News
Scientificult
Ad
Ad
Ad
Tag

University of Oxford

Browsing
Astronomy

3I/ATLAS: newly discovered interstellar object ‘may be oldest comet ever seen’

By
Top view of the Milky Way galaxy showing the estimated orbits of both our Sun and the 3I/ATLAS comet. 3I/ATLAS is shown in red dashed lines, and the Sun is shown in yellow dotted lines. The large extent of 3I’s orbit into the outer thick disk is clear, while the Sun stays nearer the core of the galaxy. M. Hopkins/Ōtautahi-Oxford team. Base map: ESA/Gaia/DPAC, Stefan Payne-Wardenaar, CC-BY-SA 4.0

3I/ATLAS: newly discovered interstellar object ‘may be oldest comet ever seen’

A mystery interstellar object discovered last week is likely to be the oldest comet ever seen – possibly predating our solar system by more than three billion years, researchers say.

The “water ice-rich” visitor, named 3I/ATLAS, is only the third known object from beyond our solar system ever spotted in our cosmic neighbourhood and the first to reach us from a completely different region of our Milky Way galaxy.

It could be more than seven billion years old, according to University of Oxford astronomer Matthew Hopkins – who is discussing his findings at the Royal Astronomical Society’s National Astronomy Meeting 2025 in Durham – and may be the most remarkable interstellar visitor yet.

Unlike the previous two objects to enter our solar system from elsewhere in the cosmos, 3I/ATLAS appears to be travelling on a steep path through the galaxy, with a trajectory that suggests it originated from the Milky Way’s ‘thick disk’ – a population of ancient stars orbiting above and below the thin plane where the Sun and most stars reside.

“All non-interstellar comets such as Halley’s comet formed with our solar system, so are up to 4.5 billion years old,” Hopkins said.

“But interstellar visitors have the potential to be far older, and of those known about so far our statistical method suggests that 3I/ATLAS is very likely to be the oldest comet we have ever seen.”

The object was first spotted on 1 July 2025 by the ATLAS survey telescope in Chile, when it was about 670 million km from the Sun.

Hopkins’ research predicts that, because 3I/ATLAS likely formed around an old, thick-disk star, it should be rich in water ice.

“This is an object from a part of the galaxy we’ve never seen up close before,” said Professor Chris Lintott, co-author of the study and presenter of the BBC’s The Sky at Night.

“We think there’s a two-thirds chance this comet is older than the solar system, and that it’s been drifting through interstellar space ever since.”

As it approaches the Sun, sunlight will heat 3I/ATLAS’s surface and trigger cometary activity, or the outgassing of vapour and dust that creates a glowing coma and tail.

Early observations already suggest the comet is active, and possibly larger than either of its interstellar predecessors, 1I/’Oumuamua (spotted in 2017) and 2I/Borisov (2019).

If confirmed, this could have implications for how many similar objects future telescopes, such as the new Vera C. Rubin Observatory, are likely to detect. It may also provide clues about the role that ancient interstellar comets play in seeding star and planet formation across the galaxy.

“We’re in an exciting time: 3I is already showing signs of activity. The gases that may be seen in the future as 3I is heated by the Sun will test our model,” said co-author Dr Michele Bannister, of the University of Canterbury in New Zealand.

“Some of the biggest telescopes in the world are already observing this new interstellar object – one of them may be able to find out!”

The discovery of 3I caught the team by the surprise. It happened as they were gearing up for the beginning of survey operations with the Vera C. Rubin Observatory, which their model predicts will discover between 5 and 50 interstellar objects.

“The solar system science community was already excited about the potential discoveries Rubin will make in the next 10 years, including an unprecedented number of interstellar objects,” said co-researcher Dr Rosemary Dorsey, of the University of Helsinki.

“The discovery of 3I suggests that prospects for Rubin may now be more optimistic; we may find about 50 objects, of which some would be similar in size to 3I. This week’s news, especially just after the Rubin First Look images, makes the upcoming start of observations all the more exciting.”

The team’s findings come from applying a model developed during Hopkins’ doctoral research, which simulates the properties of interstellar objects based on their orbits and likely stellar origins.

Just a week before the comet’s discovery, Hopkins had defended his thesis, and when 3I/ATLAS was announced, he was set to go on holiday. Instead, he found himself comparing real-time data to his predictions.

“Rather than the quiet Wednesday I had planned, I woke up to messages like ‘3I!!!!!!!!!!’,” said Hopkins. “It’s a fantastic opportunity to test our model on something brand new and possibly ancient.”

The researchers’ model, dubbed the Ōtautahi–Oxford Model, marks the first real-time application of predictive modelling to an interstellar comet.

For those keen to catch a glimpse of 3I/ATLAS, it should be visible through a reasonably-sized amateur telescope in late 2025 and early 2026.

 

Press release from the Royal Astronomical Society

Keep Reading
By
Astronomy

Hubble’s observations of Jupiter’s Great Red Spot, collected between December 2023 to March 2024

By
Eight Hubble images showing Jupiter’s Great Red Spot. The GRS appears as a bright red oval in the middle of cream-coloured cloud bands. The images trace changes in the GRS’s size, shape, brightness, colour, and twisting, over a period of 90 days between December 2023 and March 2024.

Hubble’s new observations of Jupiter’s Great Red Spot, collected over 90 days between December 2023 to March 2024

Astronomers have observed Jupiter’s legendary Great Red Spot (GRS), an anticyclone large enough to swallow Earth, for at least 150 years. But there are always new surprises – especially when the NASA/ESA Hubble Space Telescope takes a close-up look at it.

Eight Hubble images showing Jupiter’s Great Red Spot. The GRS appears as a bright red oval in the middle of cream-coloured cloud bands. The images trace changes in the GRS’s size, shape, brightness, colour, and twisting, over a period of 90 days between December 2023 and March 2024.
Using Hubble Space Telescope data spanning approximately 90 days (between December 2023 and March 2024) when the giant planet Jupiter was approximately 740 million kilometres from the Sun, astronomers measured the Great Red Spot’s size, shape, brightness, colour, and vorticity over one full oscillation cycle. The data reveal that the Great Red Spot is not as stable as it might look. It was observed going through an oscillation in its elliptical shape, jiggling like a bowl of gelatin. The cause of the 90-day oscillation is unknown.
Credit: NASA, ESA, A. Simon (GSFC)

Hubble’s new observations of the famous red storm, collected over 90 days between December 2023 to March 2024, reveal that the GRS is not as stable as it might look. The recent data show the GRS jiggling like a bowl of gelatin. The combined Hubble images allowed astronomers to assemble a time-lapse movie of the squiggly behaviour of the GRS.

“While we knew its motion varies slightly in its longitude, we didn’t expect to see the size oscillate. As far as we know, it’s not been identified before,” said Amy Simon of NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “This is really the first time we’ve had the proper imaging cadence of the GRS. With Hubble’s high resolution we can say that the GRS is definitively squeezing in and out at the same time as it moves faster and slower. That was very unexpected, and at present there are no hydrodynamic explanations.”

Hubble monitors Jupiter and the other outer solar system planets every year through the Outer Planet Atmospheres Legacy program (OPAL) led by Simon, but these observations were from a program dedicated to the GRS. Understanding the mechanisms of the largest storms in the solar system puts the theory of hurricanes on Earth into a broader cosmic context, which might be applied to better understanding the meteorology on planets around other stars.

Eight images of the giant planet Jupiter spanning approximately 90 days between December 2023 and March 2024. The planet appears striped, with brown and white horizontal bands of clouds. These stripes are called belts (sinking air) and bands (rising air). The polar regions appear more mottled.
Using Hubble Space Telescope data spanning approximately 90 days (between December 2023 and March 2024) when the giant planet Jupiter was approximately 740 million kilometres from the Sun, astronomers measured the Great Red Spot’s size, shape, brightness, colour, and vorticity over a full oscillation cycle. The data reveal that the Great Red Spot is not as stable as it might look. It was observed going through an oscillation in its elliptical shape, jiggling like a bowl of gelatin. The cause of the 90-day oscillation is unknown. The observation is part of the Outer Planet Atmospheres Legacy program (OPAL).
Credit: NASA, ESA, A. Simon (GSFC)

Simon’s team used Hubble to zoom in on the GRS for a detailed look at its size, shape, and any subtle colour changes.

“When we look closely, we see a lot of things are changing from day to day,” said Simon.

This includes ultraviolet-light observations showing that the distinct core of the storm gets brightest when the GRS is at its largest size in its oscillation cycle. This indicates less haze absorption in the upper atmosphere.

“As it accelerates and decelerates, the GRS is pushing against the windy jet streams to the north and south of it,” said co-investigator Mike Wong of the University of California at Berkeley. “It’s similar to a sandwich where the slices of bread are forced to bulge out when there’s too much filling in the middle.” 

Wong contrasted this to Neptune, where dark spots can drift wildly in latitude without strong jet streams to hold them in place. Jupiter’s Great Red Spot has been held at a southern latitude, trapped between the jet streams, for the extent of Earth-bound telescopic observations.

The team has continued watching the GRS shrink since the OPAL program began 10 years ago. They predict it will keep shrinking before taking on a stable, less-elongated, shape. 

“Right now it’s over-filling its latitude band relative to the wind field. Once it shrinks inside that band the winds will really be holding it in place,” said Simon.

The team predicts that the GRS will probably stabilise in size, but for now Hubble only observed it for one oscillation cycle.

“This is a great example of the power of Hubble’s exquisite imaging for monitoring of the atmospheres of the outer planets,” said co-investigator Patrick Irwin of the University of Oxford. “With these new observations we were able to study the dynamics and evolution of the GRS over three months, building on our understanding of the long-term properties of Jupiter obtained from the OPAL program over the past decade.”

The researchers hope that in the future other high-resolution images from Hubble might identify other Jovian parameters that indicate the underlying cause of the oscillation.

 

Press release from ESA Hubble

Keep Reading
By
Astronomy

Galaxy GS-NDG-9422 (9422): Webb finds potential missing link to first stars

By
Galaxy GS-NDG-9422; 9422 A black background sprinkled with small, colourful galaxies in orange, blue, and white. On the left, a third of the way down from the top of the image, a very faint dot of a galaxy is outlined with a white square and pulled out in a graphic to be shown magnified. In the pullout square to the right, the galaxy is a hazy white dot edged in orange, with faint blue projections opposite each other at the 11 o’clock and 5 o’clock positions.

Galaxy GS-NDG-9422 (9422): Webb finds potential missing link to first stars

Looking deep into the early universe with the NASA/ESA/CSA James Webb Space Telescope, astronomers have found something unprecedented: a galaxy with an odd light signature, which they attribute to its gas outshining its stars.

A black background sprinkled with small, colourful galaxies in orange, blue, and white. On the left, a third of the way down from the top of the image, a very faint dot of a galaxy is outlined with a white square and pulled out in a graphic to be shown magnified. In the pullout square to the right, the galaxy is a hazy white dot edged in orange, with faint blue projections opposite each other at the 11 o’clock and 5 o’clock positions.
The galaxy GS-NDG-9422 may easily have gone unnoticed. However, what appears as a faint blur in this James Webb Space Telescope image may actually be a groundbreaking discovery that points astronomers on a new path of understanding galaxy evolution in the early universe.
Detailed information on the galaxy’s chemical makeup, captured by Webb’s NIRSpec (Near-Infrared Spectrograph) instrument, indicates that the light we see in this image is coming from the galaxy’s hot gas, rather than its stars. That is the best explanation astronomers have discovered so far to explain the unexpected features in the light spectrum. They think that the galaxy’s stars are so extremely hot and massive that they are heating up the nebular gas in the galaxy to more than 80,000 degrees Celsius, allowing it to shine even brighter in near-infrared light than the stars themselves.
The authors of a new study on Webb’s observations of the galaxy think GS-NDG-9422 may represent a never-before-seen phase of galaxy evolution in the early universe, within the first billion years after the big bang. Their task now is to see if they can find more galaxies displaying the same features.
Credit: NASA, ESA, CSA, STScI, A. Cameron (University of Oxford)

Found approximately one billion years after the big bang, galaxy GS-NDG-9422 (9422) may be a missing-link phase of galactic evolution between the universe’s first stars and familiar, well-established galaxies.

“My first thought in looking at the galaxy’s spectrum was, ‘that’s weird,’ which is exactly what the Webb telescope was designed to reveal: totally new phenomena in the early universe that will help us understand how the cosmic story began,” said lead researcher Alex Cameron of the University of Oxford in the United Kingdom.

Cameron reached out to colleague Harley Katz, a theorist, to discuss the strange data. Working together, their team found that computer models of cosmic gas clouds heated by very hot, massive stars, to an extent that the gas shone brighter than the stars, was nearly a perfect match to Webb’s observations.

“It looks like these stars must be much hotter and more massive than what we see in the local universe, which makes sense because the early universe was a very different environment,” said Katz, of Oxford and the University of Chicago, U.S.A.

In the local universe, typical hot, massive stars have a temperature ranging between 40,000 to 50,000 degrees Celsius. According to the team, galaxy 9422 has stars hotter than 80,000 degrees Celsius.

The research team suspects that the galaxy is in the midst of a brief phase of intense star formation inside a cloud of dense gas that is producing a large number of massive, hot stars. The gas cloud is being hit with so many photons of light from the stars that it is shining extremely brightly.

In addition to its novelty, nebular gas outshining stars is intriguing because it is something predicted in the environments of the universe’s first generation of stars, which astronomers classify as Population III stars.

“We know that this galaxy does not have Population III stars, because the Webb data shows too much chemical complexity. However, its stars are different from what we are familiar with – the exotic stars in this galaxy could be a guide for understanding how galaxies transitioned from primordial stars to the types of galaxies we already know,” said Katz.

At this point, galaxy 9422 is one example of this phase of galaxy development, so there are still many questions to be answered. Are these conditions common in galaxies at this time period, or a rare occurrence? What more can they tell us about even earlier phases of galaxy evolution? Cameron, Katz, and their research colleagues are actively identifying more galaxies to add to this population to better understand what was happening in the universe within the first billion years after the big bang.

“It’s a very exciting time, to be able to use the Webb telescope to explore this time in the universe that was once inaccessible,” Cameron said. “We are just at the beginning of new discoveries and understanding.”

The research paper is published in the Monthly Notices of the Royal Astronomical Society.

A black background sprinkled with small, colourful galaxies in orange, blue, and white. On the left, a third of the way down from the top of the image, a very faint dot of a galaxy is outlined with a white square and pulled out in a graphic to be shown magnified. In the pullout square to the right, the galaxy is a hazy white dot edged in orange, with faint blue projections opposite each other at the 11 o’clock and 5 o’clock positions.
The galaxy GS-NDG-9422 may easily have gone unnoticed. However, what appears as a faint blur in this James Webb Space Telescope image may actually be a groundbreaking discovery that points astronomers on a new path of understanding galaxy evolution in the early universe.
Detailed information on the galaxy’s chemical makeup, captured by Webb’s NIRSpec (Near-Infrared Spectrograph) instrument, indicates that the light we see in this image is coming from the galaxy’s hot gas, rather than its stars. That is the best explanation astronomers have discovered so far to explain the unexpected features in the light spectrum. They think that the galaxy’s stars are so extremely hot and massive that they are heating up the nebular gas in the galaxy to more than 80,000 degrees Celsius, allowing it to shine even brighter in near-infrared light than the stars themselves.
The authors of a new study on Webb’s observations of the galaxy think GS-NDG-9422 may represent a never-before-seen phase of galaxy evolution in the early universe, within the first billion years after the big bang. Their task now is to see if they can find more galaxies displaying the same features.
Credit: NASA, ESA, CSA, STScI, A. Cameron (University of Oxford)

 

Press release from ESA Webb.

Keep Reading
By
Astronomy

Webb Reveals an Exoplanet Atmosphere as Never Seen Before

By
Webb Reveals an Exoplanet Atmosphere as Never Seen Before WASP-39

Webb Reveals an Exoplanet Atmosphere as Never Seen Before

The NASA/ESA/CSA James Webb Space Telescope just scored another first: a molecular and chemical profile of a distant world’s skies.

Webb Reveals an Exoplanet Atmosphere as Never Seen Before WASP-39
This image shows an artist’s impression of the planet WASP-39 b and its star. The planet has a fuzzy orange-blue atmosphere with hints of longitudinal cloud bands below. The left quarter of the planet (the side facing the star) is lit, while the rest is in shadow. The star is bright yellowish-white, with no clear features. Credit: NASA, ESA, CSA, J. Olmsted (STScI)

The NASA/ESA/CSA James Webb Space Telescope just scored another first: a molecular and chemical portrait of a distant world’s skies. While Webb and other space telescopes, including the NASA/ESA Hubble Space Telescope, have previously revealed isolated ingredients of this heated planet’s atmosphere, the new readings provide a full menu of atoms, molecules, and even signs of active chemistry and clouds. The latest data also give a hint of how these clouds might look up close: broken up rather than as a single, uniform blanket over the planet.

The telescope’s array of highly sensitive instruments was trained on the atmosphere of WASP-39 b, a “hot Saturn” (a planet about as massive as Saturn but in an orbit tighter than Mercury) orbiting a star some 700 light-years away. This Saturn-sized exoplanet was one of the first examined by the NASA/ESA/CSA James Webb Space Telescope when it began regular science operations. The results have excited the exoplanet science community. Webb’s exquisitely sensitive instruments have provided a profile of WASP-39 b’s atmospheric constituents and identified a plethora of contents, including water, sulphur dioxide, carbon monoxide, sodium and potassium.

The findings bode well for the capability of Webb’s instruments to conduct the broad range of investigations of exoplanets — planets around other stars — hoped for by the science community. That includes probing the atmospheres of smaller, rocky planets like those in the TRAPPIST-1 system.

“We observed the exoplanet with several instruments that together cover a broad swath of the infrared spectrum and a panoply of chemical fingerprints inaccessible until JWST,” said Natalie Batalha, an astronomer at the University of California, Santa Cruz, who contributed to and helped coordinate the new research. “Data like these are a game changer.”

The suite of discoveries is detailed in a set of five new scientific papers, three of which are in press and two of which are under review. Among the unprecedented revelations is the first detection in an exoplanet atmosphere of sulphur dioxide, a molecule produced from chemical reactions triggered by high-energy light from the planet’s parent star. On Earth, the protective ozone layer in the upper atmosphere is created in a similar way.

“This is the first time we have seen concrete evidence of photochemistry — chemical reactions initiated by energetic stellar light — on exoplanets,” said Shang-Min Tsai, a researcher at the University of Oxford in the United Kingdom and lead author of the paper explaining the origin of sulphur dioxide in WASP-39 b’s atmosphere. “I see this as a really promising outlook for advancing our understanding of exoplanet atmospheres with [this mission].”

This led to another first: scientists applying computer models of photochemistry to data that require such physics to be fully explained. The resulting improvements in modelling will help build the technological know-how needed to interpret potential signs of habitability in the future.

“Planets are sculpted and transformed by orbiting within the radiation bath of the host star,” Batalha said. “On Earth, those transformations allow life to thrive.”

The planet’s proximity to its host star — eight times closer than Mercury is to our Sun — also makes it a laboratory for studying the effects of radiation from host stars on exoplanets. Better knowledge of the star-planet connection should bring a deeper understanding of how these processes affect the diversity of planets observed in the galaxy.

Other atmospheric constituents detected by the Webb telescope include sodium (Na), potassium (K), and water vapour (H2O), confirming previous space- and ground-based telescope observations as well as finding additional fingerprints of water, at these longer wavelengths, that haven’t been seen before.

Webb also saw carbon dioxide (CO2) at higher resolution, providing twice as much data as reported from its previous observations. Meanwhile, carbon monoxide (CO) was detected, but obvious signatures of both methane (CH4) and hydrogen sulphide (H2S) were absent from the Webb data. If present, these molecules occur at very low levels.

To capture this broad spectrum of WASP-39 b’s atmosphere, an international team numbering in the hundreds independently analysed data from four of the Webb telescope’s finely calibrated instrument modes.

“We had predicted what [the telescope] would show us, but it was more precise, more diverse and more beautiful than I think I actually believed it would be,” said Hannah Wakeford, an astrophysicist at the University of Bristol in the United Kingdom who investigates exoplanet atmospheres.

Having such a complete roster of chemical ingredients in an exoplanet atmosphere also gives scientists a glimpse of the abundance of different elements in relation to each other, such as the carbon-to-oxygen or potassium-to-oxygen ratios. That in turn provides insight into how this planet — and perhaps others — formed out of the disc of gas and dust surrounding the parent star in its younger years.

WASP-39 b’s chemical inventory suggests a history of smashups and mergers of smaller bodies called planetesimals to create an eventual goliath of a planet.

“The abundance of sulphur [relative to] hydrogen indicated that the planet presumably experienced significant accretion of planetesimals that can deliver [these ingredients] to the atmosphere,” said Kazumasa Ohno, a UC Santa Cruz exoplanet researcher who worked on Webb data. “The data also indicates that the oxygen is a lot more abundant than the carbon in the atmosphere. This potentially indicates that WASP-39 b originally formed far away from the central star.

By precisely revealing the details of an exoplanet atmosphere, the Webb telescope’s instruments performed well beyond scientists’ expectations — and promise a new phase of exploration of the broad variety of exoplanets in the galaxy.

“We are going to be able to see the big picture of exoplanet atmospheres,” said Laura Flagg, a researcher at Cornell University and a member of the international team. “It is incredibly exciting to know that everything is going to be rewritten. That is one of the best parts of being a scientist.”

More information

Webb is the largest, most powerful telescope ever launched into space. Under an international collaboration agreement, ESA provided the telescope’s launch service, using the Ariane 5 launch vehicle. Working with partners, ESA was responsible for the development and qualification of Ariane 5 adaptations for the Webb mission and for the procurement of the launch service by Arianespace. ESA also provided the workhorse spectrograph NIRSpec and 50% of the mid-infrared instrument MIRI, which was designed and built by a consortium of nationally funded European Institutes (The MIRI European Consortium) in partnership with JPL and the University of Arizona.

Webb is an international partnership between NASA, ESA and the Canadian Space Agency (CSA).

 

Press release from ESA Webb

Keep Reading
By