 3 nights in the last half, including the obligatory crystal clear sky from dusk until dawn on the night of the full moon ...

An interesting object found on Nov 4th by LINEAR was 2007 VA85, 18th magnitude and placed at discovery in the early evening sky between Cygnus and Lyra, passing through the Cygnus star cloud during the next week. It was put on the NEO Confirmation Page and left there for nearly 5 days while the Minor Planet Center waited to see if anyone could detect any cometary features. In the end it was announced as a minor planet but with a very unusual retrograde orbit - four months after perihelion at q = 1.1 AU, with inclination = 132 degrees and period just 8.5 years. I followed it through the rich star fields of Cygnus on 5 nights, trying to catch it in enough empty sky to see whether it displayed any cometary features. Finally on 23 Nov I managed to get a total exposure of 41m 40s at a scale of 1.1"/pixel but could not detect any activity at all.

A week after 2007 VA85 was discovered, the Catalina survey's Mt Lemmon telescope picked up 2007 VW266. This was much fainter at mag. 21 and I just managed to catch it on a single night. By coincidence, it too turned out to have a short period retrograde orbit and was left on the NEO Confirmation Page for 7 days but again, no cometary features were detected by any of the seven observatories contributing astrometry. It has inclination = 108 degrees, q = 3.3 and period = 12.2 years.

In the Minor Planet Center MPCORB database there are only 18 minor planets listed with retrograde orbits and of those, 2007 VA85 and 2007 VW266 have the two shortest periods, with 2007 VA85 also having the smallest perihelion distance of the 18. In comparison, the comet with the shortest period retrograde orbit currently known is P/2006 R1 (Siding Spring) with inclination = 160 degrees, q = 1.7 AU and period = 13.3 years.