Lift-off of the American rocket is captured by NASA at Cape Canaveral

Nasa's unmanned Mars Climate Orbiter lifted off on top of a Delta 2 rocket precisely on time - nine seconds before 1846 GMT.

Mars is known to have water, some of it in the form of ice, and scientists believe this may have made it conducive to life.

However, no one knows where all its water is, and scientists are hoping the probe will find out.

A second probe - to be launched from Florida in January - will land on the surface, carrying a microphone to record the sound of wind from the Red Planet.

A TV camera attached to the rocket captured dramatic footage

A television camera strapped to the side of the booster on Friday provided a dramatic view of the high-speed climb away from the launch pad. The curvature of the Earth was clearly visible.

The orbiter's interplanetary trek began with separation from the rocket's third stage about 47 minutes into flight, high above the Indian Ocean.

"The Climate Orbiter is en route to Mars," said Nasa launch commentator Bruce Buckingham after a tracking station in Perth, Australia, confirmed the probe was on its way.

The 1,387 lb probe is due to arrive at Mars next September after a 416-million mile voyage.

For six months the craft will gently lower its orbit by skimming the planet's upper atmosphere about 200 times to slow its speed.

Another probe is scheduled to leave in January

By March, the orbiter should be circling Mars every two hours at an altitude of 262 miles, passing almost directly over the planet's poles.

Instruments will keep tabs on the Martian weather, track wispy clouds in the dusty atmosphere and examine the rock-strewn, rust-coloured surface.

The orbiter will also serve as a communications relay for a second Mars probe, scheduled for launch on 3 January.

That probe should touch down near the icy Martian north pole and analyse soil samples scooped up with a robotic arm.

The twin Mars missions, which cost about $328m, are part of a 10-year effort to determine if life existed or still survives on the planet.

The first two probes in the series, the Mars Pathfinder lander and the Mars Global Surveyor orbiter, were launched in 1996.

"The key is the water," said Ed Weiler, Nasa's head of space science.

"Follow the water. And that is what these two missions do. They really try to understand the current situation with water on Mars.