When searching for extra-terrestrial life, scientists usually seek its proxy – liquid water. Now, a new study claims that up to a third of all currently known exoplanets – or planets orbiting other stars – may have it in spades. Water is estimated to comprise up to 50% of such liquid worlds.
The work, recently presented at the Goldschmidt Conference in Boston, shows that the sizes of known super-Earths (exoplanets which are two to four times larger than Earth) are best explained by massive amounts of liquid, frozen or vaporised water.
“It was a huge surprise to realise that there must be so many water-worlds,” said lead researcher Dr Li Zeng from Harvard University.
Since the discovery of exoplanets back in 1992, as many as 4,000 have been either proposed or confirmed, pretty much all falling into two broad categories in terms of size: those with a planetary radius averaging 1.5 that of Earth, and those averaging around 2.5 times the radius of Earth.
Now, using recent mass and radius measurements from the Gaia satellite, an international group of researchers have developed a model of their internal structure.
In the paper, the research group details how they have examined the relationship between mass and radius, and how this has led them to develop a model to explain it.
“The model indicates that those exoplanets which have a radius of around x1.5 Earth radius tend to be rocky planets (of typically x5 the mass of the Earth), while those with a radius of x2.5 Earth radius (with a mass around x10 that of the Earth) are probably water worlds,” said Zeng.
This, however, does not mean that all (or any) of such exoplanets are necessarily habitable, as conditions on some of them could be quite severe even for the hardiest of biological organisms.
It does not preclude the possibility of alien life altogether, though, as there could be pockets within near-surface layers where the pressure, temperature and chemical conditions are conducive for biological evolution.
“It’s amazing to think that the enigmatic intermediate-size exoplanets could be water worlds with vast amounts of water. Hopefully atmosphere observations in the future–of thick steam atmospheres—can support or refute the new findings,” said Professor Sara Seager, Professor of Planetary Science at MIT who was not involved in the research.