Red dwarfs are the smallest and faintest members of main sequence stars — stars that convert hydrogen gas to helium at a steady rate in their cores. Although they are “cold” compared to stars like our sun, red dwarfs can be very active and burst into powerful flares. This could strip away the atmospheres of orbiting planets, making the star system a seemingly unsuitable place for such a yarny planet to form.
“Giant planets around red dwarfs have traditionally been thought to be difficult to form,” said Shubham Kanodia, a researcher in the Earth and Planetary Laboratory of the Carnegie Institution for Science and lead author of a paper published in the Astronomical Journal. , which is only studied with a small sample of Doppler measurements that typically find giant planets farther away from these red dwarfs. Until now, we didn’t have a large enough sample of planets to find them in a robust way Gas planets up close.”
There are still unsolved mysteries surrounding TOI-3757 b, the biggest of which is how a gaseous planet forms around a red dwarf star, especially such a low-density planet. However, Kanodia’s team thinks they may have a solution to the mystery.
They propose that the ultra-low density of TOI-3757 b may be caused by two factors. The first factor has to do with the planet’s rocky core. Researchers think gas giants started out as giant rocky cores, about 10 times the mass of Earth, at which point they quickly pulled in large amounts of nearby gas and formed the gas giants we see today. TOI-3757b’s star has a lower abundance of heavy elements than other M-dwarfs with gas giant planets, and this may cause the core to form more slowly and delay the onset of gas accretion, thus affecting the planet’s overall density.
A second factor could be the planet’s orbit, which is initially thought to be slightly elliptical. Some times, it gets closer to its star than others and causes a lot of excess heating that, in turn, could trigger the expansion of the planet’s atmosphere.
NASA’s Transiting Exoplanet Detection Satellite (TESS) initially discovered the planet. Kanodia’s team then made follow-up observations using ground-based instruments, including NEID and NESSI and the Red Buttes Observatory in Wyoming.
TESS measured the intersection of the planet, TOI-3757 b, in front of its star, which allowed astronomers to calculate that the planet is about 150,000 kilometers in diameter or only slightly larger than the diameter of Jupiter. The planet completed a full orbit around its host star in just 3.5 days, which is 24 times less than the nearest planet in the solar system, Mercury, which takes about 88 days to complete.
The astronomers then used the NEID and HPF to measure the star’s apparent motion along the line of sight, also known as its radial velocity. These measurements provided the planet’s mass, which was calculated to be about 1/4 the mass of Jupiter or about 85 times the mass of Earth. Knowing its size and mass, Kanodia’s team was able to calculate that TOI-3757 b has an average density of 0.27 grams per cubic centimeter, which would make it less than half as dense as Saturn (the least dense planet in the solar system), about Is a quarter the density of water (meaning if you put it in a huge tub full of water, it will float), or a density similar to marshmallows.
“Potential future observations of the planet’s atmosphere with NASA’s new James-Webb Space Telescope may help elucidate its fluffy nature,” said Jessica Libby-Roberts, a postdoctoral researcher at Penn State and second author of the paper.
“Finding more of these giant planet systems — which were once thought to be extremely rare around red dwarfs — is part of our goal of understanding how planets form,” Kanodia said.
The discovery underscores the importance of NEID, which confirms some of the candidate exoplanets currently discovered by NASA’s TESS mission, giving the new James-Webb Space Telescope important targets to follow up and begin characterizing their atmospheres. This will in turn tell astronomers what these planets are made of, how they formed, whether they might support life on potentially habitable rocky worlds, and more.