All-time Best Comet-Hunter Spots Number 1000
SOHO comets 999 and 1,000.
Credit: NASA/ESA

The best comet hunter in history recently spotted its 1,000th comet, accounting for nearly half the comets ever discovered.

The Solar and Heliospheric Observatory (SOHO), which is run by NASA and the European Space Agency, was designed to watch the Sun, but has since proved to have excellent ability at spotting comets.

The images SOHO took were posted to the internet and amateur sky-watchers had the opportunity to find and report new comets. Amateurs were finding comets so quickly that SOHO operators decided to make a contest of it, awarding a prize to the person who discovered the 1,000th comet.

Italian high school teacher Toni Scarmato got lucky on Aug. 5 and spotted comets numbers 999 and 1,000 in the same SOHO image.

"I am very happy for this special experience that is possible thanks to the SOHO satellite and NASA-EVA collaboration," Scarmato said. "I want to dedicate the SOHO 1000th comet to my wife Rosy and my son Kevin to compensate for the time that I have taken from them to search for SOHO comets."

For his accomplishment, Scarmato will receive a SolarMax DVD, a SOHO T-shirt, solar viewing glasses, and more.

A second SOHO comet-spotting contest awarded prizes to Andrew Dolgopolov of Ireland for the closest guess - within 22 minutes - of when the 1,000th comet would be spotted.

The SOHO spacecraft was engineered to watch solar eruptions and the ensuing space weather that sometimes bombards Earth.

But early on in the mission, armchair astronomers figured out they could become comet discoverers using SOHO images posted to the Web. Because SOHO is trained on the Sun, it only sees comets that whiz by the Sun, called Sun grazers.

Sun grazers are often hard to spot because they are lost in the glare from the overwhelming light produced by the Sun. But SOHO is equipped with a device that blocks light from the Sun's main disk so detailed images can be made of the solar atmosphere and surrounding space.

"Before SOHO was launched, only 16 sun grazing comets had been discovered by space observatories," said Chris St. Cyr, senior project scientist for NASA's 'Living With a Star' program at the agency's Goddard Space Flight Center. "Based on that experience, who could have predicted SOHO would discover more than 60 times that number, and in only nine years."

Some 85 percent of all SOHO comets belong to the Kreutz group, named because their orbits take them within 500,000 miles of the Sun's visible surface. Some make a trip around the Sun and head back out to the far reaches of the solar system on wildly elongated orbits. Others don't make it, being gravitationally drawn right into the star on close approach.

Other comets discovered without SOHO, such as one named Kudo-Fujikawa, have at times been watched in real time by web surfers as they dramatically sliced across SOHO's field of view. In 2003, a comet named NEAT, whose path in front of the SOHO cameras was well predicted, was smacked by a solar storm, the first such event ever recorded.

SOHO is a joint effort between NASA and the European Space Agency. It has accounted for about half of all comet discoveries, through history, in which orbits have been calculated.

A timeline for milestone comets spotted by SOHO (comet number and date spotted):

100: Feb. 4, 2000
200: Aug. 31, 2000
300: Mar. 25, 2001
400: Feb. 26, 2002
500: Aug. 14, 2002
600: Apr. 29, 2003
700: Dec. 2, 2003
800: June 11, 2004
900: Jan. 15, 2005

1000: Aug. 5, 2005