NASA’s Transiting Exoplanet Survey Satellite or TESS has found what NASA calls the two “puffiest” worlds ever found. While they’re as big as our gas giants, they’re so light and airy that their density is apparently comparable to cotton candy. One of the planets, called TOI-791 b, is nearly the same size as Jupiter but only has three percent of its mass. Meanwhile, the second planet called TOI-791 c is even larger than Jupiter but only has 5.9 percent of its mass. 

The planets were discovered by a team led by George Dansfield of Oxford University’s Department of Physics, who studied data provided by TESS. Dansfield said we’re only aware of a handful of super puffy planets, and the fact that these two are in the same star system is even rarer. NASA Ames research scientist Steve Howell explained that large planet formation is believed to drive the evolution of planetary systems, so “further study of these Jupiter-size, but far less than Jupiter-mass, planets is of high value.”

NASA launched TESS back in 2018 to detect planets outside our solar system, but are relatively close to us. The telescope looks for exoplanets in an area 400 times larger than what the Kepler mission covered. So far, TESS has found 7,931 exoplanet candidates, 897 of which have already been confirmed. For this particular planetary system, TESS was able to gather 1,122 days of data over the course of seven years.

Based on that data, researchers concluded that the super puffy planets have unusually long orbits, making them even rarer finds. They’re also locked in an orbit around their star that has them tugging on each other. That affects the timing of their transits around their host star, and that variation is what scientists used to calculate their masses. There’s still a lot they don’t know about the planets, however. NASA says researchers are hoping to know more about the chemical makeup of their atmosphere, how their spin affects their shape and, ultimately, how “cotton candy” planets like them form.