Composite graphic from JPL's C/2003 A2 Orbit Viewer showing this object coming to a very distant perihelion in January 2004.

On 8 February, MPEC 2003-C47 reported C/2003 A2 (Gleason) pre-discovery work done independently by Sebastian Hoenig and myself. I found the November 14th observations immediately after the comet's discovery MPEC 2003-A78 was published. When I included this position in an orbit calculation, the result was parabolic or slightly hyperbolic.

Since Brian Marsden wrote in the discovery MPEC that this object was most likely a Centaur showing cometary activity, I assumed that my find did not belong to the comet. The comet was moving quite slowly at that time, so no motion was visible on the Palomar/NEAT triplet.The Digitized Sky Survey (DSS) didn't show a galaxy or something else visible at that spot, but, nevertheless, I decided to wait for further follow-up. I got one set of observations on January 28 using a remote-controlled 30 cm. Meade telescope on Mallorca with the help of Jaime Nomen and Salvador Sanchez. This showed, not a Centaur orbit, but a parabolic or slightly hyperbolic orbit, and the follow-up MPEC 2003-C07 a few days later still had an e=1 orbit, too.

So I contacted Sebastian Hoenig and Maik Meyer and heard that Sebastian had also found the 14 November observations, and had reported them to Brian Marsden at the Minor Planet Center. But Marsden didn't publish this because he was quite skeptical about this hyperbolic orbit. So I investigated further and managed to find a confirmation in November 20th Palomar/NEAT images. The position in this case is almost on the edge of the triplet, the stars are not sharp, and the limiting magnitude is not as good as in the 14 November frames. But stacking all three frames showed a faint source of light exactly at the spot predicted. Again there was nothing at that position in the DSS, so I reported this to Brian and Sebastian, and Brian decided it was time to publish the information.

This comet is a record holder with the largest perihelion distance ever observed (q=11.38). Even more interesting is to speculate about whether it might have flown near an unknown massive planet that gave it enough energy to climb into this hyperbolic orbit. Horner and Evans in their paper, "Biases in Cometary Catalogues and Planet X" [PDF|from], offer a look at the problems and possibilities of using comet paths to infer the location of an undiscovered distant planet or brown dwarf orbiting the Sun.

The faint and fuzzy object at the center of this image is C/2003 A2 (Gleason), imaged by stacking 24 exposures from a 30 cm. (12") Meade telescope. The square version of the image has had its pixels doubled to show enlarged here. Together with Jaime Nomen and Salvador Sanchez at the Observatori Astronomic de Mallorca, we have again observed C/2003 A2 with the remote 30 cm. telescope. At right is a small section with the contrast quite enhanced to show this faint and diffuse magnitude 19-20 object. The field is about 7x5 arcmin and one pixel 3.72 arcsec. You can see that the stars are slighly trailed from stacking 24 images made between 0135 and 0205 UT on February 12. The comet moved at 0.14"/min in P.A. 291.5, so stacking 30 minutes of data trailed the stars about 4.2", which is hardly visible at this 3.72"/pixel scale.       For more pictures of C/2003 A2, see Spacewatch's discovery page and Manteca/Ferrando's Cometas page.–Ed.

I am quite cautious about precovery work. I submit the data only when I have the feeling that the ID is OK and that I have really measured the sought object. And, even after it is published, I check the orbit after every new set of follow-up observations become available, to see if the precovery still fits. This is even more the case with this comet. The orbit is still quite sensitive and a few more days of follow-up will be needed to see if the November 2002 pre-discovery observations still fit.

All NEAT images are available via SkyMorph. For astrometry software, I use Astrometrica, which runs under Windows and is by far the most powerful software for astrometry (not for survey-mode batch processing, but for precise follow-up astrometry).

Asked for something about himself for A/CC readers who don't already know of him and his work, Reiner Stoss responded with this:  I'm an amateur astronomer. My main interests are unusual asteroids and comets. I did a lot of NEO confirmation and follow-up work with the 0.45m telescope at Starkenburg Observatory from 1998 to 2002. Since 1999 I have been participating in the DANEOPS project on the pre- and recovery of NEOs by using archives of old photographic plates or more recent CCD frames, and by participating in special observing runs on large professional telescopes. Beside NEOs, I also watch out for TNOs and comets.