(ORDO NEWS) — Astronomers have received new data on the exoplanet WASP-107b, unique in all respects. It is one of the hottest exoplanets, located very close to its parent star. In addition, it has such a low density that scientists call it made of cotton candy. Now it turns out that the mass of its core is much lower than was thought necessary to contain the huge shell of gas that surrounds it. The research results are published in the Astronomical Journal.
WASP-107b is a super-Neptune exoplanet orbiting the star WASP-107 in the constellation Virgo, located 200 light years from Earth. The exoplanet is about the size of Jupiter, but ten times lighter than it.
Canadian scientists at the University of Montreal, along with colleagues in the US, Germany and Japan working on the WASP project, used data from the Keck Observatory in Hawaii to more accurately estimate the mass of WASP-107b. To do this, they used the method of radial velocities, which makes it possible to determine the mass of a planet by observing the oscillatory motion of its star caused by the gravitational attraction of the planet.
It turned out that the mass of WASP-107b is about one tenth of the mass of Jupiter, which is only about 30 times the mass of the Earth. Then the authors analyzed the likely internal structure of the planet and came to the surprising conclusion: at such a low density, the planet should have a solid core, no more than four times the mass of the Earth. This means that over 85 percent of the mass of WASP-107b is contained in the thick layer of gas that surrounds this core. For comparison, in Neptune, only 5 to 15 percent of its total mass is contained in the gas layer.
“This is concrete evidence that massive gas envelope accretion can be launched for nuclei that are much less massive than previously thought,” study leader Björn Benneke, professor of astrophysics at the Institute for Exoplanet Research at the University of Montreal, said in a press release. “In this study, we are exploring the very foundations of how giant planets can form and grow.”
In accordance with the classical models of gas giant formation, built on the examples of Jupiter and Saturn, in order to hold a large amount of gas before the protoplanetary disk of dust and gas that surrounds a young star dissipates, a solid core is needed at least 10 times more massive than Earth. … Therefore, the researchers initially had a lot of questions regarding the WASP-107b.
“How could a planet with such a low density form? How did it keep its huge layer of gas from leaking, especially given its proximity to the star?” – lists these questions the first author of the article, graduate student Caroline Piaulet (Caroline Piaulet).
The authors suggest that WASP-107b formed far from the star, where the gas in the disk was cold enough for gas accretion to occur quickly enough. Later, the planet moved to its current position as a result of interaction with the disk or with other planets in the system.
While observing the WASP-107 system, researchers discovered another exoplanet, WASP-107c, with a mass of about one third of the mass of Jupiter, located much further from the parent star and orbiting it in an elongated elliptical orbit.
“WASP-107c in some respects retains the memory of what happened in the WASP-107 system. The large eccentricity of its orbit hints at a rather chaotic past, with interactions between planets that could lead to significant displacements, such as suggested for WASP-107b” Piolet notes.
Scientists plan to continue studying WASP-107b with the James Webb Space Telescope, which is scheduled to launch in 2021.
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