NASA’s Webb ushers in a new era of exoplanet science with the first unequivocal detection of carbon dioxide in a planetary atmosphere outside our solar system.
After years of preparation and anticipation, exoplanet scientists are overjoyed. NASA’s James Webb Space Telescope has captured a stunningly detailed rainbow of near-infrared starlight filtering through the atmosphere of a hot gas giant exoplanet 700 light-years away. The transmission spectrum of exoplanet WASP-39 b, based on a single set of measurements made using Webb’s Near Infrared Spectrometer and analyzed by dozens of researchers, represents a hat trick of firsts: Webb’s first official scientific observation of an exoplanet . the first detailed exoplanet spectrum covering this near-infrared color spectrum. and the first unequivocal evidence for carbon dioxide in the atmosphere of a planet orbiting a distant star. The results are indicative of Webb’s ability to detect key molecules such as carbon dioxide in a wide variety of exoplanets – including smaller, cooler, rocky planets. This shows that it is capable of providing information on the composition, formation and evolution of planets across the galaxy. Watch this episode of Space Sparks to learn more about how the James Webb Space Telescope found definitive evidence of carbon dioxide in the atmosphere of a giant gas planet orbiting a Sun-like star 700 light-years away.
NASA’s Webb detects carbon dioxide in exoplanet atmospheres
NASA’s James Webb Space Telescope has recorded the first definitive evidence of carbon dioxide in the atmosphere of an exoplanet – a planet outside the solar system. This observation of a gas giant planet orbiting a Sun-like star 700 light-years from Earth provides important information about the planet’s composition and formation. The finding, which has been accepted for publication in the journal Nature, offers evidence that Webb may be able to detect and measure carbon dioxide in the thinner atmospheres of smaller, rocky planets in the future. The exoplanet, WASP-39 b, is a hot gas giant with a mass about a quarter that of Jupiter (about the same as Saturn) and a diameter 1.3 times that of Jupiter. Its extreme swelling is partly related to its high temperature (about 1,600 degrees Fahrenheit or 900 degrees Celsius). Unlike the cooler, more compact gas giants in our solar system, WASP-39 b orbits very close to its star. In fact, it is only about one-eighth the distance between the Sun and Mercury, and completes one circuit in just over four Earth days. The discovery of the planet, 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. Previous observations by other telescopes, including NASA’s Hubble and Spitzer space telescopes, revealed that the planet’s atmosphere contained water vapor, sodium and potassium. Webb’s unparalleled infrared sensitivity has now confirmed the presence of carbon dioxide on this exoplanet as well. A transmission spectrum of the hot gas giant exoplanet WASP-39 b captured by the Webb Near Infrared Spectrometer (NIRSpec) on July 10, 2022, reveals the first clear evidence for carbon dioxide on a planet outside the solar system. This is also the first detailed exoplanet transmission spectrum ever recorded, covering wavelengths between 3 and 5.5 microns. A transmission spectrum is created by comparing the starlight filtered through a planet’s atmosphere as it moves in front of the star, with the unfiltered starlight detected when the planet is next to the star. Each of the 95 data points (white circles) in this graph represents the amount of a particular wavelength of light that is blocked by the planet and absorbed by its atmosphere. Wavelengths that are preferentially absorbed by the atmosphere appear as peaks in the transmission spectrum. The peak centered around 4.3 microns represents light absorbed by carbon dioxide. The gray lines running above and below each data point are error bars showing the uncertainty of each measurement or the reasonable range of true possible values. For a single observation, the error in these measurements is extremely small. The blue line is a model that best fits the data, the known properties of WASP-39 b and its star (eg, size, mass, temperature), and assumed characteristics of the atmosphere. Researchers can vary the model’s parameters – changing unknown characteristics such as cloud height in the atmosphere and the abundance of various gases – to better match and further understand what the atmosphere is really like. The model presented here assumes that the planet is composed mostly of hydrogen and helium, with small amounts of water and carbon dioxide and a thin veil of clouds. The observation was made using the NIRSpec PRISM luminous object time-series function, which involves using a prism to spread light from a single luminous object (such as the star WASP-39) and measuring the brightness of each wavelength at set intervals. Credits: NASA, ESA, CSA, Leah Hustak (STScI), Joseph Olmsted (STScI )
Filtered Starlight
Transiting planets like WASP-39 b, whose orbits we observe from edge to edge rather than from above, can provide scientists with ideal opportunities to probe planetary atmospheres. During a transit, some of the starlight is completely obscured by the planet (causing total dimming) and some is transmitted through the planet’s atmosphere. Because different gases absorb different combinations of colors, researchers can analyze small differences in the brightness of emitted light across a spectrum of wavelengths to 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 transmission spectroscopy. A series of light curves from Webb’s Near Infrared Spectrometer (NIRSpec) shows the change in brightness of three different wavelengths (colors) of light from the WASP-39 star system over time as the planet crossed the star on July 10, 2022 .the 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 luminous object time series function, which involves using a prism to scatter light from a single luminous object (such as the star WASP-39) and measure the brightness of each wavelength at set intervals. To capture this data, Webb looked at the WASP-39 star system for more than eight hours, starting about three hours before the transit and ending about two hours after the transit was complete. The crossing itself took about three hours. Each curve shown here includes a total of 500 individual brightness measurements – about one per minute. Although all colors are blocked to some degree by the planet, some colors are blocked more than others. This is because each gas in the atmosphere absorbs different amounts of specific wavelengths. As a result, each color has a slightly different light curve. When passing WASP-39 b, light with a wavelength of 4.3 microns is not as bright as light at 3.0 microns or 4.7 microns because it is absorbed by carbon dioxide. Credits: NASA, ESA, CSA, Leah Hustak (STScI), Joseph Olmsted (STScI)
First clean detection of carbon dioxide
The research team used the Webb Near-Infrared Spectrometer (NIRSpec) for their observations of WASP-39 b. In the resulting spectrum of the exoplanet’s atmosphere, a small hill between 4.1 and 4.6 microns shows the first clear, detailed evidence of carbon dioxide ever detected on a planet outside the solar system. “As soon as the data appeared on my screen, the huge feature of carbon dioxide grabbed me,” said Zafar Rustamkulov, a graduate student at Johns Hopkins University and a member of the JWST Transiting Exoplanet Community Early Release Science team that undertook this research. “It was a special moment, crossing an important threshold in exoplanet science.” No observatory has so far measured such subtle differences in the brightness of so many individual colors in the 3 to 5.5 micron range in an exoplanet transmission spectrum. Access to this part of the spectrum is crucial for measuring the abundance of gases such as water and methane, as well as carbon dioxide. These are gases that are thought to exist on many different types of exoplanets. “The detection of such a clear carbon dioxide signal in WASP-39 b bodes well for detecting atmospheres on smaller Earth-sized planets,” said Natalie Batalha of the University of California, Santa Cruz, who leads the team. Understanding the composition of a planet’s atmosphere is essential because it tells us something about the origin of the planet and how it evolved. “Carbon dioxide molecules are sensitive tracers of planet formation history,” said Arizona State University’s Mike Line, another…
