NASA's James Webb Space Telescope (JWST) has achieved another unique milestone. The world's most powerful telescope has revealed the first molecular and chemical profile of an exoplanet, gas giant WASP-39 b. The JWST, also called Webb, and the Hubble and Spitzer Space Telescopes previously revealed isolated ingredients of the broiling distant world's atmosphere. However, Webb's observations provide a full menu of atoms, molecules and even signs of active chemistry and clouds.
WASP-39 b is a “hot Saturn”
When observed up close, the clouds might appear broken up rather than a single, uniform blanket over the exoplanet, NASA says in a statement. Webb's highly sensitive instruments were trained on the atmosphere of WASP-39 b, a "hot Saturn" orbiting a star about 700 light-years away. A hot Saturn is a planet about as massive as Saturn but in an orbit tighter than Mercury.
The unique instruments of Webb have the capacity to conduct the broad range of investigations of all types of exoplanets and probe smaller, rocky planets like those in the TRAPPIST-1 system. The TRAPPIST-1 system is a star system with an ultra-cool red dwarf star and seven Earth-size planets in the constellation Aquarius.
In the NASA statement, Natalie Batalha, an astronomer at the University of California, said those involved in the new research observed the exoplanet with multiple instruments that, together, provide a broad swath of the infrared spectrum and a splendid display of chemical fingerprints inaccessible until Webb's current mission, wherein it observed the atmosphere of WASP-39 b.
Researchers have described the suite of discoveries in a set of five new scientific papers. Of these, three are in press, which means they have been accepted for publication, and two are under review.
First detection of sulphur dioxide in exoplanet atmosphere
Webb has detected sulphur dioxide in WASP-39 b. This marks the first time sulphur dioxide has been detected in an exoplanet atmosphere. This molecule is produced from chemical reactions triggered by high-energy light from the planet's parent star. The protective ozone layer in Earth's upper atmosphere is created in a way similar to the generation of sulphur dioxide in WASP-39 b.
First detection of photochemistry on an exoplanet
Shang-Min Tsai, a researcher at the University of Oxford in the United Kingdom, and the lead author on the paper explaining the origin of sulphur dioxide in the atmosphere of WASP-39 b, said this is the first time researchers see concrete evidence of photochemistry on exoplanets. Photochemistry refers to chemical reactions initiated by energetic stellar light.
The discovery of sulphur dioxide in an exoplanet atmosphere led to another first. Scientists applied computer models of photochemistry to data that requires such physics to be fully explained. The results obtained using the models will help determine ways to interpret potential signs of habitability in the future.
Batalha said planets are sculpted and transformed by orbiting within the radiation bath of the host star, and such transformations in Earth allow life to thrive.
WASP-39 b is perfect to study radiation effects of host stars on exoplanets
WASP-39 b has a close proximity to its host star. The exoplanet is eight times closer to its host star than Mercury is to the Sun. This makes WASP-39 b a perfect laboratory to study the effects of radiation from host stars on exoplanets. If scientists understand the star-planet connection better, they will know more about how the effects of radiation determine the diversity of planets observed in the galaxy.
How Webb data can determine molecules in the exoplanet atmosphere
Webb tracked WASP-39 b as it passed in front of its star, to allow some of the star's light to filter through the planet's atmosphere. Since different types of chemicals in the atmosphere absorb different wavelengths of starlight, the colours that are missing in the starlight spectrum tell astronomers which molecules are present. Webb views the universe in infrared light, and hence, can pick up chemical fingerprints that cannot be detected in visible light.
What elements has Webb detected in the exoplanet atmosphere?
Webb has detected other atmospheric constituents including sodium, potassium and waste vapour. This confirms the observations made by space and ground-based telescopes in the past. Webb has found additional fingerprints of water, at these longer wavelengths, that have not been seen before.
The world's most powerful telescope has also detected carbon dioxide at a higher resolution. It has provided twice as much data as reported from its observations released by NASA in August, 2022.
Webb has also detected carbon monoxide. However, obvious signatures of both methane and hydrogen sulphide were absent from the telescope's data. This means that even if these molecules are present in the atmosphere of WASP-39 b, they occur at very low levels.
In order to capture the broad spectrum of WASP-39 b's atmosphere, an international team of researchers independently analysed data from four of Webb's finely calibrated instrument modes.
What the graphic of WASP-39 b’s atmosphere means
A graphic of WASP-39 b's atmosphere released by NASA shows four transmission spectra from three of Webb's instruments operated in four instrument modes. On the upper left of the graphic, one can observe data from the JWST Near Infrared Imager and Slitless Spectrograph (NIRISS). The data reveals fingerprints of potassium, water and carbon monoxide.
On the upper right region, one can find data from the Near Infrared Camera (NIRCam), which shows a prominent water signature.
The data from Near Infrared Spectrograph (NIRSpec) at the lower left shows water, sulphur dioxide, carbon dioxide and carbon monoxide. Additional NIRSpec data on the lower right region shows sodium water, carbon monoxide, carbon dioxide and sulphur dioxide.
Hannah Wakeford, an astrophysicist at the University of Bristol in the United Kingdom, who investigates exoplanet atmospheres, said the researchers had predicted what Webb would show them, but the final data was more precise, more diverse and more beautiful than she actually believed it would be.
Significance of Webb’s observations of WASP-39 b
A complete roster of chemical ingredients in an exoplanet atmosphere helps scientists obtain a glimpse of different elements in relation to each other, such as carbon-to-oxygen or potassium-to-oxygen ratios. In this way, scientists can understand how the exoplanet, and other planets, formed out of the disk of gas and dust surrounding the planet star.
How was WASP-39 b formed?
According to NASA, the chemical inventory of WASP-39 b suggests a history of smashups and mergers of smaller bodies called planetesimals. These are minute planets that could come together with many others under gravitational forces to form a planet. Therefore, WASP-39 b could have been formed due to many planetesimals coming together.
Kazumasa Ohno, a researcher from the University of Santa Cruz who worked on Webb data, said the abundance of sulphur relative to hydrogen indicated that WASP-39 b presumably experienced significant accretion of planetesimals that can deliver these ingredients to the atmosphere. He added that this indicates that the oxygen is a lot more abundant than the carbon in the atmosphere, potentially suggesting that WASP-39 b originally formed far away from the central star.
Webb's instruments promise a new phase of exploration among the broad variety of exoplanets in the galaxy.