Comet C/2025 F2 SWAN was discovered by an Australian amateur astronomer. This is how he found it.

Australia Broadcast Center

30-04-2025

Most days, Michael Mattiazzo logs into his computer and looks through public data from a spacecraft orbiting the Sun.
He's not an astronomer by trade, and he's not interested in our stellar neighbour.
Instead, he's hunting comets.
Michael has been doing this for more than two decades, and when asked why, he's delightfully honest.
"It's the kudos," he laughs.
"
It's the excitement of new discovery.
"
While most of the night sky is mapped by professional astronomical surveys, Michael studies the tiny patch of sky those surveys can miss.
"There's just a little window where a comet can approach from behind the Sun and be hidden," he says.
In March, Michael discovered a green comet called C/2025 F2 SWAN — his tenth discovery using public data from the Solar and Heliospheric Observatory (SOHO).
Observations of the comet since then suggest it started falling apart in mid-April and disintegrated before it was due to pass the Sun this week.
"The Sun is at solar maximum this year and it was just too much for this small, fragile, icy body getting so close to it," he says.
But Michael is worried his chance of finding any more comets is also fading — and C/2025 F2 SWAN may be his last.
A new state-of-the-art observatory, scheduled to be completed later this year, is likely to sniff out distant comets long before amateur astronomers can.
An old solar observatory
SOHO was not built to find comets
:
it was launched in 1995 by the European Space Agency and NASA to study the Sun.
Its mission was expected to last just two years, but it's now well past that. Later this year the spacecraft will hit three decades in space.
SOHO has been studying the Sun for almost 30 years.
(
Supplied:ESA/ATG/NASA SOHO/CC BY-SA 3.0 IGO
)
Aboard SOHO is an ultraviolet camera called SWAN that highlights ionised hydrogen and is used by scientists to peek at the solar atmosphere on the far side of the Sun.
But when the data became public around the 2000s, amateur astronomers quickly realised that glimpses of comets could sometimes be seen on the camera's edges.
When comets get close to the Sun, the water inside them turns into ionised hydrogen, making them appear "very bright", Michael says.
"SWAN is an excellent detector for comets.
Data from the SWAN all-sky map on March 27 showed a blip which was confirmed be caused by the comet.
(
(Supplied: Michael Mattiazzo)
)
"
I'm just grateful for them for providing that data for us to use.
"
How to catch a comet
But a discovery of a comet needs more than just finding a blip in SWAN data.
The sky map which SWAN produces also highlights many false positives.
Michael Mattiazzo has his own telescope, but normally discovers comets using publicly available data.
(
Supplied: Michael Mattiazzo
)
For C/2025 F2 SWAN, the telltale flash of light was discovered on March 30, 2025.
Once he was pretty sure it was a new comet, Michael needed to find it before anyone else did.
"Well, we sort of keep it secret," he says.
"I kept it quiet so that I could confirm it myself … [but] the longer you delay it, the more people can pick it up."
The comet was seen on SWAN data taken on March 27, but because the data is only released publicly a few days later,
the comet has already travelled into another area of sky
.
With only a faint smudge in one area of the sky, it's particularly hard to forecast where the comet might have moved to.
In the case of C/2025 F2 SWAN, there was another issue — it's a comet only visible in the Northern Hemisphere.
As much as he would have liked to find it himself, Michael had to request help from a larger amateur astronomy group.
After putting out the call, Qicheng Zang, an astronomer in Arizona, was the first to directly image the comet, and once it was found visually, Michael took a remote snap from a telescope in Utah.
An image of comet C/2025 F2 SWAN taken using a remote telescope in Utah on April 6.
(
Supplied: Michael Mattiazzo
)
An international rivalry
The delay in imaging the comet meant Michael wasn't the only one credited with the discovery.
It was independently seen in the SWAN data by three people: Michael, American Rob Matson, and Ukrainian Vladimir Bezugly.
All three reported the discovery on the Minor Planet Center's
"Once we get enough data positions, it's then officially announced," Michael says.
The three comet hunters have become co-discoverers on a number of comets since the early 2000s, all by closely looking at the same SWAN data.
While he does think of this as "a competition", Michael is also fond of the other two.
"Vladimir Bezugly is getting bombs dropped [on him]," he says.
"He should get a very special mention, doing this from war-torn Ukraine."
Photo shows
Retired astronomer Rob McNaught is pictured with a brightly coloured mural in Coonabarabran. The mural features Comet McNaught.
Robert H McNaught can close his eyes and pinpoint the greatest moment in his career — eyeballing for the first time one of the brightest comets in living memory.
To have a comet named after you — for example
"[Terry Lovejoy's] telescope can do automatic survey searching. So it images a patch of sky, and then it does its own processing, the way professionals do it, but at an amateur capacity," Michael says.
"That's much harder to do than spending five minutes on a PC every day looking at an ultraviolet image.
"[What I do] it's almost cheating."
While the search for comets is international, Australians have discovered more than their fair share.
Comet McNaught was the brightest comet seen since the 1960s.
(
Rob McNaught
)
Both Terry Lovejoy and Robert McNaught live in Australia,
How comet hunting has evolved
In the days of Bill Bradfield in the late 20th century, comets were discovered using amateur astronomer's own telescopes to look directly at the night sky.
When the public data from SWAN was made available, this changed the game.
According to Michael, SWAN was a "threat to the visual comet hunter".
Similarly, the soon-to-be-completed Vera C. Rubin Observatory in Chile is a threat to the comet hunters using SWAN.
"It's going to be an amazing survey," Michael says.
"
It has got a gigantic mirror on it with a gigantic camera … everything will get picked up.
"
But Michael worries that it will make it even harder for amateur astronomers to spot comets before the
experts do, particularly because the data won't be publicly available for two years after it's collected — much too late for comet discoveries.
"I think Vera Rubin is really going to shut the door on us," he says.
Rebecca McElroy, an astronomer at the University of Southern Queensland who is part of the team working on the new observatory, doesn't agree.
She thinks the time between the surveys will still leave "room for amateur discoveries", although she understands that it might make it harder than before.
The Vera C Rubin Observatory will photograph the entire available sky every few nights.
(
Supplied: Mason Productions Inc./LSST Corporation/
)
"The 8.4-metre telescope … will be home to the largest digital camera ever made," she says.
"[The telescope] will mean that the southern sky is always being watched for anything interesting that might happen."
For Dr McElroy, this means she'll be able to quickly spot supermassive black holes called quasars in the distant sky, but the telescope's sensitivity and scope means it'll see a lot more than that.
The telescope is scheduled to start making scientific observations later this year, so the days of SWAN might be almost up.
Despite this looming deadline, Michael is still optimistic there will be tiny slivers of sky that SWAN can see, but other telescopes like Vera Rubin can't.
"There might still be a little gap where [the comet] comes in on the far side of the Sun," he says.
But the best-case scenario for amateur astronomers like him is that the data is searchable.
And if scientists are looking for volunteers to comb the results for comets, Michael knows a few amateur astronomers who could be interested.
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