Small stars, big mysteries: searching for habitable planets in the Kepler sample

Finding Earth-sized planets in Kepler’s habitable zone is difficult for M stars. Updated Gaia data do not support the expected increase in frequency of Earth-sized planets with respect to M stars Finding reliable detections of Earth-sized planets in the habitable zone remains a challenge in the Kepler data sample, even for red M dwarfs (the brightest M stars for Earth watchers are Betelgeuse).

Previously, researchers thought that the Kepler sample contained a significant number of stars of the M red dwarf type (with temperatures below 4000 K), surrounded by a sufficient number of planets with sizes from 0.5 to 1.5 times its size. Earth in the habitable zone, which helps estimate their frequency.

However, updated data on stellar properties from the Gaia Space Telescope have shifted many stars from the Kepler model to earlier spectral types, and it now turns out that most stars and their planets are both larger and hotter than previously thought. Currently, there is only one partially credible candidate for an Earth-sized planet in the habitable zone under the optimistic approach, and none under the conservative approach. Researchers conducted a new study of Earth-like planets orbiting red M dwarf stars from the Kepler sample, using frequency models with updated parameters and candidate confidence pellets.

By extrapolating the models to low values ​​of the stellar distribution, the researchers estimated an occurrence rate of 8.58%. The lower limit is 8.22%, the upper limit is 17.94% for the conservative habitat method and 14.22% with a lower limit of 12.71% and an upper limit of 24.96% for with an optimistic approach. These results are consistent with previous studies, provided that important biases are taken into account. Comparing these estimates with the results of extensive studies of the distribution of Sun-like stars, the researchers concluded that the current Kepler sample does not provide enough evidence for an increase in frequency. of Earth-sized planets, from main sequence stars to M. stars. This means that in the future, the frequency distribution of planets in the Goldilocks zone and observational expectations may need to be reconsidered.

Although the Kepler data sample is too rare to detect a trend in the frequency of Earth-sized planets between early and late M red dwarfs, studies that include larger planets or data from The K2 and TESS missions are well suited to determine this relationship more precisely. . Currently, there is only reliable and incomplete data on the presence of planets capable of supporting life in the habitable zone. Scientists are continuing their research and hope that future missions such as K2 and TESS will provide more accurate and detailed results about planets orbiting different types of stars.