Tuesday, 5 October 2010

2010 September notes: 2010 RX30, 2010 RF12 and the pair 2010 RX3 and RY3

Good weather from Aug. 29 to Sept. 17 resulted in a run of 17 out of 20 nights usable for observing, but unfortunately the last half of the month could only manage three. There was plenty of NEO activity in early September, with a number of close approaches:

2010 QG2 had been discovered on the last day of August by LINEAR and was followed on the nights of Sept. 1 & 2 at mag +17.0 as it passed by at 5 Lunar Distances (LD).

The Catalina Survey Mt. Lemmon station discovered two small asteroids within about half an hour of each other on Sept. 5th and both came closer than the Moon three days later. 2010 RX30 is probably about 11 meters in diameter and passed at 0.64 LD on Sept. 8th at 09:51UT, closely followed by 2010 RF12 (~7 meters dia.) which came as close as 0.2 LD or just 6 Earth diameters at 21:12 UT the same day.
2010 RX30 was imaged on the nights of 5th, 6th and 7th Sept. and on the last night was 16th mag. and moving at 160"/min, at a distance of 1.2 LD. It was last seen by Richard Miles using the 2-m Faulkes Telescope North just half an hour before closest approach by which time it was 14-15th mag. and moving at 520"/min!
2010 RF12 was well observed by many people in the run up to its fly-by and again was tracked from Great Shefford on the nights of 5th, 6th and 7th September. When last seen, before clouds moved in it was also 16th mag. but moving slower than 2010 RX30 at 37"/min and at a distance of 1.1 LD. David Herald in Australia was the last to report positions for it, 11 hours before closest approach and by then it was 14th mag., moving at 168"/min at a range of 0.5 LD.

Just before month end, 2010 SK13 passed by at 0.7 LD and was observed on the night of 29th Sept. at mag +17 when it was 2.4 LD away. It was closest at 15:58UT on the 30th but was last reported 7 hours earlier from the Magdalena Ridge Observatory in New Mexico, before it had crossed within the orbit of the Moon.

Probably the most unusual discovery was made on Sept. 2nd, again from Mt. Lemmon. Two objects were put on the NEO confirmation page travelling at almost the same speed and in the same direction, one moving at 10.6"/min in p.a. 77.5°, the other at 10.8"/min in p.a. 78.5°. Added to that, they were of similar brightness and only 1.5° apart in the sky. They were designated 2010 RX3 and 2010 RY3 the day after discovery but unfortunately they were already mag. +21.2 and +21.4 and within a day or so of their brightest for this apparition. I managed to record both on two nights, but they were always very difficult objects and both were lost after only 7 days. The orbits for both are necessarily still somewhat uncertain after such a short arc but the elements are very similar and indicate that the two objects were probably gravitationally bound in the recent past. The JPL Small-Body Database Browser at http://ssd.jpl.nasa.gov/sbdb.cgi gives the following orbits for the two objects:

2010 RX3 2010 RY3
T = 2010 Sep.29.70 ±0.04 d T = 2010 Oct.01.85 ±0.04 d
q = 1.00365 ±0.00009 AU q = 0.99181 ±0.00004 AU
Q = 4.26 ±0.05 AU Q = 4.29 ±0.05 AU
e = 0.619 ±0.005 e = 0.624 ±0.005
a = 2.63 ±0.03 AU a = 2.64 ±0.03 AU
Peri = 202.26 ±0.02°) Peri = 206.06 ±0.02°)
Node = 172.69 ±0.03°)2000 Node = 171.99 ±0.02°)2000
Incl = 3.89 ±0.02°) Incl = 4.44 ±0.02°)
H = 25.06 H = 25.07