Welcome to Molecular Monday! On the first Monday of the month, we take a closer look at the atoms and molecules that make up our physical universe. Today, we’re looking at:
AMMONIA AND ALIEN LIFE
Water, Water Everywhere…
You know how water has that Mickey Mouse shape? That shape is really important. That slight asymmetry allows electrical charges to accumulate on opposites sides of the water molecule.
The polarization of water molecules makes water a good solvent for other polar molecules, like amino acids. This is a big reason why water is essential to life (or at least, life on Earth). Without the ability to dissolve amino acids, we’d have an awfully hard time getting them to form peptides or proteins or DNA molecules.
But could life on some alien planet substitute another chemical for water?
Ammonia, Ammonia Everywhere…
This is an ammonia molecule (chemical formula NH3).
At first glance, you might think ammonia molecules are symmetrical, with three hydrogen atoms evenly spaced around the central nitrogen atom. Symmetrical molecules have all their electrical charges perfectly balanced, and therefore are non-polar and do not act as good solvents for amino acids.
But when you turn the ammonia sideways, things look rather more promising.
The three hydrogen atoms bend toward each other, just as the two hydrogens in water do. There’s a slight asymmetry, meaning electrical charges can form. Ammonia is a polar molecule after all!
And ammonia has a few other things in common with water:
- They’re both fairly common in the universe (though water is more common).
- They both can be liquid under fairly ordinary temperature/pressure ranges (though water’s liquid phase is wider than ammonia’s).
- They can both act as a base, meaning they can accept a proton from an acid (though ammonia is slightly more basic than water).
- They can both act as an acid, meaning they can both donate a proton to a base (though water is slightly more acidic than ammonia).
The most noteworthy difference seems to be that ammonia burns easily in the presence of oxygen. That could pose serious challenges to the evolution of complex, multi-cellular organisms that need the extra kick of energy oxygen provides.
Still, water and ammonia are similar enough to attract the attention of astrobiologists, and a lot has been written about the possibility of life emerging on some distant planet in an ammonia sea.
Hypothetical Types of Biochemistry from Wikipedia.
Alternatives to Water from Xenology: An Introduction to the Scientific Study of Extraterrestrial Life, Intelligence, and Civilization.
Thalassogens from Xenology: An Introduction to the Scientific Study of Extraterrestrial Life, Intelligence, and Civilization.
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A special thank you to Kirov99 for suggesting this topic. My research tends to focus on the planets and moons of the Solar System, rather than hypothetical environments we might find elsewhere in the universe, so without the recommendation I would have probably missed this.