Astronomers using NASA’s James Webb Space Telescope have discovered a giant planet with an atmosphere rich in methane, offering scientists a rare look at a type of world that barely exists in our current catalog of known planets.
The planet, called TOI-199b, is about the size of Saturn but has temperatures surprisingly close to those found on Earth compared with most giant planets studied so far.
The findings were published in The Astronomical Journal by researchers from Pennsylvania State University and NASA Jet Propulsion Laboratory.
Most giant planets scientists study fall into two extreme groups.
In our solar system, planets like Jupiter and Saturn are very cold because they orbit far from the sun.
Outside our solar system, astronomers have discovered many “hot Jupiters,” giant planets that orbit extremely close to their stars and can reach scorching temperatures of thousands of degrees.
TOI-199b sits somewhere in between. The planet orbits its star every 100 days and has a temperature of about 175 degrees Fahrenheit.
While still hot for humans, this is much milder than most giant exoplanets scientists have observed.
The planet lies more than 330 light-years away from Earth and is one of only a small number of known temperate giant planets. More importantly, it is the first of its kind to have its atmosphere studied in detail.
To examine the atmosphere, astronomers used a method called transmission spectroscopy.
As the planet passed in front of its star, some of the starlight traveled through the planet’s atmosphere before reaching the Webb telescope.
Different gases absorb different wavelengths of light, leaving unique fingerprints that reveal the atmosphere’s chemical makeup.
The researchers observed the system for about 20 hours, including a seven-hour planetary transit. By comparing the star’s normal light with the light filtered through the atmosphere, the team identified clear signs of methane.
Scientists had predicted that temperate gas giants should contain methane, so the discovery provides important confirmation that current planetary models are likely correct.
The observations also hinted that the atmosphere may contain ammonia and carbon dioxide, although additional observations will be needed to confirm their amounts.
Researchers say studying planets like TOI-199b can help scientists better understand how planets and atmospheres form and evolve over time. Although the planet itself is not suitable for life, learning how its atmosphere behaves could improve broader theories about planetary systems, including Earth’s own atmosphere.
The success of the study also demonstrates the incredible power of the James Webb Space Telescope. Astronomers now hope to study more temperate giant planets to determine whether TOI-199b is unusual or part of a larger family of worlds that scientists are only beginning to explore.
Source: Penn State.
