Liquid water may be found on planets that have gone adrift from their stars and may have acted as stepping stones to spread cosmic life, U.S. researchers say.

Gravitational battles with other planets or passing stars can fling worlds out of their solar systems, but two scientists from the University of Chicago say these wandering worlds could continue to stay warm thanks to the decay of radioactive elements in their cores, NewScientist.com reported Monday.

Dorian Abbot and Eric Switzer say they've calculated that rocky planets with a mass similar to that of Earth could stay warm enough to keep water liquid under thick, insulating ice sheets for more than a billion years.

A planet with the same percentage of water as Earth could keep a subsurface ocean liquid if it was 3.5 times Earth's mass, they say, but a planet with 10 times Earth's water concentration could do this even if it weighed just one-third as much as Earth.

"It's a really interesting idea," Lisa Kaltenegger of the Harvard-Smithsonian Center for Astrophysics says of their theory. "But we would have to land on [a planet] and burrow down to see if life is possible."