<ul><li>Astrobiologists are questioning how to look for alien life when they don't know what it might look like</li><li>The most abundant form of extraterrestrial life is likely to be microbial</li><li>To date, around 5,000 exoplanets - planets orbiting other stars - have been found</li><li>Many exoplanets are small and rocky, like Earth, and in the habitable zones of their stars</li><li>The definition of life creates uncertainty for researchers, as it varies depending on who you ask</li><li>NASA suggests life is a self-sustaining chemical reaction capable of Darwinian evolution</li><li>Scientists have explored alternatives to terrestrial biochemistry to identify suitable conditions for other life forms</li><li>Examples of alternative biochemistries include sulfuric acid, ammonia, liquid carbon dioxide and even liquid sulfur</li><li>Astrobiologists haven't ruled out searching for minerals on rocky exoplanets as a potential sign of life</li><li>Researchers may also find evidence of life on other planets by detecting artificial radio signals from a distant civilization</li></ul>

Alien life may look nothing like life on Earth — so how should we go about looking for it?

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