Nasa has launched the first ever mission to take samples from an asteroid in the hope of preventing the space rock having a catastrophic collision with Earth later this century.
The asteroid Bennu, which measures about 1,760ft (500m) across, is expected to pass between the Earth and the Moon for the first time in 2035, and at present a collision is considered unlikely. However, a bizarre phenomenon, called the Yarkovsky effect, could change the orbit of the asteroid, placing it on a more devastating trajectory when it passes again towards the end of the 21st century.
The effect occurs because rotating asteroids absorb sunlight in some regions more than others, and when this energy is released back into space, the resulting thrust can alter the path of the asteroid.
One of the goals of Nasa's OSIRIS-REX mission is to study that phenomenon and calculate whether it could shift Bennu sufficiently to put it on a collision course with the Earth.
Simply flying so close to Earth's gravitational field in 2035 could also alter its orbit, potentially putting it on a collision course. Dante Lauretta, OSIRIS-REX principle investigator said that if that happened Bennu "may be destined to cause immense suffering and death".
Nasa said the asteroid is too small to completely destroy the Earth, but it could devastate a large area on impact. The space rock that is believed to have wiped out the dinosaurs was six miles (10km) across, 20 times larger than Bennu.
The mission will also lay the foundations for future programmes to reorientate asteroids that threaten Earth.
"If astronomers someday identify an asteroid that presents a significant impact hazard to Earth, the first step will be to gather more information about that asteroid," said Edward Beshore, Deputy Principle Investigator for the mission.
"Fortunately the ORISIS-REX mission will have given us the experience and tools needed to do the job."
Prof Daniel Scheeres, of the University of Colorado, who is leading the radio science team, added: "By visiting Bennu we can very precisely determine its orbit, determine the physical forces affecting it, and do a much better job of predicting where it will be in the next couple of hundred years.
"By then we should know if we need to start building a giant space tugboat." The mission will also take samples to find out more about the origins of life. Many scientists believe that asteroids and comets brought the first building blocks of life, and water, to Earth.