With rubble from an asteroid tucked inside, a NASA spacecraft has fired its engines and began the long journey back to earth, leaving the ancient space rock in its rearview mirror.
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The trip home for the robotic prospector, Osiris-Rex, will take two years.
Osiris-Rex reached asteroid Bennu in 2018 and spent two years flying near and around it, before collecting rubble from the surface.
The University of Arizona's Dante Lauretta, the principal scientist, estimates the spacecraft holds between 200 grams and 400 grams of mostly bite-size chunks.
It will be the biggest cosmic haul for the US since the Apollo moon rocks. While NASA has returned comet dust and solar wind samples, this is the first time it's gone after pieces of an asteroid. Japan has accomplished it twice, but in tiny amounts.
Osiris-Rex was already nearly 300 kilometres from the solar-orbiting Bennu when it fired its main engines Monday afternoon for a fast, clean getaway.
Scientists hope to uncover some of the solar system's secrets from the samples vacuumed last October from Bennu's dark, rough, carbon-rich surface. The asteroid is an estimated 490 metres wide and 4.5 billion years old.
Bennu - considered a broken chunk from a bigger asteroid - is believed to hold the preserved building blocks of the solar system. The returning pieces could shed light on how the planets formed and how life arose on earth.
Although the asteroid is 287 million kilometres away, Osiris-Rex will put another 2.3 billion kilometres on its odometer to catch up with earth.
The SUV-size spacecraft will circle the sun twice before delivering its small sample capsule to Utah's desert floor on September 24, 2023, to end the mission. It launched from Cape Canaveral in 2016.
Australian Associated Press
