Forget Star Trek, where the "aliens" are just humans with some kind of ridges on their foreheads. And even forget the traditional view of alien life; that it needs liquid water to survive.
According to a new study by the National Academies called The Limits of Organic Life in Planetary Systems, life could be completely and totally alien.
Just how alien? Well, first, let's define life on Earth. Wherever researchers find liquid water, they find microbial life too. It doesn't matter if the water is nearly freezing, hotter than boiling, deep underground, or mixed in with toxic chemicals.
Water serves as a solvent, allowing organic molecules to come in contact with one another in solution. Life also needs carbon, and several other elements to build up structures, store energy, and facilitate chemical reactions. And finally, life needs some kind of energy source, whether it's the Sun, hydrothermal, or energy from a chemical.
The multidisciplinary team of researchers threw those assumptions out the window, and brainstormed alternative elements and compounds that could serve the same functions as water and carbon here on Earth.
It turns out water, isn't the only solvent life could use. In fact, it's a pretty mediocre solvent, chemists prefer other solvents in the lab - often ammonia is used to prepare organic molecules. On another planet, life could use liquid ammonia or methane, or even liquid hydrogen if it gets cold enough. And other chemicals could stand in for carbon, fulfilling similar functions for building structure, energy storage and facilitating chemical reactions.
The result is that you could end up with life that doesn't need water, and doesn't put out the kinds of chemicals that scientists would be expecting to see.
And that's the point. The hope with this research is to give biologists new environments to explore here on Earth which were previously considered totally off limits for life. They might be lucky enough to find variants of life here on Earth which have no connection to carbon-based life - the aliens among us.
This will also give space mission designers new chemical signatures to look for when they're designing spacecraft and rover experiments designed to detect the presence of life.
Now they'll even be able to detect life as we don't know it.
The original press release is available here.
And the full text of the report is available here.
