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NASA’s James Webb Space Telescope (JWST) has made a groundbreaking discovery about an exoplanet named TOI-199b. This planet is a gas giant, similar in size to Saturn, located approximately 335 light-years away from Earth. The planet has a mass that is 0.17 times that of Jupiter and a radius that is 0.81 times that of Jupiter. It orbits a star similar to our Sun, known as a G-type star, every 104.9 days. Although its orbit lies within the star’s habitable zone, the planet is far enough away that it remains much cooler than typical gas giants found close to their stars. The temperature on TOI-199b is approximately 79 degrees Celsius, which is 175 degrees Fahrenheit.
Scientists have not studied temperate gas giant exoplanets very much. However, a new study published in The Astronomical Journal provides important details about these rare and intriguing worlds. Researchers used the JWST to observe the atmosphere of TOI-199b. They watched as the planet passed in front of its host star. This method is called transmission spectroscopy. It allows astronomers to study how matter interacts with light. By observing the wavelengths of starlight absorbed by the planet, astronomers can identify the molecules present in its atmosphere.
In the case of TOI-199b, astronomers found methane in its gaseous atmosphere. They compared these findings to longstanding models of temperate gas giant exoplanets. The results matched the models, confirming previous hypotheses. These hypotheses suggested that temperate gas giants would contain methane. TOI-199b is now designated as the first temperate gas giant exoplanet found to contain methane. The team also identified carbon dioxide and ammonia as potential molecules in the atmosphere. This discovery helps scientists understand the chemical composition of these distant worlds.
Dr. Renyu Hu, an associate professor of astronomy and astrophysics at Penn State University, is a co-author on the study. He explained the importance of this discovery. "With additional observations of this planet, we could establish the relative abundance of these various gases in its atmosphere," said Dr. Hu. He noted that this information would provide a more complete picture of a temperate gas giant’s atmosphere. Such a picture can be used to improve scientific models. It may also help scientists better understand how planets and their atmospheres form and evolve. This understanding applies to gas giants and even to Earth.