Category: comets

It has now been just over a year since the comet 3I/ATLAS first captured the world's attention as the third known object to fly through our solar system from beyond. Astronomers are still learning new things about where exactly it came from.

For the first time ever, they've been able to study charged particles in the tail of the interstellar comet. This has told them that 3I/ATLAS contains more nitrogen than the typical comet from our own solar system — revealing a tantalizing clue about how the strange comet formed.

"Finding that it's so rich in nitrogen tells us it likely formed in extremely cold conditions, far from its home star," Lea Ferellec, a research fellow at Northumbria University, said in a statement.

Ferellec's group used the William Herschel Telescope in Spain's Canary Islands. One of this telescope's instruments is a fiber-optic weave named, well, WEAVE. WEAVE lets astronomers do spectroscopy — which splits incoming light into its spectrum. Different chemical elements absorb and emit different wavelengths of light, marking that spectrum with different characteristic fingerprints. With spectroscopy, astronomers can look at a celestial object's light, pick out the fingerprints, and reconstruct the stuff inside.

Other astronomers have measured 3I/ATLAS with spectroscopy, but they've mostly examined the comet's coma, a shell of gas that forms when the sun’s heat sublimates the comet’s ice into vapor.

Of course, a coma is not the only feature that forms as a comet approaches the sun. Close in, a comet is battered by the torrent of the sun's solar wind, which pushes the comet's material away into a distinctive tail. In the process, the solar wind's high-energy particles strike the comet's molecules and electrify them into charged ions.

If astronomers can identify a tail's ions, they can find chemicals and learn information they can't from the coma alone. This is a tricky task. When fellow interstellar comet 2I/Borisov visited our solar system in 2019, astronomers identified traces of its ions, but they couldn't make out what those ions actually were.

WEAVE, which switched on in 2023, is powerful and sensitive enough to change that. When Ferellec and colleagues turned WEAVE on 3I/ATLAS in late 2025, they could count ions like nitrogen, carbon dioxide and carbon monoxide in the strange comet's tail.

Comparing these figures can hint at where a comet formed. For example, a comet with a higher ratio of nitrogen to carbon monoxide tends to have formed in a colder birthplace. Ferellic's group found that 3I/ATLAS has a much higher ratio than most of the comets that we observe in our solar system.

In particular, Ferellec and colleagues estimate that 3I/ATLAS formed somewhere colder than -240°C. If this comet was born in a distant star system, then, it formed in that system's outer reaches. In other words, 3I/ATLAS likely formed in a place where little of its star's light could touch it.

"This object gives us a rare chance to study material that formed somewhere completely different to our own solar system," Ferellec said in the statement. "Every one of these objects we study helps us understand a little more about how planets form around other stars."

Ferellec and colleagues published their work in the journal Monthly Notices of the Royal Astronomical Society on Sept. 7.

Astronomers have witnessed a small, icy body that orbits the sun out beyond Jupiter transforming into a comet, providing a missing link between comets and inert bodies called centaurs.

The object in question is called 450P/LONEOS and is named after the Lowell Observatory survey that found it back in 2004. It is a centaur, which is a breed of inactive body that orbits the sun between Jupiter and Neptune. These objects are thought to have wandered in from the Kuiper Belt beyond Pluto, their paths perhaps perturbed by distant gravitational interactions with the gas giant planets, or even a nudge from a passing star.

Because a given centaur's orbit crosses the path of at least one of Jupiter, Saturn, Uranus and Neptune, a centaur's orbit is unstable over millions of years. Consequently, the giant planets can push them even closer to the sun or kick them out of the solar system entirely.

It has long been suspected that those pushed closer to the sun turn into what are called Jupiter-family comets, which are comets with orbital periods around the sun of less than 20 years and which are influenced by the gravity of Jupiter.

To date, no one has ever seen a centaur turn into a Jupiter-family comet. The orbital period of 450P is currently 22 years, so it isn't a Jupiter-family comet yet, but astronomers led by planetary scientist Charles Schambeau of the University of Central Florida have been observing the onset of comet-like behavior on the centaur. In particular, using the Gemini North telescope in Hawaii they have seen the formation of a cloud of gas and dust called a coma around the solid nucleus of 450P, with this coma brightening in the period between 2019 and 2024, when 450P arrived at perihelion (the closest point to the sun in its orbit).

Should 450P keep up this comet-like behavior and receive one more gravitational nudge from one of the giant planets, then it could finally become a Jupiter-family comet.

"Studying objects like 450P helps us connect different stages of small-body evolution," said Schambeau in a statement. "Centaurs are likely related to trans-Neptunian objects, and some will eventually become short-period comets. By studying their activity, surface properties and volatile [substances with low boiling or sublimation points such as water and carbon dioxide] composition, we can learn how comet nuclei change as they move inward through the solar system, how long they preserve primitive ices and what physical processes turn an otherwise quiet icy body into an active comet."

Using the James Webb Space Telescope (JWST), Schambeau's team analyzed 450P's coma, finding carbon dioxide gas and suggestions of particles of crystalline ice and dust.

Its transition from a centaur into a comet is thought to have resulted from 450P having a date with destiny. By tracking back its orbit to before its 2004 discovery, astronomers found that 450P had come within 2.9 million miles (4.6 million kilometers) of Saturn in 1992. That's pretty close on solar-system scales. The object's gravitational interaction with the ringed planet caused 450P's orbit to significantly shorten so that its perihelion is now at 5.4 astronomical units 506 million miles, or 813 million km), which is only slightly beyond the orbit of Jupiter at 5.2 astronomical units.

Its last perihelion was in August 2024 and, by getting closer to the sun, 450P received substantially more heat than it has in the past.

"That increased solar heating can warm the surface and the subsurface layers of the nucleus," said Schambeau. "As those layers heat up, volatile ices or trapped gases can be released, which can drag dust away from the surface and produce a coma."

The significance of the JWST's discovery of carbon dioxide gas in 450P's burgeoning coma, coupled with the complete absence of water vapor, tells us that it is carbon-dioxide driving the activity on 450P.

"At 450P's distance from the sun, the nucleus is too cold for normal water-ice sublimation to be the main activity source, so detecting carbon dioxide gives us an important clue about what is powering the coma," said Schambeau.

While there is no water vapor, JWST has picked up hints of solid particles of crystalline water-ice.

"The possible crystalline water-ice is also interesting because it suggests that some of the ice in the coma has experienced heating or physical processing, rather than remaining completely unchanged since formation," said Schambeau.

On pristine cometary bodies and Kuiper Belt objects, ice is usually in an amorphous state, meaning the frozen water molecules are not structured or arranged in any particular way, giving the ice a porous composition that allows it to trap pockets of gas. As 450P nears the sun, the extra warmth that it receives causes the amorphous ice to morph into crystalline ice that has a more regular structure. During the transformation the gases escape, dragging dust and ice particles off the surface with them. Therefore, the presence of crystalline ice is telling us that 450P is in the process of being thermally altered from its pristine state that quite possibly harkens back to the birth of the solar system 4.5 billion years ago.

Only a very small fraction of Centaurs have ever shown signs of activity, which makes 450P's recent perihelion a very important one to have studied because it is a rare example of an early stage in a centaur's transition into a comet.

"Centaurs are scientifically important because they are thought to be transitional objects that originated further out in the solar system and are slowly evolving toward becoming Jupiter-family comets," said Schambeau. "In that sense, they give us a way to study relatively primitive material from the outer solar system while it is beginning to respond to stronger solar heating."

The findings have been accepted for future publication in the Planetary Science Journal and is currently available on the arXiv pre-print archive.

Comet 220P/McNaught has already put on an unexpectedly impressive show this summer as two dramatic outbursts of activity caused it to shine 20,000 times brighter than usual. Here's how you can spot the icy interloper before it fades in the coming weeks.

Comet 220P/McNaught orbits the sun once every 5.5-years. It reached perihelion — its closest point to the sun — on June 14. Solar heating typically increases cometary activity by causing volatile ices to turn directly into gas, releasing dust that reflects sunlight.

The comet's most recent perihelion passage was accompanied by two dramatic outbursts that saw its brightness jump to 20,000 times its usual level, making the ordinarily dim comet temporarily visible to stargazers using binoculars, telescopes, or cameras.

Comet 220P/McNaught is expected to dim significantly as it travels farther away from the sun, though it's possible that another outburst could see its brightness increase once more in the coming weeks!

McNaught's has a current brightness, or magnitude of +9.2 according to the Comet Observation Database run by the Crni Vern observatory. That would make it a challenge to spot with a pair of binoculars under less than perfect conditions, but puts it within reach of small telescopes under dark skies, where it mayappear as a faint, diffuse patch against the background stars.

Where can I find Comet 220P/McNaught in early September?

Look east around midnight local time to find the stars of the constellation Taurus rising into the late summer sky. Next, identify the "V" formation of the Hyades open star cluster shining at the heart of the constellation. Comet McNaught can be found close to the magnitude 3.59 binary star system Omicron Tauri, two stars out from the point of the stellar "V".

Comet McNaught will become easier to spot in the dark nights surrounding the new moon phase on Sept. 10-11, which will also present a perfect opportunity for . It'll also make for long- exposure photography.

Osama Fathi captured a gorgeous photo of Comet McNaught shining in the skies above Egypt as a lone Perseid blazed earthward on Aug. 15.

"I spent nearly two hours imaging the comet and the real surprise came when a meteor crossed very close to it in one frame — a wonderful and unexpected moment," Fathi told Space.com in an email. "Comets are exciting because of their unpredictability and I hope 220P continues to surprise observers with changes in its brightness and activity in the coming weeks."

Astrophotographer Dan Bartlett, meanwhile, created this breathtakingly detailed mosaic of Comet McNaught's journey through the constellation Cetus as the icy wanderer glowed in the skies over June Lake, California. The mosaic captures the comet's evolution from Aug. 6-26 as its coma and tail transformed in the wake of its Aug. 5 outburst.

Interested in capturing your own photo of Comet McNaught? Then be sure to read our guide to photographing solar system comets, along with our roundups of the best cameras and lenses for astrophotography.

Editor's Note: If you would like to share your astrophotography with Space.com's readers, then please send your photo(s), comments, and your name and location to spacephotos@space.com.

What a view. Astrophotographers in Namibia have captured a bright green comet soaring overhead in a spectacular new photograph.

What is it?

In this incredible new photograph is the comet 220P/McNaught.

Discovered by Australian astronomer Robert H. McNaught, the comet orbits our sun once every 5.5 years. Back in June, the comet reached perihelion, or the closest point in its orbit around the sun. Around that time, the comet experienced a large outburst, which brightened it about 8,000 times.

The comet brightened back up this August to about 600 times its normal brightness — and it was during this period when astrophotographers Gerald Rhemann and Michael Jäger captured it streaking across the night sky over Namibia.

To capture the moment, the pair used a 12-inch Astrograph telescope with a ZWO ASI 6200 MM Pro camera.

Why is it incredible?

It's not every day you see a comet in the night sky. Even if one is overhead, often they're too tricky or too far away to spot without a telescope, and even then it can be a challenge.

It's also incredible that the moment captured in the new image showcases the comet 220P/McNaught with such spectacular clarity and detail. It must have been something truly special to witness.

While spotting a comet like this might not happen every day, we can sometimes see the debris trailing behind a comet as its tail burns up in our atmosphere. These burnt comet bits are actually the "shooting stars" we see in the night sky during a meteor shower.

Right now, the Perseids meteor shower is on its annual parade across the night sky. This meteor shower is made up of debris shed by the comet Swift-Tuttle as it swoops by on its annual trip across the solar system. Under dark skies, skywatchers can see up to 100 shooting stars thanks to Swift-Tuttle.

A near-Earth object that astronomers believed was an asteroid for nearly three decades has been unmasked as a faint, active comet, revealing a case of cosmic mistaken identity that could help improve planetary defense.

The object, known since its discovery in 1998 as 1998 SH2, appeared to be an ordinary asteroid. It follows a 4.5-year orbit around the sun and showed no obvious signs of cometary activity, such as the glowing coma or tail produced when sunlight vaporizes surface ice.

However, during a close pass about 2 million miles (3 million kilometers) from Earth in August 2025, researchers using NASA's Deep Space Network planetary radar system noticed something unexpected: The object wasn't where orbital predictions said it should be, according to a statement from the space agency. That discrepancy prompted scientists to take a closer look, and what they found surprised them.

Using decades of precision optical astrometry — measurements of the object's position against background stars — researchers found that gravity alone couldn't explain its irregular motion. Instead, they detected tiny nongravitational forces consistent with jets of gas escaping from the object's surface as hidden ice warmed in sunlight.

"After we measured the nongravitational perturbations affecting the motion of 1998 SH2 and recognized they weren't compatible with the object being an asteroid, we suspected the object could be an active comet," Davide Farnocchia, lead author of the study and navigation engineer with NASA's Center for Near-Earth Object Studies at the Jet Propulsion Laboratory, said in the statement.

To test the idea, the team observed the object with the European Southern Observatory's Very Large Telescope in Chile and the Canada-France-Hawaii Telescope atop Mauna Kea. The observations revealed a faint but unmistakable comet tail, confirming the object's true identity.

The discovery earned 1998 SH2 a second designation: P/1998 SH2, officially recognizing it as a comet. Beyond solving the mystery, the finding has important implications for planetary defense.

Unlike rocky asteroids, comets can subtly change course as gas escaping from their surfaces acts like tiny thrusters. Identifying those nongravitational forces allows scientists to more accurately predict an object's future orbit and assess any potential impact risk.

"This work shows the importance of continuously tracking near-Earth objects," Farnocchia said in the statement. "Because of outgassing, the motion of comets is more significantly perturbed than that of asteroids.

"Detecting these perturbations can be an important diagnostic tool for planetary defense that will help understand which objects may be comets rather than asteroids, how their orbits evolve, and how that influences their Earth impact risks."

The study also suggests that 1998 SH2 may not be unique. The researchers noted that analyzing the motions of near-Earth objects with increasingly precise astrometry could reveal more hidden comets that have long been classified as asteroids because they lack obvious tails or glowing comas.

As astronomers continue to monitor the growing population of near-Earth objects, subtle orbital changes may prove just as revealing as spectacular comet tails, uncovering more examples of cosmic mistaken identity while helping scientists better understand which objects pose potential threats to Earth.

Their findings were published July 10 in the journal Nature Astronomy.

More evidence that the interstellar comet 3I/ATLAS is much older than our solar system has come to light, along with clues that it formed on the outskirts of the protoplanetary disk belonging to its parent star long ago.

Earlier this year, researchers led by Martin Cordiner of NASA's Goddard Space Flight Center revealed that data from the James Webb Space Telescope (JWST) suggested that 3I/ATLAS is between 10 and 12 billion years old, based on the ratios of its carbon and deuterium isotopes. This would make it more than twice the age of our 4.6-billion-year-old solar system. Now, new results from the Ultraviolet and Visual Echelle Spectrograph (UVES) on the European Southern Observatory's Very Large Telescope support the JWST observations of carbon isotopes, and also introduce measurements of nitrogen isotopes that arrive at very interesting conclusions.

Isotopes are versions of atomic elements with different numbers of neutrons. For example, carbon-12 contains six protons and six neutrons, while carbon-13 contains six protons and seven neutrons. Meanwhile nitrogen-14 has seven protons and neutrons each, while nitrogen-15 has seven protons and eight neutrons.

These isotopes can form through subtly different processes, at different times and in different locations in the galaxy. The ratio of these isotopes in the gases released by comet 3I/ATLAS into its coma and tail as it neared the sun and grew warmer can therefore tell us much about its origin and history.

Consequently, interstellar objects such as 3I/ATLAS "are sort of fossils from a planetary formation process that happened very far away, but we get the chance to study from much closer," said astronomer Cyrielle Opitom of the University of Edinburgh in a statement.

Opitom led the team who got the chance to observe 3I/ATLAS with the VLT. They found that the ratio of carbon-12 to carbon-13 is higher than is found in comets in our solar system or indeed in the local interstellar medium. Carbon-13 is produced in greater abundances than carbon-12 over time, typically in red giant stars, so for there to be far more carbon-12 than carbon-13 tells us that 3I/ATLAS was born long ago before carbon-13 had a chance to build in abundance across the galaxy. This finding supports the JWST carbon isotope measurements.

Additionally Opitom's team, which was co-led by Jean Manfroid and Damien Hutsemékers of the University of Liège in Belgium, measured a ratio of nitrogen-14 to nitrogen-15 in 3I/ATLAS that is more than twice as large as the value measured in comets native to our solar system. In fact, the ratio is typical of that found on the outer edge of planet-forming discs around young stars, implying 3I/ATLAS formed a long way out from its parent star, perhaps in the equivalent of its Kuiper belt.

"Unlike comets from our solar system, this interstellar visitor carries unusually high carbon and nitrogen isotopic ratios," said team-member Aravind Krishnakumar, who is also of the University of Liège.

The results give us clues to how 3I/ATLAS found itself wandering the space lanes alone for billions of years. Models indicate that migrating giant planets can kick small bodies into interstellar space, but the location of 3I/ATLAS's birth far from that planetary action means that it is quite possible instead that it was snatched from its parent star by the gravity of a passing star and was subsequently hurled into deep space.

The JWST had also previously shown that 3I/ATLAS is rich in carbon monoxide and carbon dioxide relative to water, and also contains unexpectedly high abundances of nickel and iron and a very high abundance of methanol relative to hydrogen cyanide – all of which tells us that 3I/ATLAS formed in an environment with conditions and chemistry notably alien to our own solar system.

Unfortunately similar measurements were not possible with the other two known interstellar objects – 1I/'Oumuamua was not seen to outgas, while 2I/Borisov was too faint. However, 3I/ATLAS is a tantalizing indication that studies of more interstellar objects caught entering our solar system will be able to teach us about planet-forming conditions across both space and time in our Milky Way galaxy.

"3I/ATLAS is a really exciting opportunity to probe the composition of another planetary system, one that formed long before our Sun and solar system even existed," concluded Rosemary Dorsey, an astronomer from the University of Helsinki in Finland.

The findings were published on July 6 in the journal Nature Astronomy.

NASA's James Webb Space Telescope is finding clues that are leading scientists closer to understanding the origins of the interstellar comet 3I/ATLAS.

What is it?

Comet 3I/ATLAS captured the world's attention when it was discovered nearly a year ago on July 1, 2025. The comet was first spotted by the Asteroid Terrestrial-impact Last Alert System (ATLAS), and is only the third interstellar object every discovered.

The comet swooped through our solar system, passing by Earth at a far (and safe) distance on its tour of our cosmic neighborhood. It is on a long trajectory that will take it out of our solar system, never to return.

In observations from the James Webb Space Telescope, scientists were able to look in the direction the comet as it began moving away from the sun in December of last year. While in close proximity to our star, the sun's heat warmed the comet, making it extra bright and easy to observe.

With this view, astronomers were able to calculate some of the ratios of the chemicals present in the comet. This further highlighted that the object is from out of our solar system, as they found ratios of carbon and heavy hydrogen not found in comets in our solar system.

Researchers described their results in a new paper published June 22 in the journal Nature.

Why is it incredible?

Being only the third interstellar object ever found, people were excited about 3I/ATLAS. They were so excited, in fact, that conspiracies about the object sprouted up quickly. Due to it being from outside of our solar system, some claimed that the comet could be some sort of alien spaceship, similar to the initial suspicions about the interstellar object 'Oumuamua found years earlier.

But with new information coming in from space telescopes, and astronomers eager to understand this object better, these clues are leading us closer and closer to the true origins of this strange comet.