To Bennu and Back
By Robert Trevelyan
NASA spacecraft arrives at asteroid Bennu to collect samples that will tell us about the origin of life
After a 2 billion kilometre chase, NASA’s OSIRIS-REx spacecraft has finally caught up with the asteroid Bennu.
This image of asteroid Bennu is made from 12 PolyCam images collected on 2 December by OSIRIS-REx from a distance of 24 kilometers. Image: University of Arizona
The intrepid SUV-sized probe had been soaring through space for over 2 years. On 3rd December, a week after NASA landed its cousin on Mars, OSIRIS-REx reached its target: a giant, diamond-shaped rock with the diameter of the Empire State Building, floating 122 million kilometres from Earth. As of New Year’s Eve, the probe is now successfully orbiting Bennu.
NASA’s mission: to gather samples from the ancient asteroid and return them to Earth. Scientists hope that the space rocks will give us clues to how life started on our planet.
NASA Osiris-Rex mission launches towards asteroid Bennu
The operation had been brimming with risks. Following the triumphant arrival, principal investigator Dante Lauretta tweeted the OSIRIS team are “relieved, proud, and anxious to start exploring! To Bennu and Back!”
Subsequently, on New Year’s Eve, OSIRIS successfully entered Bennu’s orbit zone – not an easy feat. The craft moved at an agonising 10cm per second relative to the asteroid. Deputy principal investigator, Heather Enos, previously warned: “Manoeuvring around a small body that basically has no gravity is a very challenging endeavour. So we do have to get a little more information to proceed every step of the way.”
The asteroid is roughly 5% the mass of Mt. Everest, which sounds big, but in space-terms is actually pretty small, generating weak gravitational attraction. This means that the spacecraft’s orbit can be altered by the slightest touch – even by sunlight. The probe will have to travel in the ‘terminator’ zone, where day meets night, keeping solar radiation constant to avoid frazzling NASA’s hopes of a steady orbit.
Finally, after 18 months of circling the asteroid, OSIRIS will eventually swing down to Bennu’s rocky surface to collect the samples. A 3 metre long robotic arm will hoover up 60g of rocks and dust in 5 seconds, before the craft slingshots back to Earth along with its precious cargo.
As well as the origin of life, NASA expects the samples to tell us more about the make-up of asteroids, with a view to one day using the hydrogen and oxygen inside them as fuel for passing spacecraft.
OSIRIS’s time with Bennu is also likely to increase our understanding of the Yarkovsky effect: a mysterious non-gravitational force that can alter the orbit of an asteroid. It is hoped that shedding light on the phenomena will improve asteroid-impact forecasts.
So how long do we have to wait for these answers?
Well, OSIRIS is due to drop its samples back to Earth around 5 years from now, with the sample capsule touching down in Utah on September 24th 2023.
If that’s too long to wait for you, a similar Japanese mission is already underway on another asteroid, Ryugu, two times the size of Bennu. The samples will be smaller and may tell us less than the OSIRIS rocks, but they are scheduled to re-enter the atmosphere in 2020.
However, if you really can’t wait for fragments of Bennu to arrive, be careful what you wish for: The asteroid is calculated to pass very close to Earth in 150 years’ time. Too close some say, with a 1 in 2,700 chance that Bennu will actually collide with Earth.
But until then, scientists will enjoy OSIRIS-REx’s discoveries over the next few years. As Dante Lauretta declared in a statement: “The exploration of Bennu has just begun. The best times are ahead of us, so stay tuned!”
Article written by Robert Trevelyan
NASA’s OSIRIS-REx: Mission to Bennu (Video)
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