NASA is preparing to launch its latest rover on a bid to discover if there is – or ever was – life on Mars. The robot buggy, called Curiosity and the size of a Mini car, will be carried on an eight-month journey to the Red Planet in the $2.5 billion unmanned mission due for launch tomorrow, Saturday 26 November.

(Update: After a perfect launch, the MSL capsule has separated from the Centaur upper stage of the rocket and is en route to Mars. Update ends.) On landing, it will trundle around at the foot of a three-mile high mountain in 96-mile wide Gale Crater. The site has been chosen because photos from orbit show it contains exposed layers of sediment rich in clays and minerals that must have formed in water. Scientists believe this makes it an ideal place to look for organic evidence of any Martian life forms. Curiosity – also known as Mars Science Laboratory – is being launched aboard an Atlas V rocket from Cape Canaveral, Florida. It was given its name by an American schoolgirl.

NASA’s last Mars lander, Phoenix, photographed ice at its landing site in the martian arctic in 2008 and carried out months of valuable research before it was killed by the encroaching winter. Before that, two small rovers called Spirit and Opportunity, spent years exploring Mars after landing in January 2004 on what were expected to be 90-day missions. Spirit has now died but Opportunity is still working.

Curiosity, which at 9ft 10in (three-metres) long is almost five times larger than the earlier rovers, is too heavy to use airbags to reach the surface. Instead it will land on Mars using a new technique called a sky crane. The spacecraft’s descent stage will fire eight thrusters, like a scifi jet backpack, to steady itself above the martian surface and then lower Curiosity to the ground on a tether.

Mission specialist Steve Lee, of NASA, told Skymania News: “Previous missions have shown that at least some part of Mars have been soaked in water. Now we’re asking if the right elements were there to foster the growth of life. We’re not necessarily going to try to find life with this mission but our primary goal is to look for organic materials on Mars and find out if it was there at the same time as water.”

There are ten instruments on board including an Xray spectrometer, radiation detector, environmental moitoring station and tool to analyee the soil. One experiment, called ChemCam, will fire laser pulses at rock and then view the resulting spark to what it is made of. Any actual alien is unlikey to be detected unless it walks up and looks straight into the mast camera. But life if it ever existed is more likely to be in microbial form.

Steve said: “The sort of life we are expecting is a kind of microbial life. We’ll first look for the organic material and later possibly look for life itself.” He added: “The reason Curiosity is so big is the kind of instruments you need to detect organics are necessarly large. We quickly discovered that using an airbag landing system would no longer work. It is not easy just to blindly scale up airbags as were used to land Spirit and Opportunity.”

If bad weather prevents a launch today, NASA has until December 18 to make another attempt. NASA and the European Space Agency have both been successful in putting spacecraft into orbt around Mars, photographing its surface in great details.

Russia has been much less successful. Its latest mission, a bid to collect a sample of Mars’ larger moon Phobos, looks doomed after the spaceprobe, Phobos-Grunt, became stuck in orbit around the Earth. European space scientists managed to contact it earlier this week using a radio dish in Australia, but latest attempts have failed to draw a reply.

Watch a great NASA JPL animation showing how the Curiosity mission should play out above. And find out much more about the Red Planet, including how to see it yourself, by visiting our special Mars pages.