Image copyright PA Image caption The near-Earth asteroid has a 1 in 650 chance of striking the planet in the next 1,500 years
Space agency NASA has launched a spacecraft to smash into an asteroid before entering the Earth’s atmosphere and breaking apart.
The historic mission aims to capture a boulder on the asteroid to hold onto until a future mission to return the sample to Earth.
The Alice spacecraft, launched on Friday, will collide with the near-Earth asteroid 2014 YU55 before tumbling into the atmosphere.
The asteroid is estimated to have a 1 in 650 chance of hitting the planet in the next 1,500 years.
The impact will be very small – less than a kilogram – with the fragments landing in the sea or in the Sahara.
Alice will spend the next 1.7 months orbiting the asteroid to capture the space rock before its crash in May 2020.
The asteroid, which is 950m across, will pass within 17,200km of Earth on the day of the spacecraft impact, when it could be visible with the naked eye in northern skies over Europe, western North America and the Antarctic region.
It has been given the designation O/2014 XE1 and travelled on a path between the orbits of Mars and Jupiter.
Titanium structures on the surface suggest that the asteroid underwent a period of erosion about 200 million years ago.
Image copyright NASA Image caption A view of a similar asteroid, 2012 DA14, from 40 years ago
NASA expects the crash to be relatively dangerous and the flight path cleared a week in advance to avoid publicity or interference.
A spacecraft lost its way in its orbit on Friday and plunged into the Pacific Ocean north of Mexico, about 800m above sea level.
Scientists will study the X-ray and UV radiation produced during the crash, looking for signs of water or organic material.
“The Alice spacecraft has chosen a thrilling but safe and very risky path to explore asteroid 2014 YU55,” said David Bennett, program scientist for NASA’s Deep Space Network at the Jet Propulsion Laboratory in Pasadena, California.
“It’s going to meet up with an asteroid that’s a very dangerous object but at its closest approach to Earth, 2010 YU55, we’ve chosen to have Alice collide with it instead of entering the atmosphere itself.”