Astronomers have just unveiled a pair of remarkably strange worlds that challenge everything we know about how planets form. Using data from NASA’s Transiting Exoplanet Survey Satellite (TESS), an international research team identified two giant planets orbiting the same distant star that are so light and airy, scientists are comparing them to cotton candy. These “super-puff” planets, located 1,113 light-years away, represent one of the most unusual discoveries in the history of space exploration.
The two planets, known as TOI-791 b and TOI-791 c, revolve around a Sun-like star called TOI-791. While they are massive in size—matching or even exceeding the scale of Jupiter—they possess an incredibly small fraction of its mass. Specifically, TOI-791 b is roughly the size of Jupiter but holds only 3% of its mass. Its companion, TOI-791 c, is even larger than Jupiter but contains just 5.9% of its mass. This extreme discrepancy results in a density so low that researchers describe it as being similar to a fresh blob of shaving foam or a cloud of spun sugar.
The discovery was made possible by the persistent work of NASA’s TESS mission, which has been scanning the skies for exoplanets since its launch in 2018. Although the mission was initially planned to last just two years, its success has led to an indefinite extension, allowing it to map thousands of potential worlds. For this specific system, the telescope collected 1,122 days of data over seven years, which allowed researchers to observe the subtle ways these two planets tug on each other.
Scientists determined the mass of these planets by analyzing the timing of their transits—the moments when they pass in front of their host star. Because the planets are locked in a gravitational dance, their orbital paths shift slightly. By measuring these variations, the team calculated the true, surprisingly low density of these giant worlds. While they are significantly larger than any rocky planet, they lack the solid, compact cores typical of gas giants in our own solar system.
Understanding how these super-puff planets form is now a top priority for the astronomical community. Current theories of planetary evolution struggle to explain how such large, low-density bodies can exist without simply evaporating or collapsing under their own gravity. Experts believe these planets likely consist mostly of hydrogen and helium, but further observation with advanced tools, such as the James Webb Space Telescope, will be necessary to confirm their exact atmospheric makeup.
Finding two such rare, low-density planets in the same solar system is an extraordinary event. Most solar systems contain a mix of different types of worlds, but the TOI-791 system provides a unique laboratory for studying the life cycle of giant, “fluffy” planets. Researchers hope that by investigating these two, they can unlock secrets about how planetary systems evolve and why some worlds become dense, rocky giants while others grow into ghostly, transparent giants that barely hold their own shape.
