Liquid water is considered the main condition for the emergence of life similar to Earth’s. It has a number of properties that allow it to be an environment for biochemical processes. However, scientists are thinking about what substances on other planets can replace it.
Why is water an important condition for the existence of life
A huge number of assumptions exist about what life on other planets may look like. Alternative biochemistry covers not only the use of other amino acids in proteins and nucleotides in DNA, but also much bolder ideas. For the most part, they remain fantastic. However, in a new article posted on the arXiv resource, scientists tried to answer the question of what on other planets could be an alternative to water.
Liquid water is considered the best biomarker, that is, a sign of the possibility of life on a celestial body. The reason is that it is a universal solvent and environment for biochemical processes, both inside and outside cells. However, there are many other liquids in the universe that can theoretically serve in such a role.
In the new study, scientists have begun by identifying the main factors that make water a good environment for life. There are four of them in total:
- it dissolves most molecules, but not all;
- it plays an important role in the metabolism of living beings;
- it does not decompose a wide range of complex organic substances;
- it does not decompose itself for billions of years under the influence of external factors.
It is believed that water is the only fairly common substance that meets all three parameters. However, scientists have decided to look for something else that has similar properties.
What can be a water substitute?
In their search for a water substitute, scientists began with ammonia NH4. In terrestrial conditions, it is a gas. But at lower temperatures, it turns into a liquid. This substance corresponds to the first three of the mentioned conditions, but breaks down under the action of ultraviolet light. Of course, there are places where this molecule is protected from it. But there, water can also exist in a liquid state. Therefore, it is unlikely that it is the main biological solvent somewhere.
Another alternative is concentrated sulfuric acid H2SO4. It meets three conditions, but it is still unknown whether sufficiently complex organic molecules can exist in it and whether it will be possible to build cells from them. Now this issue is being carefully studied, because the possibility of life in the clouds of Venus depends on it.
Finally, scientists turned their attention to carbon dioxide. Like ammonia, it exists as a liquid at low temperatures. We don’t know much about its properties in this state. It is believed that it is a fairly weak solvent, but it is even better than water embedded in biological processes. In any case, the authors of the study consider it worthy of further research.
In the end, the researchers conclude that on other planets, water can actually be replaced by other substances. Titan’s seas, for example, are rich in hydrocarbons and other complex organic molecules. Moons of a cold exoplanet like it may have oceans of CO2, NH4 and H2O. There is still a lot we don’t understand about cryogenic chemistry on cold exoplanets.So, while the waters of life probably exist in space, the seas of life on some worlds may be much more exotic.
According to phys.org
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