Nasa has postponed the launch of a major mission to study whether things can live on Mars.

Nasa administrator Michael Griffin said the Mars Science Laboratory mission must be pushed back from next year in part because of problems with motors on the six-wheeled rover designed to operate on the Red Planet.

The delay of the planned October 2009 launch to autumn 2011 is expected to add about $400 (£270 million) to the program's cost.

The mission is designed to assess if Mars can support microbial life.

It is the latest in the exploration, which scientists believe had abundant liquid water on the surface in the past and may have been home to some type of life forms.

Mr Griffin said: "I have full confidence in the JPL team (Nasa's Jet Propulsion Laboratory in Pasadena, California) to be able to work through the difficulties, but we've determined that trying for '09 would require us to assume too much risk - more than I think is appropriate for a flagship mission like Mars Science Laboratory."

He said: "A mission like this ranks just behind a manned mission in importance."

The positions of Earth and Mars relative to one another as they orbit the sun are favourable for interplanetary flights for only a few weeks every two years, officials said.

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