http://www.space.com/19157-billions-earth-size-alien-planets-aas221.html
http://blogs.scientificamerican.com/observations/2013/01/08/earth-like-planets-fill-the-galaxy,
http://news.nationalgeographic.com/news/billions-of-earthlike-planets-found-in-milky-way,
http://www.dailymail.co.uk/sciencetech/article-2258842/NASA-space-telescope-shows-17-billion-Earth-like-planets-Milky-Way.html
The numbers keep changing, depending upon what one is looking for.
http://en.wikipedia.org/wiki/Rare_Earth_hypothesis#The_right_location_in_the_right_kind_of_the_galaxy,
http://www.dailygalaxy.com/my_weblog/2011/06/the-two-billion-earthlike-planets-in-the-milky-way-how-many-will-prove-to-support-advanced-life.html,
http://www.space.com/19044-alien-earth-exoplanets-2013.html,
http://www.wired.com/wiredscience/2012/03/ten-billion-earths
