On March 25, 2024, a citizen scientist in the Czech Republic spotted a comet in an image from the Solar and Heliospheric Observatory (SOHO) spacecraft, which has now been confirmed to be the 5,000th comet discovered using SOHO data. SOHO has achieved this milestone over 28 years in space, even though it was never designed to be a comet hunter.
The 5,000th comet discovered with the Solar and Heliospheric Observatory (SOHO) spacecraft is noted by a small white box in the upper left portion of this image. A zoomed-in inset shows the comet as a faint dot between the white vertical lines. The image was taken on March 25, 2024, by SOHO’s Large Angle and Spectrometric Coronagraph (LASCO), which uses a disk to block the bright Sun and reveal faint features around it. NASA/ESA/SOHO
The comet is a small body made of
ice and rock that takes only a few years to orbit the Sun. It belongs to the
“Marsden group” of comets. This group is thought to be related to comet
96P/Machholz (which SOHO
observes when
Machholz passes near the Sun every 5.3 years) and is named for the late
scientist Brian Marsden who first recognized the group using SOHO observations.
Only about 75 of the 5,000 comets discovered with SOHO belong to the Marsden
group.
A joint mission of ESA (European
Space Agency) and NASA, SOHO launched in December 1995 to study the Sun and the
dynamics in its outer atmosphere, called the corona. A science instrument on
SOHO, called the Large Angle and Spectrometric Coronagraph (LASCO), 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
scientists 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 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 that allows anyone to report comets they find in SOHO images.
This animation shows the Solar and Heliospheric Observatory’s 5,000th comet (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. NASA/ESA/SOHO
SOHO’s 5,000th comet was found by Hanjie Tan, a Sungrazer Project participant who is
originally from Guangzhou, China, and is currently pursuing a doctoral degree
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 discoverers.
“Since 2009, I've discovered over
200 comets,” Tan said. “I got into the Sungrazer Project because I love looking
for comets. It's really exciting to be the first to see comets get bright near
the Sun after they've been traveling through space for thousands of years.”
Most of the 5,000 comets discovered
using SOHO have been found with the help of an international cadre of volunteer
comet hunters – many with no formal scientific training – participating in the
Sungrazer Project.
“Prior to the launch of the SOHO mission and the Sungrazer Project, there were only a couple dozen sungrazing comets on record – that’s all we knew existed,” said Karl Battams, a space scientist at the U.S. Naval Research Lab in Washington, D.C., and the principal investigator for the Sungrazer Project. “The fact that we’ve 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's Goddard Space Flight Center
The vast number of comets
discovered using SOHO has allowed scientists to learn more about sungrazing
comets and groups of comets that orbit the Sun. Comets discovered by the
Sungrazer Project have also helped scientists learn more about the Sun, by watching
the comets plunge through our star’s atmosphere like small solar probes.
“The statistics of 5,000 comets,
and looking at their orbits and trajectories through space, is a super unique
dataset – it’s really valuable science,” Battams said. “It’s a testament to the
countless hours the project participants have put into this. We absolutely
would never had reached this milestone if it wasn’t for what the project
volunteers have done.”
The Sungrazer Project is one of
many opportunities that anyone can get involved with to help make discoveries
with NASA during the Heliophysics
Big Year, which
extends through the end of 2024. Learn more about SOHO, the Sungrazer Project,
and other NASA science projects you can participate in:
- NASA SOHO mission website
- ESA SOHO website
- The Sungrazer Project
- Why ESA and NASA’s SOHO Spacecraft Spots So Many Comets
- 4,000th Comet Discovered by ESA & NASA Solar Observatory
- NASA Citizen Science
by Vanessa Thomas
NASA’s Goddard Space Flight Center, Greenbelt, Md.
Source: ESA, NASA Solar Observatory Discovers Its 5,000th Comet
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