We’re going to look outside our solar system at a new planet discovered in TESS data. As always, these reported discoveries always have something strange or interesting involved since “wow, we discovered an exoplanet” just isn’t cutting it anymore, what with 5,000 confirmed ones out there in the galaxy.
This particular discovery involves a planet, TOI-3757 b, about the size of Jupiter, at 1.09 Jupiter radii. Not very interesting, right? Where this one gets weird is the mass calculation; it’s only 0.268 Jupiter masses, making it very fluffy with a density of only 0.27 grams per cubic centimeter. And it’s a close-in, hot ball of fluff, orbiting its star in just 3.44 days at a very close distance of 0.038 AU or less than 6 million kilometers.
The parent star, TOI-3757, is an M dwarf, which makes it smaller and less massive than our Sun. It’s about 600 light-years away, 7.1 billion years old, and has an effective temperature of 3900 Kelvin. Intriguingly, the stellar metallicity for this star is the lowest of any M dwarf that has known gas giant planets.
And that low metallicity could be the reason TOI-3757 b has such a low density. Without a lot of metals to pull from in the protoplanetary disk, the accretion of all the gas may have been delayed and cut short. The low density could also be the result of the planet’s slightly eccentric orbit, which may have led to an inflation of the gases as a result of tidal heating differentiations.
Knowing astronomy, it’s both.