Space: NASA's Curiosity rover lands safely on Mars

NASA's control room erupted with cheers as confirmation reached Earth that the Curiosity rover successfully landed on Mars. Scientists and engineers hugged, sobbed and punched the air as the first images from the rover's cameras came down.
The first pictures, low-res thumbnails taken through the rover's rear hazard avoidance cameras and a clear dust filter, showed the Martian horizon and one of the rover's wheels. Shortly after, the front cameras took the rover's first self-portrait: its shadow on the Martian surface.
Now safely on the ground in the Gale Crater, Curiosity can begin its two-year mission: to find whether Mars has the crucial ingredients that could once have supported life.
No wonder mission control went wild: the landing was the most ambitious and daring ever attempted Movie Cameraon another world.
Curiosity's predecessors, Spirit and Opportunity, arrived on Mars swaddled in airbags that cushioned them as they crashed into the planet's surface and bounced and rolled to their final landing sites.
But Curiosity is 10 times their weight, and would punch straight through any airbag NASA could build. So mission engineers designed the Sky Crane. For the last 20 metres of its trip to the surface, Curiosity was slowly lowered on three nylon tethers from a hovering descent vehicle, held in place by retrorockets.
But that was just one element of the landing choreography. The capsule containing the rover and descent vehicle entered the Martian atmosphere at 5900 metres per second. Almost immediately, small charges detonated and ejected two blocks of tungsten – each about the size of a laptop, and weighing 75 kilograms.
Jettisoning these weights tilted the capsule so it could catch air and fly across the Martian landscape much like a skydiver in a wingsuit. The capsule steered itself using small rockets and autonomous navigation software. Similar software was used for the Apollo missions, but this is the first time that a robot on another planet navigated itself without human input.
At an altitude of 11 kilometres, the spacecraft dropped six more 25-kilogram blocks to shift its orientation once more, then deployed the largest supersonic parachute ever sent to another planet. The parachute slowed the spacecraft from 400 metres per second to 80 metres per second in less than two minutes.
At about the same time, the capsule dropped its heat shield, exposing the rover – and its cameras and landing radar – to the cold Martian air. The cameras started looking for the ground, snapping photos once every four seconds. (In the coming days, these images will be stitched together into a video of the nerve-wracking final descent.)
At 1.6 kilometres up, the parachute let go, and the descent vehicle plummeted in free fall for a fraction of a second. Then eight retrorockets roared to life, slowing the vehicle to an eventual stop for the ambitious Sky Crane manoeuvre.
"It looks a little bit crazy," admitted Adam Steltzner, who heads the landing team, in a press conference before landing. "I promise you it is the least crazy of the methods you could use to land a rover the size of Curiosity on Mars."
Curiosity is the first rover to use its own wheels as landing gear. The six wheels are half a metre in diameter and as thin as cardboard. They move independently beneath the rover, so that if it had to, it could drive over an obstacle as tall as a coffee table.
Though its landing was entirely different, Curiosity learned some tricks from Spirit and Opportunity. Those rovers' wheels had small holes by which they were clamped to their landing pads before being released. Later, the rovers' handlers found they could see when the wheels were slipping on the sandy Martian surface by measuring the distance between the marks left by these holes in the rovers' tracks.
So Curiosity also has holes in its wheels, which spell out "JPL" (for NASA's Jet Propulsion Laboratory, where the rover was built and is operated) in Morse code.
The wheels will have to wait to make their first tracks, however. First, the rover has to stretch its robotic "arm" and "neck". The former carries a suite of instruments including a camera that will be used to peer at rocks, like a geologist using a hand lens. The latter is a mast carrying high-resolution cameras that will reveal panoramas of Curiosity's surroundings, and a laser that will zap rocks from a distance to help reveal their composition.
Once it gets into its scientific stride, Curiosity will use its onboard chemistry lab to look for organic molecules required as the basic building blocks of life, and chemical energy sources that could have been used by Martian microbes.
The final destination is Aeolis Mons, a five-kilometre high mountain in the middle of Gale Crater. Gale is an impact crater, but is thought to have been full of water for hundreds of millions of years. As Curiosity climbs Aeolis Mons, it should encounter layers of sediments revealing what mission leader John Grotzinger calls "the dimension of deep time".