Webb discovers methane, carbon dioxide in atmosphere of K2-18 b
A new investigation by an international team of astronomers using data from the NASA/ESA/CSA James Webb Space Telescope into K2-18 b, an exoplanet 8.6 times as massive as Earth, has revealed the presence of carbon-bearing molecules including methane and carbon dioxide. The discovery adds to recent studies suggesting that K2-18 b could be a Hycean exoplanet, one which has the potential to possess a hydrogen-rich atmosphere and a water ocean-covered surface.
This artist’s concept shows what exoplanet K2-18 b could look like based on science data. K2-18 b, an exoplanet 8.6 times as massive as Earth, orbits the cool dwarf star K2-18 in the habitable zone and lies 120 light-years from Earth. A new investigation with the NASA/ESA/CSA James Webb Space Telescope into K2-18 b has revealed the presence of carbon-bearing molecules including methane and carbon dioxide. The abundance of methane and carbon dioxide, and shortage of ammonia, support the hypothesis that there may be an ocean underneath a hydrogen-rich atmosphere in K2-18 b. Credit: NASA, CSA, ESA, J. Olmstead (STScI), N. Madhusudhan (Cambridge University)
The first insight into the atmospheric properties of this habitable-zone exoplanet came from observations with the NASA/ESA Hubble Space Telescope, which prompted further studies that have since changed our understanding of the system.
K2-18 b orbits the cool dwarf star K2-18 in the habitable zone and lies 120 light-years from Earth in the constellation Leo. Exoplanets such as K2-18 b, which have sizes between those of Earth and Neptune, are unlike anything in our Solar System. This lack of equivalent nearby planets means that these ‘sub-Neptunes’ are poorly understood, and the nature of their atmospheres is a matter of active debate among astronomers. Exoplanets such as K2-18 b, which have sizes between those of Earth and Neptune, are unlike anything in our Solar System. This lack of analogous nearby planets means that these ‘sub-Neptunes’ are poorly understood and the nature of their atmospheres is a matter of active debate between astronomers. The suggestion that the sub-Neptune K2-18 b could be a Hycean exoplanet is intriguing, as some astronomers believe that these worlds are promising environments to search for evidence for life on exoplanets.
“Our findings underscore the importance of considering diverse habitable environments in the search for life elsewhere,”
explained Nikku Madhusudhan, an astronomer at the University of Cambridge and lead author of the paper announcing these results.
“Traditionally, the search for life on exoplanets has focused primarily on smaller rocky planets, but the larger Hycean worlds are significantly more conducive to atmospheric observations.“
The abundance of methane and carbon dioxide, and shortage of ammonia, support the hypothesis that there may be an ocean underneath a hydrogen-rich atmosphere on K2-18 b. These initial Webb observations also provided a possible detection of a molecule called dimethyl sulphide (DMS). On Earth, this is only produced by life. The bulk of the DMS in Earth’s atmosphere is emitted from phytoplankton in marine environments.
The inference of DMS is less robust and requires further validation.
“Upcoming Webb observations should be able to confirm if DMS is indeed present in the atmosphere of K2-18 b at significant levels,” explained Madhusudhan.
While K2-18 b lies in the habitable zone and is now known to harbour carbon-bearing molecules, this does not necessarily mean that the planet can support life. The planet’s large size — with a radius 2.6 times the radius of Earth — means that the planet’s interior likely contains a large mantle of high-pressure ice, like Neptune, but with a thinner hydrogen-rich atmosphere and an ocean surface. Hycean worlds are predicted to have oceans of water. However, it is also possible that the ocean is too hot to be habitable or be liquid.
“Although this kind of planet does not exist in our solar system, sub-Neptunes are the most common type of planet known so far in the galaxy,” explained team member Subhajit Sarkar of Cardiff University. “We have obtained the most detailed spectrum of a habitable-zone sub-Neptune to date, and this allowed us to work out the molecules that exist in its atmosphere.”
Characterising the atmospheres of exoplanets like K2-18 b — meaning identifying their gases and physical conditions — is a very active area in astronomy. However, these planets are outshone — literally — by the glare of their much larger parent stars, which makes exploring exoplanet atmospheres particularly challenging.
The team sidestepped this challenge by analysing light from K2-18 b’s parent star as it passed through the exoplanet’s atmosphere. K2-18 b is a transiting exoplanet, meaning that we can detect a drop in brightness as it passes across the face of its host star. This is how the exoplanet was first discovered. This means that during transits a tiny fraction of starlight will pass through the exoplanet’s atmosphere before reaching telescopes like Webb. The starlight’s passage through the exoplanet atmosphere leaves traces that astronomers can piece together to determine the gases of the exoplanet’s atmosphere.
“This result was only possible because of the extended wavelength range and unprecedented sensitivity of Webb, which enabled robust detection of spectral features with just two transits,” continued Madhusudhan. “For comparison, one transit observation with Webb provided comparable precision to eight observations with Hubble conducted over a few years and in a relatively narrow wavelength range.”
“These results are the product of just two observations of K2-18 b, with many more on the way,” explained team member Savvas Constantinou of the University of Cambridge. “This means our work here is but an early demonstration of what Webb can observe in habitable-zone exoplanets.”
The team now intends to conduct follow-up research with the telescope’s Mid-InfraRed Instrument (MIRI) spectrograph that they hope will further validate their findings and provide new insights into the environmental conditions on K2-18 b.
“Our ultimate goal is the identification of life on a habitable exoplanet, which would transform our understanding of our place in the Universe,” concluded Madhusudhan. “Our findings are a promising step towards a deeper understanding of Hycean worlds in this quest.”
Spectrum of K2-18 b, obtained with Webb’s NIRISS (Near-Infrared Imager and Slitless Spectrograph) and NIRSpec (Near-Infrared Spectrograph), displays an abundance of methane and carbon dioxide in the exoplanet’s atmosphere, as well as a possible detection of a molecule called dimethyl sulfide (DMS). The detection of methane and carbon dioxide, and shortage of ammonia, are consistent with the presence of an ocean underneath a hydrogen-rich atmosphere in K2-18 b. K2-18 b, 8.6 times as massive as Earth, orbits the cool dwarf star K2-18 in the habitable zone and lies 120 light-years from Earth. Credit: NASA, CSA, ESA, J. Olmstead (STScI), N. Madhusudhan (Cambridge University)
The team’s results are accepted for publication in The Astrophysical Journal Letters.
Notes
[1] The Habitable Zone is the region around a star where the conditions could potentially be suitable to sustain life on a planet within this region, for example allowing the presence of liquid water on its surface.
The glittering globular cluster Terzan 12 — a vast, tightly bound collection of stars — fills the frame of this image from the NASA/ESA Hubble Space Telescope. The location of this globular cluster, deep in the Milky Way galaxy in the constellation Sagittarius, means that it is shrouded in gas and dust which absorb and alter the starlight emanating from Terzan 12.
This star-studded stellar census comes from a string of observations that aim to systematically explore the relatively few globular clusters located towards the centre of our galaxy, such as Terzan 12, which is located about 15 000 light-years from Earth. Globular clusters are not uncommon in the Milky Way galaxy. Around 150 are known, mostly in its outer halo, and Hubble has revolutionised their study since its launch in 1990. However, examining clusters like Terzan 12, highly obscured by interstellar dust, is complicated by the resulting reddening of the light.
The glittering globular cluster Terzan 12 — a vast, tightly bound collection of stars — fills the frame of this image from the NASA/ESA Hubble Space Telescope. This star-studded stellar census comes from a string of observations that aim to systematically explore globular clusters located towards the centre of our galaxy, such as this one in the constellation Sagittarius. The locations of these globular clusters — deep in the Milky Way galaxy — mean that they are shrouded in gas and dust, which can block or alter the wavelengths of starlight emanating from the clusters. Here, astronomers were able to sidestep the effect of gas and dust by comparing the new observations made with the razor-sharp vision of Hubble’s Advanced Camera for Surveys and Wide-Field Camera 3 with pre-existing images. Their observations should shed light on the relation between age and composition in the Milky Way’s innermost globular clusters. Credit: ESA/Hubble & NASA, R. Cohen (Rutgers University)
When starlight passes through an interstellar cloud it can be absorbed and scattered by particles of dust. The strength of this scattering depends on the wavelength of the light, with shorter wavelengths being scattered and absorbed more strongly. This means that the blue wavelengths of light from stars are less likely to make it through a cloud, making background stars appear redder than they actually are.
Astronomers refer to the colour change caused by the scattering and absorption of starlight — appropriately — as reddening, and it is responsible for the vibrant range of colours in this image. Relatively unobscured stars shine brightly in white and blue, whereas creeping tendrils of gas and dust blanket other large portions of Terzan 12, giving stars a sinister red hue. The more dust that lies along our line of sight to the cluster, the more the light of the stars is reddened.
A similar effect is responsible for the spectacular rosy hues of sunsets here on Earth. The atmosphere preferentially scatters shorter wavelengths of light, which is why the sky overhead appears blue. As the sun sinks lower in the sky, sunlight has to pass through more of the atmosphere, which means more and more blue light is scattered and sunlight takes on a characteristically golden red hue.
Some of the stars in the photo appear starkly different in colour to their near neighbours. The brightest red stars are bloated, ageing giants, many times larger than our Sun. They lie between Earth and the cluster. Only a few may actually be members of the cluster. The very brightest hot, blue stars are also along the line of sight and not inside the cluster, which only contains ageing stars.
The reddening of stars usually poses problems for astronomers, but the scientists behind this observation of Terzan 12 were able to sidestep the effect of gas and dust by comparing the new observations made with the razor-sharp vision of Hubble’s Advanced Camera for Surveys and Wide-Field Camera 3 with pre-existing images. Their observations should shed light on the relation between age and composition in the Milky Way’s galaxy’s innermost globular clusters, comparable to astronomers’ understanding of the clusters spread throughout the rest of our galaxy.
Incidentally, the Terzan clusters suffer from something of an astronomical identity crisis: there were actually only 11 clusters discovered by the Turkish-Armenian astronomer Agop Terzan. The mix-up results from an error made by Terzan in 1971, when he rediscovered Terzan 5 — a cluster he had already discovered and reported in 1968 — and named it Terzan 11. Terzan attempted to fix his mistake, but the confusion caused has persisted in scientific studies ever since, astronomers eventually settling on the odd convention that there is no Terzan 11.
Losing and then rediscovering astronomical objects is surprisingly common, even in our own Solar System. Minor planets such as asteroids and dwarf planets are often detected and then subsequently lost because their orbits cannot be determined from only a tiny handful of observations.
This composite image shows the location of the globular star cluster Terzan 12 as seen by the NASA/ESA Hubble Space Telescope. Top: A view of a section of our Milky Way in the direction of the constellation Sagittarius. Dense clouds of dust are etched across a whitish background of stars. The object at upper right is the Rho Ophiuchi cloud complex. Bottom left: Photo of a small portion of the Milky Way which is only one-degree across – twice the angular diameter of the full moon. The globular cluster is in the image centre. Bottom Right: A new Hubble Space Telescope image of the dense cluster Terzan 12. Intervening dust scatters starlight to create multiple reddish hues. The brightest red stars in the photo are bloated, ageing giants, many times larger than our Sun. They lie between Earth and the cluster. Only a few may actually be members of the cluster. The very brightest hot, blue stars are also along the line of sight and not inside the cluster, which only contains ageing stars. The cluster is about 15,000 light-years from Earth. Credit: NASA, ESA, Stéphane Guisard, ESO, Digitized Sky Survey, ESA/Hubble, Roger Cohen (Rutgers University), Joseph DePasquale (STScI)
The NASA/ESA/CSA James Webb Space Telescope has observed the well-known Ring Nebula with unprecedented detail. Formed by a star throwing off its outer layers as it runs out of fuel, the Ring Nebula is an archetypal planetary nebula. The object is also known as M57 and NGC 6720, and is relatively close to Earth at roughly 2,500 light-years away.
This new NIRCam image provides unprecedented spatial resolution and spectral sensitivity. For example, the intricate details of the filament structure of the inner ring are particularly visible in this dataset. Credit: ESA/Webb, NASA, CSA, M. Barlow, N. Cox, R. Wesson
The new images provide unprecedented spatial resolution and spectral sensitivity, which also reveal unique details across both infrared observations. For example, the new image from NIRCam (Near-InfraRed Camera) shows the intricate details of the filament structure of the inner ring, while the new image from MIRI (Mid-InfraRed Instrument) reveals particular details in the concentric features in the outer regions of the nebulae’s ring.
Webb’s MIRI (Mid-InfraRed Instrument) reveals particular details in the concentric features in the outer regions of the nebulae’s ring (right). Credit: ESA/Webb, NASA, CSA, M. Barlow, N. Cox, R. Wesson
There are some 20,000 dense globules in the nebula, which are rich in molecular hydrogen. In contrast, the inner region shows very hot gas. The main shell contains a thin ring of enhanced emission from carbon-based molecules known as polycyclic aromatic hydrocarbons (PAHs). Roughly ten concentric arcs are located just beyond the outer edge of the main ring. The arcs are thought to originate from the interaction of the central star with a low-mass companion orbiting at a distance comparable to that between the Earth and the dwarf planet Pluto. In this way, nebulae like the Ring Nebula reveal a kind of astronomical archaeology, as astronomers study the nebula to learn about the star that created it.
The nebula is shaped like a distorted doughnut. We are gazing almost directly down one of the poles of this structure, with a brightly coloured barrel of material stretching away from us. Although the centre of this doughnut may look empty, it is actually full of lower density material that stretches both towards and away from us, creating a shape similar to a rugby ball slotted into the doughnut’s central gap.
The colourful main ring is composed of gas thrown off by a dying star at the centre of the nebula. This star is on its way to becoming a white dwarf — a very small, dense, and hot body that is the final evolutionary stage for a star like the Sun.
The Ring Nebula is one of the most notable objects in our skies. It was discovered in 1779 by astronomers Antoine Darquier de Pellepoix and Charles Messier, and was added to the Messier Catalogue. Both astronomers stumbled upon the nebula when trying to follow the path of a comet through the constellation of Lyra, passing very close to the Ring Nebula.
These observations were completed as part of the James Webb Space Telescope observing programme GO 1558. To learn more about the team’s research of these new observations, see the latest NASA Webb blog here.
The NASA/ESA/CSA James Webb Space Telescope has observed the well-known Ring Nebula with unprecedented detail. Formed by a star throwing off its outer layers as it runs out of fuel, the Ring Nebula is an archetypal planetary nebula. Also known as M57 and NGC 6720, it is both relatively close to Earth at roughly 2,500 light-years away. The new images provide unprecedented spatial resolution and spectral sensitivity, which also reveal unique details across both infrared observations. For example, the new image from Webb’s NIRCam (Near-InfraRed Camera) shows the intricate details of the filament structure of the inner ring (left), while the new image from Webb’s MIRI (Mid-InfraRed Instrument) reveals particular details in the concentric features in the outer regions of the nebulae’s ring (right). There are some 20,000 dense globules in the nebula, which are rich in molecular hydrogen. In contrast, the inner region shows very hot gas. The main shell contains a thin ring of enhanced emission from carbon-based molecules known as polycyclic aromatic hydrocarbons (PAHs). Roughly ten concentric arcs are located just beyond the outer edge of the main ring. The arcs are thought to originate from the interaction of the central star with a low-mass companion orbiting at a distance comparable to that between the Earth and the dwarf planet Pluto. In this way, nebulae like the Ring Nebula reveal a kind of astronomicalarchaeology, as astronomers study the nebula to learn about the star that created it. Credit: ESA/Webb, NASA, CSA, M. Barlow, N. Cox, R. Wesson
Webb snaps highly detailed infrared image of actively forming stars, known as Herbig-Haro 46/47
The NASA/ESA/CSA James Webb Space Telescope has captured the ‘antics’ of a pair of actively forming young stars, known as Herbig-Haro 46/47, in a high-resolution image in near-infrared light. This is the most detailed portrait of these stars, which reside only 1470 light-years away in the constellation Vela, to date.
Herbig-Haro 46/47 (NIRCam image – annotated). Credit: NASA, ESA, CSA, J. DePasquale (STScI)
To find the pair of young stars, trace the bright pink and red diffraction spikes in the image until you hit the centre: the stars are within the orange-white splotch. They are buried deeply in a disc of gas and dust that feeds their growth as they continue to gain mass. The disc is not visible, but its shadow can be seen in the two dark, conical regions surrounding the central stars.
The pair of actively forming stars has sent out jets in two directions for thousands of years. Although Herbig-Haro 46/47 has been studied by many telescopes, both on the ground and in space, since the 1950s, Webb is the first to capture them at high resolution in near-infrared light. With Webb, we can now understand more of the stars’ activity — past and present — and peer through the dusty blue nebula, which appears black in visible-light images, that surrounds them. Over time, researchers will be able to glean new details about how stars form.
The most striking details are the two-sided lobes that fan out from the actively forming central stars, represented in fiery orange. Much of this material was shot out from those stars as they repeatedly ingest and eject the gas and dust that immediately surround them over thousands of years.
When material from more recent ejections runs into older material, it changes the shape of these lobes. This activity is like a large fountain being turned on and off in rapid, but random succession, leading to billowing patterns in the pool below it. Some jets send out more material and others launch at faster speeds. Why? It’s likely related to how much material fell onto the stars at a particular point in time.
The stars’ more recent ejections appear in a thread-like blue. They run just below the red diagonal diffraction spike at two o’clock. Along the right side, these ejections make clearer wavy patterns. They are disconnected at points, and end in a remarkable uneven light purple circle in the thickest orange area. Lighter blue, curly lines also emerge on the left, near the central stars, but are sometimes overshadowed by the bright red diffraction spike.
All of these jets are crucial to the star formation process itself. Ejections regulate how much mass the stars ultimately gather. (The disc of gas and dust feeding the stars is small. Imagine a band tightly tied around the stars.)
Now, turn your eye to the second most prominent feature: the effervescent blue cloud. This is a region of dense dust and gas, known both as a nebula and more formally as a Bok globule. When viewed in mainly visible light, it appears almost completely black — only a few background stars peek through. In Webb’s crisp near-infrared image, we can see into and through the gauzy layers of this cloud, bringing a lot more of Herbig-Haro 46/47 into focus, while also revealing a wide range of stars and galaxies that lie well beyond it. The nebula’s edges appear in a soft orange outline, like a backward L along the right and bottom of the image.
This nebula is significant — its presence influences the shapes of the jets shot out by the central stars. As ejected material rams into the nebula on the lower left, there is more opportunity for the jets to interact with molecules within the nebula, causing them both to light up.
There are two other areas to look at to compare the asymmetry of the two lobes. Glance toward the upper right to pick out a blobby, almost sponge-shaped ejecta that appears separate from the larger lobe. Only a few threads of the semi-transparent wisps of material point toward the larger lobe. Almost transparent, tentacle-like shapes also appear to be drifting behind it, like streamers in a cosmic wind. In contrast, at lower left, look beyond the hefty lobe to find an arc. Both are made up of material that was pushed the farthest and possibly by earlier ejections. The arcs appear to point in different directions, and may have originated from different outflows.
Take another long look at this image. Although it appears Webb has snapped Herbig-Haro 46/47 edge-on, one side is angled slightly towards Earth. Counterintuitively, it’s the smaller right half. Though the left side is larger and brighter, it is pointing away from us.
Over millions of years, the stars in Herbig-Haro 46/47 will form fully — clearing the scene of these fantastic, multihued ejections and allowing the binary stars to take centre stage against a galaxy-filled background.
Webb can reveal so much detail in Herbig-Haro 46/47 for two reasons. The object is relatively close to Earth, and Webb’s image is made up of several exposures, which adds to its depth.
Herbig-Haro 46/47 (NIRCam image). The NASA/ESA/CSA James Webb Space Telescope has captured a high-resolution image of a tightly bound pair of actively forming stars, known as Herbig-Haro 46/47, in near-infrared light. Look for them at the centre of the red diffraction spikes. The stars are buried deeply, appearing as an orange-white splotch. They are surrounded by a disc of gas and dust that continues to add to their mass. Herbig-Haro 46/47 is an important object to study because it is relatively young — only a few thousand years old. Stars take millions of years to form. Targets like this also give researchers insight into how stars gather mass over time, potentially allowing them to model how our own Sun, a low-mass star, formed. The two-sided orange lobes were created by earlier ejections from these stars. The stars’ more recent ejections appear as blue, thread-like features, running along the angled diffraction spike that covers the orange lobes. Actively forming stars ingest the gas and dust that immediately surrounds them in a disc (imagine an edge-on circle encasing them). When the stars ‘eat’ too much material in too short a time, they respond by sending out two-sided jets along the opposite axis, settling down the star’s spin, and removing mass from the area. Over millennia, these ejections regulate how much mass the stars retain. Don’t miss the delicate, semi-transparent blue cloud. This is a region of dense dust and gas, known as a nebula. Webb’s crisp near-infrared image lets us see through its gauzy layers, showing off a lot more of Herbig-Haro 46/47, while also revealing a wide range of stars and galaxies that lie far beyond it. The nebula’s edges transform into a soft orange outline, like a backward L along the right and bottom of the image. The blue nebula influences the shapes of the orange jets shot out by the central stars. As ejected material rams into the nebula on the lower left, it takes on wider shapes, because there is more opportunity for the jets to interact with molecules within the nebula. Its material also causes the stars’ ejections to light up. Over millions of years the stars in Herbig-Haro 46/47 will form fully — clearing the scene. Take a moment to linger on the background. A profusion of extremely distant galaxies dot Webb’s view. Its composite NIRCam (Near-Infrared Camera) image is made up of several exposures, highlighting distant galaxies and stars. Blue objects with diffraction spikes are stars, and the closer they are, the larger they appear. White-and-pink spiral galaxies sometimes appear larger than these stars, but are significantly farther away. The tiniest red dots, Webb’s infrared specialty, are often the oldest, most distant galaxies. Credit: NASA, ESA, CSA, J. DePasquale (STScI)
Webb detects water vapour in the inner disk of the system PDS 70, a rocky planet-forming zone
New measurements by the NASA/ESA/CSA James Webb Space Telescope’s Mid-InfraRed Instrument (MIRI) have detected water vapour in the inner disc of the system PDS 70, located 370 light-years away. This is the first detection of water in the terrestrial region of a disc already known to host two or more protoplanets.
This artist concept portrays the star PDS 70 and its inner protoplanetary disc. New measurements from the NASA/ESA/CSA James Webb Space Telescope’s Mid-InfraRed Instrument (MIRI) have indicated the presence of water vapour in the inner disc of the system PDS 70, located 370 light-years away. This is the first detection of water in the terrestrial region of a disc already known to host two or more protoplanets, one of which is shown at upper right. Credit: NASA, ESA, CSA, J. Olmsted (STScI)
Water is essential for life as we know it. However, scientists debate how it reached the Earth and whether the same processes could seed rocky exoplanets orbiting distant stars. New insights may come from the system PDS 70, which hosts an inner disc and an outer disc that are separated by a gap of eight billion kilometres, within which are two known gas-giant planets. MIRI has detected water vapour in the system’s inner disc at distances of less than 160 million kilometres from the star — the region where rocky, terrestrial planets may be forming (the Earth orbits 150 million kilometres from our Sun).
“We’ve seen water in other discs, but not so close in and in a system where planets are currently assembling. We couldn’t make this type of measurement before Webb,” said lead author Giulia Perotti of the Max Planck Institute for Astronomy (MPIA) in Heidelberg, Germany.
“This discovery is extremely exciting, as it probes the region where rocky planets similar to Earth typically form,”
added MPIA director Thomas Henning, a co-author of the paper. Henning is co-principal investigator of Webb’s MIRI (Mid-InfraRed Instrument), which made the detection, and the principal investigator of the MINDS (MIRI Mid-Infrared Disk Survey) programme that took the data.
A wet environment for forming planets
PDS 70 is a K-type star, cooler than our Sun, and is estimated to be 5.4 million years old. This is relatively old amongst stars with planet-forming discs, which made the discovery of water vapour surprising.
Over time, the gas and dust content of planet-forming discs declines. Either the central star’s radiation and winds remove such material, or the dust grows into larger objects that eventually form planets. As previous studies failed to detect water in the central regions of similarly aged discs, astronomers suspected it might not survive the harsh stellar radiation, leading to a dry environment for the formation of any rocky planets.
Astronomers haven’t yet detected any planets forming within the inner disc of PDS 70. However, they do see the raw materials for building rocky worlds, in the form of silicates. The detection of water vapour implies that if rocky planets are forming there, they will have water available to them from the beginning.
“We find a relatively large amount of small dust grains. Combined with our detection of water vapour, the inner disc is a very exciting place,” said co-author Rens Waters of Radboud University in the Netherlands.
What is the origin of the water?
The discovery raises the question of where the water came from. The MINDS team considered two different scenarios to explain their finding.
One possibility is that water molecules are forming in place, where we detect them, as hydrogen and oxygen atoms combine. A second possibility is that ice-coated dust particles are being transported from the cool outer disc to the hot inner disc, where the water ice sublimates and turns into vapour. Such a transport system would be surprising, since the dust would have to cross the large gap carved out by the two giant planets.
Another question raised by the discovery is how water could survive so close to the star, where the star’s ultraviolet light should break apart any water molecules. Most likely, surrounding material, such as dust and other water molecules, serves as a protective shield. As a result, the water detected near PDS 70 could survive destruction.
Ultimately, the team will use two of Webb’s other instruments, the Near-InfraRed Camera (NIRCam) and the Near-InfraRed Spectrograph (NIRSpec) to study the PDS 70 system in an effort to glean an even greater understanding.
These observations were made as part of Guaranteed Time Observation program 1282. This finding has been published in the journal Nature.
New measurements from the NASA/ESA/CSA James Webb Space Telescope’s Mid-InfraRed Instrument (MIRI) have indicated the presence of water vapour in the inner disc of the system PDS 70, located 370 light-years away. This is the first detection of water in the terrestrial region of a disc already known to host two or more protoplanets. This spectrum of the protoplanetary disk of PDS 70, obtained with Webb’s MIRI instrument, displays a number of emission lines from water vapour. Credit: NASA, ESA, CSA, J. Olmsted (STScI)
Hubble sees boulders escaping from asteroid Dimorphos
Astronomers using the NASA/ESA/ Hubble Space Telescope’s extraordinary sensitivity have discovered a swarm of boulders that were possibly shaken off the asteroid Dimorphos when NASA deliberately slammed the half-tonne DART impactor spacecraft into Dimorphos at approximately 22 500 kilometres per hour. DART intentionally impacted Dimorphos on 26 September 2022, slightly changing the trajectory of its orbit around the larger asteroid Didymos.
This NASA/ESA Hubble Space Telescope image of the asteroid Dimorphos was taken on 19 December 2022, nearly four months after the asteroid was impacted by NASA’s DART (Double Asteroid Redirection Test) mission. Hubble’s sensitivity reveals a few dozen boulders knocked off the asteroid by the force of the collision. These are among the faintest objects Hubble has ever photographed inside the Solar System. The ejected boulders range in size from 1 metre to 6.7 metres across, based on Hubble photometry. They are drifting away from the asteroid at around a kilometre per hour. The discovery yields invaluable insights into the behaviour of a small asteroid when it is hit by a projectile for the purpose of altering its trajectory. Credit: NASA, ESA, D. Jewitt (UCLA)
The 37 ejected boulders range in size from 1 metre to 6.7 metres across, based on Hubble photometry. They are drifting away from the asteroid at around one kilometre per hour. The total mass in these detected boulders is about 0.1% the mass of Dimorphos. The boulders are some of the faintest objects ever imaged in the Solar System.
This opens up a new dimension for studying the aftermath of the DART experiment using the European Space Agency’s upcoming Hera mission, which is due to launch in 2024. The spacecraft will perform a detailed post-impact survey of the target asteroid Dimorphos. Hera will turn the grand-scale experiment into a well-understood and repeatable planetary defence technique that might one day be used for real [1].
The boulders are most likely not shattered pieces of the diminutive asteroid caused by the impact. They were already scattered across the asteroid’s surface, as evident in the last close-up picture taken by the DART spacecraft just two seconds before collision, when it was only 11 kilometres above the surface.
The science team that observed these boulders with Hubble estimates that the impact shook off two percent of the boulders on the asteroid’s surface. While the boulder observations by Hubble also give an estimate for the size of the DART impact crater, Hera will eventually determine the actual crater size.
Long ago, Dimorphos may have formed from material shed into space by the larger asteroid Didymos. The parent body may have spun up too quickly or could have lost material after a glancing collision with another object, among other scenarios. The ejected material formed a ring that gravitationally coalesced to form Dimorphos. This would make it a flying rubble pile of rocky debris loosely held together by the relatively weak pull of its gravity. Therefore, the interior is probably not solid, but has a structure more like a bunch of grapes.
It’s not clear how the boulders were lifted off the asteroid’s surface. They could be part of an ejecta plume that was photographed by Hubble and other observatories. Or a seismic wave from the impact may have rattled through the asteroid — like hitting a bell with a hammer — shaking loose the surface rubble.
The DART and LICIACube (Light Italian CubeSat for Imaging of Asteroids) teams have also been studying boulders detected in images taken by LICIACube’s LUKE (LICIACube Unit Key Explorer) camera in the minutes immediately following DART’s kinetic impact.
Notes
[1] Just like Hubble and the NASA/ESA/CSA James Webb Space Telescope, NASA’s DART and ESA’s Hera missions are great examples of what international collaboration can achieve; the two missions are supported by the same teams of scientists and astronomers, and operate via an international collaboration called AIDA — the Asteroid Impact and Deflection Assessment.
NASA and ESA worked together in the early 2000s to develop asteroid monitoring systems, but recognised there was a missing link in the chain between asteroid threat identification and ways of addressing that threat. In response NASA oversaw the DART mission while ESA developed the Hera mission to gather additional data on DART’s impact. With the Hera mission, ESA is assuming even greater responsibility for protecting our planet and ensuring that Europe plays a leading role in the common effort to tackle asteroid risks. As Europe’s flagship planetary defender, Hera is supported through the Agency’s Space Safety programme, part of the Operations Directorate.
Hubble sees boulders escaping from asteroid Dimorphos: this NASA/ESA Hubble Space Telescope image of the asteroid Dimorphos was taken on 19 December 2022, nearly four months after the asteroid was impacted by NASA’s DART (Double Asteroid Redirection Test) mission. Hubble’s sensitivity reveals a few dozen boulders knocked off the asteroid by the force of the collision. These are among the faintest objects Hubble has ever photographed inside the Solar System. The ejected boulders range in size from 1 metre to 6.7 metres across, based on Hubble photometry. They are drifting away from the asteroid at around a kilometre per hour. The discovery yields invaluable insights into the behaviour of a small asteroid when it is hit by a projectile for the purpose of altering its trajectory. Credit: NASA, ESA, D. Jewitt (UCLA)
Webb sees carbon-rich dust grains at redshift, in the first billion years of cosmic time
For the first time, the NASA/ESA/CSA James Webb Space Telescope has observed the chemical signature of carbon-rich dust grains at redshift ~ 7 [1], which is roughly equivalent to one billion years after the birth of the Universe [2]. Similar observational signatures have been observed in the much more recent Universe, attributed to complex, carbon-based molecules known as polycyclic aromatic hydrocarbons (PAHs). It is not thought likely, however, that PAHs would have developed within the first billion years of cosmic time. Therefore, this observation suggests the exciting possibility that Webb may have observed a different species of carbon-based molecule: possibly minuscule graphite- or diamond-like grains produced by the earliest stars or supernovae. This observation suggests exciting avenues of investigation into both the production of cosmic dust and the earliest stellar populations in our Universe, and was made possible by Webb’s unprecedented sensitivity.
This image highlights the location of the galaxy JADES-GS-z6 in a portion of an area of the sky known as GOODS-South, which was observed as part of the JWST Advanced Deep Extragalactic Survey, or JADES. This galaxy, along with others in this region, were part of a Webb study by an international team of astronomers, who observed the chemical signature of carbon-rich dust grains at redshift ~7. This is roughly equivalent to one billion years after the birth of the Universe. Similar observational signatures have been observed in the much more recent Universe, attributed to complex, carbon-based molecules known as polycyclic aromatic hydrocarbons (PAHs). It is not thought likely, however, that PAHs would have developed within the first billion years of cosmic time. Therefore, this observation suggests the exciting possibility that Webb may have observed a different species of carbon-based molecule: possibly minuscule graphite- or diamond-like grains produced by the earliest stars or supernovae. This observation suggests exciting avenues of investigation into both the production of cosmic dust and the earliest stellar populations in our Universe, and was made possible by Webb’s unprecedented sensitivity. The team’s research indicates that this particular galaxy showed significant dust obscuration and has undergone substantial metal enrichment relative to galaxies with similar mass at the same redshift. The team also believes the galaxy’s visible colour gradient may indicate a peculiar geometrical alignment of stars and dust. In this image, blue, green, and red were assigned to Webb’s NIRCam (Near-Infrared Camera) data at 0.9, 1.15, and 1.5 microns; 2.0, 2.77, and 3.55 microns; and 3.56, 4.1, and 4.44 microns (F090W, F115W, and F150W; F200W, F277W, and F335M; and F356W, F410M, and F444W), respectively. The galaxy is shown zoomed in on a region measuring roughly 1×1 arcseconds, which is a measure of angular distance on the sky. One arcsecond is equal to 1/3600 of one degree of arc (the full Moon has an angular diameter of about 0.5 degrees). The actual size of an object that covers one arcsecond on the sky depends on its distance from the telescope. Credit: ESA/Webb, NASA, ESA, CSA, B. Robertson (UC Santa Cruz), B. Johnson (Center for Astrophysics, Harvard & Smithsonian), S. Tacchella (University of Cambridge, M. Rieke (Univ. of Arizona), D. Eisenstein (Center for Astrophysics, Harvard & Smithsonian), A. Pagan (STScI)
The seemingly empty spaces in our Universe are in reality often not empty at all, but occupied by clouds of gas and cosmic dust. This dust consists of grains of various sizes and compositions that are formed and ejected into space in a variety of ways, including by supernova events. This material is crucial to the evolution of the Universe, as dust clouds ultimately form the birthplaces for new stars and planets. However, it can also be a hindrance to astronomers: the dust absorbs stellar light at certain wavelengths, making some regions of space very challenging to observe. An upside, however, is that certain molecules will very consistently absorb or otherwise interact with specific wavelengths of light. This means that astronomers can acquire information about the cosmic dust’s composition by observing the wavelengths of light that it blocks. An international team of astronomers used this technique, combined with Webb’s extraordinary sensitivity, to detect the presence of carbon-rich dust grains only a billion years after the birth of the Universe.
Joris Witstok of the University of Cambridge, the lead author of this work, elaborates: “Carbon-rich dust grains can be particularly efficient at absorbing ultraviolet light with a wavelength around 217.5 nanometres, which for the first time we have directly observed in the spectra of very early galaxies.”
This prominent 217.5-nanometre feature has previously been observed in the much more recent and local Universe, both within our own Milky Way galaxy, and in galaxies up to redshift ~ 3 [1]. It has been attributed to two different types of carbon-based species: polycyclic aromatic hydrocarbons (PAHs) or nano-sized graphitic grains. PAHs are complex molecules, and modern models predict that it should take several hundreds of millions of years before they form. It would be surprising, therefore, if the team had observed the chemical signature of a mixture of dust grains that include species that were unlikely to have formed yet. However, according to the science team, this result is the earliest and most distant direct signature for this particular type of carbon-rich dust grain.
The answer may lie in the details of what was observed. As already stated, the feature associated with the cosmic dust mixture of PAHs and tiny graphitic grains is at 217.5 nanometres. However, the feature observed by the team actually peaked at 226.3 nanometres. A nanometre is a millionth of a millimetre, and this discrepancy of less than ten nanometres could be accounted for by measurement error [3]. Equally, it could also indicate a difference in the composition of the early-Universe cosmic dust mixture that the team detected.
“This slight shift in wavelength of where the absorption is strongest suggests we may be seeing a different mix of grains, for example graphite- or diamond-like grains,” adds Witstok. “This could also potentially be produced on short timescales by Wolf-Rayet stars or supernova ejecta.”
The detection of this feature in the early Universe is surprising, and allows astronomers to postulate about the mechanisms that could create such a mix of dust grains. This involves drawing on existing knowledge from observations and models. Witstok suggests diamond grains formed in supernova ejecta because models have previously suggested that nano-diamonds could be formed this way. Wolf-Rayet stars are suggested because they are exceptionally hot towards the end of their lives, and very hot stars tend to live fast and die young; giving enough time for generations of stars to have been born, lived, and died, to distribute carbon-rich grains into the surrounding cosmic dust in under a billion years. Models have also shown that carbon-rich grains can be produced by certain types of Wolf-Rayet stars, and just as importantly that those grains can survive the violent deaths of those stars. However, it is still a challenge to fully explain these results with the existing understanding of the early formation of cosmic dust. These results will therefore go on to inform the development of improved models and future observations.
Before Webb, the observations of multiple galaxies had to be combined in order to get signals strong enough to make deductions about the stellar populations in the galaxies, and to learn about how their light was affected by dust absorption. Importantly, astronomers were restricted to studying relatively old and mature galaxies that had had a long time to form stars as well as dust. This limited their ability to really pin down the key sources of cosmic dust. With the advent of Webb, astronomers are now able to make very detailed observations of the light from individual dwarf galaxies, seen in the first billion years of cosmic time. Webb finally permits the study of the origin of cosmic dust and its role in the crucial first stages of galaxy evolution.
“This discovery was made possible by the unparalleled sensitivity improvement in near-infrared spectroscopy provided by Webb, and specifically its Near-Infrared Spectrograph (NIRSpec),” noted team member Roberto Maiolino of the University of Cambridge and University College London. “The increase in sensitivity provided by Webb is equivalent, in the visibile, to instantaneously upgrading Galileo’s 37-millimetre telescope to the 8-metre Very Large Telescope (one of the most powerful modern optical telescopes).”
NIRSpec was built for the European Space Agency by a consortium of European companies led by Airbus Defence and Space (ADS) with NASA’s Goddard Space Flight Centre providing its detector and micro-shutter subsystems. The primary goal of NIRSpec is to enable large spectroscopic surveys of astronomical objects such as stars or distant galaxies. This is made possible by its powerful multi-object spectroscopy mode, which makes use of microshutters. This mode is capable of obtaining spectra of up to nearly 200 objects simultaneously, over a 3.6 × 3.4 arcminute field of view — the first time this capability has been provided from space. This mode makes for very efficient use of Webb’s valuable observing time.
The team is also planning further research into the data and this result.
“We are planning to work further with theorists who model dust production and growth in galaxies,” shares team member Irene Shivaei of the University of Arizona/Centro de Astrobiología (CAB). “This will shed light on the origin of dust and heavy elements in the early Universe.”
These observations were made as part of the JWST Advanced Deep Extragalactic Survey, or JADES, which devoted about 32 days of telescope time to uncovering and characterising faint, distant galaxies. This programme has facilitated the discovery of hundreds of galaxies that existed when the Universe was less than 600 million years old, including some of the farthest galaxies known to date. The sheer number and maturity of these galaxies was far beyond predictions from observations made before Webb’s launch. This new result of early-Universe dust grains contributes to our growing and evolving understanding of the evolution of stellar populations and galaxies during the first billion years of cosmic time.
“This discovery implies that infant galaxies in the early Universe develop much faster than we ever anticipated,” adds team member Renske Smit of the Liverpool John Moores University in the United Kingdom. “Webb shows us a complexity of the earliest birth-places of stars (and planets) that models are yet to explain.“
The infrared image shown here was taken as part of the JADES programme (the JWST Advanced Deep Extragalactic Survey) and shows a portion of an area of the sky known as GOODS-South. This region was the focus area of Webb study for an international team of astronomers, who observed the chemical signature of carbon-rich dust grains at redshift ~7. This is roughly equivalent to one billion years after the birth of the Universe. Similar observational signatures have been observed in the much more recent Universe, attributed to complex, carbon-based molecules known as polycyclic aromatic hydrocarbons (PAHs). It is not thought likely, however, that PAHs would have developed within the first billion years of cosmic time. Therefore, this observation suggests the exciting possibility that Webb may have observed a different species of carbon-based molecule: possibly minuscule graphite- or diamond-like grains produced by the earliest stars or supernovae. This observation suggests exciting avenues of investigation into both the production of cosmic dust and the earliest stellar populations in our Universe, and was made possible by Webb’s unprecedented sensitivity. In this image, blue, green, and red were assigned to Webb’s NIRCam (Near-Infrared Camera) data at 0.9, 1.15, and 1.5 microns; 2.0, 2.77, and 3.55 microns; and 3.56, 4.1, and 4.44 microns (F090W, F115W, and F150W; F200W, F277W, and F335M; and F356W, F410M, and F444W), respectively. Credit: ESA/Webb, NASA, ESA, CSA, B. Robertson (UC Santa Cruz), B. Johnson (Center for Astrophysics, Harvard & Smithsonian), S. Tacchella (University of Cambridge, M. Rieke (Univ. of Arizona), D. Eisenstein (Center for Astrophysics, Harvard & Smithsonian), A. Pagan (STScI)
Notes
[1] The Universe is expanding. The expansion is taking place at the fundamental spacetime level, which means that light travelling through the Universe is ‘stretched’ as the Universe expands. The earlier in the Universe the light originated, the more it will have been stretched by now. Practically speaking, this stretching of light means its wavelength becomes longer. This effect is known as cosmological redshift, because the colour red has the longest wavelength of all light visible to human eyes. Because of this, cosmological time is often not measured in years, but is indicated by the redshift of the observed light. The very local Universe — where the light we observe was emitted recently and has not been notably redshifted — has a low redshift. Conversely, redshift 7 corresponds to light that was emitted about 13 billion years ago, in the very early Universe.
[2] Astronomy fundamentally involves the study of light, and light travels at a finite speed (roughly 300 million kilometres per second). Objects can only be observed by humans once light from them has reached Earth. Whilst in some ways providing a limitation, this also provides a direct opportunity to study the early as well as the present Universe. Studying light from the early Universe necessarily entails the observation of regions very distant from Earth from which it takes a huge amount of time for light to travel to us. Thus, probing these early cosmological times (or high redshifts) requires very sensitive telescopes.
[3] All scientific measurements — including those from observations and those predicted by models — will have an associated error. This is because there will always be sources of uncertainty. If a measurement falls within the bounds of the expected error, it means that it could still be accurate: in this context, that means the 226.3 nanometre feature could still account for the same mix of cosmic dust as that represented by the 217.5 nanometre feature.
Webb celebrates first year of science with close-up on the birth of Sun-like stars in the Rho Ophiuchi cloud complex
From our cosmic backyard in the Solar System to distant galaxies near the dawn of time, the NASA/ESA/CSA James Webb Space Telescope has delivered on its promise of revealing the Universe like never before in its first year of science operations. To celebrate the completion of a successful first year, a new Webb image has been released of a small star-forming region in the Rho Ophiuchi cloud complex.
The first anniversary image from the NASA/ESA/CSA James Webb Space Telescope displays star birth like it’s never been seen before, full of detailed, impressionistic texture. The subject is the Rho Ophiuchi cloud complex, the closest star-forming region to Earth. It is a relatively small, quiet stellar nursery, but you’d never know it from Webb’s chaotic close-up. Jets bursting from young stars crisscross the image, impacting the surrounding interstellar gas and lighting up molecular hydrogen, shown in red. Some stars display the telltale shadow of a circumstellar disc, the makings of future planetary systems. The young stars at the centre of many of these discs are similar in mass to the Sun or smaller. The heftiest in this image is the star S1, which appears amid a glowing cave it is carving out with its stellar winds in the lower half of the image. The lighter-coloured gas surrounding S1 consists of polycyclic aromatic hydrocarbons, a family of carbon-based molecules that are among the most common compounds found in space. Credit: NASA, ESA, CSA, STScI, K. Pontoppidan (STScI), A. Pagan (STScI)
The new Webb image released today features the nearest star-forming region to us. Its proximity at 390 light-years allows for a highly detailed close-up, with no foreground stars in the intervening space.
The showcased region contains approximately 50 young stars, all of them similar in mass to the Sun or smaller. The darkest areas are the densest, where thick dust cocoons still-forming protostars. Huge red bipolar jets of molecular hydrogen dominate the image, appearing horizontally across the upper third and vertically on the right. These occur when a star first bursts through its natal envelope of cosmic dust, shooting out a pair of opposing jets into space. In contrast, the star S1 has carved out a glowing cave of dust in the lower half of the image. It is the only star in the image that is significantly more massive than the Sun.
Some stars in the image display tell-tale shadows indicating protoplanetary discs – potential future planetary systems in the making.
From its very first deep field image unveiled in July 2022, Webb has delivered on its promise to show us more of the Universe than ever before. However, Webb has revealed much more than distant galaxies in the early Universe.
Beyond the stunning infrared images, what really has scientists excited are Webb’s crisp spectra — the detailed information that can be gleaned from light by the telescope’s spectroscopic instruments. Webb’s spectra have confirmed the distances of some of the farthest galaxies ever observed, and have discovered the earliest, most distant supermassive black holes. They have identified the compositions of planet atmospheres (or lack thereof) with more detail than ever before, and have narrowed down what kinds of atmospheres may exist on rocky exoplanets for the first time. They also have revealed the chemical makeup of stellar nurseries and protoplanetary disks, detecting water, organic carbon-containing molecules, and more. Already, Webb observations have resulted in hundreds of scientific papers answering longstanding questions and raising new ones to address with Webb.
The breadth of Webb science is also apparent in its observations of the region of space we are most familiar with — the Solar System. Faint rings of gas giants appear out of the darkness, dotted by moons, while in the background Webb shows distant galaxies. By comparing detections of water and other molecules in our solar system with those found in the disks of other, much younger planetary systems, Webb is helping to build up clues about our own origins – how Earth became the ideal place for life as we know it.
One year in, Webb’s science mission is really only just getting started. The second year of observations has already been selected, with plans to build on an exciting first year that exceeded expectations.
The first anniversary image from the NASA/ESA/CSA James Webb Space Telescope displays star birth like it’s never been seen before, full of detailed, impressionistic texture. The subject is the Rho Ophiuchi cloud complex, the closest star-forming region to Earth. It is a relatively small, quiet stellar nursery, but you’d never know it from Webb’s chaotic close-up. Jets bursting from young stars crisscross the image, impacting the surrounding interstellar gas and lighting up molecular hydrogen, shown in red. Some stars display the telltale shadow of a circumstellar disc, the makings of future planetary systems. The young stars at the centre of many of these discs are similar in mass to the Sun or smaller. The heftiest in this image is the star S1, which appears amid a glowing cave it is carving out with its stellar winds in the lower half of the image. The lighter-coloured gas surrounding S1 consists of polycyclic aromatic hydrocarbons, a family of carbon-based molecules that are among the most common compounds found in space. Credit: NASA, ESA, CSA, STScI, K. Pontoppidan (STScI), A. Pagan (STScI)
Webb makes first detection of methyl cation (CH3+), a crucial carbon molecule in a planet-forming disc system known as d203-506, in the Orion Nebula
An international team of scientists have used data collected by the NASA/ESA/CSA James Webb Space Telescope to detect a molecule [1] known as the methyl cation (CH3+) for the first time, located in the protoplanetary disc surrounding a young star. They accomplished this feat with a cross-disciplinary expert analysis, including key input from laboratory spectroscopists. This simple molecule has a unique property: it reacts relatively inefficiently with the most abundant element in our Universe (hydrogen) but reacts readily with other molecules and therefore initiates the growth of more complex carbon-based molecules. Carbon chemistry is of particular interest to astronomers because all known life is carbon-based. The vital role of CH3+ in interstellar carbon chemistry was predicted in the 1970s, but Webb’s unique capabilities have finally made observing it possible — in a region of space where planets capable of accommodating life could eventually form.
An international team of scientists have used data collected by the NASA/ESA/CSA James Webb Space Telescope to detect a molecule known as the methyl cation (CH3+) for the first time, located in the protoplanetary disc surrounding a young star. They accomplished this feat with a cross-disciplinary expert analysis, including key input from laboratory spectroscopists. The vital role of CH3+ in interstellar carbon chemistry has been predicted since the 1970s, but Webb’s unique capabilities have finally made observing it possible — in a region of space where planets capable of accommodating life could eventually form.
This graphic shows the area, in the centre of the Orion Nebula, that was studied by the team. The nebula lies about 1350 light-years from Earth. The largest image, on the left, is from Webb’s NIRCam instrument. On the right, the telescope is focused on a smaller area, where the team have used Webb’s MIRI instrument to add more depth to their study. A total of eighteen filters across both the MIRI and NIRCam instruments were used in these images, covering a range of wavelengths from 1.4 microns in the near-infrared to 25.5 microns in the mid-infrared. The detailed coverage was necessary for the team to study the light from protoplanetary discs, and analyse the unique features revealed by Webb using spectroscopy from its MIRI and NIRSpec instruments.
The region captured here in breathtaking detail by Webb is a part of the Orion Nebula known as the Orion Bar. It is an ionisation front, where energetic far-ultraviolet light from the Trapezium Cluster — located off the upper-left corner — interacts with dense molecular clouds. The energy of the stellar radiation is slowly eroding the Orion Bar, and this has a profound effect on the molecules and chemistry in the protoplanetary discs that have formed around newborn stars here.
At the very centre of the MIRI area is an ionised star-protoplanetary disc system, or proplyd, named d203-506. The pullout at the bottom right displays a combined NIRCam and MIRI image of this young system. Its extended shape is due to pressure from the harsh ultraviolet radiation striking it. The first clear images of proplyds in the Orion Nebula were obtained by the NASA/ESA Hubble Space Telescope, including d203-506. Now Webb’s extended infrared vision adds to the picture, as the team of astronomers were able to confirm that the methyl cation molecule is present in this very proplyd.
Credit:
ESA/Webb, NASA, CSA, M. Zamani (ESA/Webb), the PDRs4All ERS Team
An international team of scientists have used data collected by the NASA/ESA/CSA James Webb Space Telescope to detect a molecule known as the methyl cation (CH3+) for the first time, located in the protoplanetary disc surrounding a young star. They accomplished this feat with a cross-disciplinary expert analysis, including key input from laboratory spectroscopists. The vital role of CH3+ in interstellar carbon chemistry has been predicted since the 1970s, but Webb’s unique capabilities have finally made observing it possible — in a region of space where planets capable of accommodating life could eventually form.
This image is NIRCam’s view of the Orion Bar region studied by the team of astronomers. Bathed in harsh ultraviolet light from the stars of the Trapezium Cluster, it is an area of intense activity, with star formation and active astrochemistry. This made it a perfect place to study the exact impact that ultraviolet radiation has on the molecular makeup of the discs of gas and dust that surround new stars. The radiation erodes the nebula’s gas and dust in a process known as photoevaporation; this creates the rich tapestry of cavities and filaments that fill the view. The radiation also ionises the molecules, causing them to emit light — not only does this create a beautiful vista, it also allows astronomers to study the molecules using the spectrum of their emitted light obtained with Webb’s MIRI and NIRSpec instruments.
The two very large, bright stars are two of the three stars in the θ² Orionis system — the Trapezium Cluster is also known as θ¹ Orionis. The brightest star here, θ² Orionis A, is surrounded by particularly bright and red puffs of dust, which are reflecting the star’s light towards Earth. Its great brightness — it is visible with the naked eye — is due to the fact that θ² Orionis A is itself a ternary system made of three closely bound bright stars.
There are more proplyds visible in this image than just d203-506 — the Orion Nebula is replete with such new stars. In the very top left, a tiny star is visible within a long, dusty cocoon. This globule has formed from the star’s protoplanetary disc, as the disc is broken down by the energetic radiation of the Trapezium Cluster. Around the globule, a round shockwave is strikingly visible moving through the gas of the Orion Nebula.
Credit:
ESA/Webb, NASA, CSA, M. Zamani (ESA/Webb), the PDRs4All ERS Team
An international team of scientists have used data collected by the NASA/ESA/CSA James Webb Space Telescope to detect a molecule known as the methyl cation (CH3+) for the first time, located in the protoplanetary disc surrounding a young star. They accomplished this feat with a cross-disciplinary expert analysis, including key input from laboratory spectroscopists. The vital role of CH3+ in interstellar carbon chemistry has been predicted since the 1970s, but Webb’s unique capabilities have finally made observing it possible — in a region of space where planets capable of accommodating life could eventually form.
This hazy image is Webb’s view of a small region of the Orion Nebula, made with its MIRI instrument. Filled with gas and dust, the Orion Nebula is a rich star-forming region. The newborn and young stars emit harsh ultraviolet radiation that ionises the nebula, causing it to emit light at infrared wavelengths. MIRI is sensitive to long-wavelength, mid-infrared emission, highlighting the layers of hot gases on each side of the Orion Bar that stretches through the centre. The area captured here by MIRI is much smaller than the NIRCam view, but contains a remarkable amount of detail, thanks to MIRI’s unprecedented sensitivity at these longer wavelengths.
This zoomed-in MIRI view of the Orion Bar contains the young star-protoplanetary disc system, named d203-506, that the team of astronomers scoured for key organic molecules. MIRI’s contribution to the view of d203-506 was critical to obtaining the widest range of spectra of the system, necessary to confirm their detection of the methyl cation. In particular, the molecule has a strong spectral line at around 7 microns, a wavelength that is impossible to detect through Earth’s atmosphere, but with MIRI’s in-built spectroscopy the team was able to unambiguously confirm the methyl cation’s presence.
This version of the MIRI image has been scaled up, to match the scale of the larger NIRCam image. You can find the image in its original scale here.
Credit:
ESA/Webb, NASA, CSA, M. Zamani (ESA/Webb), the PDRs4All ERS Team
Carbon compounds [2] form the foundations of all known life, and as such are of a particular interest to scientists working to understand both how life developed on Earth, and how it could potentially develop elsewhere in our Universe. As such, interstellar organic chemistry [3] is an area of keen fascination to astronomers who study the places where new stars and planets form. Molecular ions [4] containing carbon are especially important, because they react with other small molecules to form more complex organic compounds even at low interstellar temperatures [5]. The methyl cation (CH3+) is one such carbon-based ion. CH3+ has been posited by scientists to be of particular importance since the 1970s and 1980s. This is due to a fascinating property of CH3+, which is that it reacts with a wide range of other molecules. This little cation is significant enough that it has been theorised to be the cornerstone of interstellar organic chemistry, yet until now it has never been detected. The unique properties of the James Webb Space Telescope made it the ideal instrument to search for this crucial cation — and already, a group of international scientists have observed it with Webb for the first time. Marie-Aline Martin of Paris-Saclay University, France, a spectroscopist and science team member, explains:
“This detection of CH3+ not only validates the incredible sensitivity of James Webb but also confirms the postulated central importance of CH3+ in interstellar chemistry.”
The CH3+ signal was detected in the star-protoplanetary disc [6] system known as d203-506, which is located about 1350 light years away, in the Orion Nebula. Whilst the star in d203-506 is a small red dwarf star, with a mass only about a tenth of the Sun’s, the system is bombarded by strong ultraviolet radiation from nearby hot, young, massive stars. Scientists believe that most planet-forming protoplanetary disks go through a period of such intense ultraviolet radiation, since stars tend to form in groups that often include massive, ultraviolet-producing stars. Fascinatingly, evidence from meteorites suggest that the protoplanetary disc that went on to form our Solar System was also subject to a vast amount of ultraviolet radiation — emitted by a stellar companion to our Sun that has long since died (massive stars burn brightly and die much faster than less massive stars). The confounding factor in all this is that ultraviolet radiation has long been considered to be purely destructive to the formation of complex organic molecules — and yet there is clear evidence that the only life-supporting planet that we know of was born from a disc that was heavily exposed to it.
The team that performed this research may have found the solution to this conundrum. Their work predicts that the presence of CH3+ is in fact connected to ultraviolet radiation, which provides the necessary source of energy for CH3+ to form. Furthermore, the period of ultraviolet radiation experienced by certain disks seems to have a profound impact on their chemistry. For example, Webb observations of protoplanetary disks that are not subject to intense ultraviolet radiation from a nearby source show a large abundance of water — in contrast to d203-506, where the team could not detect water at all. The lead author, Olivier Berné of the University of Toulouse, France, elaborates,
“This clearly shows that ultraviolet radiation can completely change the chemistry of a proto-planetary disc. It might actually play a critical role in the early chemical stages of the origins of life by helping to produce CH3+ — something that has perhaps previously been underestimated.”
Although research published as early as the 1970s predicted the importance of CH3+, it has previously been virtually impossible to detect. Many molecules in protoplanetary discs are observed using radio telescopes. However, for this to be possible the molecules in question need to possess what is known as a ‘permanent dipole moment’, meaning that the molecule’s geometry is such that its electric charge is permanently off balance, giving the molecule a positive and a negative ‘end’. CH3+ is symmetrical, and therefore its charge is balanced, and so lacks the permanent dipole moment necessary for observations with radio telescopes. It would theoretically be possible to observe spectroscopic lines emitted by CH3+ in the infrared, but the Earth’s atmosphere makes these essentially impossible to observe from Earth. Thus, it was necessary to use a sufficiently sensitive space-based telescope that could observe signals in the infrared. Webb’s MIRI and NIRSpec instruments were perfect for the job. In fact, a CH3+ detection had previously been so elusive that when the team first saw the signal in their data, they were not sure how to identify it. Remarkably, the team were able to interpret their result within four short weeks, by drawing on the expertise of an international team with a varied range of expertise.
The discovery of CH3+ was possible only through a collaboration among observational astronomers, astrochemical modellers, theoreticians, and experimental spectroscopists, which combined the unique capabilities of JWST in space with those of Earth-based laboratories in order to successfully investigate and interpret our local universe’s composition and evolution. Marie-Aline Martin adds:
“Our discovery was only made possible because astronomers, modellers, and laboratory spectroscopists joined forces to understand the unique features observed by James Webb.”
The PDRs4ALL ERS team‘s results have been published today in Nature.
Notes
[1] A molecule is a particle made up of two or more atoms that are held together by chemical bonds.
[2] A compound is a molecule that includes more than one element. Thus, all compounds are molecules but not all molecules are compounds. As an example, the hydrogen molecule (H2) is a molecule but not a compound, whereas the water molecule (H2O) is also a compound.
[3] Organic chemistry refers to the chemistry of carbon-based molecules and compounds. It may also be referred to as carbon chemistry.
[4] An ion is an atom or molecule that has an overall electrical charge, due to an excess or deficit in the number of negative electrons compared to the number of positive protons in the ion. A cation is an ion with a net positive charge (so a deficit of electrons).
[5] A complex organic molecule is a molecule with multiple carbon atoms.
[6] A protoplanetary disc is a rotating disc of gas and dust that forms around young stars, and from which planets can ultimately form.
Webb maps surprisingly large plume jetting from Saturn’s moon Enceladus
Interaction between moon’s plumes and Saturn’s ring system explored with Webb.
Images from the NASA/ESA/CSA James Webb Space Telescope’s NIRCam (Near-Infrared Camera) show a water vapour plume jetting from the south pole of Saturn’s moon Enceladus, extending out 40 times the size of the moon itself. The inset, an image from the Cassini orbiter, emphasises how small Enceladus appears in the Webb image compared to the water plume. Webb is allowing researchers, for the first time, to see directly how this plume feeds the water supply for the entire system of Saturn and its rings. By analysing the Webb data, astronomers have determined roughly 30 percent of the water stays within a torus, a fuzzy doughnut of water that is co-located with Saturn’s E-ring, and the other 70 percent escapes to supply the rest of the Saturnian system with water. Enceladus, an ocean world about four percent the size of Earth at just 505 kilometres across, is one of the most exciting scientific targets in our Solar System in the search for life beyond Earth. A global reservoir of salty water sits below the moon’s icy outer crust, and geyser-like volcanoes spew jets of ice particles, water vapour, and organic chemicals out of crevices in the moon’s surface informally called ‘tiger stripes’. Webb’s NIRCam was built by a team at the University of Arizona and Lockheed Martin’s Advanced Technology Center. Credit: NASA, ESA, CSA, STScI, G. Villanueva (NASA’s Goddard Space Flight Center), A. Pagan (STScI)
A water vapour plume from Saturn’s moon Enceladus spanning more than 9600 kilometres — long enough to stretch across the Eurasian continent from Ireland to Japan — has been detected by researchers using the NASA/ESA/CSA James Webb Space Telescope. Not only is this the first time such water ejection has been seen over such an expansive distance, but Webb is also giving scientists a direct look, for the first time, at how this emission feeds the water supply for the entire system of Saturn and its rings.
Enceladus, an ocean world about four percent the size of Earth at just 505 kilometres across, is one of the most exciting scientific targets in our Solar System in the search for life beyond Earth. Sandwiched between the moon’s icy outer crust and its rocky core is a global reservoir of salty water. Geyser-like volcanoes spew jets of ice particles, water vapour, and organic chemicals out of crevices in the moon’s surface informally called ‘tiger stripes’.
Previously, observatories have mapped jets hundreds of kilometres long from the moon’s surface, but Webb’s exquisite sensitivity reveals a new story.
The length of the plume was not the only characteristic that intrigued researchers. The rate at which the water vapour is gushing out, about 300 litres per second, is also particularly impressive. At this rate, you could fill an Olympic-sized swimming pool in just a couple of hours. In comparison, doing so with a garden hose on Earth would take more than 2 weeks.
NASA’s James Webb Space Telescope’s exquisite sensitivity and highly specialised instruments are revealing details into how one of Saturn’s moon’s feeds the water supply for the entire system of the ringed planet. Enceladus, a prime candidate in the search for life elsewhere in our Solar System, is a small moon about four percent the size of Earth. New images from Webb’s NIRCam (Near-Infrared Camera) have revealed a water vapour plume jetting from the south pole of Enceladus, extending out 40 times the size of the moon itself. The Integral Field Unit (IFU) aboard the NIRSpec (Near-Infrared Spectrograph) instrument also provided insights into how the water from Enceladus feeds the rest of its surrounding environment. Enceladus orbits around Saturn in just 33 hours, and as it does it sprays water and leaves behind a torus — or ‘doughnut’ — of material in its wake. This torus is depicted in the top diagram in light blue. Webb’s IFU is a combination of camera and spectrograph. During an IFU observation, the instrument captures an image of the field of view along with individual spectra of each pixel in the field of view. IFU observations allow astronomers to investigate how properties — composition in this case — vary from place to place over a region of space. The unique sensitivity of Webb’s IFU allowed researchers to detect many spectral features characteristic of water originating from the embedding torus around Enceladus and the plume itself. This simultaneous collection of spectra from the plume and the torus has allowed researchers to better understand their strong relationship. In this spectrum, the white lines are the data from Webb, and the best-fit models for water emission are overlaid in different colours –purple for the plume, green for the area central to the moon itself, and red for the surrounding torus. Webb’s NIRCam was built by a team at the University of Arizona and Lockheed Martin’s Advanced Technology Center. NIRSpec was built for the European Space Agency (ESA) by a consortium of European companies led by Airbus Defence and Space (ADS) with NASA’s Goddard Space Flight Center providing its detector and micro-shutter subsystems. Credit: NASA, ESA, CSA, STScI, L. Hustak (STScI), G. Villanueva (NASA’s Goddard Space Flight Center)
The NASA/ESA/ASI Cassini mission spent over a decade exploring the Saturnian system, and not only imaged the plumes of Enceladus for the first time but flew directly through them and sampled what they were made of. While Cassini’s position within the Saturnian system provided invaluable insights into this distant moon, Webb’s unique view from the Sun-Earth Lagrange Point 2 1.5 million kilometres from Earth, along with the remarkable sensitivity of its Integral Field Unit aboard the NIRSpec (Near-Infrared Spectrograph) Instrument, is offering new context.
The Webb observations directly demonstrate how the moon’s water vapour plumes feed the torus, a fuzzy doughnut of water that is co-located with Saturn’s E-ring. By analysing the Webb data, astronomers have determined that roughly 30 percent of the water stays within this torus, and the other 70 percent escapes to supply the rest of the Saturnian system with water.
In the coming years Webb will serve as the primary tool for observing the ocean moon Enceladus, and discoveries from Webb will help inform future Solar System satellite missions that will look to explore the depth of the subsurface ocean, how thick the ice crust is, and more.
Webb’s observations of Enceladus were completed under Guaranteed Time Observation (GTO) programme 1250. The initial goal of this programme is to demonstrate the capabilities of Webb in a particular area of science and set the stage for future studies.
The team’s results were recently accepted for publication on 17 May in Nature Astronomy. A pre-print is available here.
