An exoplanet located at 212 lightyears away it is about the same size as Jupiter, but it is 10 times lighter. The discovery challenges our conceptions of how gas giants form and grow and the types of planets that can exist.
New research published in The Astrophysical Journal suggests it is easier for gas giants to appear in a protoplanetary disk than before assumed. By “easier”, the authors of the new work, led by astronomer Björn Benneke and PhD student Caroline Piaulet of the University of Montreal, mean that in some special cases, the embryonic nuclei needed to begin the formation of gas giants may be easier than predicted. current.
Benneke and Piaulet have just completed a four-year survey of WASP-107b, a gas giant with a mass in the Neptune range but a radius the size of Jupiter. This gas giant was previously known to astronomers, but the group wanted to better understand how such an object, with its extreme low density, could have formed from its protoplanetary disk. These types of planets have been previously detected and studied, earning nicknames such as “super-fluffy planets” and “cotton candy planets”.
This world it is very close to the host star, so a year on WASP-107b lasts only 5.7 days. Using the Hawaiian Keck Observatory, the group sought to improve object mass estimates. To do this, the team measured the degree to which the exoplanet shook its host star – a technique that astronomers refer to as the radial velocity method. Astronomers have discovered that WASP-107b contains only 1.8 masses of Neptune or 30 masses of Earth. That means yes only a tenth of the mass of Jupiter, with a comparable waist. You can see where the cotton-candy comparison comes from.
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The updated figure allowed the team to estimate the composition of the internal structure of the object. The core had to be heavy enough to prevent gas from leaking into space but light enough to maintain the extremely low density observed on the planet. Thus, the solid core, scientists estimate, can not be heavier than 4 Earth masses. Moreover, 85% of the entire mass of the planet is packed in the thick layer of gas that immediately surrounds the solid core, according to the paper. By comparison, 5% up to 15% of Neptune’s mass is contained in its thick gas layer.
This was an unexpected result, as it is “significantly smaller than what is traditionally assumed to be necessary to trigger a massive accumulation of the gas envelope,” as the authors wrote in their paper (my wife accuses me of the opposite problem). In other words, the WASP-107b core does not appear to have enough mass and thus gravitational influence to facilitate the formation of a gas. giant inside the protoplanetary disk – the giant disk of dust and gas that surrounds a star during the process of planet formation. But, obvious, WASP-107b exists, so our theories about such things must be wrong or at least in need of refinement.
Indeed, the new paper “addresses the very foundations of how giant planets can form and grow,” Benneke said at a university in Montreal. statement. “It provides concrete evidence that the massive accretion of a gas tire can be triggered for nuclei that are much less massive than previously thought.”
Current models of the formation of gas giants are oriented towards the formation of Jupiter- and Saturn-like objects and suggest that embryonic nuclei must be at least 10 times heavier than Earth. Any lighter, and the core is not able to collect or accumulate sufficient amounts of gas and dust before the dissipation of the protoplanetary disk. With the new data, researchers were forced to entertain alternative scenarios.
“For WASP-107b, the most plausible scenario is that the planet formed far from the star, where the gas in the disk is cold enough for gas accretion to take place very quickly,” Piaulet said in a statement. “The planet was later able to migrate to its current position, either through interactions with the disk or with other planets in the system.”
Interesting hypothesis, but that’s exactly it. Future work will be needed to further validate this hypothesis.
During this research, the team came across another exoplanet inside the same stellar system, which is now called WASP-107c. Encouragingly, this planet – with its exaggerated orbit – suggests that Piaulet and her colleagues are on the right track with their proposed new training scenario.
WASP-107c has about a third of Jupiter’s mass, so it is considerably heavier than its companion, WASP-107b. It takes three years for this newly detected exoplanet to make a single orbit of its host star. It is not very interesting, but the elongated shape of its orbit is very much.
“WASP-107c has kept, in some respects, the memory of what happened in its system,” Piaulet said. “Its great eccentricity suggests a rather chaotic past, with interactions between planets that could have led to significant displacements, such as the one suspected for WASP-107b.”
Nice, isn’t it? It’s always good to see corroborating evidence. Looking ahead, the team will seek to better understand the chemical composition of WASP-107b, including the unexplained lack of methane. Maybe another hint of his strangeness? We will be interested to know.