A Sun-grazing comet was spotted on 25 June 2008 in images taken by a sophisticated device aboard the SOHO spacecraft. This is the 1500th comet discovery of SOHO.
Credit: SOHO(NASA & ESA)

The Solar and Heliospheric Observatory (SOHO) spacecraft is now regarded the most successful comet discoverer in history! SOHO has just has discovered its 1500th comet, making it more successful than all the other discoverers of comets throughout history put together. Amazingly, SOHO was initially designed as a solar physics mission. SOHO's history-making discovery was made on 25 June 2008, by amateur astronomer Rob Matson. This is Rob's 76th SOHO comet find.

When it comes to comet hunting, SOHO has one big advantage over all other Earth-based observers: it is situated between the Sun and Earth, and has a superb view of a region of space that can rarely be viewed from Earth. From the surface of Earth, the space within the terrestrial orbit is largely overwhelmed by the glare of the Sun, and therefore we only clearly observe close to the Sun during a total solar eclipse. 

Roughly eighty-five percent of the SOHO comet discoveries, and also this one, are fragments from a giant comet that was shattered in a death plunge around the Sun, probably thousands of years ago. The fragments are known as the Kreutz group and now approach the Sun to within 1.5 million km, when they return from deep space.

At this very close distance, most of the fragments are eventually destroyed, evaporated by the fierce solar radiation, all under the scrutiny of SOHO's sensitive detectors. One of SOHO’s twelve instruments, the Large Angle and Spectrometric Coronograph (LASCO) makes the comet discoveries.

LASCO’s images are immediately scanned by a group of highly skilled volunteers, when the data is downloaded to Earth-based computers. SOHO’s data can be on the Internet and ready for analysis just 15 minutes after it is acquired.

Enthusiasts from all over the world inspect each individual image for a tiny moving speck that could be a comet. Candidate comets are submitted to Karl Battams at the Naval Research Laboratory in Washington, DC, who checks all of SOHO's findings before sending them to the Minor Planet Center, where the comet is catalogued and has its orbit computed.

The wealth of comet information is more valuable than a mere classification. "This is allowing us to see how comets die," said Battams. When a comet periodically circles the Sun, it loses a little more of its volatile icy material every orbit, until it eventually fragments to pieces, leaving a long trail of debris. Thanks to SOHO, astronomers now have a bonanza of images showing this process. "It is a unique data set and could not have been achieved in any other way," added Battams.

SOHO has been observing the Sun and its space environment from a solar orbit for over 12 years, providing extraordinary revelations and startling discoveries. "Catching the enormous total of comets has been an unplanned bonus," said Bernhard Fleck, SOHO Project Scientist.

Further Reading

SOHO
http://sohowww.nascom.nasa.gov/
Sungrazing Comets
http://ares.nrl.navy.mil/sungrazer/index.php?p=latest_news

Aymen Mohamed Ibrahem
Senior Astronomy Specialist