Free Astronomy Magazine September-October 2019

SEPTEMBER-OCTOBER 2019 J ust over 10,000 days have passed since the discovery of the first exoplanet, and the 4,000 so far confirmed among the 3,000 known extrasolar systems have re- vealed an unpredicted variety of planetary systems. After the first random discover- ies, researchers gained experience with those planets easiest to detect − the giant ones orbiting very small stars. Then, more targeted programs were launched, such as the prolific Kepler, to discover Earth-size planets orbit- ing in the habitable zones of solar- type “dwarf” stars, a term that includes spectral classes F, G and K. At the same time, more hum- ble projects were also devel- oped that continued using the easiest way to discover planets – find those that pass in front of the discs of the most clas- sic dwarf stars, the so-called “red dwarfs” or M-types. For many years, we have believed that M dwarfs were the ideal stars around which to look for the first signs of extraterrestrial life. Now we have realized that planets in M dwarf habitable zones are subjected to extreme conditions and phenomena for a time incompatible with life as we know it. Researchers’ attention has therefore moved towards K dwarfs, but we have yet to figure out where to point the telescopes. A lmost all 4,000 exoplanets so far discovered and confirmed are cer- tainly unsuitable for hosting life as we know it. Kepler- 421 b, represented in the background, is an example of an inhospitable planet orbiting a solar- type star (G9/K0). [Harvard-Smithson- ian, Center for As- trophysics/D. A. Aguilar]