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

Today's issue status: done

• Comet C/1996 R3 by Maik Meyer
• News briefs – Colorado fireball yesterday,
  Rosetta launch scrubbed & Dawn mission news
  Part 2 – 2004 DW & planetary defense
  
• Risk monitoring
  – JPL has posted 2004 DV24 & 2004 DM44

Cover: Rosetta remains atop its Ariane 5 launcher in French Guiana this morning. At 0720 UTC (2:20am EST), with 16 minutes to go, the first launch attempt was announced to have been cancelled due to high altitude winds. The next attempt will be at 0736 UTC (2:36am EST) tomorrow morning. More info below. Image ©Copyright 2004 ESA-CNES-Arianespace.

Comet C/1996 R3   by Maik Meyer

When P/2001 RG100 was identified with C/1979 O1 by Syuichi Nakano recently (Nakano Note 995 and IAUC 8247 in early December), I thought about what other short-arc comets might have orbits that could be improved by archival work, since I now often do pre(dis)covery work with NEAT and DSS images. I decided that C/1996 R3 would be a nice comet to try. It is listed in the Catalogue of Cometary Orbits 2003 as "probably of short period," but with an orbit based on only four observations from a two-day arc:

T = 1996 May 30.292    peri = 99.606
q = 1.76959            node = 196.029
e = 1.0                incl = 5.011

It was discovered by Claes-Ingvar Lagerkvist, Stefano Mottola, and Uri Carsenty with the 1m Schmidt telescope at La Silla on 13 September 1996 (IAUC 6564 of 21 February 1997)

Since station 566 (NEAT/Haleakala at that time) was listed with observations, I looked up their images first. To my surprise, I found a triplet of

One of three new C/1996 R3 archive images found by Maik Meyer from NEAT's Haleakala telescope from 15 September 1996. The comet is the smudge at center.

images from one more day and also noticed that the measurements by NEAT at that time were just wrong. I remeasured these as well as the positions of the additional day and sent the data to the Minor Planet Center (MPC). The new orbit was quite different from the previous, with now nine observations spanning three days:

T = 1995 Nov 22.463    peri = 132.808
q = 4.48173            node = 175.055
e = 1.0                incl = 27.162

I was hoping to find some more observations with this new orbit but had no success.

Later I visited the Uppsala Planetary System Group's Another comet page and — surprise, surprise

part 2 of 2 >>

<< continued from part 1

— saw that the original discoverers had used the improved orbit to locate additional observations from October 1996 at La Silla! From that, the orbit of this comet had been improved considerably, as follows, with 12 observations from 12 September to 30 October 1996:

T = 1995 July 20.284   peri = 130.138
q = 5.20687            node = 172.710
e = 1.0                incl = 39.303

Although the comet did not turn out to be of short period, the result was a nice lesson in how important archival work can be. C/1996 R3, by the way, is one of the few unnamed comets. See the IAU Guidelines for Cometary Names about why this sometimes happens.

This article was developed from a message sent by the author to the Comets Mailing List and A/CC.

Colorado fireball:  Caught on an all-sky camera at 6:31pm and reported by more than 150 witnesses, Colorado had another February fireball yesterday evening. See Chris Peterson's early report and KGMH-TV Denver news today.

Rosetta:  An Agence France-Presse wire story, appearing on SpaceDaily today, says that the first 2004 Rosetta launch attempt was scrubbed this morning because of winds "at altitudes of between 10 and 15 kilometers (six and nine miles) [that were not] a problem for the rocket itself but if for any reason the launcher exploded or was ordered to be destroyed at this height, the debris could have scattered outside the launch area's safety zone." The Rosetta Journal entry for today confirms that this morning's cancellation was due to "Strong high altitude winds," but also notes heavy rain 36 minutes before takeoff. See yesterday for broadcast and webcast links for the second launch attempt Friday morning at 0736 UTC (2:36am EST).

Dawn mission:  First noticed at SpaceToday.net yesterday is that the Dawn mission has posted a February newsletter. It reports that "on February 6, Dawn was confirmed and approved to move into its implementation phase," and goes on to outline the ramifications of redesigning this 2006-2016 Main Belt mission to keep within tightened NASA requirements for cost, mass, and power margins. This has "increased the robustness of the mission but at some expense to the science return." Yet some of that return may be recoverable "if the flight system performance allows it." Great science and exploration are at stake here:

“ Vesta almost certainly has an iron core and may have similar crustal magnetization as Mars, while Ceres appears to be an ice planet with water-ice mantle, and rocky core similar to Europa, Ganymede and Callisto. For Ceres and these Galilean moons, thermal evolution models suggest that there may be liquid water underneath the icy crust even today. ”

more news briefs >>

<< continued from part 1

2004 DW:  The Independent of South Africa has a Cape Times article today, "New 'fossil' planet discovered," that discusses 2004 DW's environment and planetary classification. See the A/CC Major News Index for much more about this object.

To visualize large minor object sizes, a handy comparison is that Pluto's diameter is about two-thirds that of the Moon. And the largest Main Belt asteroid, 1 Ceres [link|alt], has a diameter just over one-fourth the Moon's (or two-fifths of Pluto's diameter). Early rough diameter estimates for 2004 DW run from two-thirds that of Pluto up to around the size of Pluto itself (see David Jewitt's 1000 km Scale KBOs page). Pluto's moon, Charon, and the next two to four largest known Edgeworth-Kuiper Belt objects are, or may be, a bit larger than Ceres. And the object you're standing on? The Earth is 3.8 Moon diameters wide.

Planetary defense:  The San Francisco Chronicle told its readers today that “panicky [professional] astronomers came mighty close to waking up President Bush with a nasty message” after “a frantic evening and early morning” that began when “an amateur astronomer in Europe, identified as Reiner Stoss” told “an Internet chat room” about Minor Planet Center tracking information that “meant a collision was imminent.” Southwest Research Institute planetary scientist Clark Chapman “said scientists were considering the possibility of 'the biggest atmospheric explosion of many decades on planet Earth.' ”

“ Such a scenario would not have ended life as we know it because of the small size of the asteroid, judged initially to be about 30 kilometers across, about half the size of the asteroid that famously pulverized a remote area in Siberia in 1908, but a mere pebble compared with prehistoric impacts. ”

Earth to S.F. Chronicle: That should say "30 meters across"! This, of course, is about 2004 AS1 (see Index), which is not a threat, and a planetary defense meeting that ends today (news thread). See also the Seattle Post Intelligencer today for a New York Times report.

Risk monitoring 26 Feb.

The Thursday Daily Orbit Update MPEC carries observations of 2004 DC from New Mexico Skies Observatory (Robert Hutsebaut) yesterday morning, and of 2004 DV24 from Linz Observatory in Austria last night. Today JPL joined NEODyS in listing impact solutions for 2004 DV24, while NEODyS cut its solution count by half and slightly raised its overall risk assessment for this mile-size object.

Both risk monitors reduced their solution counts by a good percentage for 2004 DC, and they converged somewhat on their overall risk assessments, with NEODyS very slightly raising, and JPL slightly lowering, ratings for this object.

JPL has posted 2004 DM44, which was announced today in MPEC 2004-D40 as discovered by LINEAR yesterday morning in New Mexico and confirmed today by Powell and Sandlot observatories in Kansas, and by Robert Hutsebaut via New Mexico Skies and Tenagra II Observatory in Arizona. JPL puts the diameter at roughly 200 meters/yards.