The chances of finding alien organisms have been boosted by the discovery of hundreds of “water worlds” capable of supporting life.
New analysis by Harvard University estimates that one in three “exoplanets” outside our solar system that are larger than Earth are likely to contain an abundance of water.
The scientists say the planets that are two to four times bigger than Earth that have the best chance of supporting life.
Analysis of data from the exoplanet-hunting Kepler Space Telescope and the Gaia mission indicates half their weight may be water – either flowing or frozen.
In comparison, the amount of water on Earth makes up just 0.02 per cent of its complete mass.
Lead researcher Dr Li Zeng, said: “It was a huge surprise to realise that there must be so many water-worlds.”
Exoplanets were first discovered in 1992 and since then about 4,000 have since been confirmed to exist.
Scientists believe they fall into two broad categories: those with a planetary radius averaging around 1.5 the size of Earth, or 2.5.
Now the group of international scientists has developed a model of their internal structure.
This is based upon their recent mass and radius measurements from the Gaia satellite.
Dr Zeng said: “We have looked at how mass relates to radius, and developed a model which might explain the relationship.”
The model indicates the smaller planets tend to be rocky planets – with typically five times as much mass as Earth.
In numbers | Kepler mission
The larger ones have about 10 times more mass – and “are probably water worlds,” said Dr Zeng.
Presenting the findings at the Goldschmidt conference in Boston, he explained: “This is water, but not as commonly found here on Earth.
“Their surface temperature is expected to be in the 200 to 500 degree Celsius range.
“Their surface may be shrouded in a water-vapour-dominated atmosphere, with a liquid water layer underneath.”