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NASA's asteroid-sampling mission will bid farewell to asteroid Bennu today

After more than two years circling a lumpy space rock called Bennu, it's finally time for NASA's OSIRIS-REx spacecraft to head back to Earth with a full load precious cargo: pieces of an asteroid.

OSIRIS-REx (known formally as Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer) collected asteroid samples from Bennu in October. Now it's time to bring those samples home to laboratories on Earth for scientists to study to understand how asteroids, and our solar system, formed.

If all goes as planned, OSIRIS-REx will head for home today (May 10) at about 4 p.m. EDT (2000 GMT); mission team members are expecting to receive confirmation about 16 minutes later that the spacecraft's thrusters began to fire. NASA will broadcast live coverage from mission control, including new images from the spacecraft's final pass over Bennu, today beginning at 4 p.m. EDT. You can watch live here at Space.com courtesy of NASA or watch the agency's coverage directly.

Related: NASA asteroid probe is overflowing with space-rock samples

NASA launched the $800-million mission in 2016 as the first U.S. asteroid sample-collection mission. The probe, which follows two successful Japanese missions to sample asteroids, collected more than 2.1 ounces (60 grams) of samples from Bennu in the fall of 2020. OSIRIS-REx will deliver that material in 2023. 

But first, the spacecraft must leave Bennu.

To do that, OSIRIS-REx will fire its thrusters for about seven minutes today in order to change its speed by nearly 600 mph (1,000 kph), according to a NASA statement. All told, the long journey home will cover about 1.4 billion miles (2.3 billion kilometers), since OSIRIS-REx must circle the sun twice to get from Bennu to Earth.

The maneuver should put the spacecraft on course to intersect with Earth's orbit, dropping its sample capsule in Utah on Sept. 24, 2023. The main spacecraft may be sent onto a new destination — in particular, its trajectory aligns conveniently for a visit to the large near-Earth asteroid Apophis in 2029, mission scientists have realized.

Meanwhile, NASA personnel will sweep in to pick up the space rock sample and bring it to NASA's astromaterials facility at the Johnson Space Center in Texas, which houses the agency's collection of moon rocks, meteorites and other celestial material.

Some studies of the material will begin right away; samples will also be preserved for future scientists to examine with new techniques that are developed. The collection of Bennu pieces will be NASA's largest delivery of solar system material since the Apollo astronauts' moon-rock souvenirs, according to the agency.

Today's departure maneuver occurs just months after a similar asteroid-sampling mission launched by Japan called Hayabusa2 landed its own capsule full of space rocks last December. Unlike OSIRIS-REx, that spacecraft sampled its asteroid target, Ryugu, multiple times during its visit.

Email Meghan Bartels at mbartels@space.com or follow her on Twitter @meghanbartels. Follow us on Twitter @Spacedotcom and on Facebook.

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Meghan Bartels
SPACE.COM SENIOR WRITER — Meghan is a science journalist based in New York City. She joined Space.com in July 2018, with previous writing published in outlets including Newsweek and Audubon. Meghan earned an MA in science journalism from New York University and a BA in classics from Georgetown University, and in her free time she enjoys reading and visiting museums. Follow her on Twitter at @meghanbartels.