Madison Reporter

A sulfur-laden atmosphere discovered on the gaseous exoplanet GJ 3470 b, located about 96 light-years from our solar system, may provide key insights into planetary formation. This planet, found in the constellation Cancer, is approximately half the size of Neptune and has a mass ten times that of Earth.

Astronomers first identified GJ 3470 b in 2012 when its shadow crossed its host star. Over the years, researchers have gathered data using Hubble and Spitzer space telescopes. Recently, two observations with the James Webb Space Telescope provided further information.

Exoplanets like GJ 3470 b are crucial for understanding planetary creation. By capturing light from a star passing through a planet’s atmosphere, astronomers can analyze its spectrum to identify molecules present.

“The thing is, everybody looks at these planets, and often everybody sees flat lines,” said University of Wisconsin–Madison astronomy professor Thomas Beatty. “But when we looked at this planet, we really didn’t get a flat line.”

Researchers observed water, carbon dioxide, methane, and sulfur dioxide in GJ 3470 b’s atmosphere. Beatty presented these findings at the American Astronomical Society's meeting in Madison and plans to publish them in Astrophysical Journal Letters with co-authors from various institutions including Arizona State University and NASA’s Ames Research Center.

GJ 3470 b is notable for being the lightest and coldest exoplanet to harbor sulfur dioxide—an indicator of active chemical reactions within its atmosphere caused by radiation breaking down hydrogen sulfide.

“We didn’t think we’d see sulfur dioxide on planets this small," Beatty noted. "It gives us a new way to figure out how these planets formed."

Understanding this process is akin to deducing a cake recipe by examining both raw ingredients and the finished product.

“Discovering sulfur dioxide in a planet as small as GJ 3470 b gives us one more important item on the planet formation ingredient list,” Beatty added.

GJ 3470 b also has unique orbital characteristics; it circles nearly over its star's poles at a close distance causing significant atmospheric loss due to stellar radiation—approximately 40% since its formation. These factors suggest past gravitational interactions that altered its orbit significantly.

“That migration history that led to this polar orbit and the loss of all this mass — those are things we don’t typically know about other exoplanet targets we’re looking at,” said Beatty. “Those are important steps in the recipe that created this particular planet.”

Further analysis by researchers specializing in proto-planetary disks and migration dynamics may help decode how such planets form.

This research was supported by grants from NASA.