So, I found the NASA Astrobiology website. This one hits the nail right on the head .. and gives an answer … right from the horse's mouth … the answer is from: David Morrison Astrobiology Senior Scientist, dated September 6, 2011 …
Quote:
Question:
When astrobiologists say " life as we know it ", what does it really mean in the search for extra-terrestrial life? What would life as we don't know it be like?
There is no clear-cut meaning for "life as we know it". Usually this phrase refers to life based on DNA or RNA, probably also including viruses (although many biologists do not consider a virus to be alive).
Sometimes the meaning is expanded to include any life that us based on the same sort of water-mediated carbon chemistry (with amino acids & proteins) as we have on Earth, but with some other inheritance mechanism that does not use DNA or RNA.
Life as we don't know it would include life that some speculate could exist on Saturn's moon Titan where the temperatures are far below the freezing point of water but other hydrocarbons might, conceivably, form the basis for carbon-based life very different from that on Earth.
Astrobiologists are uncertain how we could recognize or detect life as we don't knew it, although presumably any life would use energy to change its chemical environment, thus perhaps providing clues to its existence.
You can learn more by looking up shadow biosphere:
http://en.wikipedia.org/wiki/Shadow_biosphere, weird life
http://science.howstuffworks.com/weird-life.htm, and synthetic life http://en.wikipedia.org/wiki/Synthetic_life
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Cheers