It is not every day astronomers get a close read on a giant planet that is neither frozen nor scorching. This time, the James Webb Space Telescope has picked out methane in the atmosphere of TOI-199b, a Saturn-sized planet more than 330 light-years from Earth with temperatures researchers say are surprisingly similar to those on Earth.
The findings come from a study led by scientists from Penn State and NASA’s Jet Propulsion Laboratory at the California Institute of Technology, published May 20 in the Astronomical Journal.
TOI-199b is one of only a small number of known temperate giant planets, and researchers said this is the first time the atmosphere of one has been studied in such detail.
“One of the main advantages of studies of planets beyond our solar system, known as exoplanets, is the ability to study many different types of planets, especially ones that we don’t see in the solar system, to learn about how planetary systems form and evolve,” said Renyu Hu, associate professor of astronomy and astrophysics in the Penn State Eberly College of Science and leader of the research team.
“Since the first exoplanet was discovered in 1992 by a team that included Aleksander Wolszczan at Penn State, astronomers have found thousands of exoplanets. But only a few giant, temperate exoplanets are known and this is the first time that we have been able to study the atmosphere of one of them in detail.”
The planet orbits its star roughly every 100 days. Its temperature is estimated to be about 175 degrees Fahrenheit, making it much cooler than the hot Jupiters often studied by astronomers, but warmer than the gas giants in our solar system.
To study the atmosphere, researchers used transmission spectroscopy, looking at starlight passing through the planet’s atmosphere as TOI-199b moved across the face of its star.
“As a planet passes in front of its star, some of the star’s light passes through the planet’s atmosphere where it interacts with the elements and molecules in the atmosphere,” said Aaron Bello-Arufe, a postdoctoral researcher at JPL and the first author of the paper.
“Specific elements will absorb specific wavelengths of light, creating a fingerprint in the spectrum of light that JWST detects that reflects the atmosphere’s composition.”
Researchers gathered about 20 continuous hours of observations to set a baseline measurement of the star’s light. The transit lasted about seven hours. Scientists then compared the spectrum recorded during the transit with the baseline to work out which wavelengths were absorbed by the planet’s atmosphere.
“When we compared the spectra during the transit to the baseline, we saw that the atmosphere blocked the wavelengths of starlight absorbed by methane,” Bello-Arufe said.
“Models for the composition of temperate, gas-giant exoplanets had predicted that they would contain methane, so it is good to get confirmation that our theories are accurate.”
The observations also hinted at ammonia and carbon dioxide in the atmosphere.
“With additional observations of this planet, we could establish the relative abundance of these various gases in its atmosphere,” Hu said.
“This more complete picture of a temperate gas giant’s atmosphere can then be used to improve our models and potentially better understand how planets and their atmospheres form and evolve, including for Earth. The success of this first study of a temperate giant planet’s atmosphere also gives us confidence to dedicate more resources and observation time to study other similar planets. We can then see if this planet is unique or if there are general shared characteristics for this type of planet.”
Read more from Science Daily.
