Physicist Stephen Hawking said people should return to the Moon and go to Mars because leaving Earth may be the only way to save humanity.

Hawking said that as Earth faces climate change and pressure on natural resources, human beings need to reach beyond our planet. We are running out of space and the only places to go to are other worlds, he said. It is time to explore other solar systems. Spreading out may be the only thing that saves us from ourselves. I am convinced that humans need to leave Earth, he added. If humanity is to continue for another million years, our future lies in boldly going where no one else has gone before.

The University of Cambridge professor spoke during a visit in June to the Starmus Festival in Trondheim, Norway.

Hawking said human beings should return to the moon by the year 2020 and Mars by 2025. This, he said, will unite humans in the shared purpose of exploring the universe.

Spreading out into space will completely change the future of humanity, he said. I hope it would unite competitive nations in a single goal, to face the common challenge for us all.

Hawking added that reaching the Moon, Mars and other plants would get young people interested in space-related sciences. He said making the first moves into space would "elevate humanity" because it would have to involve many countries.

Whenever we make a great new leap, such as the Moon landings, we bring people and nations together, usher in new discoveries, and new technologies,

Hawking said. To leave Earth demands a concerted global approach, everyone should join in. We need to rekindle the excitement of the early days of space travel in the 1960s.

The European Space Agency has announced a plan to create a "Moon Village" after the International Space Station is taken out of service in 2024.

China is also reportedly interested in sending an astronaut to the Moon.

The United States is working on sending astronauts to Mars. The U.S. space agency, NASA, hopes to do this by the 2030s.