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Saturday29 November 20034:04pm MST2003-11-29 UTC 2304
Today's news about Asteroids, Comets & Meteors
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P/2001 RG100 (LINEAR)

MPEC 2003-W74 today announces precovery observations of P/2001 RG100 (LINEAR), located by Reiner Stoss in Digitized Sky Survey (DSS) archives of scanned plates from Siding Spring's 1.2m U.K. Schmidt Telescope from 23 September 1990 and Mt. Palomar's 1.2m Oschin Schmidt Telescope (POSS II) from 9 November 1993.

He also found post-discovery images via SkyMorph from NEAT with the same Palomar telescope from September 2001 and November 2002, as well as from NEAT's 1.2m Haleakala telescope in November 2001 and September 2002, some showing a coma and tail.

2001 RG100 was redesignated as a comet yesterday. Stoss tells A/CC that "I noticed that it is on a rather circular orbit and with a semimajor axis close to Jupiter. I'm no orbital dynamicist, but I guess such an orbit is quite unstable. So this made me curious and I decided to search the archives."

Today's MPEC also reports new observations this month from LONEOS and Spacewatch.

P/2001 RG100 (LINEAR) trail on
Siding Spring 23 Sept. 1990 plate The trail of P/2001 RG100 (LINEAR) moving during the long exposure of a 1.2m U.K. Schmidt Telescope photographic plate at Siding Spring, Australia on 23 Sept. 1990, as found in the Digitized Sky Survey (DSS) archive by Reiner Stoss.

In a footnote to the MPEC, Brian Marsden explains that the current orbital parameters resulted from P/2001 RG100 passing Jupiter at 0.25 AU in 1943, and will change again after another passage at 0.75 AU in 2022. Today RG100 has a semimajor axis of a=4.7629 AU and eccentricity of e=0.02809, quite a change from a=7.0 and e=0.22 prior to 1943. (The inclination went from 3 to 7.9°.)


2003 WH98 seen from Begues Obs. 28 Nov. 2003 2003 WH98 image stack from Begues Observatory from yesterday, when WH98 came within about 4.6 lunar distances of Earth, moving so fast that each background star looks like a string of pearls.
Small objects

2003 WH98 flew past Earth yesterday at 4.6 lunar distances. It was caught by Great Shefford Observatory the night before, by Tenagra II (at two separate times) and Powell observatories yesterday morning, and by Begues Observatory last night, all reported in today's Daily Orbit Update MPEC (DOU). Pepe Manteca at Begues tells A/CC that WH98 was moving "very very fast," which can be seen in his image stack at left, centered on the object's motion, where the individual background stars appear not as trails but as "strings of pearls."

Of ten small objects currently in view as illustrated by A/CC two days ago, besides 2003 WH98 and 2003 WW26 (see "Risk monitoring" below), most are in today's DOU, including 2003 WQ21. Not reported seen since its discovery MPEC eight days ago, WQ21 finally was picked up early yesterday by Powell Observatory.

The DOU reports that 2003 WE was observed Thursday night by Pla D'Arguines Observatory, which also caught 2003 WY87, which was followed by Powell in the morning. Early Friday 2003 WP21 was reported by Jornada and Desert Moon observatories, 2003 WP25 by Jornada, and 2003 WQ21 and 2003 WJ98 by Powell. And last night Consell Observatory caught 2003 WU21.

Whew! Nine out of ten, with 2003 WP7 missing but reported just yesterday from Thursday morning. It will race past (ahead of) Earth at 7.1 lunar distances next Thursday as it disappears into the Sun side of Earth's orbit.


Summary Risk Table - sources checked at 1658 UTC, 29 Nov




 2003 WW26 NEODyS 11/292061-20784-4.00-4.2507.106
JPL 11/292061-20784-3.97-4.2307.106
 2003 WGNEODyS 11/29R E M O V E D
JPL 11/292055-20551-5.95-5.95010.779
VI = count of "virtual impactors" (impact solutions)
See A/CC's Consolidated Risk Tables for more and maybe
  newer details, and check the monitors' links for latest info.
Risk monitoring 29 Nov.

The Saturday Daily Orbit Update MPEC (DOU) carries observations of 2003 WG from yesterday morning from McDonald, Jornada and Powell observatories and from the Spacewatch 1.8m telescope, and from last night from Consell Observatory, plus additional observations from Thursday from Egan, Great Shefford, and Pla D'Arguines observatories. Today NEODyS removed 2003 WG, and JPL significantly lowered its ratings for the one WG impact solution.

And the DOU has observations of 2003 WW26 from Thursday night from Pla D'Arguines Observatory and yesterday morning from Jornada and Powell observatories. Today both risk monitors again very slightly raised their overall low risk assessments for this small object.


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