Webb studies moon-forming disc around massive planet CT Cha B
The disc offers insight into how the moons of solar system gas giants like Jupiter might have formed.
The NASA/ESA/CSA James Webb Space Telescope has provided the first direct measurements of the chemical and physical properties of a potential moon-forming disc encircling a large exoplanet. The carbon-rich disc surrounding the world called CT Cha B, which is located 625 light years away from Earth, is a possible construction yard for moons, although no moons are detected in the Webb data.
Our Solar System contains eight major planets, and more than 400 known moons orbiting six of these planets. Where did they all come from? There are multiple formation mechanisms. The case for large moons, like the four Galilean satellites around Jupiter, is that they condensed out of a dust and gas disc encircling the planet when it formed. But that would have happened over 4 billion years ago, and there is scant forensic evidence today.
Webb has now provided the first direct view of material in a disc around a large exoplanet. An international team of astronomers have uncovered a carbon-rich disc encircling the world called CT Cha b, which is located 625 light-years away from Earth.
The young star the planet orbits is only 2 million years old and still accreting circumstellar material. However, the circumplanetary disc discovered by Webb is not part of the larger accretion disc around the central star. The two objects are 74 billion kilometres apart.
Observing planet and moon formation is fundamental to understanding the evolution of planetary systems across our galaxy. Moons likely outnumber planets, and some might be habitats for life as we know it. But we are now only entering an era where we can witness their formation.
This discovery fosters a better understanding of planet and moon formation, say researchers. Webb’s data is invaluable for making comparisons to our Solar System’s birth over 4 billion years ago.
“We can see evidence of the disc around the companion, and we can study the chemistry for the first time. We’re not just witnessing moon formation – we’re also witnessing this planet’s formation,” said co-lead author Sierra Grant of the Carnegie Institution for Science in Washington, D.C., USA.
“We are seeing what material is accreting to build the planet and moons,” added main lead author Gabriele Cugno of the University of Zurich in Switzerland and member of the National Centre of Competence in Research PlanetS.
Dissecting starlight
Infrared observations of CT Cha b were made with Webb’s MIRI (Mid-Infrared Instrument) using its medium resolution spectrograph. An initial look into Webb’s archival data revealed signs of molecules within the circumplanetary disc, which motivated a deeper dive into the data. Because the planet’s faint signal is buried in the glare of the host star, the researchers had to disentangle the light of the star from the planet using high-contrast methods.
“We saw molecules at the location of the planet, and so we knew that there was stuff in there worth digging for and spending a year trying to tease out of the data. It really took a lot of perseverance,” said Grant.
Ultimately, the team discovered seven carbon-bearing molecules within the planet’s disc, including acetylene (C2H2) and benzene (C6H6). This carbon-rich chemistry is in stark contrast to the chemistry seen in the disc around the host star, where the researchers found water but no carbon. The difference between the two discs offers evidence for their rapid chemical evolution over only 2 million years.
Genesis of moons
A circumplanetary disc of debris has long been hypothesized as the birthplace of Jupiter’s four major moons. These Galilean satellites must have condensed out of such a flattened disc billions of years ago, as evident in their co-planar orbits about Jupiter. The two outermost Galilean moons, Ganymede and Callisto, are 50% water ice. But they presumably have rocky cores, perhaps made of carbon or silicon.
“We want to learn more about how our Solar System formed moons. This means that we need to look at other systems that are still under construction. We’re trying to understand how it all works,” said Cugno. “How do these moons come to be? What are the ingredients? What physical processes are at play, and over what timescales? Webb allows us to witness the drama of moon formation and investigate these questions observationally for the first time.”
In the coming year, the team will use Webb to perform a comprehensive survey of similar objects to better understand the diversity of physical and chemical properties in the discs around young planets.
The James Webb Space Telescope studies the potential moon-forming disc around the massive exoplanet CT Cha B. An artistic rendering of a dust and gas disc encircling the young exoplanet, CT Cha b, 625 light-years from Earth. Spectroscopic data from the NASA/ESA/CSA James Webb Space Telescope suggest the disc contains the raw materials for moon formation. The planet appears at lower right, while its host star and surrounding protoplanetary disc are visible in the background. Credit: NASA, ESA, CSA, STScI, G. Cugno (University of Zürich, NCCR PlanetS), S. Grant (Carnegie Institution for Science), J, Olmsted (STScI), L. Hustak (STScI)
Bibliographic information:
Gabriele Cugno and Sierra L. Grant 2025, ApJL991 L46, DOI: 10.3847/2041-8213/ae0290
Hubble sees white dwarf eating piece of Pluto-like object: a new study reports the accretion of an icy extrasolar planetesimal on to WD 1647+375
In our nearby stellar neighbourhood, a burned-out star is snacking on a fragment of a Pluto-like object. With its unique ultraviolet capability, only the NASA/ESA Hubble Space Telescope could identify that this meal is taking place.
The stellar remnant is a white dwarf about half the mass of our Sun, but that is densely packed into a body about the size of Earth. Scientists think the dwarf’s immense gravity pulled in and tore apart an icy Pluto analogue from the system’s own version of the Kuiper Belt, an icy ring of debris that encircles our Solar System. The findings were reported on 18 September 2025 in the Monthly Notices of the Royal Astronomical Society.
An international team of astronomers were able to determine this carnage by analysing the chemical composition of the doomed object as its pieces fell onto the white dwarf. In particular, they detected “volatiles” (substances with low boiling points) including carbon, sulphur, nitrogen, and a high oxygen content that suggests the strong presence of water.
“We were surprised,” said Snehalata Sahu of the University of Warwick in the United Kingdom. Sahu led the data analysis of a Hubble survey of white dwarfs. “We did not expect to find water or other icy content. This is because the comets and Kuiper Belt-like objects are thrown out of their planetary systems early, as their stars evolve into white dwarfs. But here, we are detecting this very volatile-rich material. This is surprising for astronomers studying white dwarfs as well as exoplanets, planets outside our Solar System.”
Only with Hubble
Using Hubble’s Cosmic Origins Spectrograph, the team found that the fragments were composed of nearly two thirds water ice. The fact that they detected so much ice meant that the pieces were part of a very massive object that formed far out in the star system’s icy Kuiper Belt analogue. Using Hubble data, scientists calculated that the object was bigger than typical comets and may be a fragment of an exo-Pluto.
They also detected a large fraction of nitrogen – the highest ever detected in white dwarf debris systems.
“We know that Pluto’s surface is covered with nitrogen ices,” said Sahu. “We think that the white dwarf accreted fragments of the crust and mantle of a dwarf planet.”
Accretion of these volatile-rich objects by white dwarfs is very difficult to detect in visible light. These volatile elements can only be detected with Hubble’s unique ultraviolet light sensitivity. In optical light, the white dwarf would appear ordinary.
About 260 light-years away, the white dwarf is a relatively close cosmic neighbor. In the past, when it was a Sun-like star, it would have been expected to host planets and an analogue to our Kuiper Belt.
Like seeing our Sun in the future
Billions of years from now, when our Sun burns out and collapses to a white dwarf, Kuiper Belt objects will be pulled in by the stellar remnant’s immense gravity.
“These planetesimals will then be disrupted and accreted,” said Sahu. “If an alien observer looks into our Solar System in the far future, they might see the same kind of remains we see today around this white dwarf.”
The team hopes to use the NASA/ESA/CSA James Webb Space Telescope to detect molecular features of volatiles such as water vapour and carbonates by observing this white dwarf in infrared light. By further studying white dwarfs, scientists can better understand the frequency and composition of these volatile-rich accretion events.
Sahu is also following the recent discovery of the interstellar comet 3I/ATLAS. She is eager to learn its chemical composition, especially its fraction of water.
“These types of studies will help us learn more about planet formation. They can also help us understand how water is delivered to rocky planets,” said Sahu.
Boris Gänsicke, of the University of Warwick and a visitor at Spain’s Instituto de Astrofisica de Canarias, was the principal investigator of the Hubble program that led to this discovery.
“We observed over 500 white dwarfs with Hubble. We’ve already learned so much about the building blocks and fragments of planets, but I’ve been absolutely thrilled that we now identified a system that resembles the objects in the frigid outer edges of our solar system,” said Gänsicke. “Measuring the composition of an exo-Pluto is an important contribution toward our understanding of the formation and evolution of these bodies.”
Thanks to the Hubble Space Telescope, a new study reports the accretion of an icy extrasolar planetesimal on to white dwarf WD 1647+375. This artist’s concept shows a white dwarf surrounded by a large debris disc. Debris from pieces of a captured, Pluto-like object is falling onto the white dwarf. Credit: T. Pyle (Caltech, NASA’s Jet Propulsion Laboratory)
Bibliographic information:
Snehalata Sahu, Boris T Gänsicke, Jamie T Williams, Detlev G Koester, Jay Farihi, Steven J Desch, Nicola Pietro Gentile Fusillo, Dimitri Veras, Sean N Raymond, Maria Teresa Belmonte, Discovery of an icy and nitrogen-rich extrasolar planetesimal, Monthly Notices of the Royal Astronomical Society, Volume 543, Issue 1, October 2025, Pages 223–232, https://doi.org/10.1093/mnras/staf1424
Webb narrows atmospheric possibilities for Earth-sized exoplanet TRAPPIST-1 d
The exoplanet TRAPPIST-1 d intrigues astronomers looking for possibly habitable worlds beyond our solar system because it is similar in size to Earth, rocky, and resides in an area around its star where liquid water on its surface is theoretically possible. But according to a new study using data from the NASA/ESA/CSA James Webb Space Telescope, it does not have an Earth-like atmosphere.
A protective atmosphere, a friendly Sun, and lots of liquid water — Earth is a special place. Using the unprecedented capabilities of the Webb, astronomers are on a mission to determine just how special, and rare, our home planet is. Can this temperate environment exist elsewhere, even around a different type of star? The TRAPPIST-1 system provides a tantalizing opportunity to explore this question, as it contains seven Earth-sized worlds orbiting the most common type of star in the galaxy: a red dwarf.
“Ultimately, we want to know if something like the environment we enjoy on Earth can exist elsewhere, and under what conditions. While the James Webb Space Telescope is giving us the ability to explore this question in Earth-sized planets for the first time, at this point we can rule out TRAPPIST-1 d from a list of potential Earth twins or cousins,”
said Caroline Piaulet-Ghorayeb of the University of Chicago and Trottier Institute for Research on Exoplanets (IREx) at Université de Montréal, lead author of the study published in The Astrophysical Journal.
Planet TRAPPIST-1 d
The TRAPPIST-1 system is located 40 light-years away and was revealed as the record-holder for most Earth-sized rocky planets around a single star in 2017, thanks to data from NASA’s retired Spitzer Space Telescope and other observatories. Due to that star being a dim, relatively cold red dwarf, the “habitable zone” – where the planet’s temperature may be just right, such that liquid surface water is possible – lies much closer to the star than in our solar system. TRAPPIST-1 d, the third planet from the red dwarf star, lies on the cusp of that temperate zone, yet its distance to its star is only 2 percent of Earth’s distance from the Sun. TRAPPIST-1 d completes an entire orbit around its star, its year, in only four Earth days.
Webb’s NIRSpec (Near-Infrared Spectrograph) instrument did not detect molecules from TRAPPIST-1 d that are common in Earth’s atmosphere, like water, methane, or carbon dioxide. However, Piaulet-Ghorayeb outlined several possibilities for the exoplanet that remain open for follow-up study.
“There are a few potential reasons why we don’t detect an atmosphere around TRAPPIST-1 d. It could have an extremely thin atmosphere that is difficult to detect, somewhat like Mars. Alternatively, it could have very thick, high-altitude clouds that are blocking our detection of specific atmospheric signatures — something more like Venus. Or, it could be a barren rock, with no atmosphere at all,” Piaulet-Ghorayeb said.
The star TRAPPIST-1
No matter what the case may be for TRAPPIST-1 d, it’s tough being a planet in orbit around a red dwarf star. TRAPPIST-1, the host star of the system, is known to be volatile, often releasing flares of high-energy radiation with the potential to strip off the atmospheres of its small planets, especially those orbiting most closely. Nevertheless, scientists are motivated to seek signs of atmospheres on the TRAPPIST-1 planets because red dwarf stars are the most common stars in our galaxy. If planets can hold on to an atmosphere here, under waves of harsh stellar radiation, they could, as the saying goes, make it anywhere.
“Webb’s sensitive infrared instruments are allowing us to delve into the atmospheres of these smaller, colder planets for the first time,” said Björn Benneke of IREx at Université de Montréal, a co-author of the study. “We’re really just getting started using Webb to look for atmospheres on Earth-sized planets, and to define the line between planets that can hold onto an atmosphere, and those that cannot.”
The outer TRAPPIST-1 planets
Webb observations of the outer TRAPPIST-1 planets are ongoing, which hold both potential and peril. On the one hand, Benneke said, planets e, f, g, and h may have better chances of having atmospheres because they are further away from the energetic eruptions of their host star. However, their distance and colder environment will make atmospheric signatures more difficult to detect, even with Webb’s infrared instruments.
“All hope is not lost for atmospheres around the TRAPPIST-1 planets,” Piaulet-Ghorayeb said. “While we didn’t find a big, bold atmospheric signature at planet d, there is still potential for the outer planets to be holding onto a lot of water and other atmospheric components.” “Our detective work is just beginning. While TRAPPIST-1 d may prove a barren rock illuminated by a cruel red star, the outer planets TRAPPIST-1e, f, g, and h, may yet possess thick atmospheres,” added Ryan MacDonald, a co-author of the paper, now at the University of St Andrews in the United Kingdom, and previously at the University of Michigan. “Thanks to Webb we now know that TRAPPIST-1 d is a far cry from a hospitable world. We’re learning that the Earth is even more special in the cosmos.”
The James Webb Space Telescope narrows atmospheric possibilities for Earth-sized rocky exoplanet TRAPPIST-1 d. This artist’s concept depicts planet TRAPPIST-1 d passing in front of its turbulent star, with other members of the closely packed system shown in the background. The TRAPPIST-1 system is intriguing to scientists for a few reasons. Not only does the system have seven Earth-sized rocky worlds, but its star is a red dwarf, the most common type of star in the Milky Way galaxy. If an Earth-sized world can maintain an atmosphere here, and thus have the potential for liquid surface water, the chance of finding similar worlds throughout the galaxy is much higher. In studying the TRAPPIST-1 planets, scientists are determining the best methods for separating starlight from potential atmospheric signatures in data from the NASA/ESA/CSA James Webb Space Telescope. The star TRAPPIST-1’s variability, with frequent flares, provides a challenging testing ground for these methods. Credit: NASA, ESA, CSA, J. Olmsted (STScI)
Webb captures evidence of a lightweight planet around TWA 7
Astronomers using the NASA/ESA/CSA James Webb Space Telescope have captured compelling evidence of a planet with a mass similar to Saturn orbiting the young nearby star TWA 7. If confirmed, this would represent Webb’s first direct image discovery of a planet, and the lightest planet ever seen with this technique.
The international team, led by Dr. Anne-Marie Lagrange, CNRS researcher at the Observatoire de Paris-PSL and Université Grenoble Alpes in France, detected a faint infrared source in the disc of debris surrounding TWA 7 using JWST’s Mid-Infrared Instrument (MIRI) and its coronagraph. The source is located about 1.5 arcseconds from the star on the sky which, at the distance of TWA7, is roughly fifty times the distance of the Earth to the Sun. This matches the expected position of a planet that would explain key features seen in the debris disc.
Using the coronagraph on Webb’s Mid-Infrared Instrument (MIRI) on 21 June 2024, the team carefully suppressed the bright glare of the host star to reveal faint nearby objects. This technique, called high-contrast imaging, enables astronomers to directly detect planets that would otherwise be lost in the overwhelming light from their host star. After subtracting residual starlight using advanced image processing, a faint infrared source was revealed near TWA 7, distinguishable from background galaxies or Solar System objects. The source is located in a gap in one of three dust rings that were discovered around TWA 7 by previous ground-based observations. Its brightness, colour, distance from the star, and position within the ring are consistent with theoretical predictions for a young, cold, Saturn-mass planet sculpting the surrounding debris disc.
“Our observations reveal a strong candidate for a planet shaping the structure of the TWA 7 debris disc, and its position is exactly where we expected to find a planet of this mass,”said Dr. Lagrange.
“This observatory enables us to capture images of planets with masses similar to those in the solar system, which represents an exciting step forward in our understanding of planetary systems, including our own,”
added co-author Mathilde Malin of Johns Hopkins University and the Space Telescope Science Institute in Baltimore.
Initial analysis suggests that the object — referred to as TWA 7b — could be a young, cold planet with a mass around 0.3 times that of Jupiter (~100 Earth masses) and a temperature near 320 Kelvin (roughly 47 degrees Celsius). Its location aligns with a gap in the disc, hinting at a dynamic interaction between the planet and its surroundings.
Debris discs filled with dust and rocky material are found around both young and older stars, although they are more easily detected around younger stars as they are brighter. They often feature visible rings or gaps, thought to be created by planets that have formed around the star, but such a planet has yet to be detected within a debris disc. Once verified, this discovery would mark the first time a planet has been directly associated with sculpting a debris disc and could offer the first observational hint of a trojan disc — a collection of dust trapped in the planet’s orbit.
TWA 7, also known as CE Antliae, is a young (~6.4 million years old) M-type star located about 111 light-years away in the TW Hydrae association. Its nearly face-on disc made it an ideal target for Webb’s high-sensitivity mid-infrared observations.
The findings highlight Webb’s ability to explore previously unseen, low-mass planets around nearby stars. Ongoing and future observations will aim to better constrain the properties of the candidate, verify its planetary status, and deepen our understanding of planet formation and disc evolution in young systems.This preliminary result showcases the exciting new frontier that JWST is opening for exoplanet discovery and characterisation.
These observations were taken as part of the Webb observing programme #3662. The results have been published today in Nature.
Astronomers using the NASA/ESA/CSA James Webb Space Telescope have captured compelling evidence of a planet with a mass similar to Saturn orbiting the young nearby star TWA 7. If confirmed, this would represent Webb’s first direct image discovery of a planet, and the lightest planet ever seen with this technique. Using the coronagraph on Webb’s Mid-Infrared Instrument (MIRI) on 21 June 2024, the team carefully suppressed the bright glare of the host star to reveal faint nearby objects. This technique, called high-contrast imaging, enables astronomers to directly detect planets that would otherwise be lost in the overwhelming light from their host star. After subtracting residual starlight using advanced image processing, a faint infrared source was revealed near TWA 7, distinguishable from background galaxies or Solar System objects. The source is located in a gap in one of three dust rings that were discovered around TWA 7 by previous ground-based observations. Its brightness, colour, distance from the star, and position within the ring are consistent with theoretical predictions for a young, cold, Saturn-mass planet sculpting the surrounding debris disc. Initial analysis suggests that the object — referred to as TWA 7b — could be a young, cold planet with a mass around 0.3 times that of Jupiter (~100 Earth masses) and a temperature near 320 Kelvin (roughly 47 degrees Celsius). In this image from MIRI, light from the star TWA 7 has been subtracted. The location of the star is marked with a circle and a star symbol at the centre of the image. This leaves light from the debris disc around the star, as well as other infrared sources, visible. The bright spot to the upper right of the star is the source identified as TWA 7b, within the debris disc. The more distant orange spot visible in the left of the image is an unrelated background star. Only a single MIRI band was used in this image (seen here in orange). The blue colour visible in the image results from an additional band taken by the SPHERE instrument of ESO’s Very Large Telescope (VLT), which showcases the location of the disc surrounding the host star and the exoplanet creating a gap within the disc that is revealed by MIRI. Credit: ESA/Webb, NASA, CSA, A.M. Lagrange, M. Zamani (ESA/Webb)
Findings suggest giant exoplanets in HR 8799 system likely formed like Jupiter and Saturn.
The NASA/ESA/CSA James Webb Space Telescope has captured direct images of multiple gas giant planets within an iconic planetary system. HR 8799, a young system 130 light-years away, has long been a key target for planet formation studies.
The NASA/ESA/CSA James Webb Space Telescope has provided the clearest look yet at the iconic multi-planet system HR 8799. The observations detected carbon dioxide in each of the planets, which provides strong evidence that the system’s four giant planets formed much like Jupiter and Saturn, by slowly building solid cores that attract gas from within a protoplanetary disk. Colours are applied to filters from Webb’s NIRCam (Near-Infrared Camera), revealing their intrinsic differences. A star symbol marks the location of the host star HR 8799, whose light has been blocked by a coronagraph. The colours in this image, which represent different wavelengths captured by Webb’s NIRCam, tell researchers about the temperatures and composition of the planets. HR 8799 b, which orbits around 10.1 billion kilometres from the star, is the coldest of the bunch, and the richest in carbon dioxide. HR 8799 e orbits 2.4 billion kilometres from its star, and likely formed closer to the host star, where there were stronger variations in the composition of material. In this image, the colour blue is assigned to 4.1 micron light, green to 4.3 micron light, and red to the 4.6 micron light. Credit: NASA, ESA, CSA, STScI, W. Balmer (JHU), L. Pueyo (STScI), M. Perrin (STScI)
The observations indicate that the well-studied planets of HR 8799 are rich in carbon dioxide gas. This provides strong evidence that the system’s four giant planets formed much like Jupiter and Saturn, by slowly building solid cores that attract gas from within a protoplanetary disk.
The results also confirm that Webb can infer the chemistry of exoplanet atmospheres through imaging. This technique complements Webb’s powerful spectroscopic instruments, which resolve the atmospheric composition.
“By spotting these strong carbon dioxide features, we have shown there is a sizable fraction of heavier elements, like carbon, oxygen, and iron, in these planets’ atmospheres,” said William Balmer, of Johns Hopkins University in Baltimore. “Given what we know about the star they orbit, that likely indicates they formed via core accretion, which is an exciting conclusion for planets that we can directly see.”
This graph shows a spectrum of one of the planets in the HR 8799 system, HR 8799 e, which displays the amounts of near-infrared light detected from the planet by Webb at different wavelengths. The blue and yellow lines are a best-fit model for an atmosphere that would be either low or high in metals heavier than helium, including carbon, also known as metallicity. The Webb data is consistent with a high metallicity planet. Spectral fingerprints of carbon dioxide and carbon monoxide appear in data collected by Webb’s NIRCam (Near-Infrared Camera). Credit: NASA, ESA, CSA, STScI, W. Balmer (JHU), L. Pueyo (STScI), M. Perrin (STScI)
Balmer is the lead author of the study announcing the results published today in The Astrophysical Journal. Balmer and his team’s analysis also includes Webb’s observation of a system 97 light-years away called 51 Eridani.
HR 8799 is a young system about 30 million years old, a fraction of our solar system’s 4.6 billion years. Still hot from their tumultuous formation, the planets within HR 8799 emit large amounts of infrared light that give scientists valuable data on how they formed.
Giant planets can take shape in two ways: by slowly building solid cores with heavier elements that attract gas, just like the giants in our solar system, or when particles of gas rapidly coalesce into massive objects from a young star’s cooling disk, which is made mostly of the same kind of material as the star. Knowing which formation model is more common can give scientists clues to distinguish between the types of planets they find in other systems.
“Our hope with this kind of research is to understand our own solar system, life, and ourselves in comparison to other exoplanetary systems, so we can contextualize our existence,” Balmer said. “We want to take pictures of other solar systems and see how they’re similar or different when compared to ours. From there, we can try to get a sense of how weird our solar system really is—or how normal.”
Of the nearly 6,000 exoplanets discovered, few have been directly imaged, as even giant planets are many thousands of times fainter than their stars. The images of HR 8799 and 51 Eridani were made possible by Webb’s NIRCam (Near-Infrared Camera) coronagraph, which blocks light from bright stars to reveal otherwise hidden worlds.
The NASA/ESA/CSA James Webb Space Telescope’s NIRCam (Near-Infrared Camera) captured this image of Eridani 51 b, a cool, young exoplanet that orbits 17.7 billion kilometres from its star. Its distance is equivalent to a location between the orbits of Neptune and Saturn in our solar system. The observations detected the planet is rich in carbon dioxide, providing strong evidence that the planet formed much like Jupiter and Saturn, by slowly building a solid core that attracted gas from within a protoplanetary disk. The 51 Eridani system is 96 light-years from Earth. This image includes filters representing 4.1-micron light as red. Credit: NASA, ESA, CSA, STScI, W. Balmer (JHU), L. Pueyo (STScI), M. Perrin (STScI)
This technology allowed the team to look for infrared light emitted by the planets in wavelengths that are absorbed by specific gases. The team found that the four HR 8799 planets contain more heavy elements than previously thought.
“Webb’s unique capabilities are allowing us to explore the wide diversity of these directly-imaged planets for the first time. This gives us important clues as to how such planetary systems have formed.” said Emily Rickman of the European Space Agency, a co-author of the study. “These new observations reiterate how valuable the HR 8799 multi-planet system is as a stepping stone to understand the formation of exoplanetary systems and of our own Solar System.”
The team is paving the way for more detailed observations to determine whether objects they see orbiting other stars are truly giant planets or objects such as brown dwarfs, which form like stars but don’t accumulate enough mass to ignite nuclear fusion.
“We have other lines of evidence that hint at these four HR 8799 planets forming using this bottom-up approach,” said Laurent Pueyo, an astronomer at the Space Telescope Science Institute in Baltimore, who co-led the work. “How common is this for planets we can directly image? We don’t know yet, but we’re proposing more Webb observations to answer that question.”
“We knew Webb could measure colours of the outer planets in directly imaged systems,” added Rémi Soummer, director of STScI’s Russell B. Makidon Optics Lab and former lead for Webb coronagraph operations. “We have been waiting for 10 years to confirm that our finely tuned operations of the telescope would also allow us to access the inner planets. Now the results are in and we can do interesting science with it.”
The NIRCam observations of HR 8799 and 51 Eridani were conducted as part of Guaranteed Time Observations programmes 1194 and 1412 respectively.
By observing NGC 346, Webb finds planet-forming discs lived longer in early Universe: new data refutes current theories of planet formation in Universe’s early days
The NASA/ESA/CSA James Webb Space Telescope just solved a conundrum by proving a controversial finding made with the NASA/ESA Hubble Space Telescope more than 20 years ago.
This image features NGC 346, one of the most dynamic star-forming regions in nearby galaxies, as seen by the NASA/ESA/CSA James Webb Space Telescope. NCG 346 is located in the Small Magellanic Cloud (SMC), a dwarf galaxy close to our Milky Way. Credit: NASA, ESA, CSA, STScI, A. Pagan (STScI)
In 2003, Hubble provided evidence of a massive planet around a very old star, almost as old as the Universe. Such stars possess only small amounts of heavier elements that are the building blocks of planets. This implied that some planet formation happened when our Universe was very young, and those planets had time to form and grow big inside their primordial discs, even bigger than Jupiter. But how? This was puzzling.
This side-by-side comparison shows a Hubble image of the massive star cluster NGC 346 (left) versus a Webb image of the same cluster (right). While the Hubble image shows more nebulosity, the Webb image pierces through those clouds to reveal more of the cluster’s structure. NGC 346 has a relative lack of elements heavier than helium and hydrogen, making it a good proxy for stellar environments in the early, distant universe. Credit: NASA, ESA, CSA, STScI, O. C. Jones (UK ATC), G. De Marchi (ESTEC), M. Meixner (USRA), A. Nota (ESA)
To answer this question, researchers used Webb to study stars in a nearby galaxy that, much like the early Universe, lacks large amounts of heavy elements. They found that not only do some stars there have planet-forming discs, but that those discs are longer-lived than those seen around young stars in our Milky Way galaxy.
“With Webb, we have a really strong confirmation of what we saw with Hubble, and we must rethink how we model planet formation and early evolution in the young Universe,” said study leader Guido De Marchi of ESA’s European Space Research and Technology Centre in Noordwijk, Netherlands.
A different environment in early times
In the early Universe, stars formed from mostly hydrogen and helium, and very few heavier elements such as carbon and iron, which came later through supernova explosions.
“Current models predict that with so few heavier elements, the discs around stars have a short lifetime, so short in fact that planets cannot grow big,” said the Webb study’s co-investigator Elena Sabbi, chief scientist for Gemini Observatory at the National Science Foundation’s NOIRLab in Tucson. “But Hubble did see those planets, so what if the models were not correct and discs could live longer?”
To test this idea, scientists trained Webb on the Small Magellanic Cloud, a dwarf galaxy that is one of the Milky Way’s nearest neighbors. In particular, they examined the massive, star-forming cluster NGC 346, which also has a relative lack of heavier elements. The cluster served as a nearby proxy for studying stellar environments with similar conditions in the early, distant Universe.
This is a NASA/ESA/CSA James Webb Space Telescope image of NGC 346, a massive star cluster in the Small Magellanic Cloud, a dwarf galaxy that is one of the Milky Way’s nearest neighbors. With its relative lack of elements heavier than helium and hydrogen, the NGC 346 cluster serves as a nearby proxy for studying stellar environments with similar conditions in the early, distant Universe. Ten, small, yellow circles overlaid on the image indicate the positions of the ten stars surveyed in this study. Credit: NASA, ESA, CSA, STScI, O. C. Jones (UK ATC), G. De Marchi (ESTEC), M. Meixner (USRA)
Hubble observations of NGC 346 from the mid 2000s revealed many stars about 20 to 30 million years old that seemed to still have planet-forming discs around them. This went against the conventional belief that such discs would dissipate after 2 or 3 million years.
“The Hubble findings were controversial, going against not only empirical evidence in our galaxy but also against the current models,” said De Marchi. “This was intriguing, but without a way to obtain spectra of those stars, we could not really establish whether we were witnessing genuine accretion and the presence of discs, or just some artificial effects.”
Now, thanks to Webb’s sensitivity and resolution, scientists have the first-ever spectra of forming, Sun-like stars and their immediate environments in a nearby galaxy.
“We see that these stars are indeed surrounded by discs and are still in the process of gobbling material, even at the relatively old age of 20 or 30 million years,” said De Marchi. “This also implies that planets have more time to form and grow around these stars than in nearby star-forming regions in our own galaxy.”
By observing NGC 346, Webb finds planet-forming discs lived longer in early Universe: new data refutes current theories of planet formation in Universe’s early days. This image features NGC 346, one of the most dynamic star-forming regions in nearby galaxies, as seen by the NASA/ESA/CSA James Webb Space Telescope. NCG 346 is located in the Small Magellanic Cloud (SMC), a dwarf galaxy close to our Milky Way. Credit: NASA, ESA, CSA, STScI, A Pagan (STScI)
A New Way of Thinking
This finding refutes previous theoretical predictions that when there are very few heavier elements in the gas around the disc, the star would very quickly blow away the disc. So the disc’s life would be very short, even less than a million years. But if a disc doesn’t stay around the star long enough for the dust grains to stick together and pebbles to form and become the core of a planet, how can planets form?
The researchers explained that there could be two distinct mechanisms, or even a combination, for planet-forming discs to persist in environments scarce in heavier elements.
First, to be able to blow away the disc, the star applies radiation pressure. For this pressure to be effective, elements heavier than hydrogen and helium would have to reside in the gas. But the massive star cluster NGC 346 only has about ten percent of the heavier elements that are present in the chemical composition of our Sun. Perhaps it simply takes longer for a star in this cluster to disperse its disc.
The second possibility is that, for a Sun-like star to form when there are few heavier elements, it would have to start from a larger cloud of gas. A bigger gas cloud will produce a bigger disc. So there is more mass in the disc and therefore it would take longer to blow the disc away, even if the radiation pressure were working in the same way.
“With more matter around the stars, the accretion lasts for a longer time,” said Sabbi. “The discs take ten times longer to disappear. This has implications for how you form a planet, and the type of system architecture that you can have in these different environments. This is so exciting.”
The science team’s paper appears in the 16 December 2024 issue of The Astrophysical Journal.
This graph shows, on the bottom left in yellow, a spectrum of one of the 10 target stars in this study (as well as accompanying light from the immediate background environment). Spectral fingerprints of hot atomic helium, cold molecular hydrogen, and hot atomic hydrogen are highlighted. On the top left in magenta is a spectrum slightly offset from the star that includes only light from the background environment. This second spectrum lacks a spectral line of cold molecular hydrogen. On the right is the comparison of the top and bottom lines. This comparison shows a large peak in the cold molecular hydrogen coming from the star but not its nebular environment. Also, atomic hydrogen shows a larger peak from the star. This indicates the presence of a protoplanetary disc immediately surrounding the star. The data was taken with the microshutter array on the James Webb Space Telescope’s NIRSpec (Near-Infrared Spectrometer) instrument. Credit: NASA, ESA, CSA, J. Olmsted (STScI)
Scientists discover Barnard b, a planet orbiting the closest single star to our Sun
This artist’s impression shows Barnard b, a sub-Earth-mass planet that was discovered orbiting Barnard’s star. Its signal was detected with the ESPRESSO instrument on ESO’s Very Large Telescope (VLT), and astronomers were able to confirm it with data from other instruments. An earlier promising detection in 2018 around the same star could not be confirmed by these data. On this newly discovered exoplanet, which has at least half the mass of Venus but is too hot to support liquid water, a year lasts just over three Earth days. Credits: ESO/M. Kornmesser
Using the European Southern Observatory’s Very Large Telescope (ESO’s VLT), astronomers have discovered an exoplanet orbiting Barnard’s star, the closest single star to our Sun. On this newly discovered exoplanet, which has at least half the mass of Venus, a year lasts just over three Earth days. The team’s observations also hint at the existence of three more exoplanet candidates, in various orbits around the star.
Located just six light-years away, Barnard’s star is the second-closest stellar system — after Alpha Centauri’s three-star group — and the closest individual star to us. Owing to its proximity, it is a primary target in the search for Earth-like exoplanets. Despite a promising detection back in 2018, no planet orbiting Barnard’s star had been confirmed until now.
Graphic representation of the relative distances between the nearest stars and the Sun. Barnard’s star is the second closest star system to the Sun, and the nearest single star to us. Credits: IEEC/Science-Wave – Guillem RamisaThis chart shows the constellation of Ophiuchus (the Serpent-Bearer), which straddles the celestial equator. The chart shows the location of Barnard’s Star and marks most of the stars visible to the unaided eye on a clear dark night… Credits: ESO, IAU and Sky & Telescope
The discovery of this new exoplanet — announced in a paper published today in the journal Astronomy & Astrophysics — is the result of observations made over the last five years with ESO’s VLT, located at Paranal Observatory in Chile.
“Even if it took a long time, we were always confident that we could find something,”
says Jonay González Hernández, a researcher at the Instituto de Astrofísica de Canarias in Spain, and lead author of the paper. The team were looking for signals from possible exoplanets within the habitable or temperate zone of Barnard’s star — the range where liquid water can exist on the planet’s surface. Red dwarfs like Barnard’s star are often targeted by astronomers since low-mass rocky planets are easier to detect there than around larger Sun-like stars. [1]
Barnard b [2], as the newly discovered exoplanet is called, is twenty times closer to Barnard’s star than Mercury is to the Sun. It orbits its star in 3.15 Earth days and has a surface temperature around 125 °C.
“Barnard b is one of the lowest-mass exoplanets known and one of the few known with a mass less than that of Earth. But the planet is too close to the host star, closer than the habitable zone,” explains González Hernández. “Even if the star is about 2500 degrees cooler than our Sun, it is too hot there to maintain liquid water on the surface.”
For their observations, the team used ESPRESSO, a highly precise instrument designed to measure the wobble of a star caused by the gravitational pull of one or more orbiting planets. The results obtained from these observations were confirmed by data from other instruments also specialised in exoplanet hunting: HARPS at ESO’s La Silla Observatory, HARPS-N and CARMENES. The new data do not, however, support the existence of the exoplanet reported in 2018.
In addition to the confirmed planet, the international team also found hints of three more exoplanet candidates orbiting the same star. These candidates, however, will require additional observations with ESPRESSO to be confirmed.
“We now need to continue observing this star to confirm the other candidate signals,” says Alejandro Suárez Mascareño, a researcher also at the Instituto de Astrofísica de Canarias and co-author of the study. “But the discovery of this planet, along with other previous discoveries such as Proxima b and d, shows that our cosmic backyard is full of low-mass planets.”
ESO’s Extremely Large Telescope (ELT), currently under construction, is set to transform the field of exoplanet research. The ELT’s ANDES instrument will allow researchers to detect more of these small, rocky planets in the temperate zone around nearby stars, beyond the reach of current telescopes, and enable them to study the composition of their atmospheres.
This wide-field image shows the surroundings of the red dwarf known as Barnard’s Star in the constellation of Ophiuchus (the Serpent-Bearer). This picture was created from material forming part of the Digitized Sky Survey 2. The centre of the image shows Barnard’s Star captured in three different exposures. The star is the fastest moving star in the night sky and its large apparent motion can be seen as its position changes between successive observations — shown in red, yellow and blue.. Credits: ESO/Digitized Sky Survey 2 Acknowledgement: Davide De Martin E — Red Dots
Notes
[1] Astronomers target cool stars, like red dwarfs, because their temperate zone is much closer to the star than that of hotter stars, like the Sun. This means that the planets orbiting within their temperate zone have shorter orbital periods, allowing astronomers to monitor them over several days or weeks, rather than years. In addition, red dwarfs are much less massive than the Sun, so they are more easily disturbed by the gravitational pull of the planets around them and thus they wobble more strongly.
[2] It’s common practice in science to name exoplanets by the name of their host star with a lowercase letter added to it, ‘b’ indicating the first known planet, ’c’ the next one, and so on. The name Barnard b was therefore also given to a previously suspected planet candidate around Barnard’s star, which scientists were unable to confirm.
The team is composed of J. I. González Hernández (Instituto de Astrofísica de Canarias, Spain [IAC] and Departamento de Astrofísica, Universidad de La Laguna, Spain [IAC-ULL]), A. Suárez Mascareño (IAC and IAC-ULL), A. M. Silva (Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, Portugal [IA-CAUP] and Departamento de Física e Astronomia Faculdade de Ciências, Universidade do Porto, Portugal [FCUP]), A. K. Stefanov (IAC and IAC-ULL), J. P. Faria (Observatoire de Genève, Université de Genève, Switzerland [UNIGE]; IA-CAUP and FCUP), H. M. Tabernero (Departamento de Física de la Tierra y Astrofísica & Instituto de Física de Partículas y del Cosmos, Universidad Complutense de Madrid, Spain), A. Sozzetti (INAF – Osservatorio Astrofisico di Torino [INAF-OATo] and Istituto Nazionale di Astrofisica, Torino, Italy), R. Rebolo (IAC; IAC-ULL and Consejo Superior de Investigaciones Científicas, Spain [CSIC]), F. Pepe (UNIGE), N. C. Santos (IA-CAUP; FCUP), S. Cristiani (INAF – Osservatorio Astronomico di Trieste, Italy [INAF-OAT] and Institute for Fundamental Physics of the Universe, Trieste, Italy [IFPU]), C. Lovis (UNIGE), X. Dumusque (UNIGE), P. Figueira (UNIGE and IA-CAUP), J. Lillo-Box (Centro de Astrobiología, CSIC-INTA, Madrid, Spain [CAB]), N. Nari (IAC; Light Bridges S. L., Canarias, Spain and IAC-ULL), S. Benatti (INAF – Osservatorio Astronomico di Palermo, Italy [INAF-OAPa]), M. J. Hobson (UNIGE), A. Castro-González (CAB), R. Allart (Institut Trottier de Recherche sur les Exoplanètes, Université de Montréal, Canada and UNIGE), V. M. Passegger (National Astronomical Observatory of Japan, Hilo, USA; IAC; IAC-ULL and Hamburger Sternwarte, Hamburg, Germany), M.-R. Zapatero Osorio (CAB), V. Adibekyan (IA-CAUP and FCUP), Y. Alibert (Center for Space and Habitability, University of Bern, Switzerland and Weltraumforschung und Planetologie, Physikalisches Institut, University of Bern, Switzerland), C. Allende Prieto (IAC and IAC-ULL), F. Bouchy (UNIGE), M. Damasso (INAF-OATo), V. D’Odorico (INAF-OAT and IFPU), P. Di Marcantonio (INAF-OAT), D. Ehrenreich (UNIGE), G. Lo Curto (European Southern Observatory, Santiago, Chile [ESO Chile]), R. Génova Santos (IAC and IAC-ULL), C. J. A. P. Martins (IA-CAUP and Centro de Astrofísica da Universidade do Porto, Portugal), A. Mehner (ESO Chile), G. Micela (INAF-OAPa), P. Molaro (INAF-OAT), N. Nunes (Instituto de Astrofísica e Ciências do Espaço, Universidade de Lisboa), E. Palle (IAC and IAC-ULL), S. G. Sousa (IA-CAUP and FCUP), and S. Udry (UNIGE).
The European Southern Observatory (ESO) enables scientists worldwide to discover the secrets of the Universe for the benefit of all. We design, build and operate world-class observatories on the ground — which astronomers use to tackle exciting questions and spread the fascination of astronomy — and promote international collaboration for astronomy. Established as an intergovernmental organisation in 1962, today ESO is supported by 16 Member States (Austria, Belgium, Czechia, Denmark, France, Finland, Germany, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom), along with the host state of Chile and with Australia as a Strategic Partner. ESO’s headquarters and its visitor centre and planetarium, the ESO Supernova, are located close to Munich in Germany, while the Chilean Atacama Desert, a marvellous place with unique conditions to observe the sky, hosts our telescopes. ESO operates three observing sites: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope and its Very Large Telescope Interferometer, as well as survey telescopes such as VISTA. Also at Paranal ESO will host and operate the Cherenkov Telescope Array South, the world’s largest and most sensitive gamma-ray observatory. Together with international partners, ESO operates ALMA on Chajnantor, a facility that observes the skies in the millimetre and submillimetre range. At Cerro Armazones, near Paranal, we are building “the world’s biggest eye on the sky” — ESO’s Extremely Large Telescope. From our offices in Santiago, Chile we support our operations in the country and engage with Chilean partners and society.
Press release from European Southern Observatory – ESO
Webb images of Epsilon Indi Ab, a cold exoplanet 12 light-years away
An international team of astronomers using the NASA/ESA/CSA James Webb Space Telescope have directly imaged an exoplanet roughly 12 light-years from Earth. While there were hints that the planet existed, it had not been confirmed until Webb imaged it. The planet is one of the coldest exoplanets observed to date.
The planet, known Epsilon Indi Ab, is several times the mass of Jupiter and orbits the K-type star Epsilon Indi A (Eps Ind A), which is around the age of our Sun, but slightly cooler. The team observed Epsilon Indi Ab using the coronagraph on Webb’s MIRI (Mid-Infrared Instrument). Only a few tens of exoplanets have been directly imaged previously by space- and ground-based observatories.
“Our prior observations of this system have been more indirect measurements of the star, which actually allowed us to see ahead of time that there was likely a giant planet in this system tugging on the star,” said team member Caroline Morley of the University of Texas at Austin. “That’s why our team chose this system to observe first with Webb.”
“This discovery is exciting because the planet is quite similar to Jupiter — it is a little warmer and is more massive, but is more similar to Jupiter than any other planet that has been imaged so far,” added lead author Elisabeth Matthews of the Max Planck Institute for Astronomy in Germany.
A Solar System analog
Previously imaged exoplanets tend to be the youngest, hottest exoplanets that are still radiating much of the energy from when they first formed. As planets cool and contract over their lifetime, they become significantly fainter and therefore harder to image.
“Cold planets are very faint, and most of their emission is in the mid-infrared,” explained Matthews. “Webb is ideally suited to conduct mid-infrared imaging, which is extremely hard to do from the ground. We also needed good spatial resolution to separate the planet and the star in our images, and the large Webb mirror is extremely helpful in this aspect.”
Epsilon Indi Ab is one of the coldest exoplanets to be directly detected, with an estimated temperature of 2 degrees Celsius — colder than any other imaged planet beyond our Solar System, and colder than all but one free-floating brown dwarf [1]. The planet is only around 100 degrees Celsius warmer than gas giants in our Solar System. This provides a rare opportunity for astronomers to study the atmospheric composition of true solar system analogs.
“Astronomers have been imagining planets in this system for decades; fictional planets orbiting Epsilon Indi have been the sites of Star Trek episodes, novels, and video games like Halo,” added Morley. “It’s exciting to actually see a planet there ourselves, and begin to measure its properties.”
Not quite as predicted
Epsilon Indi Ab is the twelfth closest exoplanet to Earth known to date and the closest planet more massive than Jupiter. The science team chose to study Eps Ind A because the system showed hints of a possible planetary body using a technique called radial velocity, which measures the back-and-forth wobbles of the host star along our line of sight.
“While we expected to image a planet in this system, because there were radial velocity indications of its presence, the planet we found isn’t what we had predicted,” shared Matthews. “It’s about twice as massive, a little farther from its star, and has a different orbit than we expected. The cause of this discrepancy remains an open question. The atmosphere of the planet also appears to be a little different than the model predictions. So far we only have a few photometric measurements of the atmosphere, meaning that it is hard to draw conclusions, but the planet is fainter than expected at shorter wavelengths.”
The team believes this may mean there is significant methane, carbon monoxide, and carbon dioxide in the planet’s atmosphere that are absorbing the shorter wavelengths of light. It might also suggest a very cloudy atmosphere.
The direct imaging of exoplanets is particularly valuable for characterization. Scientists can directly collect light from the observed planet and compare its brightness at different wavelengths. So far, the science team has only detected Epsilon Indi Ab at a few wavelengths, but they hope to revisit the planet with Webb to conduct both photometric and spectroscopic observations in the future. They also hope to detect other similar planets with Webb to find possible trends about their atmospheres and how these objects form.
These results were taken with Webb’s Cycle 1 GO programme #2243 and have been published today in Nature.
This image of the gas-giant exoplanet Epsilon Indi Ab was taken with the coronagraph on the NASA/ESA/CSA James Webb Space Telescope’s MIRI (Mid-Infrared Instrument). A star symbol marks the location of the host star Epsilon Indi A, whose light has been blocked by the coronagraph, resulting in the dark circle marked with a dashed white line. Epsilon Indi Ab is one of the coldest exoplanets ever directly imaged. Light at 10.6 microns was assigned the color blue, while light at 15.5 microns was assigned the color orange. MIRI did not resolve the planet, which is a point source. Credit: ESA/Webb, NASA, CSA, STScI, E. Matthews (Max Planck Institute for Astronomy)
Webb hints at possible atmosphere surrounding 55 Cancri e, a rocky exoplanet
Researchers using the NASA/ESA/CSA James Webb Space Telescope may have detected atmospheric gases surrounding 55 Cancri e, a hot rocky exoplanet 41 light-years from Earth. This is the best evidence to date for the existence of a rocky planet atmosphere outside our Solar System.
Renyu Hu from NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, USA, is the lead author of a paper published today in Nature.
“Webb is pushing the frontiers of exoplanet characterisation to rocky planets,” Hu said. “It is truly enabling a new type of science.”
Super-hot super-Earth 55 Cancri e
55 Cancri e is one of five known planets orbiting a Sun-like star in the constellation Cancer. With a diameter nearly twice that of Earth and a density slightly greater, the planet is classified as a super-Earth: larger than Earth, smaller than Neptune, and likely similar in composition to the rocky planets in our Solar System.
To describe 55 Cancri e as rocky, however, could give the wrong impression. The planet orbits so close to its star (about 2.25 million kilometres, or one twenty-fifth of the distance between Mercury and the Sun) that its surface is likely to be molten – a bubbling ocean of magma. In such a tight orbit, the planet is also likely to be tidally locked, with a dayside that faces the star at all times and a nightside in perpetual darkness.
In spite of numerous observations since it was discovered to transit in 2011, the question of whether or not 55 Cancri e has an atmosphere – or even could have one, given its high temperature and the continuous onslaught of stellar radiation and wind from its star – has gone unanswered.
“I’ve worked on this planet for more than a decade,” said Diana Dragomir, an exoplanet researcher at the University of New Mexico in the USA and a co-author of the study. “It’s been really frustrating that none of the observations we’ve been getting have robustly solved these mysteries. I am thrilled that we are finally getting some answers!”
Unlike gas-giant atmospheres, which are relatively easy to spot (the first was detected by the NASA/ESA Hubble Space Telescope more than two decades ago), thinner and denser atmospheres surrounding rocky planets have remained elusive.
Previous studies of 55 Cancri e using data from NASA’s now-retired Spitzer Space Telescope suggested the presence of a substantial atmosphere rich in volatiles (molecules that occur in gas form on Earth) like oxygen, nitrogen, and carbon dioxide. But researchers could not rule out another possibility: that the planet is bare, save for a tenuous shroud of vaporised rock, rich in elements like silicon, iron, aluminium, and calcium.
“The planet is so hot that some of the molten rock should evaporate,” explained Hu.
This artist’s concept shows what the exoplanet 55 Cancri e could look like. Also called Janssen, 55 Cancri e is a so-called super-Earth, a rocky planet significantly larger than Earth but smaller than Neptune, which orbits its star at a distance of only 2.25 million kilometres (0.015 astronomical units), completing one full orbit in less than 18 hours. In comparison, Mercury is 25 times farther from the Sun than 55 Cancri e is from its star. The system, which also includes four large gas-giant planets, is located about 41 light-years from Earth, in the constellation Cancer. Observations from Webb’s NIRCam and MIRI suggest that the planet may be surrounded by an atmosphere rich in carbon dioxide (CO2) or carbon monoxide (CO). Because it is so close to its star, the planet is extremely hot and is thought to be covered in molten rock. Researchers think that the gases that make up the atmosphere could have bubbled out of the magma. The star, 55 Cancri, is a K-type star nearly the same size and mass as the Sun, but slightly cooler and dimmer. It is just bright enough to see with the naked eye in a very dark sky. The star and planet are so close to each other that the star would appear 70 times wider in the planet’s sky than the Sun appears in our sky. In addition, because the planet is likely to be tidally locked, from any given point the star would appear fixed in the sky. This artist’s concept is based on new data gathered by NIRCam and MIRI as well as previous observations from other ground- and space-based telescopes, including NASA’s Hubble and the now-retired Spitzer space telescopes. Webb has not captured any images of the planet. Credit: NASA, ESA, CSA, R. Crawford (STScI)
Measuring subtle variations in infrared colours
To distinguish between the two possibilities, the team used Webb’s NIRCam (Near-Infrared Camera) and MIRI (Mid-Infrared Instrument) to measure 4- to 12-micron infrared light coming from the planet.
Although Webb cannot capture a direct image of 55 Cancri e, it can measure subtle changes in the light from the whole system as the planet orbits the star.
By subtracting the brightness during the secondary eclipse, when the planet is behind the star (starlight only), from the brightness when the planet is right beside the star (light from the star and planet combined), the team was able to calculate the amount of various wavelengths of infrared light coming from the dayside of the planet.
This method, known as secondary eclipse spectroscopy, is similar to that used by other research teams to search for atmospheres on other rocky exoplanets, like TRAPPIST-1 b.
This lightcurve shows the change in brightness of the 55 Cancri system as the rocky planet 55 Cancri e, the closest of the five known planets in the system, moves behind the star. This phenomenon is known as a secondary eclipse. When the planet is beside the star, the mid-infrared light emitted by both the star and the dayside of the planet reaches the telescope, and the system appears brighter. When the planet is behind the star, the light emitted by the planet is blocked and only the starlight reaches the telescope, causing the apparent brightness to decrease. Astronomers can subtract the brightness of the star from the combined brightness of the star and planet to calculate how much infrared light is coming from the dayside of the planet. This is then used to calculate the dayside temperature and infer whether or not the planet has an atmosphere. The graph shows data collected using the low-resolution spectroscopy mode on Webb’s Mid-Infrared Instrument (MIRI) in March 2023. Each of the purple data points shows the brightness of light ranging in wavelength from 7.5 to 11.8 microns, averaged over intervals of about five minutes. The grey line is the best fit, or model lightcurve that matches the data most closely. The decrease in brightness during the secondary eclipse is just 110 parts per million, or about 0.011 percent. The temperature of the planet calculated from this observation is about 1800 kelvins (around 1500 degrees Celsius), which is significantly lower than would be expected if the planet has no atmosphere or only a thin rock-vapour atmosphere. This relatively low temperature indicates that heat is being distributed from the dayside to the nightside of the planet, possibly by a volatile-rich atmosphere. Credit: NASA, ESA, CSA, J. Olmsted (STScI), A. Bello-Arufe (JPL)
55 Cancri e is cooler than expected
The first indication that 55 Cancri e could have a substantial atmosphere came from temperature measurements based on its thermal emission, the heat energy given off in the form of infrared light. If the planet is covered in dark molten rock with a thin veil of vaporised rock, or has no atmosphere at all, the dayside should be around 2200 degrees Celsius.
“Instead, the MIRI data showed a relatively low temperature of about 1540 degrees Celsius,” said Hu. “This is a very strong indication that energy is being distributed from the dayside to the nightside, most likely by a volatile-rich atmosphere.”
While currents of lava can carry some heat around to the nightside, they cannot move it efficiently enough to explain the cooling effect.
When the team looked at the NIRCam data, they saw patterns consistent with a volatile-rich atmosphere.
“We see evidence of a dip in the spectrum between 4 and 5 microns — less of this light is reaching the telescope,” explained co-author Aaron Bello-Arufe, also from JPL. “This suggests the presence of an atmosphere containing carbon monoxide or carbon dioxide, both of which absorb these wavelengths of light.”
A planet with no atmosphere or only vaporised rock in an atmosphere would not have this specific spectral feature.
“This is exciting news,” said co-author Yamila Miguel from Leiden Observatory and the Netherlands Institute for Space Research (SRON), both in the Netherlands. “We’ve spent the last ten years modelling different scenarios, trying to imagine what this world might look like. Finally getting some confirmation of our work is priceless!”
Bubbling magma ocean
The team thinks that the gases blanketing 55 Cancri e would be bubbling out from the interior, rather than being present since the planet’s formation.
“The primary atmosphere would be long gone because of the high temperature and intense radiation from the star,” said Bello-Arufe. “This would be a secondary atmosphere that is continuously replenished by the magma ocean. Magma is not only crystals and liquid rock, there’s a lot of dissolved gas in it, too.”
In all likelihood, any atmosphere surrounding the planet would be more complex and quite variable as a result of interactions with the magma ocean. In addition to carbon monoxide or carbon dioxide, there could be gases like nitrogen, water vapour, sulphur dioxide, some vaporised rock, and even short-lived clouds made of tiny droplets of lava condensed from the air.
While 55 Cancri e is far too hot to be habitable, researchers think it could provide a unique window for studying interactions between the atmospheres, surfaces and interiors of rocky planets, and perhaps provide insights into the early Earth, Venus and Mars, which are thought to have been covered in magma oceans in the past.
“Ultimately, we want to understand what conditions make it possible for a rocky planet to sustain a gas-rich atmosphere, a key ingredient for a habitable planet,” said Hu.
This research was conducted as part of Webb’s General Observers (GO) Program 1952. Analysis of additional secondary eclipse observations of 55 Cancri e are currently in progress. In the future, the team hopes to capture a full phase curve with Webb in order to map temperature differences from one side of the planet to the other, to get a better sense of the planet’s weather, climate and more detailed atmospheric conditions.
A thermal emission spectrum captured by Webb’s NIRCam (Near-Infrared Camera) in November 2022, and MIRI (Mid-Infrared Instrument) in March 2023, shows the brightness (y-axis) of different wavelengths of infrared light (x-axis) emitted by the super-Earth exoplanet 55 Cancri e. The spectrum shows that the planet may be surrounded by an atmosphere rich in carbon dioxide or carbon monoxide and other volatiles, not just vaporised rock. The graph compares data collected by NIRCam (orange dots) and MIRI (purple dots) to two different models. Model A, in red, shows what the emission spectrum of 55 Cancri e should look like if it has an atmosphere made of vaporised rock. Model B, in blue, shows what the emission spectrum should look like if the planet has a volatile-rich atmosphere outgassed from a magma ocean that has a volatile content similar to Earth’s mantle. Both MIRI and NIRCam data are consistent with the volatile-rich model. The amount of mid-infrared light emitted by the planet (MIRI) shows that its dayside temperature is significantly lower than it would be if it did not have an atmosphere to distribute heat from the dayside to the nightside. The dip in the spectrum between 4 and 5 microns (NIRCam data) can be explained by absorption of those wavelengths by carbon monoxide or carbon dioxide molecules in the atmosphere. The spectrum was made by measuring the brightness of 4- to 5-micron light with Webb’s NIRCam GRISM spectrometer, and 5- to 12-micron light with the MIRI low-resolution spectrometer, before, during and after the planet moved behind its star (the secondary eclipse ). The amount of each wavelength emitted by the planet (y-axis) was calculated by subtracting the brightness of the star alone (during the secondary eclipse) from the brightness of the star and planet combined (before and after the eclipse). Each observation lasted about eight hours. Note that the NIRCam data have been shifted vertically to align with Model B. Although the differences in brightness between each wavelength in the NIRCam band were derived from the observation (the data suggest a valley between 4 and 5 microns), the absolute brightness (the vertical position of that valley) could not be measured precisely because of noise in the data. Credit: NASA, ESA, CSA, J. Olmsted (STScI), R. Hu (JPL), A. Bello-Arufe (JPL), M. Zhang (University of Chicago), M. Zilinskas (SRON Netherlands Institute for Space Research)
Hubble finds water vapour in the atmosphere of GJ 9827d, a small exoplanet
Astronomers using the NASA/ESA Hubble Space Telescope observed the smallest exoplanet where water vapour has been detected in its atmosphere, GJ 9827d. At only approximately twice Earth’s diameter, the planet GJ 9827d could be an example of potential planets with water-rich atmospheres elsewhere in our galaxy.
“This would be the first time that we can directly show through an atmospheric detection that these planets with water-rich atmospheres can actually exist around other stars,” said team member Björn Benneke of the Université de Montréal. “This is an important step toward determining the prevalence and diversity of atmospheres on rocky planets.”
However, it remains too early to tell whether Hubble spectroscopically measured a small amount of water vapour in a puffy hydrogen-rich atmosphere, or if the planet’s atmosphere is mostly made of water, left behind after a primaeval hydrogen/helium atmosphere evapourated under stellar radiation.
“Our observing programme was designed specifically with the goal of not only detecting the molecules in the planet’s atmosphere, but of actually looking specifically for water vapour. Either result would be exciting, whether water vapour is dominant or just a tiny species in a hydrogen-dominant atmosphere,” said the science paper’s lead author, Pierre-Alexis Roy of the Université de Montréal.
“Until now, we had not been able to directly detect the atmosphere of such a small planet. And we’re slowly getting into this regime now,” added Benneke. “At some point, as we study smaller planets, there must be a transition where there’s no more hydrogen on these small worlds, and they have atmospheres more like Venus (which is dominated by carbon dioxide).”
Because the planet is as hot as Venus at roughly 425 degrees Celsius, it definitely would be an inhospitable, steamy world if the atmosphere were predominantly water vapour.
At present the team is left with two possibilities. The planet is still clinging to a hydrogen-rich envelope laced with water, making it a mini-Neptune. Alternatively, it could be a warmer version of Jupiter’s moon Europa, which has twice as much water as Earth beneath its crust.
“The planet GJ 9827d could be half water, half rock. And there would be a lot of water vapour on top of some smaller rocky body,” said Benneke.
If the planet has a residual water-rich atmosphere, then it must have formed farther away from its host star, where the temperature is cold and water is available in the form of ice, than its present location. In this scenario, the planet would have then migrated closer to the star and received more radiation. The hydrogen was then heated and escaped, or is still in the process of escaping, the planet’s weak gravity. The alternative theory is that the planet formed close to the hot star, with a trace of water in its atmosphere.
The Hubble programme observed the planet during 11 transits — events in which the planet crossed in front of its star — that were spaced out over three years. During transits, starlight is filtered through the planet’s atmosphere and carries the spectral fingerprint of water molecules. If there are clouds on the planet, they are low enough in the atmosphere that they don’t completely hide Hubble’s view of the atmosphere, and Hubble is able to probe water vapour above the clouds.
Hubble’s discovery opens the door to studying the planet in more detail. It’s a good target for the NASA/ESA/CSA James Webb Space Telescope to do infrared spectroscopy to look for other atmospheric molecules.
GJ 9827d was discovered by NASA’s Kepler Space Telescope in 2017. It completes an orbit around a red dwarf star every 6.2 days. The star, GJ 9827, lies 97 light-years from Earth in the constellation Pisces.
This is an artist’s conception of the exoplanet GJ 9827d, the smallest exoplanet where water vapour has been detected in its atmosphere. The planet could be an example of potential planets with water-rich atmospheres elsewhere in our galaxy. It is a rocky world, only about twice Earth’s diameter. It orbits the red dwarf star GJ 9827. Two inner planets in the system are on the left. The background stars are plotted as they would be seen to the unaided eye looking back toward our Sun, which itself is too faint to be seen. The blue star at upper right is Regulus, the yellow star at bottom centre is Denebola, and the blue star at bottom right is Spica. The constellation Leo is on the left, and Virgo is on the right. Both constellations are distorted from our Earth-bound view from 97 light-years away. Credit: NASA, ESA, Leah Hustak and Ralf Crawford (STScI)
