Unique ‘Super-Puff’ Planet As Big As Jupiter But 10 Times Lighter Discovered
A unique exoplanet discovered by a team of planetary scientists could change our understanding of how gas giants like Jupiter and Saturn are formed.
Analysis of WASP-107b, a giant exoplanet about 212 light years from Earth, has found that despite being roughly the size of Jupiter, the planet is 10 times lighter than our Solar System’s largest gas giant, making it one of the least dense exoplanets ever discovered.
WASP-107b, which as been dubbed a ‘super-puff’ or ‘cotton candy’ planet, looks set to have ‘big implications’ for our understanding of the conditions necessary for gas giants to form, according to a new study published in the Astronomical Journal.
The study was conducted by a research team from the Universite de Montreal in Canada, led by astrophysicist Bjorn Benneke, which in 2019 identified the first habitable exoplanet containing water. According to Benneke, this latest discovery is similarly groundbreaking, challenging ‘the very foundations of how giant planets can form and grow.’
Benneke told Phys.org the study ‘provides concrete proof that massive accretion of a gas envelope can be triggered for cores that are much less massive than previously thought’.
WASP-107b was first detected in 2017, and is thought to be more than 16 times closer to its host star, WASP107, than Earth is to the sun. At about 1/10th the mass of Jupiter, WASP-107b is still some 30x larger in mass than our home planet, yet analysis showed that the planet’s core is only four times larger than that of Earth.
That means that the vast majority of WASP-107b’s mass comes from the ‘gas layer’ that surrounds the core. It’s a characteristic that surprised the scientists, with the similarly-sized gas giant Neptune getting only between 5-15% of its mass from this gas layer.
The findings challenge what was previously thought to be necessary for gas giants to form, with astrophysicists until now believing that a massive core, at least 10 times larger than Earth’s was needed to allow the planets to reach a stable critical mass.
The unique nature of WASP-107b means its not clear how the planet even came to exist. One theory explained by super-puff planet expert Eve Lee is that the exoplanet actually formed further away from its host star, ‘where the gas in the disc is cold enough that gas accretion can occur very quickly,’ before drifting closer over time.
The research team plans to continue to study WASP-107b, with team member Caroline Piaulet explaining that the unique nature of the planet makes it a valuable target for research. ‘Exoplanets like WASP-107b that have no analogue in our Solar System allow us to better understand the mechanisms of planet formation in general and the resulting variety of exoplanets,’ she said. ‘Its great eccentricity hints at a rather chaotic past.’
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