The James Webb Space Telescope has been able to directly detect carbon dioxide in the atmosphere of an exoplanet for the first time. This will help it better understand the origin of the HR 8799 system.
Carbon dioxide in other systems
The James Webb Space Telescope has made the first direct measurements of carbon dioxide on a planet outside the solar system in HR 8799, a multi-planet system 130 light-years away that has long been a key site for studying planet formation.
The observations provide strong evidence that the system’s four giant planets formed much like Jupiter and Saturn by slowly building solid nuclei. It also shows that James Webb can do more than determine the composition of the atmosphere from starlight measurements. It can directly analyze the chemical composition of exoplanet atmospheres.
“By detecting these strong carbon dioxide features, we have shown that the atmospheres of these planets have a significant fraction of heavier elements such as carbon, oxygen and iron. Given what we know about the star they orbit, that likely indicates they formed via core accretion, which for planets that we can directly see is an exciting conclusion,” said William Balmer, an astrophysicist at Johns Hopkins University who led the work.
Planetary formation in HR 8799
HR 8799 is a young system about 30 million years old, a fraction of our solar system’s 4.6 billion years. Still hot after rapid molding, the planets of HR 8799 emit large amounts of infrared light, providing valuable data on how their formation compares to that of stars or brown dwarfs.
Giant planets can form in two ways: slowly creating hard cores that attract gas, like our solar system, or rapidly collapsing from the cooling disk of a young star into massive objects. Knowing which model is more common can give scientists clues to distinguish the types of planets they find in other systems.
“Our hope with this kind of research is to understand our own solar system, life, and ourselves in comparison to other exoplanetary systems, so we can contextualize our existence,” Balmer said. “We want to take pictures of other solar systems and see how they’re similar or different when compared to ours. From there, we can try to get a sense of how weird our solar system really is—or how normal.”
Direct observation of exoplanets
Very few exoplanets have been directly photographed because distant planets are thousands of times fainter than their stars. By obtaining direct images at specific wavelengths accessible only to JWST, the team paves the way for more detailed observations to determine whether the objects they see orbiting other luminaries are really giant planets, or objects such as brown dwarfs that form like nuclei.
The achievement was made possible by James Webb coronagraphs blocking light from bright luminaries, as happens during a solar eclipse, to reveal hidden worlds. This gave the team the ability to search for infrared light in a range of wavelengths that detect specific gases and other details of the atmosphere.
Focusing on the 3-5 micrometer wavelength range, the team found that the four planets of HR 8799 contained heavier elements than previously thought, another hint that they formed in the same way as the gas giants of our solar system.
The observations also provided the first-ever detection of the most distant planet HR 8799 e at 4.6 micrometers and 51 Eridani b at 4.1 micrometers, demonstrating James Webb’s sensitivity in observing faint planets near bright stars.
James Webb observes spectra of exoplanet atmospheres
In 2022, one of James Webb’s key observational techniques indirectly detected carbon dioxide on another exoplanet called WASP-39 b by tracking how its atmosphere changes starlight as it passes in front of its star.
“This is what scientists have been doing for transiting planets or isolated brown dwarfs since the launch of JWST,” said Laurent Pueyo, an astronomer at the Space Telescope Science Institute.
Rémi Soummer, who heads the optics laboratory at the Space Telescope Science Institute and previously directed the Webb coronagraph, added: “We knew JWST could measure colors of the outer planets in directly imaged systems. We have been waiting for 10 years to confirm that our finely tuned operations of the telescope would also allow us to access the inner planets.”
“Now the results are in, and we can do interesting science with it.”
The team hopes to use the James Webb chronographs to analyze more giant planets and compare their composition to theoretical models.
According to phys.org
