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

Today's issue status: done

• News briefs – asteroid taxonomy, comet news, readings & large EKBO discovery
• 2003 VB12 news
• Risk monitoring – JPL has posted 2004 GU9
  & NEODyS has posted 2004 GB2

Cover: At left is the Hubble Space Telescope's view of 2003 VB12 (aka "Sedna") on 16 March 2004 as released to the public today, enlarged to 300%. It is seen trailed, moving from upper-right to lower-left during 0539-0622 UT with one bright star in the background. The inset image (enlarged 400%) resolves Sedna's disk at no more than one full pixel width, which "sets an upper limit" of "1,000 miles" for diameter (1,600 km.). See more info below. Credit: NASA, ESA & M. Brown (Caltech).

Asteroid taxonomy:  Petr Scheirich announces today a revision of his well-done Asteroid Groups page with different ways of looking at the various asteroid classifications with images, animations, and graphs.

Comet news:  MPEC 2004-G34 today shows that an oddball asteroidal object has been redesignated as comet C/2004 DZ61 (Catalina-LINEAR). It comes to perihelion on May 26th further away from the Sun than Mars and travelling a very eccentric (e=0.9559) and highly inclined (i=66.8°) path.

Readings:  The University of Chicago has a news release today, "Scientists size-up, classify meteorite that nearly landed in their backyards." National Geographic has an article today, "Undetectable Asteroids Could Destroy Cities, Experts Say." And the Eastern Arizona Courier reports today, "K-9s used to protect telescope," about the University of Arizona Police Department division at Mount Graham (see also "Readings" yesterday).

Large EKBO discovery:  MPEC 2004-G32 today announces 2004 GV9, which generated some "buzz" on the Minor Planet Mailing List (MPML) yesterday after being put on the NEO Confirmation Page. It was discovered with NEAT's Mt. Palomar telescope in southern California yesterday morning and followed up early today by six other observatories.

The MPEC's first preliminary calculation, using an assumed eccentricity, seems to put this object in the group of Edgeworth-Kuiper Belt (aka trans-Neptunian) objects classified as "Cubewano" or "classical" EKBOs — those far enough away from the Sun to be free of Neptune's gravitational influence. But, with further observation, it may yet be put in the resonant "Plutino" or "scattered" (SKBO) classifications.

And so brightness and size estimates are also highly preliminary, but 2004 GV9 looks like a candidate for top-ten largest known. At the MPEC's H of 3.9, and using albedo p of 0.09 to 0.12 from David Jewitt's 1000 km Scale KBOs page, the resulting rough width estimate is 635 to 735 km. (395-455 miles). (See info about how to run these numbers for yourself.)

When 2003 VB12 was announced by the Spitzer Space Telescope (SST) March 15th, part of the news was that the SST itself couldn't see this object, which was interpreted to mean that VB12 is "less than 1,700 kilometers (about 1,000 miles) in diameter." Today the Space Telescope Science Institute (STScI) announced what the Hubble Space Telescope couldn't see: no resolvable disk and no predicted satellite.

Joint but somewhat different news releases were issued by NASA headquarters, "Sedna Mystery Deepens With Hubble Images Of Farthest Planetoid" (link), and by STScI, "Hubble Observes Planetoid Sedna, Mystery Deepens" (link). It is reported that an upper limit on diameter was set at 1,600 km. (1,000 miles) since VB12 appeared as no more than one full pixel width in the Hubble camera (see above).

And there is also this in the two news releases:

“ Brown based [his prediction of a satellite] on his earlier observations of apparent periodic changes in light reflecting from Sedna's mottled surface. The

resulting light curve gives a rotation period...
    NASA Hqs.: ...of 40 days.
    STScI: ...exceeding 20 days (but not greater than
      50 days).
If true, Sedna would be the slowest rotating object in the solar system after Mercury and Venus. ”

Alan Harris told the Minor Planet Mailing List (MPML) today that he is "skeptical" of the rotation period, and refuted two key points. He states that the record for slowest rotation actually belongs to Main Belt asteroid 288 Glauke, with a "period of around 1200 hours (2 months)," and MBA 1220 Crocus "is not far short of 40 days at a period of 737 hours." Furthermore, "Tidal friction is physically incapable of slowing the spin of a solid body to a period as long as 40 days."

News coverage:

• Astronomy.com, "Sedna’s rotation baffles astronomers"
• Reuters, "Surprise from Solar System's Edge: Moonless Sedna"
• Space.com, "Weird Object Beyond Pluto Gets Stranger"
• BBC, "Sedna has no moon say astronomers"

Also related to 2003 VB12, but not to today's news, is an interview with co-discoverer David Rabinowitz today at the Jewish Ledger, "Yale researcher helps to discover a new planet."

Risk monitoring 14 April

NEODyS today posted 2004 GB2, but there were no new observations in today's Daily Orbit Update MPEC (DOU) for it and the other other object posted by JPL yesterday. The Minor Planet Center Last Observation page, however, shows that the Spacewatch 1.8m telescope in Arizona observed both GB2 and 2004 GE2 this morning.

Today's DOU does have 14 positions reported for 2001 FB90 from 22, 23, 26, and 27 March 2001 from the image archive of NEAT's telescope on Haleakala in Hawaii. This is within the previous observing arc that had only 12 observations. Today JPL slightly lowered its overall risk ratings for this object, for which it has three impact solutions in the years 2021, 2067, and 2091. And NEODyS went from one to three impact solutions (in 2021, 2067, and 2080) and raised its low ratings for this object, which JPL puts at about 345 meters/yards wide.

JPL has posted 2004 GU9, which was announced today in MPEC 2004-G31 as discovered yesterday morning by LINEAR in New Mexico and confirmed overnight by eight other observatories. JPL puts its width at 190 meters/yards.