A world close to a Sun-like star is so close to it that astronomers have to wonder how it got there. Scientists are sure it couldn’t have been there in the first place. When it became possible to measure the size and mass of this planet, it became clear what had happened to it.

Most of the more than five thousand exoplanets currently discovered in space have masses much larger than Earth, despite being extremely close to their stars. The thing is that such worlds are the easiest to notice: the main method of their search is the so-called traversal method. When a particularly large and close planet passes through the disk of its star, the star’s light is slightly dimmed. As you can easily guess, this happens at intervals. This is how astronomers understand that the star is not alone.

Small worlds are also found and are located much further from their sun, but those dangerously close to their star raise special questions. These are called ultrashort periodic. This means they have a very short rotation period – less than one Earth day. Scientists are trying to understand how they got there. According to calculations, planets cannot form at such small distances from stars. Therefore they are brought there through gravitational interaction with other planets.

For this reason, the star system K2-360 (EPIC 201595106), located 764 light-years from Earth, is an important demonstration example. It is almost the same as the Sun in terms of mass. Two planets are observed nearby: both are much closer to it than Mercury is to the Sun (there are about 58 million kilometers between our star and its first planet).

Planet K2-360 was 13.5 million kilometers away from its sun, and K2-360 b was exactly three million kilometers away. It completes the orbit of the more distant star in less than 10 Earth days.

The nearest “year” lasts only 21 hours. It is also remarkable in terms of size and mass ratio: with one and a half Earth radius, it “weighs” almost as much as eight Earths. This gives a density of about 11 grams per cubic centimeter, similar to that of lead. According to planetary scientists, K2-360 b may be half iron and half other elements.

Recently the K2-360 system was studied by an international team of researchers led by experts from the Astrobiology Center of the National Institute of Sciences NINS (Japan). As they write in their article Scientific ReportsThe dense structure of K2-360 b indicates that it is not a full planet, but only what is left of it – a “bare” solid inner core devoid of all outer shells. According to estimates, the entire planet was 9-11 times heavier than the Earth, that is, it belonged to the sub-Neptunian category: Neptune is 17 times larger than our planet.

This scenario supports the existence of a second planet weighing approximately 15 Earths. However, its size has not yet been determined because this planet does not pass through the disk of the star. It is calculated based on the “behavior” of the armature (it oscillates slightly when moving around the common center of mass). In any case, as the researchers assumed, it was this second planet that once “pushed” the ancient sub-Neptune to certain death, into the hell of the star.