Free Astronomy Magazine September-October 2021

SEPTEMBER-OCTOBER 2021 T his artist’s impression shows the dust and gas around the double star system GG Tauri-A. Seven years ago, researchers using ALMA detected gas in the re- gion between two discs in this binary system. This may allow planets to form in the gravitationally perturbed environment of the binary. Half of Sun-like stars are born in binary systems, meaning that these findings will have major conse- quences in the hunt for exoplanets. [ESO/L. Calçada] ceiving from its K5V spectral type star (diameter and mass 60% com- pared to the Sun) the radiation nec- essary to support an Earth-like biosphere. By calculating the amount of photosynthetically active radiation (light between 400 and 700 nanometers) that each planet receives from its star, the re- searchers found that stars with surface tempera- tures below one half that of the Sun cannot sustain an Earth-like biosphere, since they are unable to supply sufficient energy at the appropriate wave- lengths. In less unfavor- able cases (temperatures around 3000 Kelvin), oxy- genic photosynthesis would still be possible, but plants would not be able to pro- duce a biosphere like ours. It is easy to guess that the results obtained by the Covone team cut off all red dwarfs (spectral type M, with tem- peratures of about 2000-3000 Kelvin) from the possibility of feed- ing a complex biosphere − as if the frequent solar flares from these stars, which flood the surrounding planets with intense streams of X- ray and UV radiation, were not enough to preclude their possibility. S ize comparison between Kepler-442b and Earth. [CC BY-SA 4.0]