SOHO discovered its 2000th comet 26/12. With the help from citizen scientists around the world, SOHO has become the single greatest comet finder of all time. This is all the more impressive since SOHO was not specifically designed to find comets, but to monitor the sun.

Of course, it is not SOHO itself that discovers the comets -- that is the province of the dozens of amateur astronomer volunteers who daily pore over the fuzzy lights dancing across the pictures produced by SOHO's LASCO camera.

Over 70 people representing 18 different countries have helped spot comets over the last 15 years by searching through the publicly available SOHO images online.

The 1999th and 2000th comet were both discovered on December 26 by Michal Kusiak (photo below), an astronomy student at Jagiellonian University in Krakow, Poland. Kusiak found his first SOHO comet in November 2007 and has since found more than 100.

It took SOHO 10 years to spot its first 1000 comets, but only 5 more to find the next 1000. That's due partly to increased participation from comet hunters and work done to optimize the images for comet-sighting, but also due to an unexplained systematic increase in the number of comets around the sun. Indeed, December alone has seen an unprecedented 37 new comets spotted so far, a number high enough to qualify as a "comet storm."

LASCO, the instrument on-board SOHO that has been used to find comets, was not designed primarily for that purpose. The LASCO's camera blocks out the brightest part of the sun in order to better watch emissions in the sun's much fainter outer atmosphere, or corona. LASCO’s comet finding skills are a natural side effect -- with the sun blocked, it's also much easier to see dimmer objects such as comets.

Approximately 85% of the comets discovered with LASCO are thought to come from a single group known as the Kreutz family, believed to be the remnants of a single large comet that broke up several hundred years ago. The Kreutz family comets are “sungrazers” – bodies whose orbits approach so near the Sun that most are vaporized within hours of discovery – but many of the other LASCO comets boomerang around the sun and return periodically.

One frequent visitor is comet 96P Machholz. Orbiting the sun approximately every six years, this comet has now been seen by SOHO three times.

Source: NASA
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