The bizarre “ cotton candy ” planet changes our sense of what is possible

A localized 212 light- exoplanetyears old is roughly the same size as Jupiter, but it’s 10 times lighter. Discovery challenges our views on the formation and growth of gas giants and the types of planets that may exist.

New research published in The Astrophysical Journal suggests it is easier for gas giants to emerge in a protoplanetary disc than before assumed. By “easier”, the authors of the new article, led by astronomer Björn Benneke and doctoral student Caroline Piaulet from the University of Montreal, mean that in some special cases, the embryonic nuclei needed to initiate training gas giants may be lighter than current models predict.

Benneke and Piaulet just completed a four-year investigation into WASP-107b, a gas giant with 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 already been detected and studied, earning it nicknames like “super puff planets” and “cotton candy planets”.

This world is very close to its host star, so a year on WASP-107b is only 5.7 days long. Using the Keck Observatory in Hawai’i, the group sought to improve estimates of the object’s mass. To do this, the team measured the degree to which the exoplanet caused its host star to oscillate – a technique astronomers call the radial velocity method. Astronomers have discovered that WASP-107b contains just 1.8 masses of Neptune, or 30 land masses. It means he has just a tenth of the mass of Jupiter, with a comparable waist circumference. You can see where the cotton candy comparison comes in.

The updated figure allowed the team to estimate the composition of the object’s internal structure. The core had to be heavy enough to prevent gas from escaping into space but light enough to maintain the extreme low density observed on the planet. Thus, the solid core, scientists believe, cannot be heavier than 4 earth masses. What’s more, 85% of the planet’s total mass is packaged in the thick layer of gas immediately surrounding the solid core, according to the article. By comparison, 5% up to 15% of the mass of Neptune is contained in its thick layer of gas.

This was an unexpected result, as it is “significantly less than what is traditionally assumed to be necessary to trigger massive accretion of the gas envelope,” as the authors wrote in their article (my wife accuses me of reverse problem). In other words, the core of WASP-107b does not appear to have sufficient mass, and therefore gravitational influence, to facilitate the formation of a gas giant inside the protoplanetary disk – the gigantic disk of dust and gas that surrounds a star during the process of forming the planet. But, obviously, WASP-107b exists, so our theories on such things must be wrong or at least need some refinement.

Indeed, the new article “addresses the very foundations of the formation and growth of giant planets,” Benneke said at a university in Montreal. declaration. “This provides concrete proof that massive accretion of a gas shell can be triggered for nuclei that are much less massive than previously thought.”

Current models of gas giant formation are biased in favor of the formation of Jupiter- and Saturn-like objects, and they suggest that embryonic nuclei must be at least 10 times heavier than Earth. Any lighter, and the nucleus is unable to collect or accrete sufficient amounts of gas and dust before the protoplanetary disc dissipates. With the new data, the researchers were forced to design 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 that gas accretion can occur very quickly,” said Piaulet in the press release. “The planet was then 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 stumbled upon another exoplanet inside the same star system, which is now called WASP-107c. Encouragingly, this planet – with its exaggerated orbit – suggests that Piaulet and his colleagues are on the right track with their proposed new training scenario.

WASP-107c has about one-third the mass of Jupiter, so it’s 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’s not very interesting, but the elongated shape of its orbit is very interesting.

“WASP-107c has in some ways kept the memory of what happened in its system,” Piaulet said. “Its great eccentricity hints at a rather chaotic past, with interactions between the planets that could have led to important displacements, like that suspected for WASP-107b.”

Good right? Always good to see corroborating evidence. Going forward, the team will seek to better understand the chemical makeup of WASP-107b, including its inexplicable lack of methane. Maybe another clue to his quirk? We will be interested to know.