Although in recent months the stunning images of the cosmos captured by him James Webb Space Telescope (JWST)this great observatory of NASA and ESA has just obtained another scoop: the chemical fingerprint of the atmosphere of an exoplanet, where sulfur dioxide (SO2).
The telescope’s highly sensitive instrument suite focused on the atmosphere of a “hot Saturn,” a planet as massive as Saturn that orbits a star about 700 light-years away, known as WASP-39 b.
The detection of sulfur dioxide in the atmosphere of WASP-39 b provides the first evidence of photochemistry (chemical reactions initiated by energetic starlight) on exoplanets.
While Webb and other space telescopes, including Hubble and Spitzer, have previously revealed compounds isolated from the atmosphere of this hot planet, the new readings provide a full menu of atoms, molecules and even signs of active chemistry and of the presence of clouds. The new data also hints at what these clouds would look like up close: split up rather than a single, uniform layer over the planet.
“We are observing the exoplanet with multiple instruments that, together, provide a wide swath of the infrared spectrum and a panoply of chemical fingerprints inaccessible until JWST,” he says. Natalie Batalhaan astronomer at the University of California at Santa Cruz (USA), who contributed and helped coordinate the new research.
The set of discoveries is detailed in a set of five new scientific articles, which will be published in a high-impact journal and are now available. Among the unprecedented revelations is the first detection in the atmosphere of an exoplanet of sulfur dioxide, a molecule produced from chemical reactions triggered by high-energy light from the planet’s parent star. On Earth, the protective ozone layer in the upper atmosphere is created in a similar way.
A peculiar sign and reaction
«In the first data we saw a very peculiar signal in the atmosphere of this planet whose origin we cannot understand. Now, with this analysis, we have been able to infer that it was the trace left by the sulfur dioxide produced by the high radiation that the planet receives from its star in the upper layers of the atmosphere,” he indicates. Jorge LilloBoxpostdoctoral researcher at the Center for Astrobiology (CAB, CSIC-INTA) who has participated in the study.
According to Shang-Min Tsaia researcher at the University of Oxford in the United Kingdom and lead author of the paper explaining the origin of sulfur dioxide in the atmosphere of WASP-39 b, “This is the first time we have seen concrete evidence of photochemistry (chemical reactions initiated by energetic starlight) on exoplanets.
At an estimated temperature of 1,600 degrees Fahrenheit (900 degrees Celsius) and an atmosphere composed mainly of hydrogen, WASP-39 b is not believed to be habitable. But the new work points the way to finding potential traces of life on a habitable planet.
With its 900ºC and hydrogen-rich atmosphere, WASP-39 b is not thought to be habitable, but the new work points the way to finding potential traces of life on a habitable planet.
The planet’s proximity to its host star, eight times closer than Mercury is to our Sun, also makes it a laboratory for studying the effects of radiation from host stars on exoplanets. A better understanding of the star-planet connection should lead to a deeper understanding of how these processes create the diversity of planets observed in the galaxy.
In addition to sodium, potassium, and water, the Webb telescope also saw carbon dioxide at high resolution, providing twice as much data as reported in your previous observations.
Meanwhile, it was found carbon monoxide, but the obvious signatures of methane and hydrogen sulfide were absent from Webb’s data. If present, these molecules are found at very low levels, a significant finding for scientists conducting inventories of exoplanet chemistry to better understand the formation and development of these distant worlds.
Three instruments: NIRSpec, NIRCam and NIRISS
Webb observes the universe in infrared light, at the red end of the light spectrum beyond what human eyes can see; that allows the telescope to pick up chemical signatures that cannot be detected in visible light. In total, three instruments have been used to characterize in depth the atmosphere of this planet in the infrared range: NIRSpec, NIRCam and NIRISS.
This plot shows four transmission spectra from three of JWST’s instruments operated in four modes. A transmission spectrum is made by comparing the filtered starlight through a planet’s atmosphere as it moves in front of the star, with the unfiltered starlight detected when the planet is next to the star. Each of the data points (white circles) in these plots 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. / NASA, ESA, CSA, Joseph Olmsted (STScI)
“You can really narrow down the properties of these planets by having such a broad spectrum,” he says. Adina Feinsteina graduate student at the University of Chicago and first author of the paper focusing on spectrum observations using NIRISS, “then you start to get the full picture [de las atmósferas] that you couldn’t get before.”
Some of the light from the star filters through the planet’s atmosphere as it passes by, and different atmospheric chemicals absorb different colors of the starlight spectrum. The missing colors tell astronomers which molecules are present.
To see the light of WASP-39 b, Webb followed the passage of the planet in front of its star, which allowed some of the light from the star to filter through the planet’s atmosphere. Different types of chemicals in the atmosphere absorb different colors of the starlight spectrum, so the missing colors tell astronomers which molecules are present.
Having such a comprehensive list of chemical ingredients in an exoplanet’s atmosphere also gives scientists an idea of the abundance of different elements in relation to each other, such as the ratios of carbon to oxygen or potassium to oxygen.
Clues to exoplanet formation
That, in turn, provides insight into how this planet, and perhaps others, formed from the disk of gas and dust that surrounded the parent star in its younger years. The chemical inventory of WASP-39 b suggests a history of crushing and merging of smaller bodies called planetesimales to create an eventual giant planet.
The new findings provide a good idea of the ability of Webb’s instruments to perform the wide range of investigations of exoplanets (planets around other stars) that the scientific community expects. That includes probing the atmospheres of smaller, rocky planets like those in the TRAPPIST-1 system.
“These results are a confirmation of the ability of the JWST instruments to explore the atmospheres of all types of exoplanets, including small and rocky worlds,” he stresses. Enric Palléa researcher at the Instituto de Astrofísica de Canarias (IAC) who has participated in the study.
For his part, David Barreda CAB researcher, points out that others in orbit, such as PLATO, or on Earth, such as the ELT that is being built in Chile, will be added to the Webb telescope in the future, projects in which the Center for Astrobiology also participates.