Free Astronomy Magazine November-December 2020

NOVEMBER-DECEMBER 2020 British Columbia, produced with data from NASA’s Kepler mission, one Earth-like planet could exist in the Milky Way for every five Sun-like stars. G-type stars, those more similar to the Sun, are about 7% of the total. K-type stars, slightly smaller than the Sun but even more promising from an astrobiological point of view, are about 13% of the total. According to these per- centages, within 2000 light years from Earth there could be 2 million planets sim- ilar to ours. All uninhabited? There are those who worry that our first radio transmissions, theoretically having reached about 100 light years away (actu- ally already dispersed in the background noise of the universe), could inform other intelligent life forms of our existence. As we have seen, the traces of ancient terres- trial civilizations have probably already reached far beyond, and their involuntary message, which continues to whiz through the Milky Way, is much easier to discover than a faint radio wave. ! I n this represen- tation of the Milky Way, a green circle indi- cates the region within which the pollution of our atmosphere may have been ob- served in the last 2000 years. [Robert Hurt (SSC/JPL/Caltech)]