Are there any signs of alien life out there?
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It is hard to determine if we have detected signs of alien life yet as the tools we currently use for astrobiology are limited.  What actually is life? It’s getting increasingly complicated to come up with an answer that takes in all the “lifeforms” discovered and that might have once existed on our planet. One frequently used definition of life is “a self-sustaining system capable of Darwinian evolution.” But there are literally several hundred more.

Ironically, some astrobiologists argue that we really won’t know what life is until we find an alternative to the basic structure found on Earth – the same DNA, metabolism and carbon-based blueprint shared by all known life. In other words, ET life could tell us what life really is.

A corollary to this line of thinking is the ever-present concern that a rover or lander has, or will, come across an example or signature of life present or past and not know it. This reality helps explain the emphasis that astrobiology puts on understanding the origins and logic of early life on Earth. In addition to its inherent importance, origin-of-life research guides the search for extraterrestrial life.

As yet we have not discovered unambiguous signs of life on other planets, but this could also be due in part to the need for new telescopes, processing data from SETI and the return of samples from Mars.
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