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

Today's issue status: done

 Front section

• News briefs – meteor news, occultation news
  + bits & pieces
• Risk monitoring

• 2003 UR292 by Reiner Stoss

Cover: Jose-Luis Ortiz caught 2003 UR292 on July 20th (main image) and 22nd (cropped frame) using the 1.5m f/8 Ritchey-Chritien telescope at Sierra Nevada Observatory in Spain. Scale is 0.46"/pixel but the cropped frame is binned 4x4 instead of 2x2 due to high winds and was pixel-doubled at A/CC to match the main image. Motion on the first night was 0.0042"/min. and the second night 0.0066"/min, and totalled 13 arsecs in the 47.25 hours between the two positions. See more about this unusual distant object below.

Meteor news:  Space.com has a “Preview of Summer Meteor Showers” from yesterday, and National Geographic yesterday posted an item dated July 27th about the North and South Delta Aquarids.

Occultation news:  David Dunham has posted an expanded tale and lessons learned from his adventures with placing multiple remote telescopes to catch stellar occultations in early July (see July 11th news).

There will be an occultation by the very large near-Earth asteroid 1685 Toro during 11:21 to 11:33 UT on August 13th. The star shadow will pass diagonally across Kansas and New Mexico and then southeastern Arizona, as told about by David Dunham and mapped by Steve Preston.

Bits & pieces:  The Richmond, Virginia Times-Dispatch has an article from yesterday telling that an award was conditionally made Thursday to fund the U.S. Geological Survey's deepest-ever drilling project, a $1.2 million effort “to plunge nearly dead-center into the [Chesapeake Bay] crater, boring through 7,200 feet beginning late next summer.” It says that “Determining what rocked the Chesapeake Bay will help other geologists investigating craters that also date to the

late Eocene, some 34 to 36.5 million years ago, such as the Popigai crater in northern Siberia.” See the news Index for other recent articles about this, the largest known impact structure in the USA.

The Australian Associated Press has a wire report at NineMSN today that the Faulkes Telescope South at Siding Spring Observatory in New South Wales “is now operational.” The 2-meter telescope is reported to be the third largest in Australia, and is dedicated to robotic educational use. See also a previous A/CC report.

Risk monitoring 24 July

The Saturday Daily Orbit Update MPEC (DOU) has observation of 2004 NL8 from Francisquito Observatory in southern California from yesterday morning and early today from Great Shefford Observatory in England. Today NEODyS and JPL again lowered their risk assessments for this object.

Previously, the Thursday DOU had observations of 2004 NL8 from Wednesday morning from Powell Observatory in Kansas and Francisquito Observatory, and from early Thursday from KLENOT in the Czech Republic. That day, Thursday, both risk monitors lowered their risk ratings for 2004 NL8.

2003 UR292

A unique object in the outer Solar System

By Reiner Stoss, Observatorio Astronomico de Mallorca

Distant object 2003 UR292 was announced in MPEC 2003-Y84 from 2003 December 29 as being discovered by the Deep Ecliptic Survey (DES) with the 4m Mayall Telescope at Kitt Peak in Arizona. Discovery took place on 24 October 2003, and the second night was made one dark run later, on 2003 November 20, enabling the Minor Planet Center (MPC) to provisionally designate the object and calculate a first orbit with a semimajor axis of 39.29 AU, an eccentricity of 0.33, and an inclination of about 2.7 degrees.

Brian Marsden noted in this discovery announcement that “the assumed perihelic 2:3 Neptune libration orbit keeps 2003 UR292 more than 20 AU from Neptune over a 14000 year period.” This meant that, with too few observations available, several assumptions had to be made to determine a first “realistic” orbit. One of these assumptions was that only an orbit that keeps the object from having close encounters with Neptune could be real. Neptune is the only major perturber out there, and nothing would stay in an orbit close to it for a long time. Finding such an object would be very unlikely.

No further follow-up observations were done, but the Spacewatch group reported a set of prediscovery observations from 2003 October 19 extending the arc slightly, by five days to a total of 32 days. The new MPC-calculated orbit now gave a=39.34 AU, e=0.33 and i=2.6°, still a typical Plutino orbit. While such an observed arc is sufficient for inner Solar System objects to determine their type of orbit, it is by far too short usually for objects in the outer Solar System, which take hundreds of years to complete just one orbit around the Sun.

No additional follow-up was done on this magnitude V=21.5 object by early 2004 and it went out of view in the day sky. Things got interesting again a few months later, however, when I selected it as possible precovery target.

On July 2nd I started a precovery run based on the MPC orbit. I searched the NEAT CCD frames archive (SkyMorph) and the scanned photographic plate archive of the Digitized Sky Survey (DSS), but, after many tedious hours, I returned with nothing. In such cases the first question is, is the reported brightness maybe erroneous and the object actually much fainter, making it impossible to be detected on NEAT or DSS imagery? This is quite normal for trans-Neptunian object (TNO) discoveries, as there seems to be kind of a race for who finds the brightest (thus biggest) objects. . .  Or is the brightness pretty accurate, but the (assumed) orbit isn't? >>

<< 2003 UR292 continued from panel 1

Optimisticaly selecting the second possibility, which would maintain prospects for this object to be precovered in the mentioned archives, I began to calculate various orbits myself, based on the same set of available observations, but without constraints forbidding close Neptune encounters. These orbits had various combinations of a and e, from low a and e of almost circular orbits (inevitably close to the orbit of Neptune), up to very large a and e of highly elliptical orbits, but without regular close approaches to Neptune.

Integrating these orbits into the past, a new run through the archives was done and images retrieved. Contrary to precovery work on fast-moving NEOs, where more or less well visible trails have to be found, precovery searches for TNOs require looking for point source-like objects. Plates from consecutive nights are mostly not available, so one has to compare plates taken months or years apart and search for a faint blob visible on one plate but not on the other, and then confirm this with at least a few other blobs, each appearing on other predicted plates. Only by this it is possible to validate the identity of the blob as being the sought TNO and not some sort of image artifact, variable star, plate flaw, or whatever.

Things are a bit more easy on CCD frames, which are typically taken half-an-hour apart, and at least three of them

2003 UR292 in 6 Oct. 2002 frames from NEAT's Mt. Palomar 1.2m telescope.

are available per night. Some triplets in the NEAT CCD frame archive were even taken to search for TNOs, and were exposed much longer than the usual NEO-hunting frames, and have more time between them, to see slow-moving TNO candidates move from frame to frame.

First precovery positions
Two such triplets were predicted for 2003 UR292, one from 2002 October 5 and another from the next day. The latter showed an object moving right as predicted for UR292 and was clearly real. The offset from the predicted position based on the first self-calculated orbit, with a=33.29 AU and e=0.20, was +184 arcsec in right ascension and +80 arcsec in declination. By comparison, the offset to the prediction based on the MPC orbit was +1186 arcsec in right ascension and +482 arcsec in declination, thus explaining why previous searches based on the MPC orbital elements failed. >>

<< 2003 UR292 continued from panel 2

A quick look at the 2002 October 5 triplet showed a faint object moving at the same speed and P.A. (position angle) with the same offset to the predicted position. These two triplets were measured and the observations included into the orbit, which now showed a semimajor axis of 32.24 AU and an eccentricity of 0.17. The only difference from the self-calculated search-orbit was that this one was based on observations from the 2002 opposition and was not just an assumed orbit based on a short 32-day arc in 2003 alone.

Would such an orbit close to Neptune be stable, and thus possible at all, or was there an error somewhere? A period of about 183 years was too different from the P=165 years of Neptune to be a Neptune Trojan, the only kind of object able to orbit close to Neptune for longer time periods.

Additional precovery positions
These two nights would satisfy the MPC terms for a precovery, but it was obvious that Brian Marsden would be rather sceptical about such a report, especially if it would shift the orbit of an assumed Plutino TNO to an unstable Neptune approacher, something very unlikely to exist. Therefore more precovery observations were needed and, with the improved orbit, these were found near where predicted on NEAT/Palomar images from 2001 October 6, 11, and 17.

Searches on older DSS plates, however, returned no secure candidates.

2003 UR292 now had observations from three oppositions and the nature of the unusual orbit discovery seemed to be confirmed. The precovery was reported to the MPC and, as expected, Brian Marsden seemed sceptical, replying that “it is difficult to see how the object can avoid very close approaches to Neptune.” Additionally it was possible to fit a more reasonable TNO orbit to the observations from 2003 and 2002 alone, he told me, so, if the measurements from 2001 were erroneous, this would change the whole situation.

As the object was visible on the triplets from 2001 only after stacking the three frames of each set together, there was still a very small possibility that the three 2001 detections were noise at the right position, although this was very unlikely based on my precovery experience.

Precovery published
Brian Marsden decided to publish the precovery on 2004 July 3 in MPEC 2004-N19, to “allow confirmation or maybe denial” of my precovery soon, he told me, even though the bright Moon was approaching the region where 2003 UR292 was located and no new observations were expected for the next two weeks. Additionally, at about 100° solar elongation in the morning sky, its predicted motion was almost zero. >>

<< 2003 UR292 continued from panel 3

This prevented the few TNO astrometrists from going after it, since at least two nights are needed to show motion and allow an identification. Nevertheless, a recovery in the 2004 opposition with a few precise measurements was needed to clearly confirm the unusual orbit discovery and to put an end to this mystery (or, to start the mystery for the Solar System dynamics folks).

New observations
The help came from an observatory usually known rather for TNO photometry work, but in this case its director, Jose Luis Ortiz of the Instituto de Astrofisica de Andalucia (IAA) and also a member of the Observatorio Astronomico de Mallorca (OAM) team, agreed to help and to make available some time at the IAA's Sierra Nevada Observatory 1.5m telescope, high in the mountains of southern Spain.

Some very deep CCD frames taken in the pre-dawn sky of July 20 and 22 clearly showed 2003 UR292 only a couple of arcsecs from its expected position (see cover above), finally confirming the close Neptune orbit once and for all.

Now that the precovery and its resulting unique orbital type for 2003 UR292 have been confirmed, it is up to the folks doing long-range numerical integrations to see how this object came into this orbit and where it will go in the future. So that

EasySky view of 2003 UR292 position 2004 July 20.

this work can be done with the best available starting parameters, more 2003 UR292 astrometry is highly desired.

A first conclusion
Pasquale Tricarico has done a quick integration into the past and future for 2003 UR292 with his ORSA software, based on just the nominal orbit. According to his analysis, the only thing we can say so far is that 2003 UR292 is subject to periodic close approaches to Neptune, which can just perturb UR292's orbit (encounter distance at ~1 AU) or send it on a different orbit (encounter distance at ~0.3 AU), with a somewhat small ejection chance (no ejection in 2x10⁵ years).

article conclusion >>

<< 2003 UR292 continued from panel 4

A vote for SkyMorph
Finally, it should be mentioned that the service provided by SkyMorph is highly appreciated and one hopes that this vital service will get funding again soon to be able to maintain its work for the entire asteroid and comet community, and to also extend its image archive to more recent frames. Many sincere thanks to Thomas McGlynn, who has developed and is maintaining SkyMorph.

To cite this article, please use: Stoss, R., 2003 UR292: A unique object in the outer Solar System, A/CC 24 July 2004, http://www.hohmanntransfer.com/mn/0407/24.htm#03ur292

References in addition to links in text:
The DANEOPS Project
TNO-Suche im DSS
Astrometrica track and stack software
FindOrb orbit determination software
A/CC 2003 UR292 news thread