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Monday22 December 20038:41pm MST2003-12-23 UTC 0341
Today's news about Asteroids, Comets & Meteors
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Late news:  Monday evening in Pasadena, JPL has posted 2003 YD45, which was announced right after midnight UT in MPEC 2003-Y47 as having been discovered by LINEAR Saturday morning. JPL puts YD45's width at 343 meters/yards.

Small objects
In the period from yesterday back to December 13th, when A/CC Major News last summarized observations of the smallest near-Earth asteroids [fn], ten of these objects were tracked, including four new discoveries. 2003 XZ12, YN1, and YR1 were found by LINEAR, and 2003 YW1 by Spacewatch with its 0.9m telescope. (2003 YR1 was announced at H=21.2, now H=22.3.) Confirmation was provided for one or more of these objects by Great Shefford, Ondrejov, Powell, Sabino Canyon, and Tenagra II observatories, the Observatorio Astronomico de Mallorca (OAM), KLENOT, and the Spacewatch 1.8m telescope. Further follow-up for 2003 XZ12 came from Great Shefford and Powell observatories and Klenot on the 17th and/or 18th. Powell and Tenagra II followed 2003 YR1 on the 19th and Great Shefford on the 20th. 2003 YN1 hasn't been reported since its December 19th discovery MPEC, but 2003 YW1 was caught by LINEAR this morning.

A population of small near-Earth asteroids (NEAs) passes by too dimly and too quickly to be easily discovered or followed long enough to calculate an orbit allowing good prediction of future returns. To come sufficiently close to be seen at all, such objects likely have an orbit that would be considered potentially hazardous, except they are too small for that categorization. The official hazard dividing line is absolute magnitude (brightness) H>22.0, which translates to less than a median width of about 135 meters/yards by standard conversion formula, but possibly as large as 240 meters. Higher H means smaller size, down to as small as H=30.1, perhaps three meters wide.

Smallest asteroids
during 14-21 Dec. 2003.

Animation from EasySky screen shots showing the known smallest (H>22.0) asteroids in Earth's neighborhood during 14-21 December. Those reported observed last week are circled and identified. The ecliptic grid is set at 15 lunar distances.

The Spacewatch 1.8m telescope provided follow-up for small objects 2003 SN215 and WP25 on December 18th, and on the 14th caught 2003 WH166, which was also reported by Desert Moon Observatory on the 13th and KLENOT on the 18th. Linz Observatory observed 2003 WJ98 on the 18th, while Jornada Observatory got 2003 WW26 on the 14th. And 2003 WY153 had its last impact solutions eliminated after observations from Great Shefford on the 16th and 17th and from Powell on the 17th.

There was also archive work reported with newly located or remeasured positions for small NEAs 2001 QF96, 2002 PX39, and 2003 UW5.


Risk monitoring 22 Dec.

The Monday Daily Orbit Update MPEC (DOU) carries observations of 2003 YT1 from San Marcello Pistoiese Observatory Saturday night in Italy and Jornada Observatory early yesterday in New Mexico. Correction: It was originally reported here that NEODyS, which updated its risk assessment for YT1 yesterday ahead of the next DOU has done so again today, raising its overall risk rating and still having only one solution, but a solution that is less than eight years away. In fact, NEODyS was not working ahead of the DOUs in this case. It and JPL had both issued new YT1 risk assessments based on San Marcello Pistoiese's observations received before the Monday DOU. When that DOU appeared with those and Jornada's new observations, NEODyS updated, but the day passed without JPL issuing a new assessment incorporating the Jornada data.

The European Spaceguard Central Node today posted a 2003 YT1 observing campaign (dated December 20th):

Summary Risk Table - sources checked at 0326 UTC, 23 Dec




 2003 YT1 NEODyS 12/222011-20111-2.30-2.3003.003
JPL 12/222017-210122-1.65-2.1902.654
 2003 YD45JPL 12/232030-210382-3.79-4.7702.112
 2003 XMNEODyS 12/21R E M O V E D
JPL 12/212059-20591-4.51-4.51016.835
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.
Note that only objects recently in view are shown here.
[The] object will remain visible in the evening sky at small solar elongations, further observations are required as soon as possible, certainly before any conflict with moon light in a week from now. Since there are large margins for orbital improvement, all the collision solutions should be eliminated fairly soon; however, the relative large size of this object does impose a rapid reaction from observers. 

No new observations of 2003 XM were reported in today's DOU.

Update at 0341 UTC:  JPL has posted 2003 YD45.


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