There is much debate as to the likelihood that there is intelligent life, or even life at all, on planets other than earth. Some scientists believe that some planets and moons in our solar system are capable of supporting life, or have been in the past, notably Mars and one of Jupiter's moons, Europa. Life is thought to require carbon, hydrogen, oxygen, nitrogen, sulfur, phosphorus, and water. Earth, being the third planet from the sun, is just at the right temperature for liquid water to exist and is massive enough to trap a thick atmosphere, which protects it from comets, meteors, and ultraviolet and cosmic radiation, all of which are damaging to life.
Are there other planets that have factors making them capable of supporting life? The Drake equation, developed by astrophysicist Dr. Frank Drake, has been proposed as a tool to predict the likelihood that there are other intelligent civilizations that have the ability to communicate with humans, via radio waves, light waves, or some advanced technology. While there is currently no evidence of extraterrestrial life, I believe that there is good reason to believe that primitive life, and possibly other intelligent civilizations, exist. The enormous number of planets available and the likelihood of the necessary factors converging, as described by the Drake equation below, make this plausible. The numbers that follow, which were proposed by Dr. Drake and his colleagues in 1961, are theoretical and have been modified by discoveries made since then, but they show how this might be possible.
The number of intelligent civilizations in the Milky Way capable of communicating with humans (N) equals the product of:
R* - average yearly rate of star formation in the Milky Way
fp - fraction of those stars that have planets
ne - average number of these planets capable of supporting life per star that has planets
f? - fraction of the above that develop life ...