Life solvent comparator
All the life we know uses water, but is it the only option? Compare water with two alternatives astrobiologists study, ammonia and methanol, property by property.
Try it
How to use the simulator
All the biochemistry we know happens in water, but life on other worlds might use a different liquid. The comparator sets water against two commonly proposed alternatives, ammonia and methanol, on the properties that matter most for life: the temperatures over which they stay liquid, how well they dissolve things, whether they form hydrogen bonds and how common they are in the universe.
Controls
- Solvent buttons: pick water, ammonia or methanol to see its profile.
- Property buttons: choose a property to compare all three on it.
Things to try
- Compare liquid ranges at 1 atm: water stays liquid across 100°C, ammonia across only about 44°C, and at very low temperatures.
- Look at polarity and hydrogen bonding. They're what let a solvent dissolve salts and build structures like membranes.
- Remember that pressure shifts the boiling point but barely moves the melting point. Higher pressure widens the liquid range only at the top.
Loading simulator…
What a solvent for life needs
The chemistry of life happens in solution: molecules have to move, meet and react. A good solvent should stay liquid over a wide temperature range, dissolve charged substances well (that is, be polar) and form hydrogen bonds that help shape proteins and membranes.
Water excels at all of that. Its dielectric constant, about 80, is very high, which makes it great at pulling ions apart. It stays liquid across 100 °C at normal pressure, and it is one of the most abundant molecules in the universe.
The alternatives
Ammonia (NH₃) is also polar and forms hydrogen bonds, though weaker ones. At normal pressure it is only liquid between −78 and −33 °C, but higher pressure raises its boiling point: at about 29 atmospheres it stays liquid up to about 65 °C. It could work on cold worlds or ones with very dense atmospheres.
Methanol has a very wide liquid range (−98 to 65 °C) but is less polar (dielectric constant about 33) and far less abundant. Other proposals, such as the liquid methane and ethane on Titan, are nonpolar and would demand a very different biochemistry.
Worked example
Example: comparing liquid ranges at 1 atm
- Water: 0 to 100 °C, a 100 °C range.
- Ammonia: −78 to −33 °C, only about 45 °C.
- Methanol: −98 to 65 °C, about 163 °C.
- Methanol wins on range, but water wins on polarity, hydrogen bonding and abundance. Click each property in the comparator to see the details.
In Project Hail Mary
The novel features a life form from another planet that lives in a high-pressure, high-temperature environment very different from ours. The comparator shows what properties the liquid in its biochemistry would need.
Frequently asked questions
Why is water such a good solvent?
Because its molecule is bent, with a partial negative charge on the oxygen and positive charges on the hydrogens. That lets it surround ions and polar molecules and pull them apart.
Is there liquid ammonia in the solar system?
Moons such as Titan are thought to have underground water oceans with dissolved ammonia, and ammonia lowers the freezing point, which helps keep those oceans liquid.
What does "life as we don't know it" mean?
The idea that other biochemistries, with other solvents or other elements, might be possible. None has been observed, but it is studied to know what to look for on other worlds.