Webb Detects Carbon Dioxide in Exoplanet Atmosphere
Webb demonstrates its spectroscopic power with the first unequivocal detection of carbon dioxide in a planetary atmosphere outside the Solar System.
The NASA/ESA/CSA James Webb Space Telescope has found definitive evidence for carbon dioxide in the atmosphere of a gas giant planet orbiting a Sun-like star 700 light-years away. The result provides important insights into the composition and formation of the planet, and is indicative of Webb’s ability to also detect and measure carbon dioxide in the thinner atmospheres of smaller rocky planets.
WASP-39 b is a hot gas giant with a mass roughly one quarter that of Jupiter (about the same as Saturn) and a diameter 1.3 times that of Jupiter. Its extreme puffiness is related in part to its high temperature (about 900 °C). Unlike the cooler, more compact gas giants in our Solar System, WASP-39 b orbits very close to its host star — only about one eighth of the distance between the Sun and Mercury — completing one circuit in just over four Earth-days. The planet’s discovery, reported in 2011, was based on ground-based detections of the subtle, periodic dimming of light from its host star as the planet transits, or passes in front of the star.
Transiting planets like WASP-39 b, whose orbits we observe edge-on rather than from above, can provide researchers with ideal opportunities to probe planetary atmospheres.
During a transit, some of the starlight is eclipsed by the planet completely (causing the overall dimming) and some is transmitted through the planet’s atmosphere. The atmosphere filters out some colours more than others, depending on factors such as what it is made of, how thick it is, and whether or not there are clouds. (We observe this effect in our own atmosphere as the colour and quality of daylight changes depending on how hazy or humid the air is, or where the Sun is in the sky.)
Because different gases absorb different combinations of colours, researchers can analyse small differences in the brightness of the transmitted light across a spectrum of wavelengths and hence determine exactly what an atmosphere is made of. With its combination of inflated atmosphere and frequent transits, WASP-39 b is an ideal target for this technique, known as transmission spectroscopy. The team used Webb’s Near-Infrared Spectrograph (NIRSpec) to make this detection.
In the resulting spectrum of the exoplanet’s atmosphere, the small hill between 4.1 and 4.6 microns is anything but trivial to exoplanet researchers. It is the first clear, detailed, indisputable evidence for carbon dioxide ever detected in a planet outside the Solar System.
“As soon as the data appeared on my screen, the whopping carbon dioxide feature grabbed me,” said Zafar Rustamkulov, a graduate student at Johns Hopkins University in the United States and member of the transiting exoplanet team. “It was a special moment, crossing an important threshold in exoplanet sciences.”
Even without the strong carbon dioxide feature, this spectrum would be remarkable. No observatory has ever measured such subtle differences in the brightness of so many individual colours across the 3- to 5.5-micron range in an exoplanet transmission spectrum before. Access to this part of the spectrum is crucial for measuring the abundances of gases like water and methane, as well as carbon dioxide, which are thought to exist in the atmospheres of many different types of exoplanets.
“Detecting such a clear signal of carbon dioxide on WASP-39 b bodes well for the detection of atmospheres on smaller, terrestrial-sized planets,” said Natalie Batalha of the University of California at Santa Cruz, USA, who leads the team of researchers studying transiting exoplanets with Webb.
“It's amazing to see the ESA NIRSpec instrument producing this incredible data so early in the mission, when we know we can still improve on the data quality moving forward,” added Sarah Kendrew, ESA Webb MIRI Instrument and Calibration Scientist at the Space Telescope Science Institute in Baltimore, USA.
Understanding the composition of a planet’s atmosphere is important because it tells us something about the origin of the planet and how it evolved. “Carbon dioxide molecules are sensitive tracers of the story of planet formation,” said team member Mike Line of Arizona State University, USA. “By measuring this carbon dioxide feature, we can determine how much solid versus how much gaseous material was used to form this gas giant planet. In the coming decade, Webb will make this measurement for a variety of planets, providing insights into the details of how planets form and the uniqueness of our own Solar System.”
These results also build upon existing research by the NASA/ESA Hubble Space Telescope. “Over the last few decades the Hubble Space Telescope has been setting the precedent for what mysteries these atmospheres contain, from clouds scattering obscuring molecular features, to detections of water vapour absorption, and escaping atmospheres,” said team member Hannah Wakeford of University of Bristol in the United Kingdom. “Webb will complement and extend these studies with higher resolution, wavelength coverage, and precision to reveal the key trends in the data pointing to the formation and evolution of these planets.”
The NIRSpec prism observation of WASP-39 b is just one part of a larger investigation that includes observations of the planet using a number of instruments, as well as observations of two other transiting planets. The investigation, which is part of the Early Release Science program, was designed to provide the exoplanet research community with robust Webb data as soon as possible.
“Seeing the data for the first time was like reading a poem in its entirety, when before we only had every third word,” added team member Laura Kreidberg of the Max Planck Institute for Astronomy in Heidelberg, Germany. “These first results are just the beginning; the Early Release Science data have shown that Webb performs beautifully, and smaller and cooler exoplanets (more like our own Earth) are within its reach.”
“The goal is to analyse the Early Release Science observations quickly and develop open-source tools for the science community to use,” explained Vivien Parmentier from Oxford University in the United Kingdom. “This enables contributions from all over the world and ensures that the best possible science will come out of the coming decades of observations.”
Illustration (Artist’s Impression) of WASP-39 b and Its Star
This is an illustration (artist’s impression) showing what the exoplanet WASP-39 b could look like, based on current understanding of the planet.
WASP-39 b is a hot, puffy gas giant planet with a mass 0.28 times that of Jupiter (0.94 times that of Saturn) and a diameter 1.3 times that of Jupiter, orbiting just 0.0486 astronomical units (4 520 000 miles) from its host star. The star, WASP-39, is fractionally smaller and less massive than the Sun. Because it is so close to its star, WASP-39 b is very hot and is likely to be tidally locked, meaning that one side faces the star at all times.
Data collected by Webb’s Near-Infrared Spectrograph (NIRSpec) show unambiguous evidence for carbon dioxide in the atmosphere, while previous observations from Hubble, Spitzer, and other telescopes indicate the presence of water vapour, sodium, and potassium, as well. The planet probably has clouds and some form of weather, but may not have atmospheric bands like those of Jupiter and Saturn.
This illustration is based on indirect transit observations
from Webb as well as other space and ground-based telescopes. Webb has
not captured a direct image of this planet.
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
Centre providing its detector and micro-shutter subsystems.
NASA, ESA, CSA, and J. Olmsted (STScI)
Hot Gas Giant Exoplanet WASP-39 b (NIRSpec Transmission Spectrum)
A transmission spectrum of the hot gas giant exoplanet WASP-39 b, captured by Webb’s Near-Infrared Spectrograph (NIRSpec) on 10 July 10 2022, reveals the first definitive evidence for carbon dioxide in the atmosphere of a planet outside the Solar System. This is the first detailed transmission spectrum ever captured that covers wavelengths between 3 and 5.5 microns.
A transmission spectrum is made by comparing starlight filtered through a planet’s atmosphere as it moves in front of the star, to the unfiltered starlight detected when the planet is beside the star. Each of the 95 data points (white circles) on this graph represents the amount of a specific wavelength of light that is blocked by the planet and absorbed by its atmosphere.
This spectrum was made by measuring the change in brightness of each wavelength over time as the planet transited its star. The planet’s atmosphere absorbs some wavelengths more than others. Wavelengths absorbed by the atmosphere appear as peaks in the transmission spectrum. The hill centred around 4.3 microns represents the light absorbed by carbon dioxide.
The grey lines extending above and below each data point are error bars that show the uncertainty of each measurement, or the reasonable range of possible values. For a single observation, the error on these measurements is extremely small.
The blue line is a best-fit model that takes into account the data, the known properties of WASP-39 b and its star (e.g., size, mass, temperature), and the assumed characteristics of the atmosphere. Researchers can vary the parameters in the model — changing unknown characteristics like cloud height in the atmosphere and abundances of various gases — to get a better fit and further understand what the atmosphere is really like. The model shown here assumes that the planet is made primarily of hydrogen and helium with small amounts of water and carbon dioxide, with a thin veil of clouds.
The observation was made using the NIRSpec PRISM bright object time-series mode, which involves using a prism to spread out light from a single bright object (like the star WASP-39) and measuring the brightness of each wavelength at set intervals of time.
WASP-39 b is a hot gas giant exoplanet that orbits a Sun-like star roughly 700 light-years away, in the constellation Virgo. The planet orbits extremely close to its star (less than 1/20 of the distance between Earth and the Sun) and completes one orbit in just over four Earth-days. The planet’s discovery, based on ground-based observations, was announced in 2011. The star, WASP-39, is roughly the same size, mass, temperature, and colour as the Sun.
The background illustration of WASP-39 b and its star is based on current understanding of the planet from Webb spectroscopy and previous ground- and space-based observations. Webb has not captured a direct image of the planet or its atmosphere.
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 Centre providing its detector and micro-shutter subsystems.
Credit:NASA, ESA, CSA, and L. Hustak (STScI). Science: The JWST Transiting Exoplanet Community Early Release Science Team
Hot Gas Giant Exoplanet WASP-39 b (NIRSpec Transit Light Curves)
A series of light curves from Webb’s Near-Infrared Spectrograph (NIRSpec) shows the change in brightness of three different wavelengths (colours) of light from the WASP-39 star system over time as the planet transited the star on 10 July 2022. A transit occurs when an orbiting planet moves between the star and the telescope, blocking some of the light from the star.
This observation was made using the NIRSpec PRISM bright object time-series mode, which involves using a prism to spread out light from a single bright object (like the star WASP-39) and measure the brightness of each wavelength at set intervals of time.
To capture this data, Webb stared at the WASP-39 star system for more than eight hours, beginning about three hours before the transit and ending about two hours after the transit was complete. The transit itself lasted about three hours. Each curve shown here includes a total of 500 individual brightness measurements — about one per minute.
Although all colours are blocked to some extent by the planet, some are blocked more than others. This occurs because different gases in the atmosphere absorb different amounts at different wavelengths. As a result, each colour has a slightly different light curve. During the transit of WASP-39 b, light with a wavelength of 4.3 microns is not as bright as 3.0-micron or 4.7-micron light because it is absorbed by carbon dioxide.
WASP-39 b is a hot gas giant exoplanet that orbits a Sun-like star roughly 700 light-years away, in the constellation Virgo. The planet orbits extremely close to its star (less than 1/20 of the distance between Earth and the Sun) and completes one orbit in just over four Earth-days. The planet’s discovery, from ground-based observations, was announced in 2011.
The background illustration of WASP-39 b and its star is based on current understanding of the planet from Webb spectroscopy and previous ground- and space-based observations. Webb has not captured a direct image of the planet or its atmosphere.
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 Centre providing its detector and micro-shutter subsystems.
Credit:NASA, ESA, CSA, and L. Hustak (STScI). Science: The JWST Transiting Exoplanet Community Early Release Science Team
Space Sparks Episode 4: Webb Detects Carbon Dioxide in Exoplanet Atmosphere
Watch this Space Sparks episode to learn more about how the James Webb Space Telescope has found definitive evidence for carbon dioxide in the atmosphere of a gas giant planet orbiting a Sun-like star 700 light-years away.
Credit:Directed by: Bethany Downer and Nico Bartmann
Editing: Nico Bartmann
Web and technical support: Enciso Systems
Written by: Bethany Downer
Music: STAN DART - Organic Life
Footage and photos:
NASA, ESA, CSA, and STScI, NASA's Goddard Space Flight Center
Conceptual Image Lab, ESO, E. Slawik, N. Risinger, D. De Martin, D.
Lennon, E. Sabbi, N. Bartmann, M. Zamani
Fuente: ESA/Hubble/Webb Information Centre
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