OSIRIS-REx, NASA's sample return mission to asteroid Bennu


  • OSIRIS-REx collected a sample of Bennu in 2020 and returned it to Earth in September 2023.
  • Asteroids like Bennu are very old and may have brought water and the building blocks of life to ancient Earth.
  • We need sample return missions because some lab experiments can only be done on Earth.

Why did we collect a sample from asteroid Bennu?

Our Solar System is filled with countless asteroids, comets, and other small worlds left over from the disk of dust and gas that formed the planets 4.5 billion years ago. We think some of these worlds slammed into early Earth, bringing water and organics here that formed the basis of life as we know it.

On Earth, weather and geological processes constantly alter the surface. But that's not the case on asteroids, which have remained largely unchanged. By studying them, we can see what our infant Solar System was like.

Although modern spacecraft instruments can tell us a lot about other worlds, there are certain kinds of experiments that can only be done on Earth.

What we really needed was a sample, so OSIRIS-REx — which stands for Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer — returned one to Earth in 2023. The spacecraft launched in September 2016, arrived at Bennu in December 2018, and successfully collected a sample in October 2020. It returned the sample to Earth in September 2023. The samples were found to contain both water and carbon — key ingredients that helped life begin on Earth.

Bennu bits in the OSIRIS-REx sample collector
Bennu bits in the OSIRIS-REx sample collector A view of the outside of the OSIRIS-REx sample collector. Sample material from asteroid Bennu can be seen on the middle right. Scientists have found evidence of both carbon and water in initial analysis of this material. The bulk of the sample is located inside.Image: NASA/Erika Blumenfeld & Joseph Aebersold

What is OSIRIS-REx doing now?

After dropping off the sample collection capsule containing material from Bennu, the OSIRIS-REx spacecraft diverted away from Earth. Its eventual goal is the potentially hazardous near-asteroid Apophis. On April 13, 2029, Apophis will pass closer to Earth than our geostationary satellites, at a distance of 30,600 kilometers (19,000 miles) from the Earth. The OSIRIS-REx spacecraft will spend 18 months studying the asteroid up close and has taken on a new mission name, OSIRIS-APEX, short for OSIRIS-Apophis Explorer.

How much does OSIRIS-REx cost? 

The OSIRIS-REx mission is projected to cost $1.16 billion over 15 years. We have additional context to help you fully understand this number.

Asteroid Bennu
Asteroid Bennu This mosaic of asteroid Bennu was created using 12 separate images captured in December 2018 by NASA's OSIRIS-REx spacecraft.Image: NASA/Goddard/University of Arizona/Edited by The Planetary Society

How OSIRIS-REx worked

OSIRIS-REx is a van-sized spacecraft weighing more than 2 metric tons, with half of that weight in fuel at launch. It has a 3-meter-long (10-foot-long) sample arm and solar panels that fold back, which gave it extra room to maneuver near Bennu’s surface and protect it from debris kicked up during sample collection. The spacecraft's small instrument deck is packed with science gear to study Bennu’s composition, map the surface, and more.

Upon arrival, OSIRIS-REx found that Bennu was much rockier than expected, with no areas that met the mission's original safety criteria for collecting a sample. Fortunately, the spacecraft navigates with high precision, comparing the view from its cameras to stored images of Bennu’s landscape. This allowed scientists to settle on a sample location no larger than a few parking spaces.

In October 2020, OSIRIS-REx collected a sample by high-fiving Bennu with a cylindrical device called TAGSAM at the end of its sample arm. Upon touching the asteroid, TAGSAM fired a blast of nitrogen gas into the surface, stirring rocks and soil into a small collection chamber. The operation was so successful, that a flap on the sample collection chamber was jammed open by asteroid material.

What did OSIRIS-REx teach us about defending Earth from asteroids? 

Bennu is a near-Earth asteroid, meaning its orbit carries it close to Earth. Small worlds like Bennu, which is just 500 meters (a third of a mile) across, can have their orbits altered by small forces like heat emission in ways we don’t fully understand. These forces can add up over time and mean the difference between an asteroid missing Earth or slamming into it. OSIRIS-REx studied one of these forces, called the Yarkovsky effect.

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OSIRIS-REx touches Bennu NASA's OSIRIS-REx spacecraft successfully collected a sample from asteroid Bennu on October 20, 2020.Video: NASA Goddard

Planetary Society involvement

We helped name asteroid Bennu!

In 2013, The Planetary Society, the University of Arizona, and MIT held a naming contest for OSIRIS-REx's target asteroid, which was formally known as 1999RQ36. 9-year-old Michael Puzio won the competition with his proposed name Bennu, after a deity from ancient Egyptian mythology.

"Bennu was a large heron and the living symbol of Osiris. The winged OSIRIS-REx and its heron-like TAGSAM also evoke attributes of Bennu, as does the egg shape of the asteroid itself. Bennu means 'The Ascending One', 'to shine' and suits the NEO which will shine in our skies in 2023 at the return of OSIRIS-REx."

Mike Puzio and Bill Nye
Mike Puzio and Bill Nye Mike Puzio and Bill Nye at the launch of the OSIRIS-REx spacecraft.Image: Larry Puzio

We also collected names to travel aboard OSIRIS-REx through our Messages from Earth program. If you sent your name, you can look up your certificate here.

Sample collection is a very important tool for planetary scientists to study our Solar System. Find out how we're working to reduce the cost of sample collection with PlanetVac.

Academic resources

  • Lauretta, D. S., Balram-Knutson, S. S., Beshore, E., Boynton, W. V., Drouet d’Aubigny, C., DellaGiustina, D. N., Enos, H. L., Golish, D. R., Hergenrother, C. W., Howell, E. S., Bennett, C. A., Morton, E. T., Nolan, M. C., Rizk, B., Roper, H. L., Bartels, A. E., Bos, B. J., Dworkin, J. P., Highsmith, D. E., … Sandford, S. A. (2017). Osiris-Rex: Sample return from asteroid (101955) Bennu. Space Science Reviews, 212(1-2), 925–984.

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