Image copyright NASA Image caption The asteroid Bennu is slated to be captured by the spacecraft in 2020
NASA has successfully launched a spacecraft to crash into an asteroid.
The space agency’s Philae lander is due to rendezvous with the target asteroid in 2018 and then, in March 2020, strike it.
Scientists hope the target could provide clues about the solar system’s history, particularly the formation of the solar system 4.6 billion years ago.
The Atlas V rocket carrying the Philae probe lifted off from the Cape Canaveral Air Force Station in Florida at 17:34 GMT (11:34 BST).
The lander is being launched by the European Space Agency’s Rosetta space probe, which landed a probe on a comet in 2014.
This year, Rosetta will continue its journey to a previously-undiscovered comet and then, in November, it will stop communicating with Earth and slip into a hibernation.
The mission’s name, Philae, refers to a Polish mathematician and astronomer who in 1605 first recorded the existence of comets.
Nasa hopes Philae’s planned encounter with the asteroid Bennu, which is up to half a mile wide, will help scientists better understand asteroids and their possible role in helping to deliver water, chemicals and organic material to Earth.
Philae’s 65kg (150lb) solar panel will be unfurled during the 90-minute drop down to the asteroid.
From there, its three scientific instruments will be activated. These include a yearning-tongue radio microphone which has already played back nine seconds of sound in a display of the craft’s craftiness.
The instruments will determine whether the sample of material dropped onto the surface of the asteroid is less rock than scientists initially hoped.
After the space probe descends by its scheduled 5.4 miles (8km) to the surface, it will begin to “thread the needle” using reflector and reflector antennas to try to get a better grip on the surface than expected.
That should determine whether the impact makes the asteroid unstable or stable.
The craft will use its telescopic camera to track the way asteroids are rotating on its surface, and it will record images of the debris that comes crashing down upon it.
Speaking ahead of the launch, European Space Agency (Esa) head of missions Dave Parker said the idea was “almost an out-of-body experience” when Philae began to take information from Rosetta on board.
“We know a lot more about the moon, Mars and Earth than we know about asteroids, and we need to go on a journey of discovery to learn how they work, how they formed and where they were when we were born.”
The $1.6bn (£1.1bn) mission, which uses two solar arrays to deliver batteries and living equipment for Philae to recharge, is one of the most complex science missions ever to take place.
Esa has already faced problems in the past with its asteroid missions. The recent crash of Philae’s predecessor spacecraft, Beagle 2, with Comet 67P also ended in failure because of the ill-fated re-entry of its Phoenix lander in 2008.
Rosetta, while not as complicated as the mission in which Philae will operate, was also delayed several times because of Rosetta’s slow climbing to its comet destination. It is now set to make its last attempt to “touch down” on Comet 67P before Rosetta plunges into it in November.
Philae also faces some technical challenges with its craft, which has an extraordinary level of complexity and tech sophistication for the time it is operating.
That includes a little space-age addition, the harpoons that would be used to point the landing harpoon into a soft landing target on the surface of Bennu. These were not yet ready for use when the craft, which has twice been stranded in the darkness of space, was ejected into space.
Philo will face a much harder task that Rosetta – travelling at 30,000 mph, will rely on the guidance of its onboard solar panels to continuously and accurately orient itself to the surface.
But, working day and night in just 85% of sunlight for 40 days, Philae will deploy a series of harpoons that will point the landing site towards the centre of the large gap between the main orbit of the Rosetta mothership and the moon, as revealed by surface images from Rosetta.
Image copyright Philae
Philo and Rosetta will also carry gas sensors to measure atmospheric composition, and chemical-based filters, which will allow water vapour, carbon dioxide and dust from the surface of the comet to be analysed.
Comet 67P, which is very hot and contains a steady stream of radio waves streaming from its interior, is a target because it was probably most closely formed by tiny fragments of the same type