WITH rubble from an asteroid tucked inside, a NASA spacecraft fired its engines and began the long journey back to Earth on Monday, leaving the ancient space rock in its rearview mirror. 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 last fall. The University of Arizona’s Dante Lauretta, the principal scientist, estimates the spacecraft holds between a half pound and 1 pound (200 grams and 400 grams) of mostly bite-size chunks. Either way, it easily exceeds the target of at least 2 ounces (60 grams).

 

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. Scientists described Monday’s departure from Bennu’s neighbourhood as bittersweet.

 

“I’ve been working on getting a sample back from an asteroid since my daughter was in diapers and now she’s graduating from high school, so it’s been a long journey,” said NASA project scientist Jason Dworkin. Added Lauretta: “We have gotten used to being at Bennu and seeing new and exciting images and data coming back to us here on Earth.” Osiris-Rex was already nearly 200 miles (300 kilometers) from the solar-orbiting Bennu when it fired its main engines Monday afternoon for a fast, clean get-away.