Bright green Comet SWAN falls apart after once-in-a-lifetime appearance in our night sky
Comet SWAN (C/2025 F2) was discovered in March with the Solar Wind Anisotropies (SWAN) instrument on Nasa's Solar and Heliospheric Observatory (SOHO) spacecraft, hence why SWAN is in the comet's name.
Since its discovery, hundreds of observations of the comet have been logged into the International Astronomical Union's Minor Planet Center from observatories around the world.
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Comet SWAN was set to reach perihelion, the closest distance to the Sun, around May 1, raising hopes the possibility of unaided-eye viewing could be on the table later this month.
But recent observations show the comet didn't make it past the final approach.
"It looks like there's not much left of it, and it seems to be just clouded dust at this point that's gradually getting more diffuse and flying apart," said Dr. Qicheng Zhang, a post-doctoral astronomer at Lowell Observatory in Arizona.
Zhang studies comets that get very close to the Sun, known as sun-grazers, such as Comet C/2024 G3 ATLA's approach in January.
Comet SWAN was a smaller comet and Zhang said this is likely the factor that led to its early end.
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"The thing with small comets is that they tend to get spun up really easily by just random variations in their outgassing," he said. "When the ice on them starts to sublimate and create gas. It tends to not come out perfectly symmetrically. And that asymmetry starts to like, torque the thing and just spin it up."
As a comet spins up, it starts to fall apart, which is likely what is happening to Comet SWAN now before it ceases to be an active comet.
Comet SWAN has been observed by professional and amateur astronomers worldwide with its notable green coloring. Zhang said this coloring is likely from diatomic carbon.
"Comets have a lot of organic material. When you toss it out into space, you get UV rays from the Sun that hit those complicated organic molecules, which happen to contain a lot of carbon. And when they get broken down, you'll get pieces that contain essentially just two carbon atoms stuck together. And that's essentially just the green that we see in these comets," Zhang said.
The comet's orbital period is 1.4 million years, so even if it survived perihelion, it would be the last chance to see it in our lifetime.
So long, Comet SWAN.Original article source: Bright green Comet SWAN falls apart after once-in-a-lifetime appearance in our night sky
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