Record-Breaking Marshmallow Planet – It’s A Cold, Peculiar World On A Very Slanted Orbit

Scientists have confirmed the existence of over 6,100 planets beyond the Solar System in the Milky Way. Something that has become clear pretty much from the very beginning of the search for exoplanets is that there are truly some oddballs when it comes to worlds beyond the Solar System. Newly discovered TOI-4507 b is proudly among those.

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Let’s start with its class. As reported in a paper awaiting peer review, TOI-4507 b is considered a super-puff or marshmallow planet. Basically, it has an extremely low density, with a size comparable to Jupiter but a mass much smaller than Saturn. It actually weighs no more than 30 times our planet and has a radius of about 72 percent of Jupiter’s own. But the gas giant in the Solar System weighs 318 times as much as Earth, so the density of this world is very small.

This is peculiar, but it is not the first marshmallow planet discovered. Others have sported this extreme low density. What's peculiar about it is that the other super-puffs have low density because they orbit very close to their star, so the starlight heats them up and they swell to impressive sizes. For TOI-4507 b, this is not the case.

While its star is of a class that is slightly brighter and slightly more massive than our Sun, and it is much younger than our Sun at 700 million years, the world is still orbiting at a considerable distance compared to the common range for marshmallow planets.

“[W]e present the discovery and characterization of TOI-4507 b, a cold planet transiting a young F star with an orbital period of 105 days. Our observations reveal that the planet has an unusually low density, making it one of the longest-period super-puffs known to date,” the authors wrote in the paper.

It might be possible that the low density is an illusion. The size of the planet might be overestimated due to the presence of a large opaque ring system. That would be a neat explanation instead of having to wonder how a cold planet ended up with such low density. The weirdness, though, doesn’t end here.

The research team was able to measure the star’s rotation and the obliquity of the planet’s orbit. It is very slanted, at an almost polar orbit with 82 degrees tilt with respect to the star’s orbital plane. This makes TOI-4507 b one of the longest-period planets for which the stellar obliquity has been measured, on top of being the longest-period and youngest super-puff planet yet discovered. 

How it got like this is a mystery, but the team hopes that it will be followed up by observatories such as JWST to test the current models and provide more insights into its origin.

The paper describing this world is available on the arXiv and has been submitted for publication to the AAS journals. 

[H/T: Space.com]