SOHO: World’s Greatest Comet Finder

When you consider the pantheon of renowned comet discoverers, you'll come across the names of such gifted observers as Rob McNaught (57 finds) Gene and Carolyn Shoemaker (32 between them), David Levy (22), and even Caroline Herschel.

Launched in December 1995, the Solar and Heliospheric Observatory (SOHO) was designed to study the Sun — not to discover comets. Yet it's recorded twice the number of comets found by astronomers in the previous 300 years.
NASA / ESA / Alex Lutkus
However, the all-time record for the most comet discoveries belongs not to one of these Earthlings but instead to an aging spacecraft called the Solar and Heliospheric Observatory. Just a couple of days ago, SOHO recorded its 2,000th comet! That's many times more than its nearest rival, the LINEAR telescope, which has been conducting an automated ground-based sky survey (primarily for asteroids) since the 1990s.

Launched in 1995 to monitor solar activity, SOHO also sweeps up lots and lots of comets that happen to be zipping very near (and heading into) the Sun. So it's been spectacularly successful at something it wasn't really designed to do. The observatory hit the 1,000-comet mark five years ago.

SOHO doesn't find these comets on its own — the mission's scientists aren't alerted by flashing lights or alarm bells each time one is detected. Instead, in almost all cases the interlopers are spied by dozens of amateurs around the world who watch for moving objects in real-time images from the observatory's Large Angle and Spectrometric Coronagraph Experiment (LASCO).

SOHO's 2,000th comet, spotted in this LASCO coronagraphic image on December 26, 2010, by Polish amateur astronomer Marcin Kusiak.
SOHO / Karl Battams
Credit for spotting SOHO's 1,999th and 2,000th comets goes to Marcin Kusiak, an astronomy student in Krakow, Poland. He's apparently got a keen eye for this work, having spied more than 100 SOHO comets in the past three years.

With the launch of the Solar Terrestrial Relations Observatory (STEREO) in 2006, researchers now have two sets of more robotic eyes to monitor the Sun's corona — and would-be comet hunters have even more images to scan.

Yet LASCO continues to snap images every 12 minutes through a pair of coronagraphs that cover the near-Sun real estate out to about 13 million miles (21 million km). In fact, last August ground controllers reapportioned the spacecraft's telemetry to give the instrument more bandwidth. That's because NASA's latest Sun-watcher, the Solar Dynamics Observatory, lacks a camera with LASCO's capabilities.

If you'd like to try finding a comet in SOHO and STEREO images, check out the official sungrazer website. You can also get rolling by reading through the informative FAQ posted here by veteran SOHO spotter Tony Hoffman. There's also a comet-hunter chat group, and you'll enjoy this enlightening Hoffman interview by science writer Elizabeth Howell.

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