07/02/06

ANATOMY OF A COMET DISCOVERY 

From the Director:

In the small world of Near Earth Object observers, this was pretty big news.  A worldwide call for confirmation observations was posted by the Minor Planet Center (MPC) at the Smithsonian Astrophysical Observatory (SAO) on the evening of May 31st, 2004 for a faint, fast-moving object that was observable in the last few hours before dawn.  I put the object, along with a recently discovered asteroid needing more positional data, on my target list for the evening and didn't think much more of it, other than holding out little hope that I'd get anything on my CCD plates.  It was fast,  very faint - estimated at magnitude 19.5, and the nearly-full moon was reaching maximum luminosity - each one on its own a very negative factor.  And to make matters worse, when I glanced at my paper star chart I could see that it was going to be right in the middle of one of the densest regions of the Milky Way, which means that the object of interest would be blanked out much of the time by background stars. 

When I reviewed the CCD frames in the wee hours of May 31st after shutting down the telescope, I caught a glimpse of a moving object dodging between nearby stars.  I had had problems getting the CCD imager well-focused that evening, so I was not surprised that this object looked a bit oblong and blurry.  I noted the precise time the image was captured and carefully measured its position and brightness - mag. 18.5 - a little lower than predicted, but within reasonable limits.  I was fairly certain that it was the targeted object.  I was also disappointed, because generally at least two, and preferably three images are needed to report an astrometric observation.  I did save my one, lonely point of data, and then crawled into bed for a nice weekend sleep-in.

I programmed the same object for imaging the following evening, but held out even less hope of getting any useful data; the moon was yet brighter and 15 degrees closer to the target position than the night before.  I set my alarm for 3:30am on the morning of June 1st so I could grab the images as soon as the telescope parked itself at the end of the programmed observing run.  This time I got three consecutive images of the object of interest, and was also surprised because it still looked a little oblong and blurry.  Unfortunately, it was also so close to some nearby background stars that the software I was using wouldn't let me "snap" to the centroid of the object - it kept snapping to the nearby stars.  I was worried that by not being able to snap to its software-calculated centroid, any position that I read manually would be of insufficient precision.  And by not being able to snap to its centroid, I couldn't get a photometry (brightness magnitude) reading either.  I jotted down my manual position measurements (sans photometry), and at least got the precise time of exposure from the software.

Because this object had languished for a couple of days on the critical confirmation list posted by the MPC, I was concerned that there wasn't much data coming in due to the now full moon and dense field of background stars.  Usually objects are taken off the list within 24 hrs when sufficient confirmation observations have been received, after which an official discovery announcement is made.  I sent an e-mail to Dr. Timothy Spahr, one of the the Near Earth Objects specialists at SAO, and also pasted in my single software-assisted measurement and three manual observations, suggesting that they might somehow be of use if they were desperately short of data.  I got a surprisingly quick response from SAO, informing me that all my observations were in fact fine (they do some fancy statistics to determine their "residuals" or departures from a smooth arc along the object's predicted path) and would be used in the orbit calculations.  Dr. Spahr also informed me for the first time that this was a suspected comet with an unusual orbit, and was already on its way back to some lonely corner of the solar system.

The object stayed on the critical list for the next two nights and I tried to get additional measurements, but the Moon won the battle of the photons - decisively.  During this time I had been corresponding with a fellow astronomer named Peter Birtwhistle, who runs a garden observatory similar to mine, on the outskirts of London, England.  Peter had gone through a comet discovery process before, and said that the delay in making a discovery announcement was the norm.  Apparently the comet scientists have to do some additional analysis of the suspected comet's shape and apparent direction of any tail-like form before they can say for certain that it is a comet.  On June 3rd at about 11:30am Eastern time, the Smithsonian Astrophysical Observatory announced the discovery of comet C/2004 K3 LINEAR.  By tradition, comets are named after their discoverer - in this case the Lincoln Near Earth Asteroid Research (LINEAR) facility, near Socorro, NM.  The official discovery announcement can be found here:

http://cfa-www.harvard.edu/mpec/K04/K04L04.html

Note the apertures of the telescopes involved in this discovery!  Mostly large research telescopes, a few medium-sized ones, and then mine and Peter's 30cm telescopes.  It pays to be willing to roll up your sleeves when the going gets tough!

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There is an interesting postscript to this story which illustrates the behind-the-scenes bickering that sometimes goes on in the scientific community.  I ended up getting caught in a mild “spat” that came about as a result of Francisquito’s involvement in the C/2004K3 discovery.  Click here to find out more.