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A World of Fluffy 'Marshmallows' With Incredibly Low Density Discovered : ScienceAlert

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If exoplanet research is to be believed, the Milky Way galaxy could be like some kind of fantasy candy land.

First, there was the discovery of exoplanets with cotton candy density. Now astronomers say they’ve discovered a world comparable to marshmallow density. They say it’s the fluffiest exoplanet ever discovered orbiting a red dwarf star.

This is important. This means that worlds with significant gas envelopes can be found near small, stormy dwarf stars that astronomers previously suspected could rip off much of their atmospheres from closely orbiting planets.

This will have implications for our understanding of the habitability of planets orbiting red dwarf stars, as atmospheres are thought to be one of the fundamental planetary features that allow life to form and thrive.

“Giant planets around red dwarf stars were traditionally thought to be difficult to form,” says planetary astronomer Shubham Kanodia of the Carnegie Institute for Science’s Earth and Planets Laboratory.

“So far this has only been looked at with small samples from Doppler studies, which typically find giant planets farther away from these red dwarf stars. Until now, we didn’t have a large enough planet sample to find gas planets nearby.

Red dwarf stars are the most numerous in the Milky Way. They’re so small, cool, and dim—so dim that not a single one of them can be seen with the naked eye, despite making up about 73 percent of all stars in the Milky Way.

Because they’re small, they burn slower and much less hot than stars like our Sun, meaning they have significantly longer lifetimes. The lifetime of our sun is estimated to be about 10 billion years. Red dwarf stars are expected to live for trillions of years. This longevity, combined with the abundance of red dwarf stars, means that life could arise on a planet orbiting a red dwarf star if it were to arise anywhere.

But red dwarfs can also be really grumpy, whipping up the space around them with powerful flares that can teleport and sterilize and de-atmosphere all nearby orbiting exoplanets. And because these stars are so cold, for an exoplanet to have a temperature conducive to life as we know it, that planet must be within its glow range. So, you know, it’s a problem.

But maybe not, as this new world suggests. Named TOI-3757b, it is a gas giant orbiting a red dwarf star in the constellation Auriga, about 580 light-years away.

TOI-3757b was detected using the TESS space telescope, which finds exoplanets by detecting regular drops in light caused by the planet passing in front of the star. If you know how bright the star is, how much light is blocked tells you how big the exoplanet is. From this we know that TOI-3757b is slightly larger than Jupiter.

Next, to get the exoplanet’s mass, the researchers looked for changes in the star’s light, indicating the gravitational pull exerted by the exoplanet. Since gravity is about mass, this gave us a mass of about 85 Earths.

Jupiter, by content, is about 318 Earths by mass and has an average density of 1.33 grams per cubic centimeter. The average density of TOI-3757b is 0.27 grams per cubic centimeter. It’s an extremely fluffy exoplanet – so fluffy it’s unclear how it could have formed so close to its star: it completes its orbit every 3.43 days.

Kanodia and colleagues think there may be two factors at play. First, gas giants form with a rocky core around which gas accumulates and creates a thick, expansive atmosphere. Since the red dwarf star is low in heavy elements compared to other red dwarfs, which are gas giants, perhaps the rocky core formed a little more slowly, which would delay gas accumulation and affect the earth’s density.

Second, the orbit looks slightly oval, which means its distance from the star has changed. Maybe the atmosphere warms and expands as we get closer.

Other astronomers have suggested that puffy exoplanets may have extended ring systems like Saturn; however, Kanodia and other researchers found that TOI-3757b is too close to its star to maintain a stable ring system. So probably a really fluffy atmosphere.

The team hopes to find and study other such marshmallow worlds to help understand how they formed and survived in a place where it must have been difficult to do so.

“Finding more systems with giant planets that were once thought to be extremely rare around red dwarfs is part of our goal of understanding how planets form,” says Kanodia.

We hope they are adequately equipped with sugary snacks.

The team’s research has been published Astronomy Journal.

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