Unexpectedly dense exoplanet calls into question the theory of planet formation

Object K2-25b is almost entirely composed of a core, and its gas envelope is very thin. How it happened is a mystery to scientists.

Astronomers have discovered an unusual exoplanet in the Hyades Cluster, located 153 light-years from Earth. It has an unusually high density for its age – relatively small by galactic standards: its mass is 25 times that of Earth, and its diameter is only 3.5 times that of our planet. This discovery contradicts generally accepted theories of planetary formation. An article about a strange space object designated K2-25b, has been published in the Arxiv.org project archive.

The exoplanet was observed using the 0.9-meter WYIN telescope located at Kitt Peak National Observatory in the Sonora Desert, Arizona, as well as through the Hobby-Eberley telescope at McDonald Observatory, Texas. The orbital period of K2-25b around its star, a red dwarf, is 3.5 days. In size, K2-25b is slightly smaller than Neptune, which is quite standard for the planetary systems of the Milky Way. But its density, on the contrary, is very unusual.

According to generally accepted theories of the formation of giant planets, they are formed from a relatively small rocky-ice core with a mass of 5-10 times that of the Earth, which is then enveloped in a gas shell, whose mass exceeds the mass of our planet by hundreds of times. The result is a gas giant like Jupiter. However, K2-25b consists almost entirely of a core, and its gas envelope is very thin. How the planet managed to assemble such a supermassive core and why its gravity did not form a huge shell, scientists cannot yet answer.

Optical diffuser

However, astronomers in the near future hope to get more data on the unusual object. They are assisted in their observations of the K2-25b by an extremely simple device – an optical diffuser. It scatters light from distant stars, allowing it to cover more pixels on the receiving equipment.

Thanks to this, it is possible to more accurately measure the fluctuations in the brightness of a star when the planet passes between it and the observer, and from these fluctuations – to determine the parameters of the planet itself. At the same time, such a diffuser costs only about $500.