The US space agency on Thursday launched a probe to the long-watched asteroid Bennu, which astronomers say could menace future generations on Earth.
The Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer (OSIRIS-REx) spacecraft launched at 7:05 pm (2305 GMT) from Cape Canaveral Air Force Station, NASA said.
"Our @OSIRISREx spacecraft is on its way, and everything is on the timeline," NASA said on Twitter.
The mission is the United States' first to sample an asteroid.
The asteroid, with a diameter greater than the height of the Empire State building, was discovered in 1999 and was found to have the possibility of passing dangerously close to Earth in the 22nd century.
Though the risk to Earth is very slight, NASA still considers the rocky object one of the most dangerous known asteroids.
The spacecraft would reach Bennu in August 2018, get close enough in 2020 to scoop up a sample of between 60 and 2,000 grams using a robotic arm, then return to Earth in 2023. It will travel more than 650 million kilometres over the entire trip.
In addition to improving the understanding of asteroids that could impact Earth, the mission will help scientists investigate the solar system's evolution and the history of Bennu over the last 4.5 billion years, NASA said.
A Japanese space probe called Hayabusa launched in 2003 toward a near-Earth asteroid, collected samples more than two years later and returned the samples to Earth in 2010.
The European Space Agency (ESA) sent the robotic lander Philae to the comet 67P/Churyumov-Gerasimenko in the first mission in history to rendezvous with a comet. Philae landed on 67P/Churyumov-Gerasimenko in November 2014, but a faulty thruster caused it to miss its intended location, leaving it short of sunlight to charge its secondary batteries, and contact was broken off.
NASA will be aiming its OSIRIS-REx, a 6-metre-long, 2,100-kilogram spacecraft built by Lockheed Martin, at Bennu, which has a diameter of about 490 metres. Before taking samples, it is to take photographs and other examinations using five scientific instruments and cameras.
Scientists project that Bennu could hit Earth when its estimated trajectory passes between the Earth and the moon in 2135, because Earth's own gravity will impact the rock's orbit, according to Dante Lauretta, professor of planetary science at Arizona University.
NASA has concluded that the possibility of Earth being hit by Bennu may be just 1 in 2,700. But experts estimate that the impact would be about 80,000 times more powerful than that of the atomic bomb that destroyed Hiroshima, Japan, at the end of World War II.