The universe is big, and there are all kinds of stars.
The protagonist of this article is a strange planet called WASP-107b, which is one of the least densest known planets and has been called a "super puff" and "marshmallow" planet by astronomers. A new study suggests that WASP-107b refreshes our understanding of gas giant planet formation.
Back in 2017, astronomers first discovered WASP-107b. It's a gas giant planet about 212 light-years from Earth in the direction of the constellation of Virgo, and the most impressive thing is that it looks unusually fluffy — about the size of Jupiter, but only one-tenth the mass of Jupiter.
Now, Caroline Piaulet of the University of Montreal's Institute of Exoplanet Research is leading a team to conduct an in-depth study of the peculiar WASP-107b and get some interesting new discoveries.
Pialette's team first re-evaluated the mass of WASP-107b by analyzing the observation data from the Keck Observatory, and calculated that the mass of WASP-107b was about 30 times the mass of Earth, that is, about one-tenth of the mass of Jupiter.
They then conducted a series of analyses to try to determine the most likely internal structure of WASP-107b, and came to a surprising conclusion that the mass of the planet's solid core at such a low density would certainly not exceed 4 times the mass of Earth. This means that more than 85% of wasp-107b's mass is present in a thick layer of gas wrapped around the solid-state core. In contrast, Neptune, which has a mass close to WASP-107b, has a gaseous layer mass of only 5%-15% of the total mass.
What's more, the WASP-107b solid-state core is surprisingly small, refreshing our understanding of gas giant planet formation.
The classical model of gas giant planet formation is based on the well-known Jupiter and Saturn. The model suggests that the mass of the solid-state core would need to be at least 10 times the mass of Earth to accumulate large amounts of gas before the protoplanetary disk dissipates, forming a gas giant planet. Without a large enough solid-state core, gas giants cannot build and retain a gaseous outer layer.
But why did WASP-107b exist? Its solid-state kernel mass is much smaller than the theoretical lower limit. One hypothesis suggests that the planet may have originally formed farther away from the star, where the gas was warm enough to be rapidly accreted before migrating to its current location. As for why the migration occurred? This may be the result of interactions with protoplanetary disks or other planets.
With the help of the Keck Observatory, Piarette's team discovered a second planet, WASP-107c, around the star WASP-107, which has a mass well beyond WASP-107b and is about one-third the mass of Jupiter. In addition, wasP-107c's distance to the star is much larger than WASP-107b, with an orbital period of about three years and a revolution of only 5.7 days.
Interestingly, the WASP-107c orbital eccentricity is high and is a distinct ellipse. This suggests that a turbulent past may have been staged, perhaps related to the migration of WASP-107b in the above conjecture.
In addition to its history, there are many mysteries about WASP-107b that have yet to be revealed. For example, in 2018, the Hubble Space Telescope discovered that the planet's atmosphere has very low levels of methane.
"It's strange because these kinds of planets are supposed to be rich in methane." We are now reanalyzing Hubble's observational data based on the quality of our latest assessments to see how the results are, as well as investigating possible mechanisms for explaining methane deletions. Piarette introduced.
The findings have been published in the journal Astronomy, and researchers plan to continue working on WASP-107b, with james Webb expected to bring more clues to the upcoming future launch.