Since its launch in September 2016, NASA’s OSIRIS-REx spacecraft has travelled nearly four billion kilometres across the solar system and back, visiting an asteroid named Bennu, collecting a sample and returning it to Earth.
At just 500 metres across, Bennu is about the same size as the length of five football fields, which makes it the smallest object ever to be orbited by a spacecraft.
OSIRIS-REx arrived back to Earth on 24 September 2023, releasing the capsule containing pieces of Bennu. The capsule entered Earth’s atmosphere and landed on the Utah Test and Training Range in Utah's West Desert.
Our team in Canberra and our two sister Deep Space Network stations around the world in Spain and the United States have been with the mission every step of the way and will continue to support OSIRIS on its extended mission to explore another asteroid, Apophis.
What was OSIRIS-REx doing while it was hanging out with Bennu?
OSIRIS-REx (which stands for Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer) took a little over two years to reach Bennu and then spent two-and-a-half-years performing a detailed study of the asteroid with every instrument it had available.
The spacecraft got its first glimpse of Bennu in August 2018 and started analysing the composition and structure of the carbonaceous asteroid. Once it entered orbit around the asteroid the OSIRIS mapped Bennu’s surface to find the best place to collect a sample.
The mission team had their work cut out for them as Bennu has an extremely rocky surface with lots of hazardous boulders. The team selected a collection site in what was thought to be a young crater meaning they could collect rocks and dust ‘recently’ exposed providing a pristine sample and insight into Bennu’s history.
On 20 October 2023 the robotic sample arm briefly touched the surface of Bennu collecting at least 60 grams of regolith (dirt and rocks). Completing its final flyover of Bennu in April 2021, OSIRIS-Rex started heading back home.
What’s so important about this rock?
Bennu is a 4.5 billion year old asteroid which may hold clues to life on Earth and importantly, information necessary for our future survival on this planet.
Images of Bennu appear to show that it’s a ‘rubble pile’, a collection of rocks and boulders that have accumulated under gravity over billions of years, and scientists are hopeful that they’ll find water-bearing minerals that contain organic compounds, which are the building blocks of life on earth.
Scientists are also learning more about the asteroid’s trajectory and its physical and chemical properties to gain critical insights into what to do to mitigate any future collision scenarios.
Bennu travels around the Sun every 1.2 years, and its path occasionally cross the Earth’s orbit. Given what astronomers know of the asteroid’s orbit, there is currently a 1 in 2700 chance that it could impact Earth in the mid to late 22nd century.
Bennu isn’t a ‘dinosaur-killer’ type asteroid, but could potentially cause significant damage if it were to blast through our atmosphere and hit anywhere on the planet.
Knowing more about asteroids like Bennu will help unlock the secrets of the formation of the early solar system, give further insights into the story of life on Earth, and provide greater knowledge to protect ourselves from potential threats from space.
What’s next for OSIRIS?
Now that it’s successfully returned the sample capsule, the OSIRIS spacecraft has a new target in sight. About 20 minutes after releasing the sample capsule, the spacecraft fired its engines to divert past Earth and is now on its way to asteroid Apophis. NASA’s Deep Space Network will continue to support this extended mission OSIRIS-APophis EXplorer (OSIRIS-APEX) which should encounter the roughly 370m diameter S-type asteroid in 2029.