In our continuing quest to discover alien life one question keeps popping up. How will we recognize alien life when we find it?
Life is a word with multiple meanings. We don’t yet have a perfect definition for what life is, but it hasn’t stopped us from trying.
What we have done is define some of life’s main attributes.
1. Life is chemistry based, an ordered network of chemical reactions.
2. Life is also not in equilibrium, it needs a source of energy to organize itself.
3. Life can adapt and self-improve.
4. Life is enclosed in cells.
5. Life molecules work well with water
Life as we know it is built on four types of molecules, proteins, nucleic acids (our DNA), sugars (carbs), and lipids or fat.
We are biased in our definition, especially that last one that needs water. That’s what life on Earth needs. Still, an excellent starting point. This rules out stars, gas clouds in between them, or anywhere too cold or too hot for liquid water to exist.
NASA defines life as a self-sustaining chemical system capable of Darwinian evolution. (OMG, evolution. Hold on to your hat’s folks, this podcast is for the brave and adventurous.
As the knowledge of our cosmic neighborhood grows, we will use these definitions as a guide to help us find signatures of alien life.