On March 25, 2024, Hanjie Tan, an astronomy Ph.D. student in Prague, Czech Republic, spotted a comet in an image from the ESA/NASA Solar and Heliospheric Observatory (SOHO) spacecraft, which has now been confirmed to be the 5,000th comet discovered using the SOHO data. The observatory has achieved this milestone over 28 years in space, even though it was never designed to be a comet hunter.
A joint mission of ESA and NASA, SOHO launched in December 1995 to study the Sun and the dynamics in its outer atmosphere, called the corona.
The spacecraft’s Large Angle and Spectrometric Coronagraph (LASCO) instrument uses an artificial disk to block the blinding light of the Sun so scientists can study the corona and environment immediately around the Sun.
This also allows SOHO to do something many other spacecraft cannot — see comets flying close to the Sun, known as sungrazing comets or sungrazers.
Many of these comets only brighten when they’re too close to the Sun for other observatories to see and would otherwise go undetected, lost in the bright glare of our star.
While astronomers expected SOHO to serendipitously find some comets during its mission, the spacecraft’s ability to spot them has made it the most prolific comet-finder in history — discovering more than half of the comets known today.
In fact, soon after the spacecraft launched, people around the world began spotting so many comets in its images that mission scientists needed a way to keep track of them all.
In the early 2000s, they launched the NASA-funded Sungrazer Project that allows anyone to report comets they find in SOHO images.
“When LASCO was launched, no one had any idea that it would turn out to be the most prolific discoverer in history,” said U.S. Naval Research Laboratory researcher Dr. Karl Battams, the principal investigator of LASCO and the Sungrazer Project.
“The amount of data and science returned has just been beyond our wildest dreams.”
The 5,000th discovery was…
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