A probe from the U.S. space agency NASA is scheduled later Monday to fire its thrusters and leave the orbit of the asteroid Bennu, beginning a two-year journey back to Earth, complete with samples from the asteroid’s surface.The Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer (OSIRIS-REx) is scheduled to fire its thrusters for about seven minutes, taking it out of the asteroid’s orbit and setting it on a homeward course.OSIRIS-REx first rendezvoused with the asteroid in 2018. Last October, the craft dropped to Bennu’s surface, sunk its “sampling head” 48.8 centimeters into the asteroid and simultaneously fired a pressurized charge of nitrogen gas to churn up surface material and drive it into its the collection chamber.After gathering what NASA believes to be about 60 grams of material, the probe lifted off and continued to orbit the asteroid.NASA said Monday’s departure sequence is the mission’s most significant maneuver since it arrived at Bennu in 2018. The spacecraft’s thrusters must change its velocity by 958 kilometers per hour to set it on a path to intersect Earth, expected in September 2023.The space agency said there is no direct path back to Earth for the probe, as it must travel to where the planet will be in the future. The course will require it to orbit twice around the sun, covering 2.3 billion kilometers before it will catch up with Earth.Last year, the Japanese Haybusa2 spacecraft successfully returned to Earth with samples it collected from the surface of the Ryugu asteroid. 
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