New research on WASP-107b reveals gas giants may form more readily than thought. This ultra-low-density 'cotton candy' planet orbits 211 light-years from Earth.
Our solar system hosts a remarkable variety of worlds: rocky planets like Earth, Venus, Mars, and Mercury; gas giants such as Jupiter and Saturn; ice giants including Uranus and Neptune; and even dwarf planets like Pluto and Ceres. Yet one intriguing type remains absent—the 'super-puffs' or 'cotton candy' planets, known for their exceptionally low densities.
These rare exoplanets are scarce across the cosmos. WASP-107b, circling an orange dwarf star 211 light-years away in the constellation Virgo, exemplifies this class. Discovered in 2017, it has now undergone detailed scrutiny, with findings published in The Astronomical Journal.
Astrophysicist Caroline Piaulet and her team at the University of Montreal analyzed four years of data from Hawaii's Keck Observatory, tracking the star's wobble due to the planet's gravity. This refined the planet's mass estimate: WASP-107b is slightly smaller than Jupiter but 10% less massive, yielding a density of only 0.13 grams per cubic centimeter.
Further modeling revealed its solid core is no larger than about 4.6 Earth masses, meaning over 85% of its mass resides in its vast, puffy atmosphere.
Orbiting perilously close to its star with a 5.7-day period, the planet's surface reaches 462°C, causing its atmosphere to evaporate. 'How did such a low-density planet form, and how has it retained its massive gas envelope despite proximity to its star?' Piaulet wonders.
Traditional models of gas giant formation draw from Jupiter and Saturn, which boast cores at least 10 times Earth's mass—thought essential for rapid gas accretion from the protoplanetary disk. WASP-107b challenges this.
'For WASP-107b, the most likely scenario is that it formed far from its star, where disk gas was cold enough for swift accretion,' explains co-author Eve Lee. 'It then migrated inward, possibly via disk interactions or encounters with other planets.'
Observations also confirmed a second planet, WASP-107c, orbiting farther out in 1,088 days on a highly eccentric path—likely perturbed by WASP-107b.
Future studies with advanced telescopes like the James Webb Space Telescope will probe WASP-107b further, illuminating gas giant formation mechanisms.
