Sunday, 11 October 2009

2009 September notes: 2009 SH2, 2009 SN103, 2009 SU104, LCROSS and Herschel

September was a busy time for NEOs, with the Minor Planet Center's NEO Confirmation Page (NEOCP) listing many newly discovered objects during the month. On Sept. 17th and again on 26th more than 30 new and potentially interesting objects were on the NEOCP page and by the end of the month an extra 106 NEOs had been added to the MPC's database.
Apollo 2009 SH2 was discovered by Gordon Garradd at Siding Spring on Sept. 18th as an 18th mag. object and was due to make a fly-by of Earth within 3 Lunar Distances (LD) by the end of the month. It reached mag +16 when last seen from Great Shefford on Sept. 29th.
Another Apollo 2009 SN103, this one discovered by the Catalina Sky Survey on Sept. 25th was 19th mag., already within 4 LD of Earth and moving at 11"/min. It would reach its closest to Earth (1.2 LD) at about 05h UT on Sept. 28 as it overtook the Earth on its way to perihelion on Oct. 30th. It was observed from Great Shefford 6 hours before closest approach when it had brightened to 16th mag. and had accelerated to a speed of 138"/min. It was also caught the next night in central Gemini, moving slower at 86"/min but with the phase angle increasing very rapidly, it was 18th mag., fading quickly and was a much more difficult target to record.
It is estimated that 2009 SN103 is only about 8 meters in diameter. Another close approach NEO discovered by the Catalina Sky Survey on Sept. 27th and estimated at about 20 meters diameter was 2009 SU104. This Apollo has a very eccentric orbit taking it very close to the orbit of Venus at perihelion, out to 4.2 AU at aphelion. At this apparition it was on its way to perihelion in Nov., crossing the Earth's orbit just after the Earth had passed by. It was observed at its closest at 2.5 LD on Oct 1st when it was mag. 16 and moving east to west at 223"/min in Equuleus.
Several distant artifical satellites were also followed during the month, including LCROSS on Sept. 12th & 16th before it disappeared into southerly declinations until a few days before its impact with the Moon on Oct 9th. The Herschel telescope was also recorded on Sept. 17th at 19th mag. Ephemerides generated from previous astrometry obtained for this object were useless to try and pick it up again as the spacecraft undergoes frequent orbital manoeuvres to keep it near the second Lagrange point (L2). The JPL Horizons ephemeris allowed Herschel to be picked up without problem, moving at 3"/min.

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