Tuesday6 January 20049:50pm MST2004-01-07 UTC 0450 back top next  



The 5 March 2003 discovery image of tiny 2003 EM1 — the streak at left caught by Crni Vrh Observatory in Slovenia while imaging comet C/2001 RX14. See A/CC's report of the discovery and follow-up.
Used with permission, ©2003 Crni Vrh Observatory. North is up and east is left.


The Asteroid/Comet Connection's
daily news journal about
asteroids, comets, and meteors


Today's issue status: done
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Locations of Earth, 2003 EM1,
and C/2001 RX14 (LINEAR)
on 5 March 2003

EasySky screen shot with the positions of Earth, 2003 EM1, and C/2001 RX14 on 5 March 2003. EM1 rarely pops out from inside Earth's orbit and rounds Earth where it can be seen with optical telescopes.

Stardust post-encounter – part 1/2 Major News for 6 Jan. 2004 back top next  

Stardust post-encounter

A webcast Stardust mission "post-encounter science briefing" was held at 1pm this afternoon at JPL in Pasadena, Calif. Principal investigator Don Brownlee said that a half-dozen or so jets were seen to be active on 81P/Wild 2 [link|alt], and "there must be" around a dozen of these where gas escapes from the surface of the comet at "sonic speed."

Tom Economou reported that the spacecraft didn't encounter much dust until a few minutes before the closest approach, and then it was hit with several large distinct bursts, possibly associated with individual jets, but that is yet to be determined. Benton Clark said that the spacecraft had to fire its thrusters autonomously more than a thousand times to keep itself traveling oriented behind its protective Whipple Shields. These are estimated to have taken about "ten million" hits, of which Brownlee says up to a dozen were particles large enough to penetrate the shields, apparently without causing serious damage.

[continued]  

81P/Wild 2 imaged by
Stardust on 2 Jan. 2004
Credit: NASA/JPL

Image courtesy of NASA/JPL with this caption: This image was taken during the close approach phase of Stardust's Jan 2, 2004 flyby of comet Wild 2. It is a distant side view of the roughly spherical comet nucleus. One hemisphere is in sunlight and the other is in shadow — analogous to a view of the quarter moon. Comet Wild 2 is about five kilometers (3.1 miles) in diameter.

Stardust post-encounter – part 2/2 Major News for 6 Jan. 2004 back top next  

  [continued from part 1]

Economou estimates from dust instrument feedback that the aerogel collector caught "hundreds of thousands of particles." Clark noted that, when the capsule returns with those in 2006, it will be the fastest atmospheric entry ever made by a man-made object.

A flyby movie was shown, and one new close-up image has been released that gives the appearance of a baked potato with a huge dent near one end. Brownlee described that feature as definitely not an impact crater. It has steep walls and a flat floor, except for some off-center peaks. Early opinion is that the comet's jets emanate from the vertical walls of this feature and other depressions. Mission manager Tom Duxbury noted that there are albedo variations "as we go down in some of these depressions."

The surface of 19P/Borrelly [link|alt] was marked by large mesa-like features. Brownlee commented that these two comets may be intrinsically different, or it may be that, as a comet evolves with repeated solar passages, that the depressions seen

on Wild 2 grow until what is left are the mesas seen on Borrelly, which has had more exposure to the Sun than the relatively pristine Wild 2.

Brownlee also noted that the steepness of so many large cliffs indicates that the surface has "some strength." A few cracks have been spotted, so "evidently there is some crustal activity."

Duxbury said that the navigation crew was still working on establishing the actual trajectory, which will enable a 3D reconstruction of the flyby and of the comet. However, the spacecraft probably didn't fly close enough to the comet to gauge mass and density.


This report was written by A/CC editor Bill Allen directly from watching the science briefing. Here are additional news items that appeared after that news event:

News briefs – part 1/2 Major News for 6 Jan. 2004 back top next  
News briefs

Rosetta:  AFP reports today on SpaceDaily, "Europe sets date for launch of comet hunter" Rosetta for February 26th, announced in an Arianespace news release today.

Comets everywhere:  A Harvard-Smithsonian Center for Astrophysics news release from yesterday (illustration), "Suns Of All Ages Possess Comets, Maybe Planets," tells about observation of C/2002 X5 (Kudo-Fujikawa) [link|alt] during its close perihelion passage last year (A/CC's report) and what was learned about other solar systems. About C/2002 X5:

The [SOHO] UVCS data revealed a dramatic tail of carbon ions streaming away from the comet, generated by evaporating dust. The instrument also captured a spectacular 'disconnection event,' in which a piece of the ion tail broke off and drifted away from the comet. Such events are relatively common, occurring when the comet passes through a region of space where the Sun's magnetic field switches direction. More remarkable than the morphology of the carbon ion tail was its size [containing] a massive amount of carbon, weighing as much as five supertankers. 

Spanish fireballs:  The Guardian has an article today, "Police on meteor alert after huge balls of fire light up Spanish sky," and BBC has an article today, "Spain continues meteorite search." Please note that some important corrections were made to A/CC's report of yesterday. In addition, Marco Langbroek tells A/CC:

There appears to be some confusion over the trajectory. From N.W. Spain to the S.E. Mediterranean is mentioned in several places, but this appears to be the distribution of sighting reports, not the trajectory. A N.W.-to-S.E. trajectory is incompatible with the video from Leon, as the fireball moves in the "wrong" direction on that video. In the video, it moves at about a 45-degree angle to the left. This is only possible for someone north of the trajectory looking south, if the directions given in the news were correct, but that cannot be, given the character of shadow and sunlight visible on the apartment building in the video.
      A final note concerning the reported "fires" — meteorites do not cause fires. They are not "hot" when they reach the ground.

Langbroek has since posted his own report on the Dutch Meteor Society site with a link to the Leon video and interesting info about the likelihood of fragment survival and meteor stream relationship.

[continued]  

News briefs – part 2/2 Major News for 6 Jan. 2004 back top next  

  [continued from part 1]

EKBO news:  The January edition of Distant EKOs is now available. Included is a list of objects reclassified as scattered disk objects and abstracts for more than a dozen scientific papers submitted or recently published.

Namings:  Asteroid names were updated by the Minor Planet Center yesterday. Details tomorrow.

Absolute magnitudes aren't absolute. Francesco Manca of Sormano Observatory points out to A/CC that 2003 WH166, which has been included in special A/CC small object reports as recently as Sunday, was yesterday newly categorized by the Minor Planet Center as potentially hazardous when the calculation of its intrinsic brightness was changed from H=22.2 to 21.9. That represents a 14.4% growth, or about 20 meters/yards, in the rough median width estimate.

2003 YQ1 is another borderline object. It was announced at H=20.7 in MPEC 2003-Y26 of December 19th, but was put at H=22.0 by the time it was last seen on December 30th (reported then by Siding Spring Observatory). That was a drop of 45%, from about

250 meters down to 135, using the standard brightness-to-size conversion formula.

Risk monitoring - part 1/1 Major News for 6 Jan. 2004 back top next  
Risk monitoring 6 Jan.

2004 AF is a two-kilometer object announced overnight in MPEC 2004-A31 as discovered early yesterday by LINEAR in New Mexico and followed up last night by the JATE Asteroid Survey in Hungary and Table Mountain Observatory in southern California. The Minor Planet Center (MPC) put this object's absolute magnitude at H=16.4, and JPL, which soon posted the object with one low-rated impact solution, put it at H=16.0, a difference that works out to a third of a kilometer by the standard but inexact brightness/size conversion formula.

NEODyS posted 2004 AF this morning. Further observations were not reported in the Tuesday Daily Orbit Update MPEC (DOU).

Today's DOU does have new data for 2003 YH136 from Siding Spring Observatory yesterday in Australia, and today both risk monitors again slightly lowered their risk estimates for this half-kilometer object.

Summary Risk Table - sources checked at 0448 UTC, 7 Jan

Object

Assessment

Years

VI
PS
cum
PS
max
T
S
Arc 
days
 2004 AF NEODyS 1/62006-2080107-1.96-2.3600.965
JPL 1/62058-20581-4.50-4.5000.965
 2003 YS70 NEODyS 12/282057-20808-7.72-8.1504.992
JPL 12/282057-20856-7.97-8.3704.992
 2003 YH136 NEODyS 1/62031-20311-3.70-3.7008.327
JPL 1/6<2031-20502-3.81-3.8108.327
 2003 YD45JPL 1/32074-20741-6.33-6.33010.354
NEODyS 12/30R E M O V E D
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.
http://www.HohmannTransfer.com/mn/0401/06.htm
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