AFP
Are we alone? Or was there once life on another planet?
NASA's $US2.5 billion ($A2.40 billion) dream machine, the Mars Science Laboratory, aims to take the first steps toward finding out when it nears Mars' surface on Monday.
The planet is Earth's closest neighbour, and scientists have found signs of water there, hinting that some form of life was once likely, even though Mars is now a dry place with a thin atmosphere, extreme winters and dust storms.
NASA said it will find out if its Mars Science Laboratory and rover, Curiosity - designed to hunt for soil-based signatures of life and send back data to prepare for a future human mission - is due to land safely at 3.31pm (AEST) on Monday.
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That will be about 14 minutes after the touchdown actually happens due to the time it takes for spacecraft signals to travel from Mars to Earth.
As of late Saturday, the laboratory was approximately 420,039km from Mars, closing in at around 13,000km/h.
"Curiosity remains in good health with all systems operating as expected," NASA said in a statement.
The nuclear-powered rover is the biggest ever built for planetary exploration, weighing in at one tonne, about the size of a small car, and carries a complex chemistry kit to zap rocks, drill soil and test for radiation.
The landing is a daring and unprecedented manoeuvre that involves penetrating the atmosphere at a speed of 21,240km/h, slowing down with the help of a supersonic parachute and dropping down gently with tethers from a rocket-powered sky crane.
"This is the most challenging landing we have ever attempted," said Doug McCuistion, director of NASA's Mars exploration program.
Two NASA orbiters will be crossing overhead as the lander approaches the surface, and a third orbiter operated by the European Space Agency will also send data back to Earth.
The Mars Science Laboratory began its journey to the Red Planet more than eight months ago when it took off from the Florida coast in late November 2011.
"It gets scarier every day," said McCuistion, noting that only about 40 per cent of past attempts by global space agencies to send spacecraft to Mars have succeeded.
"Can we do this? Yeah, I think we can do this," he said.
"But that risk still exists. It is going to be tough."
A live broadcast of the landing will be on www.nasa.gov beginning at 1.30pm (AEST) Monday.
The landing site for the rover is a flat area known as Gale Crater, which lies near a mountain that scientists hope the rover will be able to climb in the search for sediment layers that could be up to a billion years old.
If the landing succeeds, NASA hopes to have some low-resolution black and white images taken from cameras on the rear of the rover shortly afterward.
The rover's chemistry kit contains a rock-zapping laser, 17 cameras, a drill, radiation detectors, water sensors, and tools to scoop soil and check for carbon-based compounds that are the building blocks for life.
Curiosity may start to roll for its first drive in September, with its first scoop samples expected late in the month and its first drilling attempt in October or November.
If the landing fails, McCuistion vowed that NASA would continue its efforts to explore Mars.
"We will pick ourselves up and dust ourselves off ... We will do it again," he said.
"Human spirit gets driven by these kinds of challenges ... to explore our surroundings, to understand what is out there, and obviously look at 'Are we alone?'"

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NASA rover on course for Mars landing

And by the way "NO. We are not alone but don't expect any government on earth to tell you this because they don't want to accidentally destroy human civilization by telling the world that. There are just too many millions that would freak out and kill themselves and their families. Especially, this year. So, Know the Truth and the Truth will Set you Free!"