Season 17, Episode 27: Could There Be Silicon-Based Life?

Hey StarTalkians! In season 17, episode 27, Neil and Chuck sat down with astrobiologist and bacteriology professor Betül Kaçar to talk about the origins of life and astrobiology. Towards the end of the interview, they discuss a topic that will be familiar to any sci-fi fans: the possibility silicon-based life.

How Did Life Begin? with Betül Kaçar - StarTalk Radio

(from 52:57)

One of the most memorable examples in fiction are the rock creatures from Star Trek’s “The Devil in the Dark”, but is such a thing really possible? Dr. Kaçar implied it was, but they didn’t have time to go into much detail, so here’s the whole story.

Why Silicon?

As explained on the podcast, the main reason people take the idea of silicon-based life seriously is because of its similarity with carbon. It’s in the same group of the periodic table, which means it has the same valency as carbon. As Neil explains, this is basically saying it has the same outer electron configuration.

This means – theoretically – it could produce a similar range of compounds, with silicon taking carbon’s place as a “scaffold” for complex chemical structures. A 2020 paper goes into this in detail.

The Problems with Silicon

Many discussions of this topic breeze past a few substantial issues for the sake of the Trek­-style thought experiment. Firstly, and most importantly for “life as we know it,” silicon-based compounds are often vulnerable to hydrolysis, so they can’t survive for long in water.

The argument about valency also misses some detail. Yes, silicon can make the same number of covalent bonds as carbon, but a fully-bonded carbon atom has a full outer electron orbital, while silicon doesn’t. Silicon bonds are also more strongly polarized than carbon bonds, and these factors combined leads to some different behavior.

Silicon-Based Molecules Can Work

As Dr. Kaçar describes, scientists have had some success in making silicon-based organic molecules using enzymes, and other researchers [3] have incorporated silicon-carbon bonding into amino acids. This is why the theory still seems solid, despite some issues.

Life, But Not as We Know It

Shockingly, silicon-based molecules tend to be more stable in sulfuric acid than in water, and could have an advantage over carbon in hot environments. So while Earth-like environments aren’t ideal, silicon-based life could be found on a Venus-like world we’d consider uninhabitable.