A ‘Super-Puff’ Planet Like No Other – As Big as Jupiter but 10 Times Lighter

Artistic presentation of the exoplanet WASP-107b and its star, WASP-107. Some light currents of the star through the extended gas layer of the exoplanet. ESA / Hubble, NASA, m. Cornmasser

Main mass of giant Exoplanet Much lower than the WASP-107b that was deemed necessary for the creation of giant gas envelopes such as nearby planets Jupiter And Saturn planet, Astronomers of the Universito de Montreal have found.

This tricky discovery has led to Ph.D. Carolyn Piulet, a student at UDM’s Institute for Research on Exoplanets (IREX), suggests that gas-giant planets form much more easily than before.

Piulet is part of the groundbreaking research team of UdeM Astrophysics professor Björn Beneke, who announced the first discovery of water on an exoplanet located in the habitable zone of its star in 2019.

Published today (January 18, 2021) Astronomical Journal New analyzes of the internal structure of the WASP-107b “have huge implications” with colleagues from Canada, the US, Germany and Japan, Beneck said.

“This work addresses the very foundation of how giant planets can grow and develop,” he said. “This provides solid evidence that large-scale accretion of the gas envelope can be triggered for a core that is much lower than we might have thought.”

As big as jupiter but 10 times lighter

WASP-107b was first discovered in 2017 around WASP-107, which was in the Virgo constellation about 212 light years before Earth. This planet is very close to its star – 16 times more close to the Sun than the Earth. As large as Jupiter but 10 times lighter, WASP-107b is one of the least dense exoplanets known: a type that astrophysicists have dubbed “super-puff” or “cotton-candy” planets.

Piulet and his team first used observations of WASP-107b obtained at the KAK Observatory in Hawaii to more accurately assess its mass. They used the radial velocity method, which allows scientists to determine the mass of a planet by observing the staggered motion of its host star due to the gravitational pull of the planet. They concluded that the mass of WASP-107b is about one-tenth that of Jupiter or about 30 times that of Earth.

The team then conducted an analysis to determine the most likely internal structure of the planet. They came to a surprising conclusion: With such a low density, the planet must have a solid core no more than four times the mass of Earth. This means that more than 85 percent of the mass is included in the thick layer of gas that surrounds this core. by comparison, Neptune, Which has the same mass as WASP-107b, accounts for only 5 to 15 percent of its total mass in gas.

“We had a lot of questions about WASP-107b,” Piaulet said. “How can a planet with such a low density be made? And how did it keep its huge layer of gas from escaping, especially given the planet’s proximity to its star.

“This prompted us to conduct an in-depth analysis to determine the history of its formation.”

Make a gas giant

Planets are in the form of dust and gas that surround a young star called a protoplanetary disk. Classical models of gas-giant planet formation are based on Jupiter and Saturn. Of these, a solid core needs to accumulate a large amount of gas at least 10 times more than the Earth before it disintegrates from the disk.

Without massive cores, gas-giant planets were not considered capable of crossing the critical threshold required to create and maintain their massive gas envelopes.

Then how to explain the existence of WASP-107b, which has a much less massive core? A professor at McGill University and a world-renowned expert on super-puff planets such as WREP-107b, Eve Lee, a member of IREx, has several hypotheses.

“For WASP-107b, the most plausible scenario is that the planet is formed far away from the star, where the gas in the disc is cold enough that gas emissions can occur very quickly,” she said. “The planet was later able to move to its current position, either through interactions with the disk or with other planets in the system.”

Exploring each other planet, WASP-107c

Keck observations of the WASP-107 system take much longer than previous studies, allowing the UdeM-led research team to make an additional discovery: the existence of another planet, WASP-107c, with its mass One-third Jupiter, which is significantly higher than WASP-107b.

WASP-107c is also far from the central star; It takes three years to complete an orbit around it, compared to only 5.7 days for the WASP-107b. It is also interesting: the craze of this second planet is high, which means that the trajectory around its star is more oval than circular.

“WASP-107c has in some ways maintained the memory of what happened in its system,” Piaulet said. “Its large eccentricity hints at the chaotic past of the past, with interactions between planets that could cause significant displacement, such as those suspected for WASP-107b.”

Many more questions

Beyond the history of its formation, there are still many mysteries surrounding WASP-107b. Study of planet’s atmosphere Hubble Space Telescope A surprise published in 2018 came out: it contains very little methane.

“Strange, because for a planet of this type, methane must be abundant,” Piulet said. “We are now looking at Hubble’s observations with the new mass of the planet to see how this would affect the results, and to test whether the mechanism could explain the destruction of methane.”

The young researcher plans to continue studying WASP-107b, with the hope of James Webb Space Telescope Is set to launch in 2021, which will provide a more accurate idea of ​​the structure of the planet’s atmosphere.

“Exoplanets such as WASP-107b that are no analogs in our solar system allow us to understand the mechanisms of planet formation in general and the diversity resulting from exoplanets,” she said. “It inspires us to study them in great detail.”

References: “WASP-107b’s Density Is Even Less: A Case for the Physics of Gas Envelope Addition and Orbital Migration, by Caroline Piaulet, Björn Beneke, Ryan A. Rubengel, Andrew W. Howard, Eve J. Lee, Daniel Thorngren. study”. Ruth Angus, Meryn Peterson, Joshua E. Shilder, Michael Werner, Laura Kreidberg, Tareeq Jouni, Ian JM Crossfield, David R. Siardi, Eric A. Pettigura, John Livingston, Courtney D. Dressing, Benjamin J. Fulton, Charles Beachman, Jessie L. Kristiansen, Varujan Gorjian, Kevin K. Harddegree-Ullmann, Jessica Crick and Ivan Sinukoff, 18 January 2021, Astronomical Journal.
DOI: 10.3847 / 1538-3881 / abcd3c

In addition to Piulet (IREx Ph.D. student, Université de Monterel) and professors Björn Benecke (IREX, Université de Montréal) and Eve Lee (IXX, McGill Space Institute, McGill University), the research team includes Daniel Thorngren (IRECTOR Postrector) Huh. Fellow, Universito de Monterrell) and Marin Peterson (Irex M.Sc student), and 19 other co-authors from Canada, the United States, Germany, and Japan.

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