One of my favorite hobbies is playing video games or roleplaying games. It’s a pleasant way to waste an hour or so on a rainy afternoon, especially if I can spend it with a few friends. I especially like fantasy and science fiction games, not for the action or the competition, but because I love the worlds and creatures people design. I had a friend who played Mass Effect with a gigantic human-superiority complex, but I just couldn’t do that. I had way too much fun running around, talking to drunken turians or preachy hanar.

One of the things that, in my opinion, set Mass Effect apart in terms of creature design was the sheer amount of work that went into it. Species had long, complex histories, distinct cultures, and completely visualized biologies. They even included minutia like space microbes and right-vs-left-handed sugars. It’s obvious that they put a lot of thought into their game.

Now, we’re probably never going to find mysterious ruins on Mars and shoot through the galaxy fighting Reapers, but one of the fun things about astrobiology is that we’re not completely blind. We have yet to find aliens, but through a little deduction we can actually put together some pretty complex guesses about what they’d look like.

I should note before we begin that, one, I’m not an expert and, two, I’m talking about the most probable aliens. It’s totally possible that I will be one-hundred percent wrong, but we’re going off what’s most likely, not what’s possible. Anyways:

Step 1: The Basics

Before we can talk about how to recognize extraterrestrial life, we have to recognize, well, life itself. The specific definition is surprisingly tricky for people to agree on and is still being refined, but it’s pretty much recognized that life must:

Be able to organize itself

Be able to maintain that organization

Be able to take in energy from its environment

Be able to respond to changes in its environment

Be able to reproduce itself

If it can’t do these, it can’t be alive. From these we can make a couple of guesses. It’s really hard to organize yourself if you aren’t distinct from your environment, so we can bet that aliens will have some sort of cells. We’ll probably never see sentient gas clouds or energy beings. These cells will be chemical. As to what kind of chemicals, we can make some guesses too.

Carbon and water-based life dominate Earth and likely will dominate the universe. Why carbon and water? First of all, they’re abundant. The four most common elements in the universe are hydrogen, helium, oxygen, and carbon (remember that water is just hydrogen and oxygen combined into a single molecule). Furthermore, water is an excellent solvent. Nearly anything dissolves in it. The most notable exception? Hydrocarbons, long carbon-oxygen-hydrogen molecules. They’re what’s known as hydrophobic, they shy away from water and, in large structures, can keep water out of an area.

So if I wanted to make some cells – large structures that keep fluid chemicals separated – my immediate choice would be carbon and water. There are, of course, other hypothetical solutions. Silicon can also form this kind of hydrophobic bond and ammonia can sometimes do water’s job, but neither are as plentiful and most of the other options start to need some strange environments to work, so I feel like it’s safe to say aliens will be carbon and water-based. This also means that aliens will need liquid water.

Furthermore, maintaining this organization will require some way for the cells to stick to a plan – a way to store information. On Earth, this is accomplished through complex chemicals structures – our DNA and RNA. Without these structures our cells wouldn’t be able to produce the right proteins, take in energy, or reproduce. It’d be a hot mess. So we can assume that aliens will also have some form of genetics.

So what do we have so far? Well, from a bit of thinking, we can guess that aliens will be made of carbon-and-water cells, live on planets with liquid water, and will probably have something close to DNA. Not bad for a first step.

Next time I’ll get into a bit more of the fun stuff, like how they’d evolve, what they’d look like, and where we could expect to find them.