Among the Earth-like planets, those located very close to their star and whose transit period is less than a day stand out. More than 100 such objects are known; they are candidates for destruction under the influence of tidal forces. An international team of scientists described such a record case in the red dwarf TOI6255.

With current spectrographs, we cannot observe a full Earth equivalent over a period of one year. However, ultra-short-period Earth-like objects do exist. Due to their proximity to the star, they receive thousands of times more heat than our planet. In addition, their primary hydrogen-helium atmospheres have been destroyed, making it easier to study the subsurface according to the composition of the secondary gas shell. Such observations can be made by the James Webb telescope by changing the orbital phase of the infrared radiation and secondary eclipses.

A planet close to a star will be destroyed by tidal forces. As studies have shown, fragments of a solid body dragged by a star change the composition of the photosphere in a certain way. The best candidates for being absorbed by their star are ultra-short-period planets like TOI6255 b. A paper about its discovery was published on the preprint server by a large group of scientists led by Fei Dai from the Institute of Astronomy at the University of Hawaii (USA).

The orbiting TESS telescope observed the star TOI6255 in 2022 and detected two signals from possible planets. The source was studied in more detail using spectrographs Keck Planet Finder at the 10-meter Keck Telescope in Hawaii and CARMENIt is located in the 3.5-meter telescope at the Calar Alto Observatory in Spain.

Scientists estimated the star’s mass to be only 0.35 solar masses, and also confirmed the existence of a rocky planet (TOI6255 b) with an orbital period of 5.7 hours. It is the same size as Earth, only 1.44 times more massive. According to the authors of the study, the planet’s iron core makes up 45 to 30 percent of its mass, the rest of the silicate mantle is most likely molten due to the high temperature on the surface (over 1,300 Kelvin). Such worlds are called lava worlds.

Due to its close proximity to the star, the planet is likely deformed. Calculations have shown that it has an ellipsoidal shape with a 15 percent difference in the length of the axes. A decrease of just 13 percent in the orbital period would bring the planet to the Roche limit, after which it would be torn apart by tidal forces. Such objects are known, but TOI6255b holds the record. If the Q factor of the Q star is correct, it would take 400 million years to reach the Roche limit and could be wrong by an order of magnitude.

There are three known planets that are beginning to be destroyed by tidal forces: KOI-2700 b, KIC 12557548 b, and K2-22b. However, their reference periods are longer than TOI6255 b. Scientists have not found any signs of mass loss on the newly discovered world—at least not yet.