For the first time, astronomers have found unequivocal evidence of carbon dioxide in the atmosphere of an exoplanet (a planet outside our solar system).
The discovery, accepted for publication in Nature and published online on August 25, demonstrates the power of the James Webb Space Telescope (JWST) to provide unprecedented observations of exoplanet atmospheres.
Natalie Batalha, professor of astronomy and astrophysics at UC Santa Cruz, leads the team of astronomers that made the detection, using JWST to observe a Saturn-mass planet called WASP-39b orbiting very close to a sun-like star about 700 light. Earth years.
“Previous observations of this planet with Hubble and Spitzer had given us tantalizing hints that carbon dioxide might be there,” Batalha said. “The JWST data showed an unmistakable feature of carbon dioxide that was so prominent it was practically calling out to us.”
Carbon dioxide is an important component of the atmospheres of the planets in our solar system, found in rocky planets such as Mars and Venus, as well as gas giants such as Jupiter and Saturn. For exoplanet researchers, it is important both as a gas they are likely to detect on small rocky planets and as an indicator of the global abundance of heavy elements in the atmospheres of giant planets.
“Carbon dioxide is actually a very sensitive measuring stick, the best we have, for heavy elements in the atmospheres of giant planets, so the fact that we can see it so clearly is really fantastic,” said the co-author Jonathan Fortney, professor of astronomy and astrophysics. at UCSC and director of the Other Worlds Laboratory.
Stars and gas giant planets are made up primarily of the lightest elements, hydrogen and helium, but the abundance of heavier elements, what astronomers call “metallicity,” is a critical factor in planet formation, Fortney explained.
“The ability to determine the amount of heavy elements in a planet is critical to understanding how it formed, and we will be able to use this carbon dioxide dipstick for a bunch of exoplanets to build a comprehensive understanding of the composition of the giant planet.” He said.
Batalha’s team observed WASP-39b as part of a JWST Early Release Science program to study transiting exoplanets. A transiting planet passes in front of its star as seen from Earth, allowing astronomers to analyze starlight passing through the planet’s atmosphere, where gases such as carbon dioxide absorb certain wavelengths of the light
Using the Near Infrared Spectrograph (NIRSpec) on JWST, the team obtained a high-resolution “transmission spectrum” that showed the light transmitted through WASP-39b’s atmosphere separated into its wavelengths. wave components Batalha said the data produced “exquisite light curves” and showed that the NIRSpec instrument is exceeding expectations for transmission spectroscopy. This bodes well for observations of small rocky planets, which are expected to have carbon dioxide in their atmospheres (when they have atmospheres), but will not give as strong a signal as a giant planet like WASP-39b.
“This detection will serve as a useful benchmark for what we can do to detect carbon dioxide on terrestrial planets in the future,” Batalha said. “It is the most likely atmospheric gas we will detect with JWST in atmospheres of Earth-sized exoplanets.”
In addition to carbon dioxide, the researchers detected another interesting feature in the spectrum of WASP-39b that they have not yet identified. “It’s a mystery function for now,” Batalha said. “In this paper, we have focused on a narrow range of infrared colors; this is just a preview of the features we expect to see across the spectrum.”
Fortney noted that WASP-39b appears to have a similar composition to Saturn. Saturn’s metallicity is 10 times that of the Sun, and WASP-39b also appears to be enriched in heavy elements about 10 times relative to the Sun.
“This is very interesting, and we would like to know if all Saturn-mass planets have the same metallicity,” he said. “It was exciting to see this in another system, because we didn’t know what to expect when we went from the planets in our solar system to the atmospheres of exoplanets.”
Located in the constellation Virgo, WASP-39b is more than 20 times closer to its star than Earth is to the sun. Although it has about the same mass as Saturn, it is less dense and 50 percent larger, likely due to heating from being so close to its host star. Previous observations showed that it had a relatively clear sky, making it a good target for transmission spectroscopy.
When the first JWST data were released in July, UCSC exoplanet researchers were hosting 45 visiting astronomers for the Other Worlds Laboratory’s annual Summer Exoplanet Program. “We were all huddled around the laptop getting our first look at the spectrum and marveling,” Batalha said. “It’s a tremendous, almost euphoric feeling to see something for the first time that no other human has seen before; that’s what science is all about.”
In addition to Batalha and Fortney, the JWST transiting exoplanet community early launch science team includes Xi Zhang, associate professor of Earth and planetary sciences at UCSC, postdoctoral fellow Aarynn Carter, student graduate student Sagnick Mukherjee, former student Zafar Rustamkulov (now a graduate student at Johns). Hopkins), and former postdoctoral fellow Natasha Batalha (now at NASA Ames), as well as a long list of co-authors around the world.
The James Webb Space Telescope is an international program led by NASA with its partners the European Space Agency and the Canadian Space Agency, and is operated by the Space Telescope Science Institute.
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