Scientists believe our galaxy could contain a staggering 60 billion planets that might be capable of supporting life.

Based on data from NASA's Kepler spacecraft, scientists had predicted there should be one Earth-size planet in the habitable zone of each red dwarf, the most common type of star.

But a group of researchers has now doubled that estimate after considering how cloud cover might help an alien planet support life.

Cloud cover is crucial for life, as clouds not only reflect sunlight to cool things off - they keep the planet warm enough to sustain life.

A new study by the University of Chicago and Northwestern University said that the Milky Way alone could contain 60 billion planets orbiting red dwarf stars that could support life.

It also suggests new ways for astronomers to test whether planets orbiting red dwarfs have cloud cover.

The researchers based their study, which appeared in Astrophysical Journal Letters, on rigorous computer simulations of cloud behaviour on alien planets.

This cloud behaviour dramatically expanded the estimated habitable zone of red dwarfs, which are much smaller and fainter than stars like the sun.

Dorian Abbot, assistant professor in geophysical sciences at the University of Chicago, said: 'Clouds cause warming and they cause cooling on Earth.

'They reflect sunlight to cool things off and they absorb infrared radiation from the surface to make a greenhouse effect.

'That's part of what keeps the planet warm enough to sustain life.'

The planets believed capable of supporting life fall in habitable zones where they are the right temperature to be able to have liquid water on their surfaces - a requirement of life as we know it.

As red dwarf stars are slightly cooler and less bright than our sun, the planets are usually closer to their star.

Ends/AMA/06/07/13