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[Music]

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OSIRIS-REx was designed to retrieve
a sample

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from asteroid Bennu
and return it to Earth.

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So, of the more than 1 million
known asteroids

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in our solar system, why Bennu?

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First, as a near-Earth asteroid,
Bennu is easy to reach.

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It takes about 14 months to orbit
the Sun and comes close to Earth

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once every six years.

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To get there, OSIRIS-REx was launched
in 2016 on an Atlas V

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rocket with a single booster
and a Centaur upper stage.

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It also got a big assist from Earth's
gravity in 2017,

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allowing it to match Bennu's orbital tilt.

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The second reason that Bennu was
chosen was its size and spin rate.

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Bennu measures about half a kilometer
in diameter and rotates

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on its axis once every 4.3 hours,

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which is actually pretty slow
compared to many smaller asteroids.

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This allowed OSIRIS-REx to map
Bennu’s surface up close,

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and to match its velocity,
briefly touch down, and collect a sample.

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Before OSIRIS-REx arrived, scientists
thought that Bennu's slow rotation

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meant a low risk of flinging away
most of its sampleable material.

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But shortly after arrival,
Bennu was caught on camera ejecting

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hundreds of pebbles.

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It turns out that Bennu
regularly sheds small particles,

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but it still had plenty of loose material left
on its surface for sample collection.

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The third reason for choosing
Bennu was its composition.

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We don't know what ingredients
were present during the formation of life

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on Earth, but primitive asteroids
like Bennu serve

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as time capsules, preserving material
from the dawn of the solar system.

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Spectrometers on OSIRIS-REx
confirmed that 

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Bennu is rich in carbon-based
molecules,

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including organics
that are the stuff of life.

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When the Bennu sample is analyzed,
it will help scientists to better

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understand the formation
of the solar system and our own origins.

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So why this particular asteroid?

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Proximity to Earth, the right size
and spin, and a carbon-rich composition.

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That is why we chose Bennu.

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[Music]

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[Beeps]