The James Webb Space Telescope (JWST) has detected methane and water vapor in the atmosphere of a Jupiter-like world about 163 light-years away.
Astronomers made this discovery by using this powerful infrared space telescope to observe the planet outside the solar system. exoplanet WASP-80 b passes over the face of its red dwarf star, which it orbits about once every three Earth days.
Astronomers have so far observed water vapor in the atmospheres of a dozen planets, but the detection of methane - although commonly found in the atmospheres of solar system worlds such as Jupiter, Saturn, Uranus and Neptune - using space-based spectroscopy is still a long way off . rarer. That's what the team, including Arizona State University scientists Luis Welbanks and Michael Line of the School of Earth and Space Exploration, and Bay Area Environmental Research Institute (BAERI) researcher Taylor Bell, have now done with the James Webb Space Telescope.
"This was the first time we had seen such a clear spectral feature of methane with our eyes in the spectrum of an exoplanet, not unlike what we could see half a century ago in the spectra of the solar system's giant planets" , says Welbanks. said in a statement.
To be clear, this is not the first time the JWST has detected methane in the atmosphere. The observatory discovered such molecules, for example, around exoplanet K12-18b earlier this year.
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WASP-80 b is classified as a 'warm Jupiter' because it is not as close to its host star as the so-called hot Jupiters, but is still closer than the so-called cold Jupiters. The original Jupiter, the largest planet in our solar system and the gas giant from which this category of planets gets their name, is technically a 'cold Jupiter'.
Because of this relative proximity, distinguishing WASP-80 b from its red dwarf star is not an easy task. In fact, they are even the possibilities of the $10 billion JWST. It's the equivalent of spotting one human hair from 9 miles away.
Fortunately, astronomers have a way to meet the challenge. They essentially wait for WASP-80 b to pass by the face of the red dwarf it orbits, and then observe a collective spectrum associated with the planet.
Because chemical elements and molecules absorb light at characteristic wavelengths, viewing the combined spectra and comparing them to the star's solo spectra reveals distinctive fingerprints of specific molecules in a planet's atmosphere.
'Using the transit method, we observed the system as the planet moved in front of its star from our perspective, making the starlight we see a little fainter. It's kind of like when someone walks in front of a lamp and dims the light. ', said Welbanks.
"During this time," Welbanks continued, "a thin ring of the planet's atmosphere around the planet's day/night boundary is illuminated by the star, and at certain colors of light where the molecules in the planet's atmosphere absorb light, the atmosphere appears thicker and blocks more starlight, creating a deeper darkening compared to (with) other wavelengths where the atmosphere appears transparent.
"This method helps scientists like us understand what the planet's atmosphere is made of by seeing which colors of light are being blocked," the researcher explains.
But the team didn't stop there. The scientists also used another method to measure WASP-80 b's atmosphere.
You're getting warmer... while you're chasing methane
Like all planets, WASP-80 b emits some of its light in the form of thermal radiation. Both the wavelength category and the intensity of this light depend on the temperature of the planet.
This proximity of WASP-80 b to its star gives the planet a surface temperature of 1,025 degrees Fahrenheit (552 degrees Celsius). This compares to Jupiter's typical hot temperatures of 2150 degrees Fahrenheit (1177 degrees Celsius) and our Jupiter's positively frigid temperatures at minus 235 degrees Fahrenheit (-148 degrees Celsius).
Warm and hot Jupiters are also tidally linked to their stars, meaning they have warmer permanent 'day sides' that always face the star, and permanent cooler 'night sides' that always face space.
Just before WASP-80 b eclipses its star, its dayside faces Earth, meaning that measuring a dip in light coming from the star during the eclipse reveals infrared light coming from the planet due to its thermal emissions. This gives astronomers 'eclipse spectra' showing light absorption patterns associated with molecules in a planet's atmosphere. These patterns appear more or less as a reduction in the planet's emitted light at specific wavelengths.
The best of both worlds
By combining the eclipse and transit data, the team was able to see how much light at different wavelengths was blocked and emitted by WASP-80 b's atmosphere. The researchers then used two different models to simulate what the atmosphere of a planet like WASP-80 b would look like under the extreme conditions of a warm Jupiter.
One model was strict and took into account existing physics and chemistry to determine the levels of methane and water that would be expected from such a world. The other model was more flexible, trying millions of different combinations of the methane and water amounts and temperatures to find the recipe that best fit the data. Comparing transit and eclipse data with both models led the team to the same, clear conclusion.
They had definitely detected methane in the atmosphere of WASP-80 b.
"Before JWST, methane had gone largely unnoticed, despite expectations that it could have been detected with the Hubble Space Telescope on planets where it should have been abundant," Line explains. "This lack of detections generated a flood of ideas ranging from the intrinsic depletion of carbon to its photochemical destruction to the mixing of deeply methane-depleted gas."
The next step is to investigate what the chemical composition of WASP-80 b can tell scientists about the exoplanet's characteristics, formation history and evolution in relation to the amount of methane and water. Such studies would also allow the team to infer things like the ratio of carbon to oxygen in the atmosphere. This ratio is something that varies depending on where exactly a planet forms around a star; it could reveal whether WASP-80 b formed where it now sits, or whether it was born further away before migrating to its star.
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The team will also compare the atmospheres of warm Jupiters outside the solar system with those of planets orbiting the Sun, using samples and data collected by space missions that have already visited Jupiter and Saturn.
"Methane is not only an important gas in tracing atmospheric composition and chemistry on giant planets, but it is also hypothesized, in combination with oxygen, to be a possible hallmark of biology," Welbanks concluded. "One of the main goals of the Habitable Worlds Observatory, the next NASA flagship mission after JWST and Roman, is to search for gases such as oxygen and methane in Earth-like planets around Sun-like stars."
The team's research was published in the journal on November 22 Nature.
