At 6:30am BST, NASA's Curiosity rover touched down on Mars, making it the seventh successful attempt to land a man-made object on the planet, and the largest such object yet.
Following its launch from Cape Canaveral in November last year, the mission has covered the 563 million kilometer distance without concern, but the most dangerous aspect of the trip was always going to be the last seven minutes of the descent to Mars. The Martian atmosphere is thin enough that it isn't capable of slowing objects travelling at interplanetary velocity down enough for them to make a safe landing, while being thick enough that the friction is capable of doing serious damage to an unprotected craft.
Once the rover hit the atmosphere, it had to execute a complicated series of manouvers, first deploying a massive parachute, then rocket thrusters, and then, at the very end, hovering just above the surface and lowering the car-sized rover down on nylon strings. And it had to do all of this without any aid from the control room on Earth, due to the 14 minutes it takes for radio signals from Mars to reach earth. So by the time we heard that the rover had hit the atmosphere, it had actually been sitting on the planet – dead or alive – for seven minutes.
NASA's video explaining the "seven minutes of terror" – unfortunately officially called "EDL", for "entry, descending, landing" – conveys the sheer scale of the challenge:
Now that it has arrived, the rover's first task is to explore Gale crater, its landing site. The crater contains a number of interesting geological features, including what appears to be a 5km high mountain formed out of sedimentary rock, which would make it one of the largest artifacts of running water on Mars.
But that preliminary mission is unlikely to be the rover's only one. NASA's increasingly successful missions to send rovers to Mars have been typified by the flexibility which the mobile design offers. The Pathfinder mission, which deposited a lander (a stationary craft) and a rover (named Sojourner) on Mars in 1997, was intended to last a week to a month, but ended up returning usable data for three. The follow-up rovers, Spirit and Opportunity, landed in 2004 with 90 days of planned experiments. Spirit eventually got stuck in late 2009 and stopped sending signals back to Earth in 2010, while its twin Opportunity is still active, 3,026 days after its mission was supposed to end.
But Curiosity is a different scale of mission – literally. While Sojourner was 65cm long and weighed 10.5kg, and Spirit and Opportunity 1.6m and 180kg, Curiosity is over 3m long and weighs almost a tonne. Rather than being powered by solar panels, which runs the risk of outages during dust storms and the Martian night, it contains a plutonium battery, which generates heat to be turned into electricity. It also has a laser which can burn holes in rocks from up to 7 meters away,
in case of attack to analyse the chemical composition of the planet, and sensors which detect visible light, x-rays, neutrons and ultraviolet radiation, all for science. In essence, NASA has landed a nuclear power, laser-armed SUV on Mars for one fifth the cost of the Olympics. Oh, and it tweets.