The Solar and Heliospheric Observatory (SOHO) spacecraft, which follows planet Earth in its orbit around the Sun, has now discovered 5,000 confirmed comets.
The discovery comes after 28 years of observations, even thought SOHO was never intended to be a comet hunter.
The 5,000th comet was discovered on 25 March 2024 when a citizen scientist in the Czech Republic spotted it in a SOHO image.
Comets are bodies of ice and rock that orbit the Sun, and every now and then their orbit takes them into the inner Solar System.
When this happens, heat from the Sun often causes a coma and tail to appear, making them prominent objects to view in the night sky.
Some comets take hundreds of years to return; some don't take nearly as long.
SOHO's 5,000th comet takes only a few years to orbit the Sun and belongs to the 'Marsden group' of comets.
These comets are thought to be related to comet 96P/Machholz, named after the scientist Brian Marsden who discovered the group using observations made by SOHO.
Comet 96P/Machholz passes the Sun every 5.3 years, making it a very short-period comet.
Discovering the 5,000th SOHO comet
This 5,000th SOHO comet was discovered by Hanjie Tan, who participates in the NASA-funded Sungrazer Project, which enables citizen scientists to report comets they find in SOHO images.
Originally from Guangzhou, China, Tan is working on a doctoral degree in astronomy in Prague in the Czech Republic.
"Since 2009, I've discovered over 200 comets," he says.
"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."
NASA says most of the 5,000 comets discovered by SOHO have been found with the help of citizens working with 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," says said Karl Battams, a space scientist at the U.S. Naval Research Lab and principal investigator for the Sungrazer Project.
"The fact that we’ve finally reached this milestone – 5,000 comets – is just unbelievable to me."
If you fancy yourself as a citizen comet hunter, find out more about how to get involved in the Sungrazer Project.
