This extremely fluffy exoplanet is changing our understanding of planetary formation

UNITED STATES (VOP TODAY NEWS) — One of the lowest-density exoplanets we’ve ever found in the Milky Way galaxy, it challenges our understanding of how giant planets form.

Called WASP-107b, it orbits an orange dwarf star 211 light-years away, and was already known as one of the lowest-density exoplanets, announced in 2017.

This means that its core is less massive than originally thought, and this discovery could be quite significant for the study of exoplanets in general.

“This paper looks at the very foundations of how giant planets can form and grow,” said astrophysicist Bjorn Bennecke of the University of Montreal in Canada.

“This is concrete evidence that massive gas envelope accretion can be triggered for nuclei that are less massive than previously thought.”

Such low density planets are very rare and unusual. They are the size of gas giants, but their density is much, much lower. WASP-107b is only slightly smaller than Jupiter, but its mass is less than 10 percent of the mass of Jupiter, resulting in a density of only 0.13 grams per cubic centimeter.

The exoplanet is also dangerously close to its host star. Its orbital period is only 5.7 days, so close that the temperature is 736 Kelvin (462 degrees Celsius or 865 degrees Fahrenheit) and the atmosphere is rapidly evaporating.

A new study by physicist Caroline Piaulet of the University of Montreal was the first to refine the mass of WASP-107b using four-year observations from the Keck Observatory to measure how far the star moved in response to the orbiting exoplanet’s gravity tug.

Then, using the new calculations, the team performed a detailed analysis of the structure of WASP-107b. Much to their surprise, they found that more than 85 percent of the exoplanet’s mass is in its atmosphere.

In itself, this is not so strange; It is believed that the core of Jupiter accounts for 5 to 15 percent of the planet’s mass. But Jupiter as a whole is more massive, which means that its core is more massive. Jupiter is also much further from its star.

“How could a planet with such a low density have formed? And how does it keep its gas level from leaking, especially given the planet’s proximity to its star?

So far, our understanding of the formation of gas giants has been based primarily on the ones we can most easily study: Saturn and Jupiter.

They have massive cores that are 10 times the mass of Earth, so astronomers thought such a massive core was necessary for the formation of gas giants. This will provide mass before triggering uncontrolled accretion and the rapid accumulation of as much gas and dust as possible.

“For WASP-107b, the most likely scenario is that the planet was formed far from a star, where the gas in the disk is cold enough for gas accretion to occur very quickly,” said astronomer Iva Lee of McGill University in Canada.

“Later, the planet was able to move to its current position either through interactions with the disk or with other planets in the system.”

This could make it a great exoplanet for studying how large a core must be to trigger the formation of gas giants. The team plans to re-observe WASP-107b with more sensitive instruments to help solve this mystery.

“Exoplanets like WASP-107b, unparalleled in our solar system, allow us to better understand the mechanisms of planet formation in general and the resulting diversity of exoplanets,” Piaule said.


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