Scientists find exoplanet with density of marshmallow: հow does it survive next to red dwarf?

American astronomers using a telescope in Arizona have discovered an interesting exoplanet – TOI-3757 b: although the planet is the size of Jupiter, its density is very low – about the same as a marshmallow or a bottle cap. If a huge tub of water could be found to hold this planet, it would float on the surface of the water and not sink.

According to scientists, TOI-3757 b can safely be called the lowest density exoplanet orbiting the red dwarf. Its diameter reaches 150,000 kilometers, and the density, according to the scientists' calculations, is only about 17 grams per cubic foot (or 0.27 grams per cubic centimeter). That's four times less than the mass of Jupiter and two times less than the mass of Saturn. By comparison, the density of our Earth is about 5.5 grams per cubic centimeter, and the density of Jupiter is only 1.3.

Of course, there are exoplanets with lower densities. But the peculiarity of TOI-3757 b is that it revolves around a cold red dwarf (in our Milky Way, more than 70% of the stars are red dwarfs), and it is very close to it – even closer than Mercury to the Sun. It takes only 3.5 Earth days for this exoplanet to complete a full revolution around a red dwarf.

TOI-3757 b and the red dwarf around which it orbits are in the constellation of Ascendant, 580 light years from Earth. Scientists don't quite understand how the gas giant TOI-3757 b can "survive" next to a red dwarf that could easily destroy it.

Although red dwarfs are cooler than stars like our Sun, they often emit powerful flares that are thought to rob nearby planets of their atmosphere. As noted by Shubham Canodia, a researcher at the Carnegie Institution's Earth and Planets Laboratory and first author of a paper published in The Astrophysical Journal, it has traditionally been thought that giant planets rarely form near red dwarfs – conditions are not particularly conducive to their evolution.

So how did TOI-3757 b form? One possible reason for its existence, scientists believe the slow evolution: the rocky core of the planet may have formed very slowly, and if it failed to accrete volumes of gas comparable with those of other planets, the density of the planet turned out to be so low. Scientists also believe that the orbit of this exoplanet may be elliptical. If so, TOI-3757 b will occasionally approach the red dwarf particularly close, and at such times the planet will become hotter and its atmosphere will thin out.