OSIRIS-REx
The largest asteroid sample ever returned, full of salts, water-formed minerals and life's building blocks.
Key facts
- Agency
- NASA (United States)
- Type of mission
- Asteroid sample return
- Target
- Asteroid 101955 Bennu
- Launched
- 8 September 2016
- Samples returned
- 121.6 g of rock and dust
- Status
- Samples returned 2023; spacecraft continuing as OSIRIS-APEX
OSIRIS-REx arrived at the near-Earth asteroid Bennu in December 2018. Bennu is about 490 metres wide, dark and spinning-top shaped, and it surprised everyone: instead of smooth fields of fine gravel, it was strewn with boulders, and it threw small pebbles off into space from time to time.
The sample
On 20 October 2020 the spacecraft reached down with its arm to a crater called Nightingale and fired a burst of nitrogen gas to stir up the surface. The sampling head sank into the ground far more easily than expected, showing that Bennu's surface is as loose as a pit of plastic balls. So much material was collected that some leaked out before the lid was closed.
The capsule landed in the Utah desert on 24 September 2023 with 121.6 grams of rock and dust, the largest sample ever brought back from an asteroid.
What it found
Bennu's grains are closely related to the CI and CM chondrites. They contain clays, magnetite, carbonates and phosphates, including a rare magnesium–sodium phosphate. They also contain salts left behind when salty water evaporated inside Bennu's parent body, including sodium carbonates and other minerals that have never been seen in meteorites, which may be too delicate to survive in Earth's damp air.
The organic chemistry is rich: 14 of the 20 amino acids that life on Earth uses to build proteins, all five of the bases used in DNA and RNA, and abundant ammonia.
What next
The spacecraft, renamed OSIRIS-APEX, is on its way to the asteroid Apophis, arriving in 2029.
Key dates
| Date | What happened |
|---|---|
| 8 September 2016 | OSIRIS-REx launched on an Atlas V rocket. |
| 3 December 2018 | Arrived at the asteroid Bennu. |
| 31 December 2018 | Entered orbit around Bennu, the smallest body ever orbited by a spacecraft. |
| 20 October 2020 | Touched down at the Nightingale site and collected a sample. |
| 10 May 2021 | Left Bennu for Earth. |
| 24 September 2023 | The sample capsule landed in Utah with 121.6 g of material. |
See where this mission fits among all the others in the mission timeline.
Did you know?
If the spacecraft had stayed in contact with Bennu's surface a little longer, its sampling head would have kept sinking: the ground behaved almost like a fluid.
Bennu has a small chance of hitting Earth late in the 22nd century, about 1 in 2,700, which is why its orbit is studied so carefully.