Are we Alone in the Universe?

あらすじ

Use the Drake equation to calculate the number of civilisations in our galaxy. For fifty years, the Search for Extra Terrestrial Intelligence has been scanning the galaxy for a message from an alien civilisation. So far to no avail, but a recent breakthrough suggests they may one day succeed. Horizon joins the planet hunters who've discovered a new world called Gliese 581 c. It is the most Earth-like planet yet found around another star and may have habitats capable of supporting life. NASA too hopes to find fifty more Earth-like planets by the end of the decade, all of which dramatically increases the chance that alien life has begun elsewhere in the galaxy.