Where did asteroid Bennu come from?

Uploaded on August 25, 2016

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Where did asteroid Bennu come from?

2016-08-25 - Will it hit the Earth someday? OSIRIS-REx presents a video that explores Bennu's past. (Credits: Canadian Space Agency, University of Arizona)

Female Speaker: Where did asteroid Bennu come from, and will it hit the Earth someday? Join the 3-2-1 science team as we explore Bennu’s solar system travels.

This is asteroid Bennu, the target of the OSIRIS-REx sample return mission. Mission scientists are using cutting-edge research to find out where Bennu’s from and where it’s going.

Bennu is called a Near Earth Object because it has an orbit that brings it close to Earth. Most asteroids aren’t very close to the Earth. They live in the asteroid belt between the orbits of Mars and Jupiter, but some asteroids like Bennu slip out of the asteroid belt and become Near Earth Objects.

A long, long time ago—scientists think about a billion years ago—Bennu wasn’t its own asteroid. It was part of a giant asteroid in the asteroid belt. Then another asteroid got in the way and after a big collision, all that was left of the giant asteroid was Bennu and a bunch of other fragments called a family. Those fragments slowly spread out because of the push of sunlight due to the Yarkovsky effect, until some of them, including Bennu, escaped the asteroid belt and headed toward the Earth. But Bennu’s family isn’t the only family in the asteroid belt. Lots of other nearby collisions created fragments that escaped with Bennu to become Near Earth Objects.

Scientists try to trace Bennu and other Near Earth Objects back to their families by matching three main characteristics:  orbit, colour and albedo, which measures surface brightness.

Bennu’s colour and albedo match those of several families in the asteroid belt. Of those families, the two whose orbits are most likely to send asteroids like Bennu toward the Earth are known for now as the new Polana and Eulalia families. Of those two, the new Polana family is more efficient at sending us Bennu-like objects, so scientists think Bennu came from the new Polana family.

After it escaped its family, Bennu’s orbit changed until it became a Near Earth Object. Bennu’s orbit makes it a potentially hazardous asteroid which could possibly threaten Earth one day. Scientists are tracking Bennu’s orbit, and they predict that it will come closer to the Earth than the Moon, in 2135, in about 200 years. This close approach will change Bennu’s orbit, making it difficult to predict where it will go next.

The OSIRIS-REx mission spacecraft will carefully measure the small deviations in Bennu’s orbit caused by the Yarkovsky effect and attempt to better predict the odds of an Earth impact in the future.

You can learn more about the OSIRIS-REx mission from the other videos in the 3-2-1 science series. 

This video is an OSIRIS-REx production. OSIRIS-REx is a partnership of the University of Arizona, NASA, Goddard Space Flight Centre and Lockheed Martin.

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