The sketch shows a geological tree of exoplanets. They appear from swirling gas and dust disks (protoplanetary). With the help of the Keck Observatory and the Kepler telescope, scientists have found that small planets are divided into rocky, super-earths and mini-Neptunes.
The first exoplanet was found in the 1990s. Now there are 3,500 of them. However, during the last revision of the classification, two subspecies were identified: rocky terrestrial and large mini-Neptunes. The data was checked at the Keck Observatory and at the Kepler telescope.
It turns out that our galaxy has identified two common types: rocky, whose size is 1.75 times that of the Earth, as well as mini-Neptunes, covered with gas and 2-3.5 times larger than our planet.
The Kepler mission was launched in 2009 and confirmed more than 2300 exoplanets. The telescope is configured to search for planets located close to the stars (closer than the distance of Mercury-Sun). In size, they stand between the Earth and Neptune. In our system, such celestial bodies can not be found. However, the new data surprised scientists, since almost every star in question has a similar planet. Then why are they not in the solar system?
To search for planets, Kepler focuses on emptiness in starlight (a planet with an orbital passage covers the light with itself). Size correlated with the failure parameters. To obtain accurate data, it is necessary to have a star characteristic. For this purpose, the Keck Observatory was used. With its help, it was possible to investigate the spectral data that led to the exact dimensions of the planets. This allowed us to calculate the size of 2000 exoplanets. And here, astronomers stumbled upon a surprise - a serious failure between rocky lands and mini-Neptunes.
The reason for this failure is unclear. But there are two plausible explanations. Perhaps the Universe loves to create earth-like planets. But for some mysterious reasons, some of them begin to accumulate gas and go into the category of mini-Neptunes. Such planets resemble stones with a gas shell. The second option - the planet lose gas. Perhaps the star's radiation is so strong that it burns a gas layer that cannot be recovered, so the planet is stuck in a new class.
Scientists plan to investigate the composition of heavy elements in the found planets. Particular attention is focused on mini-Neptunes, because it is still not clear how they manage to create so easily near other stars, but not near the Sun.