Is it life, Jim?

I recently read an article in the Daily Galaxy about how astrobiologists are anticipating finding non-carbon based life forms. The article explores the possibility of non-traditional life forms, and makes many claims—among them that life could theoretically be found in gas clouds in space, plasma in stars, and in neutron stars. All of these are the stuff of extreme science fiction, but could such "life" really exist?

In order to answer that we have to define what something is when it is alive. After consulting Webster's New World Dictionary and, it seems the simplest definition is something that has a metabolism, engages in growth, reproduction, and adaptation to its environment. In order for something to metabolize, grow, reproduce, and adapt it has to have some kind of structure.

NGC-604 Stellar Nursery
Photo courtesy NASA via Wikimedia Commons
This rules out even the bizarre so-called life forms such as those proposed by the article which sited three possible extreme environments that its author was hopeful to find new forms of life—gas clouds, inside stars, and on neutron stars. Gas clouds in space show some electrical activity, but nothing that is actually reproducing, metabolizing, etc. Hot stars are made of plasma, and plasma is a form of matter where the electrons are dissociated from their atoms, meaning the atoms can't really do much in the way of chemistry required to meet any of the definitions of life. Neutron stars are in an even greater state of dissociation, the gravity is so intense that the atoms have broken up into electron layers, neutron layers (hence the name), etc.  No bio-chemistry at all is possible here. At best I think we might find something analogous to a virus in such extreme environments, but I doubt it since even viruses (which are not alive, as they do not metabolize or grow) require more structure than these environments provide. But what about the alternate structured life forms the article suggests?
Neutron Star Structure
Courtesy Robert Schulze
Wikimedia Commons

Life here on Earth is carbon-based, meaning that the basic element that comprises most of life's basic structure is carbon. Without carbon there could be no DNA, no cells, no food, no proteins—you get the picture. I'm sure you've heard the term "organic" in reference to things that are natural or having to do with living things, and with good reason. In chemistry, "organic" means "containing carbon atoms."

But why carbon? Without getting too much into the details, carbon is 1) abundant since even smaller stars can make it, and 2) it forms stable, complex bonds with other elements. Taken together, both reasons make carbon an extremely likely choice for life everywhere in the universe. Even silicon, which is often sited as an alternative element to carbon in possible extra-terrestrial life, does not form nearly the number of stable bonds that carbon does, and research into the possibility of silicon-based life has shown that the element, for all its similarities to carbon, can't naturally form the complex structures required for a self-replicating system (like DNA), making it an unlikely candidate to replace carbon in alien biochemistry. I invite you to read NASA's research summary on the topic.

But what about alternative structures that still use carbon?  Ah! Here is a much more likely area for life not as we know it to exist.

Mono Lake, CA, USA-Photo courtesy Michael Gäbler via Wikimedia Commons

In recent years there was some excitement about the possibility that this wasn't entirely true. In 2010 a microbe called GFAJ-1 in California's Mono Lake was found to be thriving in an environment that consisted primarily of arsenic. The scientists who discovered this thought that GFAJ-1 might be using arsenic instead of phosphorus in its DNA (phosphorus is important for the backbone that supports the ladder-like structure), since arsenic and phosphorus are chemically similar. If this were to be true, it would mean that life could exist in much more extreme environments than we thought possible (and carbon based life already exists in some very extreme environments in the form of a group of organisms called Extremophiles). Unfortunately, it was later found that GFAJ-1 has a strong preference for phosphorus over arsenic, and the substitution was likely an adaptation to its arsenic-concentrated environment.

Snottites in Cueva de Villa Luz in Southern Mexico

Photo Courtesy NASA & Wikimedia Commons
GFAJ-1 (along with my personal favorite, snottites that live in acid-rich environments) illustrates the point that life can exist in some pretty weird places. With new planets being discovered all the time, and with more and more of them being analyzed as Earth-like, I am quite hopeful that we will find life on other planets. I would even go so far as to say it is inevitable. What has really got me excited, is that since it is very likely such life will be carbon-based, there is the possibility that if such life proves to be sentient like we are, there is an increased chance that we will be able to understand each other. We'll certainly have more in common with another carbon-based life form than we would with anything else.


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