Free Astronomy Magazine September-October 2021

8 ASTRO PUBLISHING the light of the two stars excessively reduces the darkening due to tran- sits. Not surprisingly, TESS has found both giant planets and planets sim- ilar in size to ours around single stars, while the latter seem much rarer in binary star systems. The results obtained by Lester’s team confirmed those of Horch’s team: an unspecified but not negli- gible number of “Earths” could hide in binary star systems. Here is how Lester commented on this conclu- sion: “Since roughly 50% of stars are in binary systems, we could be missing the discovery and the chance to study a lot of Earth-like planets. Astronomers need to know whether a star is single or binary be- fore they claim that no small planets exist in that system. If it is single, then we could say that no small planets exist. But if the host is in a binary, we would not know whether a small planet is hidden by the com- A single 60 msec speckle frame (top left), the integrated sum of 1,000 speckle frames (top right), the Fourier power spectrum (bottom left) and the re- sulting recon- structed diffraction- limited image (bottom right). Adapted from Scott and Howell (2018). [GeminiFocus, 2019] G emini South on the summit of Cerro Pachón in Chile (left) and Gemini North on the summit of Maunakea in Hawai’i (right). [Gemini/NSF/AURA] After having identified and charac- terized the 92 pairs, the researchers were able to confirm that the aver- age separation between the compo- nents is about 100 AU, while binary stars without planetary systems are on average about 40 AU separated. This does not necessarily mean that below 100 AU of separation no Earth-sized planets can form, but that we currently cannot observe them (by their transits across the stellar disc) precisely because, as al- ready mentioned above, the sum of