This illustration shows what exoplanet WASP-39b might look like, based on current knowledge of the planet.
WASP-39b is a hot, puffy gas giant with a mass 0.28 times Jupiter (0.94 times Saturn) and a diameter 1.3 times larger than Jupiter, orbiting just 0.0486 astronomical units (4 500,000 miles) from its star. The star, WASP-39, is slightly smaller and less massive than the Sun. Because it is so close to its star, WASP-39 b is very hot and is susceptible to tidal lock, with one side always facing the star.
Data collected by Webb’s Near-Infrared Spectrograph (NIRSpec) shows unambiguous evidence of carbon dioxide in the atmosphere, while previous observations from NASA’s Hubble and Spitzer space telescopes, as well as other telescopes, indicate the presence of water vapor, sodium, and potassium. The planet probably has clouds and some form of weather, but it may not have atmospheric bands like those of Jupiter and Saturn. Credit: NASA, ESA, CSA, Joseph Olmsted (STScI)
NASA’s Webb ushers in a new era of exoplanet science with the first unambiguous detection of carbon dioxide in a planetary atmosphere outside our solar system.
After years of preparation and anticipation, exoplanet scientists are thrilled. NASA’s James Webb Space Telescope has captured a stunningly detailed rainbow of near-infrared starlight filtered through the atmosphere of a giant hot gas 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 spectrograph and analyzed by dozens of researchers, represents a triplet of primates – the first official scientific observation of an exoplanet by Webb; the first detailed spectrum of exoplanets covering this near-infrared color range; and the first indisputable evidence of carbon dioxide in the atmosphere of a planet orbiting a distant star.
The results indicate 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 throughout the galaxy.
NASA’s Webb detects carbon dioxide in an exoplanet’s atmosphere
NASA’s James Webb Space Telescope has captured 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 composition and formation of the planet. The discovery, 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 small, rocky planets in the future.
The exoplanet, WASP-39b, is a hot gas giant with a mass about a quarter of Jupiter’s (about the same as Saturn’s) and a diameter 1.3 times larger than 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 a circuit in just over four Earth days. The discovery of the planet, reported in 2011, was made based on ground-based detections of the subtle and periodic attenuation of light from its host star as the planet transits or passes in front of the star.
Previous observations from other telescopes, including NASA’s Hubble and Spitzer Space Telescopes, have revealed that the planet’s atmosphere contains water vapor, sodium and potassium. Webb’s unparalleled infrared sensitivity also confirmed the presence of carbon dioxide on this exoplanet.
A transmission spectrum of the hot gas giant exoplanet WASP-39 b captured by Webb’s Near Infrared Spectrograph (NIRSpec) on July 10, 2022, reveals the first clear evidence of carbon dioxide in a planet outside the solar system. It is also the first detailed transmission spectrum of exoplanets ever captured covering wavelengths between 3 and 5.5 microns.
A transmission spectrum is created by comparing starlight filtered through a planet’s atmosphere as it moves in front of the star, with unfiltered starlight detected when the planet is next to 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. Wavelengths that are preferentially absorbed by the atmosphere appear as peaks in the transmission spectrum. The peak centered around 4.3 microns represents the light absorbed by carbon dioxide.
The gray lines extending above and below each data point are error bars that indicate the uncertainty of each measurement or the reasonable range of possible true values. For a single observation, the error on these measurements is extremely small.
The blue line is the best fit model that takes into account the data, known properties of WASP-39 b and its star (eg size, mass, temperature), and assumed characteristics of the atmosphere. Researchers can vary model parameters, changing unknown characteristics such as the height of clouds in the atmosphere and the abundance of various gases, to get a better fit and better understand what the atmosphere really looks like.
The model presented here assumes that the planet is composed primarily 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 bright object time series mode, which involves using a prism to scatter light from a single bright object (like the star WASP-39) and measuring the brightness of each wavelength at predetermined time intervals.
Transiting planets such as WASP-39b, whose orbits we observe from the edges rather than above, can provide scientists with ideal opportunities to study planetary atmospheres. During transit, some of the starlights are completely eclipsed by the planet (causing general attenuation) and some are transmitted through the planet’s atmosphere.
Since different gases absorb different combinations of colors, researchers can analyze small differences in the brightness of transmitted light across a spectrum of wavelengths to determine exactly what an atmosphere is made of. With its combination of a puffy atmosphere and frequent transits, WASP-39b is an ideal target for transmission spectroscopy.
A series of light curves from Webb’s Near Infrared Spectrograph (NIRSpec) show the change in brightness of three different wavelengths (colors) of light from the WASP-39 star system over time as the planet transited through l star on July 10. 2022. A transit occurs when an orbiting planet moves between the star and the telescope, blocking some of the star’s light.
This observation was made using the NIRSpec PRISM bright object time series mode, which involves using a prism to scatter light from a single bright object (like the star WASP-39) and measure the brightness of each wavelength at predetermined time intervals.
To capture this data, Webb watched 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 ended.
The transit itself took about three hours. Each curve presented here comprises a total of 500 individual brightness measurements, approximately one per minute.
Although all colors are blocked to some degree by the planet, some colors are blocked more than others. This happens because each gas in the atmosphere absorbs different amounts of specific wavelengths. As a result, each color 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 the light of 3.0 microns or 4.7 microns because it is absorbed by carbon dioxide. carbon.