A super puffy exoplanet is challenging everything that scientists believed they knew about how giant planets were created. The planet, which is called WASP-107b, orbits an orange dwarf star about 211 light-years away from us.
When it was first discovered back in 2017, scientists knew that it is one of the lowest density exoplanets ever found but they didn’t realize until recently that it was even “puffier” than previously hypothesized as the core of the planet is a lot smaller than originally estimated.
“Super-puff” planets contain very low density and are quite rare. While they are similar in size to other gas giants, they have an exceptionally lesser amount of density. And WASP-107b is particularly unique as it is only a bit smaller than Jupiter but has less than 10% of its mass, meaning that it has only 0.13 grams of density per cubic centimeter.
In addition to its incredibly low density, it also completes a full orbit around its host star in a very short amount of time of just 5.7 days. Based on its proximity to the star, the exoplanet has an estimated surface temperature of 865 degrees Fahrenheit (463 degrees Celsius).
The researchers came to these conclusions by studying data taken by the Keck Observatory and were able to calculate how much the host star moved because of the gravitational tug caused by WASP-107b. They were then able to calculate the exoplanet’s structure and found that its solid core was only about 4.6 times the mass of Earth. That would indicate that over 85% of the exoplanet’s mass is located in its “puffy” atmosphere.
Caroline Piaulet, who is a physicist at the University of Montreal, weighed in on the uniqueness of the exoplanet by asking, “How could a planet of such low density form? And how did it keep its huge layer of gas from escaping, especially given the planet's close proximity to its star?”
Furthermore, there is evidence of a second exoplanet (called WASP-107c) that is orbiting the star but is located a lot further away than WASP-107b. It takes the second planet 1,088 days to complete a full orbit around the star and it has a very odd oval-shaped orbit which could indicate that there may be another space body in the area.
Eve Lee, who is an astronomer at McGill University in Canada, detailed what may have happened to explain WASP-107b’s current location, “For WASP-107b, the most plausible scenario is that the planet formed far away from the star, where the gas in the disc is cold enough that gas accretion can occur very quickly,” adding, “The planet was later able to migrate to its current position, either through interactions with the disc or with other planets in the system.”
Björn Benneke, who is an astrophysicist at the University of Montreal in Canada, weighed in on how significant this information is in regards to how huge planets are created, “This work addresses the very foundations of how giant planets can form and grow,” adding, “It provides concrete proof that massive accretion of a gas envelope can be triggered for cores that are much less massive than previously thought.” (An artist’s impression of WASP-107b orbiting its star can be seen here.)
Their research was published in The Astronomical Journal where it can be read in full.