We're used to seeing them as stars in the sky, but planets could soon be home to humans if Stephen Hawking has his way.
The world-renowned scientist believes humans must colonise planets elsewhere in the universe because of the risk a disaster will destroy the Earth.
Astrophysicist Professor Hawking insists the survival of the human race depends on it finding new homes on other planets. He believes global warming, nuclear war or a genetically engineered virus could wipe out the earth.
Speaking at a news conference in Hong Kong the 64-year-old scientist said humans could have a permanent base on the moon in 20 years and colony on Mars in the next 40 years.
He said: "We won't find anywhere as nice as Earth unless we go to another star system. It is important for the human race to spread out into space for the survival of the species.