Are we alone in the Universe?
There have been searches for life on other planets. Two spacrafts named Viking landed on Mars in 1976 searching for the building blocks of life. The Viking Landers conducted biological experiments. Some of the results were promising but not conclusive. A recent Phoenix lander detected perchlorate salts on Mars. But the question of microbial life on Mars remains unresolved. The latest Mars probe, the Curiosity rover, may come closer to answering the question about life on other worlds.
Decades ago, very few scientists believed there was any life beyond Earth. The prevailing view was that we humans were alone in the universe and life was a chemical quirk that happened only once-an act of God, if you will.
Now the pendulum has swung the other way. The current belief is that the condition for life are not that hard to duplicate. Life on Earth is based on five elements: carbon, oxygen, hydrogen, nitrogen and phosphorus. Those elements are known to be plentiful in the universe.
Discovery of other planets
Astronomers have already discovered planets around other suns or stars. NASA recently announced that the Kepler spacecraft found several planets similar to the size of Earth orbiting distant stars. Some of these planets are about the right distance from their sun to possibly support life.
Our own Milky Way Galaxy has between two hundred billion and four hundred billion stars. There are an estimated one hundred to two hundred billion galaxies in the known universe. So just based on probabilities, life should be plentiful out there. But mathematical probabilities do not constitute proof. The Search for Extraterrestrial Intelligence SETI is the name of scientific project being conducted by groups that are listening for radio transmissions from outer space.
How we can contact with Aliens
Our most likely contact from any intelligent alien life forms will come from listening to their radio transmissions. The blood Contact, by astronomer and writer Carl Sagan, and the movie by the same name, seems to be the most realistic scenario of what the detection and interaction might look like. Which direction to look in, which radio frequencies to listen on, and which methods of communication to use are all unknown. The search has been uncoordinated and sporadic.