by The James Webb Space Telescope (JWST) has detected methane and water vapor in the atmosphere of a Jupiter-like world located about 163 light years away.
Astronomers made the discovery using this powerful infrared space telescope to observe the extrasolar planet or “exoplanetWASP-80 b passes by the face of its parent red dwarf star, which it orbits approximately once every 3 Earth days.
So far, astronomers have detected water vapor in the atmospheres of about a dozen planets, but detecting methane (although commonly found in the atmospheres of solar system worlds such as Jupiter, Saturn, Uranus, and Neptune) using spectroscopy space has been much more difficult. rarer. That’s what the team, which includes 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 saw such an obvious methane spectral feature with our eyes in a spectrum of transiting exoplanets, not unlike what could be seen in the spectra of the solar system’s giant planets half a century ago,” Welbanks said. he said in a statement.
To be clear, this is not the first time JWST has discovered atmospheric methane. For example, the observatory discovered such molecules around the exoplanet K12-18b. at the beginning of this year.
Related: The Hubble Telescope investigates a nearby exoplanet and discovers that it is the size of Earth
A needle in a cosmic haystack
WASP-80 b is classified as a “warm Jupiter” because it is not as close to its parent star as so-called hot Jupiters, but it is closer than so-called cold Jupiters. The original Jupiter, the largest planet in our solar system and the gas giant for which this category of planets is named, is technically a “cold Jupiter.”
Because of this relative proximity, distinguishing WASP-80 b from its red dwarf star is no easy task. In fact, it is even the capabilities of the $10 billion JWST. It is the equivalent of detecting a single human hair from a distance of 14.5 kilometers (9 miles).
Fortunately, astronomers have a way to meet the challenge. They basically wait for WASP-80 b to transit 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, looking at the combined spectra and comparing them to the star’s individual 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, causing the light from the star we see to dim a bit. It’s like when someone walks past a lamp and turns it on. light dims.” Welbanks said.
“During this time,” Welbanks continued, “the star illuminates a thin ring of the planet’s atmosphere around the planet’s day/night boundary, and in certain colors of light where molecules in the planet’s atmosphere absorb light, the atmosphere appears It is thicker and blocks more starlight, causing deeper dimming compared to other wavelengths where the atmosphere appears transparent.
“This method helps scientists like us understand what the planet’s atmosphere is made of by seeing what colors of light are blocked,” the researcher explained.
But the team didn’t stop there. The scientists also used another method to measure the atmosphere of WASP-80 b.
You’re getting hot… while you hunt for methane
Like all planets, WASP-80 b emits part 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 to its star gives the planet a surface temperature of 1,025 degrees Fahrenheit (552 degrees Celsius). This compares to Jupiter’s typical warm temperatures of 2,150 degrees Fahrenheit (1,177 degrees Celsius) and our Jupiter’s positively frigid temperatures of minus 235 degrees Fahrenheit (-148 degrees Celsius).
Hot Jupiters are also tidally locked to their stars, meaning they have hotter permanent “day sides” that always face the star, and cooler permanent “night sides” that always face space.
Just before WASP-80 b eclipses its star, its dayside points toward Earth, meaning that measuring a dip in light coming from the star during the eclipse reveals infrared light coming from the planet as a result of its thermal emissions. This provides astronomers with “eclipse spectra” with light absorption patterns connected to molecules in a planet’s atmosphere. These patterns appear as a reduction in the light emitted by the planet at specific wavelengths.
The best of both worlds
Combining the eclipse and transit data allowed the team to see how much light WASP-80 b’s atmosphere was blocking and emitting at different wavelengths. 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 could be expected in such a world. The other model was more flexible, testing millions of different combinations of methane and water abundances 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.
“Prior to JWST, methane had been largely undetected, despite expectations that it could have been detected with the Hubble Space Telescope on planets where it should have been abundant,” Line explained. “This lack of detections generated a flood of ideas ranging from the intrinsic depletion of carbon to its photochemical destruction and the mixing of depleted gas in the depths of methane.”
The next step is to explore what WASP-80’s chemical composition can tell scientists about the exoplanet’s characteristics, its formation history, and its evolution in regards to methane and water abundance. These studies would also allow the team to infer things like the ratio of atmospheric carbon to oxygen. This ratio is something that varies depending on exactly where a planet forms around a star; could reveal whether WASP-80 b formed where it is now or was born further away before migrating toward 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, taking advantage of samples and data collected by space missions that have already visited Jupiter and Saturn.
“Methane is not only an important gas for tracking atmospheric composition and chemistry on giant planets, but it is also hypothesized to be, in combination with oxygen, a possible signature of biology,” Welbanks concluded. “One of the key goals of the Habitable Worlds Observatory, NASA’s next flagship mission after JWST and Roman, is to search for gases such as oxygen and methane on Earth-like planets around Sun-like stars.”
The team’s research was published Nov. 22 in the journal Nature.
