1000 Planets

"In 1961, University of California, Santa Cruz astronomer and astrophysicist Dr. Frank formulated the Drake equation. This controversial equation multiplies estimates together with the following conditions:

• Level of star formation that matches.
  
• The fraction of these stars surrounded by planets.
  
• Total world similar to Earth per-system planets.
  
• The fraction of planets where intelligent life evolved.
  
• The fraction of communicative planets possible.
  
• Age of the possible communicative civilizations.

The Drake equation is used to estimate that there are approximately 10,000 planets in the Milky Way galaxy containing intelligent life with the potential to communicate with Earth. Based on observations from the Hubble Space Telescope, there are at least 125 billion galaxies in the universe. It is estimated that at least ten percent of all stars have planetary systems similar to the sun, for example, there are 6.25 × 10^18 stars with orbiting planets in the universe. Even if we assume that only one out of a billion of these stars have planets supporting life, there will be some 6.25 × 10^9 (billion) life-supporting planetary systems in the universe." — Potential and Shortcomings for Life In the Universe, VIRGOEZ23 blog It appears that, according to astrophysicist Drake, only 6.25 billion planetary systems in our universe contain life. Given that 10% of them may be at our level of civilization, that gives us 625 million possible humanoid lifeforms, assuming that carbon-based life is the ideal. Closer to home, there are 10,000 planets with the potential for life. If ten percent of those planets have civilizations at our current level or greater, then we have one thousand potential candidates to home in on using our radio-telescopes and observatories in orbit around our Earth. Thus, it makes sense to concentrate our radio-telescopes on potential extraterrestrial life within 50 light-years of earth. My reasoning for that close a distance to Earth is that intelligent life will be able to return a message within each generation's lifetimes. Hopefully their message is as simple as the ones that NASA has sent out since the Voyager spacecraft was launched in the 1970s, as well as radio-telescope messages from the SETI project, which has gone into hiatus due to funding issues. See reference below for possible habitable planets.

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Reference:
Potential and Shortcomings for Life In the Universe (translated from Bahasa Melayu and Indonesian):
http://translate.googleusercontent.com/translate_c?depth=1&hl=en&rurl=translate.google.com&sl=ms&tl=en&u=http://virgoez23.blogspot.ca/2013/04/potensi-dan-kelemahan-kehidupan-di-luar-planet-bumi.html&usg=ALkJrhi8sXsZe9Z0OqMRVKlM7eI3LjEONw

You might wish to change the translating language to Indonesian, as the blog's owner switches between Bahasa Melayu to Indonesian. As well, the translation is a best guess, and would need a native English speaker who understands the rules and syntax of their mother tongue.

List of habitable planets: http://en.wikipedia.org/wiki/HabCat