In yet another demonstration of its ability to unravel the mysteries of the cosmos, NASA’s most powerful space telescope has identified the molecular and chemical profile of an exoplanet’s atmosphere. Since its launch earlier this year, the James Webb Telescope has astounded space enthusiasts, with its powerful infrared capabilities providing scientists with a previously unseen window into deep space.
NASA’s James Webb Space Telescope has detected carbon dioxide in the atmosphere of a planet outside the solar system for the first time. This observation of a gas giant planet orbiting a Sun-like star 700 light-years away provides important information about the planet’s composition and formation. The finding, accepted for publication in Nature, offers evidence that in the future Webb may be able to 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 (roughly the same as Saturn) and a diameter 1.3 times that of Jupiter. Its extreme puffiness is caused in part by 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, only about one-eighth the distance between the Sun and Mercury, completing one circuit in just over four Earth days.
Detecting such a clear signal of carbon dioxide on WASP-39 b bodes well for the detection of atmospheres on smaller, terrestrial-sized planets. As soon as the data appeared on my screen, the whopping carbon dioxide feature grabbed me.
Natalie Batalha
The planet was discovered in 2011 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 from other telescopes, including NASA’s Hubble and Spitzer space telescopes, revealed the presence of water vapor, sodium, and potassium in the planet’s atmosphere. Webb’s unmatched infrared sensitivity has now confirmed the presence of carbon dioxide on this planet as well.
Filtered Starlight
Transiting planets, such as WASP-39 b, whose orbits we observe from the side rather than from above, can provide excellent opportunities for researchers to study planetary atmospheres. During transit, some of the starlights is completely eclipsed by the planet (causing the overall dimming), while others are transmitted through the planet’s atmosphere.
Because different gases absorb different color combinations, researchers can use small differences in the brightness of transmitted light across a spectrum of wavelengths to determine exactly what is in an atmosphere. WASP-39 b is an ideal target for transmission spectroscopy due to its inflated atmosphere and frequent transits.
First Clear Detection of Carbon Dioxide
The research team used Webb’s Near-Infrared Spectrograph (NIRSpec) for its observations of WASP-39b. In the resulting spectrum of the exoplanet’s atmosphere, a small hill between 4.1 and 4.6 microns presents the first clear, detailed evidence of 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 and member of the JWST Transiting Exoplanet Community Early Release Science team, which undertook this investigation. “It was a special moment, crossing an important threshold in exoplanet sciences.”
No observatory has ever measured such subtle differences in brightness of so many individual colors across the 3 to 5.5-micron range in an exoplanet transmission spectrum before. Access to this part of the spectrum is critical for measuring the abundances of gases such as water and methane, as well as carbon dioxide, which are thought to exist in a variety 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, Santa Cruz, who leads the team.
Understanding the composition of a planet’s atmosphere is important because it tells us something about the planet’s origin and evolution. “Carbon dioxide molecules are sensitive tracers of the story of planet formation,” said Mike Line of Arizona State University, another member of this research team. “We can determine how much solid material was used to form this gas giant planet by measuring this carbon dioxide feature. JWST will make this measurement for a variety of planets over the next decade, providing insight into the details of how planets form as well as the uniqueness of our own solar system.”
Early Release Science
WASP-39 b NIRSpec prism observations are part of a larger investigation that includes observations of the planet using multiple Webb instruments, as well as observations of two other transiting planets. The investigation, which is part of the Early Release Science program, was created with the goal of providing the exoplanet research community with robust Webb data as soon as possible.
“The goal is to quickly analyze the Early Release Science observations and develop open-source tools for the science community to use,” said Vivien Parmentier, an Oxford University co-investigator. “This allows contributions from all over the world and ensures that the best science possible comes from the coming decades of observations.”
