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Washington - The question of life on Mars has preoccupied scientists and science fiction buffs for many years.
Ray Bradbury, the writer who died last week, set the literary standards for such speculation in his Martian Chronicles, a short story collection from the 1950s that imagined a fictional colonisation of Mars by Earth's humans and their conflicts with Martian natives.
On Monday, Nasa scientists said that the next step in the search for life on Mars is to begin on August 6, when a new rover, Curiosity, is to touch down in a crater that has shown signs of having water at some point of the red planet's history.
The goal of the mission is to “follow the water” at one of several locations on Mars that have had liquid water as part of their environment, said Mike Meyer, Nasa’s lead scientist on the mission, in a webcast news conference.
The target of exploration is Gale Crater, a relatively flat plain at the base of Mount Sharp whose heights and layered sediments have “the potential to have been able to support microbial life”, Meyer said.
The mountain's sediments may also provide a glimpse into the weather history of the planet, Meyer said in a webcast briefing to reporters.
Curiosity is now onboard Nasa's Mars Scence Laboratory, which after its launch in November 2011 is making its final approach to orbit around Mars before deploying the rover.
As the US human space programme turns its attention away from near-Earth orbit to the longer journey to Mars for humans, scientists hope that the $2.5-billion Curiosity mission will help shed light on whether any kind of life is possible on Earth's nearest neighbour in the solar system.
At 900kg, Curiosity is far bigger than any of its predecessors such as Spirit and Opportunity, and has a longer time fuse.
The rover, the size of a large sport-utility vehicle at about 3 metres long and 2 metres high, will be the first rover equipped with a drill to take rock and soil samples. Opportunity and Spirit could only scrape up bits of rock and dirt for on-site analysis.
Its mission will be to record a full Martian year of life, equivalent to about two Earth years. That's different from the short 60- and 90-day missions of its predecessors. While Spirit and Opportunity both astonished Nasa by outliving their life span by years, each had to move swiftly to accomplish its initial goals.
Curiosity, on the other hand, because of its complexity and capacity, will be “slow going” as controllers on Earth test communication links.
“We have here a marathon and not a sprint, so early going will seem somewhat slow,” said Pete Theisinger, project manager at the Jet Propulsion Laboratory in Pasadena, California.
Nasa's Dave Lavery, the top mission executive, warned that landing Curiosity will be a “risky business,” since only 40 percent of Mars missions have been successful. Both the unpredictable Martian landscape and weather as well as the engineering challenges of landing such a large vehicle work against success, he said.
But scientists will have more control over the landing of Curiosity, which is the first rover equipped with thrusters to pinpoint the target. That compares to the less focused “drift down” landings in the past.
Nasa has worked since the launch to fine-tune the landing zone by experimenting with the thrusters on Curiosity models in the US desert. They have narrowed the landing zone to a 20 by 7 kilometre target instead of the original 20 by 25 kilometre target area.
The move will considerably reduce the amount of time Curiosity needs to reach Mount Sharp by up to four months, Theisinger said.
Curiosity will likely not be able to identify microbial life of any kind with instruments on board, Meyer said. But there's a chance the rover will come across an “aqueous body” with mineral precipitates, which could identify a “consortium of microbes.”
“We would be thrilled to find something like that which would merit a return,” Meyer said. - Sapa-dpa