Sean Raymond, a University of Colorado researcher, said these solar systems feature gas giants known as "Hot Jupiters" which orbit extremely close to their parent stars, even closer than Mercury to our sun.

The close-orbiting gassy planets may help encourage the formations of smaller, rocky, Earth-like planets, they reported in the journal Science.

Raymond said: "We now think there is a new class of ocean-covered, and possibly habitable, planets in solar systems unlike our own."

Computer simulations

The team from Colorado, Penn State University and Nasa's Goddard Space Flight Centre Maryland ran computer simulations of various types of solar systems forming.

They found that the gas giants may help rocky planets form close to the suns, and may help pull in icy bodies that deliver water to the young planets.

Raymond said: "These gas giants cause quite a ruckus."

"I think there are definitely habitable planets out there. But any life on these planets could be very different from ours.

"There are a lot of evolutionary steps in between the formation of such planets in other systems and the presence of life forms looking back at us."

As many as 40 per cent of the 200 or so known planets around other stars are Hot Jupiters, the researchers said.