How to find alien life?

 Initially, the speculation about extraterrestrial life focused on the erdnächsten celestial bodies: the Moon and the planets of our own solar system, particularly our two neighboring planets Mars and Venus. In addition, has long been speculated that our solar system with its planets in the universe is a special case, or whether there are planets in the universe in large numbers. Scientists have already succeeded in astronomy to detect exoplanets. Further evidence of liquid water have been (which is generally regarded as one of the conditions necessary for life) in our solar system, including on Jupiter's moon Europa, which gave rise to new speculation about extraterrestrial life in our own solar system.

Even though it is more likely than not that there are extraterrestrial intelligent life, it is assumed that there is relative (to extremely) rarely distributed in the universe. Most people now believe that enormous distance between us and alien civilizations lie. In light of today seem to mostly promising, especially the following approaches to search and contact potential:

communication via radio waves, which can in principle be carried over long distances (but only with the speed of light),

the space with manned or unmanned spacecraft or probes

future technologies that we are still not known.

So far there is no compelling evidence for the existence of aliens at all, let alone the actual visit of extraterrestrials on Earth. The serious science focuses on the search for signs of (primitive) life or its traces on meteorites, our neighboring planets and their moons, on the one hand, and to search for radio signals that could arise from intelligent extraterrestrial life in alien solar systems.

Either way, if is not found in the immediate vicinity (a few light years) comparable civilization intelligent life, a communication between us and the aliens will probably not come about because the running times - at least for our human existence - too long.

2009 was concerned, on the occasion of the International Year of Astronomy, the Pontifical Academy of Sciences with the search for extraterrestrial beings.