The exoplanet discovery space hosts all kinds of interesting “super” worlds. There are super-Earths, super-Neptunes and, of course, super-Jupiters. Recently, the WIYN telescope on Kitt Peak in Arizona made a follow-up observation of a gas giant discovered by TESS (the Transiting Exoplanet Survey Satellite). The world is fluffy and strange and it orbits around a red giant star. Oddly enough, it shouldn’t even exist. Yet it is fortunately orbiting a star some 580 light-years from Earth.
The gas giant planet in question is called TOI-3757 b. From measurements by WIYN and TESS, as well as other telescopes, the average density of TOI-3757 b is found to be 0.27 grams per cubic centimeter. That makes it less than half the density of Saturn and about a quarter the density of water. That’s about the density of a marshmallow. Such a puffy feature is hard to believe, especially since the star it orbits isn’t exactly the best place to host gas giants.
“Giant planets around red dwarf stars are traditionally considered difficult to form,” says Shubham Kanodia, a researcher at the Carnegie Institution for Science’s Earth and Planets Laboratory and first author of an article published in The Astronomical Journal about TOI- 3757 b. “So far this has only been examined with small samples from Doppler surveys, which have generally found giant planets further away from these red dwarf stars. So far we haven’t had a sample large enough number of planets to find nearby gaseous planets robustly.
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How a red dwarf threatens a gas giant
Why aren’t red dwarf star systems optimal habitats for fluffy giant planets? They’re definitely cooler than their brighter, bigger star family counterparts. You’d think that would make them a bit friendlier to the gas giants. But these little stars can also be active. Astronomers see them occasionally emit powerful flares that can destroy a planet’s atmosphere. So how did TOI-3757 b get here? The research team has a few ideas to explain this puzzle.
It is possible that TOI-3757 b’s extra-low density dates back to the formation of its interior. Typically, gas giants are born with rocky cores that can be up to about ten times the mass of Earth. Their gravity draws huge amounts of gas from the protoplanetary nebula. This is how you get Jupiters and Saturns (for example). It is likely that this did not happen with TOI-3757 b. Its red dwarf star is low in heavy elements compared to other M dwarfs to gas giants. This is an important clue. This means that the rocky core of the planet formed more slowly. This is because it took longer to gather enough rock material from the nebula. If that’s true, then the planet didn’t accumulate as much gas during its formation, which affected the overall density of the planet.
There’s a second clue that could explain Planet Marshmallow. Its elliptical orbit brings it closer to the star at times. This heats the atmosphere more than normal and causes it to swell.
Marshmallow Dip
Of course, there is still much to discover about this planet, and astronomers are eager to study it in more detail. “Potential future observations of this planet’s atmosphere using NASA’s new James Webb Space Telescope could help shed light on its puffy nature,” said University postdoctoral researcher Jessica Libby-Roberts. of Pennsylvania State.
This is especially true because finding even one of these planets around a red dwarf means there are likely to be more. In the grand scheme of exoplanet studies, understanding a puffy Jupiter orbiting an active cool star will give astronomers greater insight into how planets form around many different types of stars.
For more information
A “marshmallow” world orbiting a red dwarf star
TOI-3757 b: A low-density gas giant orbiting a solar-metallic M dwarf
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