A study examining the amounts of water present in the atmospheres of 19 exoplanets was carried out by a team of astrophysicists at the University of Cambridge. The researchers concluded that although water, mainly in the form of water vapour, is common in exoplanet atmospheres, the level of presence is lower than expected.
As explained on Space.com Nikku Madhusudhan, one of the authors of the study, the chemical substances that were most commonly found in the atmospheres of other planets were sodium and potassium, whose amounts were consistent with expectations unlike water vapor. It was precisely the amount of water that surprised Madhusudhan himself, who, together with his colleagues, examined the atmospheres of the 19 exoplanets thanks to the data collected by various space and terrestrial telescopes.
The planets analyzed had surface temperatures ranging from 20° to 2000° centigrade and various sizes, from mini-Neptune with 10 times the Earth’s mass to gaseous supergiants with 600 times the Earth’s mass, so a good catalogue of planets although the number analyzed (19) was not so high.
At present, however, forecasts remain uncertain as to how much water can actually hide on average in exoplanets, also because it is not so easy to detect it in gaseous planets. An example could be Jupiter in our solar system: as explained by Luis Welbanks, another author of the study and astrophysicist at the University of Cambridge, Jupiter is so cold that water vapour begins to condense and is no longer visible in the thick gaseous atmosphere. On Jupiter there could be a lot of water or very little water, but with the tools we have available today it is not yet known.
This should not, however, weaken the research of extraterrestrial life: as the researchers explain, in fact on Earth there is not that much water at mass level. According to Madhusudhan the Earth itself could be considered “slightly below sufficient” as far as the amount of water is concerned so the fact that there is a smaller amount of water on exoplanets compared to the theories previously formulated should not necessarily represent bad news as far as their habitability is concerned.