Scientists have discovered an exoplanet with extremely low density

(ORDO NEWS) — The dimensions of the gas giant TOI-3757 b are slightly larger than those of Jupiter, but the density is many times lower and is comparable to the density of a bottle cap.

It is not clear how such a “loose” planet can survive in close proximity to a restless red dwarf, capable of easily destroying its rarefied outer shells.

Observations by the American National Observatory Kitt Peak made it possible to notice a very unusual exoplanet. It lies about 580 light-years away in the constellation Auriga, orbiting the red dwarf TOI-3757.

The planet itself is a gas giant, reminiscent of our Jupiter and close to it in size. However, its density is almost five times less and is comparable to the density of a bottle cap.

Red dwarfs are the smallest and faintest of the main sequence stars. Despite this, they are characterized by extremely unstable activity, now and then throwing out powerful bursts of radiation and particles.

This makes their environment not the most favorable place for the formation and evolution of planets, especially gas giants, which are characterized by low density. If such exoplanets appear around red dwarfs, then usually in distant orbits, at a decent distance from the restless star.

All the more unexpected was a new discovery made using the 3.5-meter WIYN telescope by the method of radial velocities – by weak deviations in the position of a star, which are caused by a planet rotating around it.

The planet TOI-3757 b is located in the red dwarf system, its diameter reaches 150 thousand kilometers (slightly larger than Jupiter), and its mass is only 85 Earth masses.

It turns out that the density of TOI-3757 b is only 0.27 grams per cubic centimeter, which is comparable to the density of cork (0.24 grams per cubic centimeter).

Recall that the density of our Earth is about 5.5 grams per cubic centimeter, and, for example, Jupiter is only 1.3. Of course, even lower density exoplanets are known . However, TOI-3757 b is extremely close to its star – much closer than even Mercury is to the Sun. It completes a full annual orbit in just 3.5 of our days.

The authors of the article name two factors that can explain the appearance of such a “chubby” world in close proximity to a red dwarf. First, the star TOI-3757 is relatively poor in heavy elements, from which the formation of gas giants begins.

It is believed that such planets grow from a massive – larger than the entire Earth – rocky core, which collects the surrounding gas. If there are few heavy elements in the protoplanetary disk, the core could form much more slowly, and the gas could accumulate longer, forming rarefied shells.

In addition, the orbit of TOI-3757 b is slightly elongated, and, possibly, when approaching the star, its atmosphere can additionally heat up and expand, which leads to a decrease in the density estimates of the planet.

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