SOHO-600: The Comet in the Field of Dreams

Big number, modest comet.
Comet SOHO-600 was a small,
moderately bright speck in LASCO C2
on April 29, 2003. (Image courtesy
SOHO/LASCO consortium. SOHO is a
project of international cooperation
between ESA and NASA.)

The number of comets discovered in SOHO (Solar and Heliospheric Observatory) images approached the 600 mark with none of the hoopla that preceded SOHO-500. It wasn't until April 28, when the tally reached 599, that I was even aware it was getting close. That evening, I gave the images particular attention, and I was not to be disappointed.

On the black-and-white C2 image for 23:26 UT, I noticed a moderately bright, fuzzy speck at the edge of the image near where a Kreutz comet would be expected to enter the field. It seemed a promising candidate, but no new images were posted so I couldn’t confirm it or rule it out. I tuned the TV to Field of Dreams , which I watched as I waited for new images. The movie was almost over by the time another image finally came up (at 01:27 UT April 29), and due to the two-hour gap between photos I was unable to determine if either of the two spots near the object’s expected location was actually a comet or just random noise. A third image, though, showed a blotch with the predicted position and brightness (SOHO’s Kreutz fragments fade steadily while vaporizing as they plunge towards the Sun), so I filed a report. It was confirmed soon after by Rob Matson, who had been tracking the same object but had missed the second frame.

The next day, Derek Hammer of the SOHO team verified my find as the spacecraft's 600th comet. Although confirmed by the SOHO staff, my find has yet to receive an International Astronomical Union designation. Due to budget cuts leading to understaffing at SOHO--which wasn't designed for comet hunting in the first place--there is a backlog of more than 50 SOHO comets that have neither been officially announced nor had orbits published.

SOHO-600 appears to be an average Kreutz sungrazer fragment, moderately bright but certainly no “barn-burner”. The next SOHO comet, found just 12 hours after mine by Germany's Rainer Kracht, was also a Kreutz comet, though with a notably different path—perhaps from a different subgroup. Kracht followed a day later with a unique double comet belonging to no known comet group. He has been the most successful SOHO comet hunter in the past two years, finding more than 90 comets since August 2001, many previously overlooked in images from SOHO's early days; in the same period, I have found just four. Kracht may ultimately challenge Michael Oates, the most prolific SOHO comet hunter, who currently has 141 finds.

But first, on to SOHO-700. As of May 18, SOHO’s total tally is up to 612.

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