OSIRIS-REx, NASA's Mission to Asteroid Bennu

Facts Worth Sharing

  • NASA’s OSIRIS-REx spacecraft will return a sample of asteroid Bennu to Earth in 2023.
  • Asteroids, comets, and other small worlds are leftover planet-building materials from the birth of our solar system. Some may have brought water and the building blocks of life to Earth.
  • Sample return is important because certain kinds of scientific experiments can only be done on Earth. OSIRIS-REx's samples will help us understand the solar system's early days.

Why We Need OSIRIS-REx

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 carbon-containing materials called 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 see what our infant solar system was like. Bennu is a near-Earth asteroid containing carbon and water. 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 need is a sample, so OSIRIS-REx—a backronym that stands for Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer—will bring us one in 2023. The spacecraft launched in September 2016, arrived at Bennu in December 2018, and successfully collected a sample in October 2020.

OSIRIS-REx will also help us learn more about defending our planet from dangerous asteroids. 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 will study one of these forces, called the Yarkovsky effect.

In 2013, The Planetary Society, University of Arizona, and MIT held a naming contest for asteroid Bennu, which until then had been called 1999 RQ36. 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!

The OSIRIS-REx mission is projected to cost $1.16 billion over 15 years. The Planetary Society has 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 Works

OSIRIS-REx is a van-sized spacecraft weighing more than 2 metric tons, with half of that weight in fuel. It has a 3-meter-long sample arm and solar panels that fold back, giving 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 high-fived 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 collection chamber. The operation was so successful, a flap on the sample collection chamber was jammed open by asteroid material! 

OSIRIS-REx will leave Bennu in May 2021 and return to Earth in 2023, where it will drop the sample collection capsule into our planet’s atmosphere. The capsule will land via parachute in the Utah desert.

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

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