2024-04-05 16:15:32
SOHO is an international collaboration project between ESA and NASA. SOHO’s science ranges from the warm interior of the Sun, through its visible surface and turbulent atmosphere, to distant regions where the wind from the Sun fights the wind of atoms coming from among the stars. Credit: ESA
Designed for solar observation, Soho has become a prolific comet explorer, with the discovery of the 5,000th comet marking a significant milestone and showcasing the contribution of volunteer comet hunters.
On March 25, 2024, a citizen scientist in the Czech Republic spotted a comet in an image from the Solar and Heliosphere Observatory (SOHO) spacecraft, now confirmed to be the 5,000th comet discovered using SOHO data. SOHO achieved this milestone during 28 years in space, even though it was never designed to be a comet hunter.
A comet is a small body made of ice and rock that only takes a few years to orbit the sun. It belongs to the “Marsdan group” of comets. This group is thought to be related to Comet 96P/Machholz (which SOHO observes as Machholtz passes by the Sun every 5.3 years) and is named after the late scientist Brian Marsden who first identified the group through SOHO observations. Only about 75 of the 5,000 comets discovered with SOHO belong to the Marsden group.
The 5,000th comet discovered with the Solar and Heliosphere Observatory (SOHO) spacecraft is indicated by a small white box in the upper left of this image. An enlarged inset shows the comet as a faint spot between the white vertical lines. The image was taken on March 25, 2024, by SOHO’s Large Angle and Spectrometric Coronagraph (LASCO), which uses the disk to block the bright Sun and reveal faint features around it. Credit: NASA/ESA/SOHO
The unexpected role of SOHO
A joint mission of ESA (European Space Agency) and NASA, SOHO launched in December 1995 to study the Sun and the dynamics of its outer atmosphere, called the corona. A scientific instrument on SOHO, called the Large Angle and Spectrometric Coronagraph (LASCO), uses an artificial disk to block the sun’s blinding light so that scientists can study the corona and the environment immediately around the sun.
It also allows SOHO to do something that many other spacecraft can’t – see comets flying close to the Sun, known as “sweating” or “bathing” comets. Many of these comets only brighten when they are too close to the Sun for other stargazers to see, otherwise they would go undetected, lost in our star’s bright glare. While scientists expected SOHO to consistently find some comets during its mission, the spacecraft’s ability to spot them has made it the most prolific comet explorer in history—discovering more than half of the comets known today.
Community participation and achievement
In fact, shortly after SOHO 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, which allows anyone to report comets they find in SOHO images.
This animation shows the observatory’s 5,000th comet and the heliosphere (circled) moving across the field relative to background stars. The images in this sequence were taken with the spacecraft’s Large Angle and Spectrometric Coronagraph (LASCO) instrument. Credit: NASA/ESA/SOHO
5,000 of the comet Soho’ was found by Hanjie Tan, a Sungrazer project participant originally from Guangzhou, China, currently pursuing a PhD in astronomy in Prague, Czech Republic. Tan has been participating in the Sungrazer project since he was 13 years old and is one of the project’s youngest comet explorers.
“Since 2009, I have discovered over 200 comets,” Tan said. “I joined the Sungrazer project because I love looking for comets. It’s really exciting to be the first to see comets light up near the sun after they’ve been traveling through space for thousands of years.”
Most of the 5,000 comets discovered by SOHO were found with the help of an international team of volunteer comet hunters—many without formal scientific training—participating in the Sungrazer project.
“Prior to the launch of the SOHO mission and Project Sungrazer, there were only a few dozen comets with documented solar eclipses – that’s all we knew about their existence,” said Carl Batams, a space scientist at the US Naval Research Laboratory in Washington, DC. and Principal Investigator of the Sungrazer Project. “The fact that we finally reached this milestone – 5,000 comets – is just unbelievable to me.”
SOHO’s 5,000th comet was discovered with the help of volunteers participating in the NASA-funded Sungrazer Project. Credit: NASA Goddard Space Flight Center
The vast number of comets discovered by SOHO allowed scientists to learn more about solar comets and groups of comets orbiting the Sun. Comets discovered by Project Sungrazer have also helped scientists learn more about the Sun, by watching the comets plunge through our star’s atmosphere like little solar probes.
“The statistics of 5,000 comets, and looking at their orbits and trajectories in space, is a super unique data set – it’s really valuable science,” Batams said. “This is a testament to the countless hours that the project participants invested in this. We would never have reached this milestone if it weren’t for what the project volunteers did.”
Project Sungrazer is one of many opportunities anyone can get involved with to help make discoveries with NASA during the Big Year of Heliophysics, which runs through the end of 2024. Learn more about SOHO, Project Sungrazer, and other NASA science projects. Participate in:
- NASA Soho mission site
- ESA SOHO website
- Project Sungrazer
- Why does ESA and NASA’s SOHO spacecraft locate so many comets?
- The 4,000th comet discovered by ESA and NASA’s Solar Observatory
- NASA Citizen Science
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