Astrobiology: The Story of our Search for Life in the Universe
Astrobiologists study the origin, evolution, and distribution of life in the universe. This includes identifying evidence left behind by life that once survived on the ancient Earth, and extends to the search for life beyond our planet.
When looking for signs of life on other worlds, what are they looking for?
Things called biosignatures. For example, when you sign a piece of paper, your signature is evidence of your existence. Similarly, biosignatures are anything that can prove that life was once, or is, present in an environment.
If we were very very lucky, we might spot something we know is life with a powerful telescope or receive a "phone call" or radio signal from alien civilizations. Those types of biosignatures would be obvious. But they would only let us identify advanced life.
For most of Earth’s history (billions of years), single-celled life like bacteria and archaea have been around. Humans have only been making radio transmissions for hundreds of years. So we have a better chance of finding life if we look for signs that have been around for very long periods of time.
Patterns in ancient rocks that were created by life are a great example. That can be anything like a dinosaur footprint or structures built by microorganisms, like stromatolites.
Molecules can also be biosignatures, like DNA left behind for detectives to discover. But DNA doesn’t last very long on its own in most environments, so other molecules like lipids (like natural oils, wax, and fat) might be a better choice if you are looking for signatures of life from millions (or billions) of years ago.
Even the balance of gases in a planet’s atmosphere can be a sign of past or present life. On Earth, biology plays a major role in maintaining the delicate composition of gases like nitrogen, oxygen, and carbon dioxide in the air that we breathe.
These are just a few examples of signs astrobiologists look for when searching for life amongst the stars! Research into these biosignatures inform many of our biggest missions, from observatories like the Hubble Space Telescope and the Webb Space Telescope to our Mars Sample Return endeavor.
Want to learn more about the search for life? Check out the latest issue of our comic-book style graphic history novel, Astrobiology: The Story of our Search for Life in the Universe. This new chapter is all about biosignatures.
Explore life in the universe with us by following NASA Astrobiology on Twitter and Facebook.
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