2018: Arrival at Bennu — A World Full of Surprises 

This week, we are recapping noteworthy OSIRIS-REx mission events each day so you can catch up on anything you may have missed so far in NASA’s first mission to collect a sample from an asteroid.  

(Post #2 in a series of four)

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After traveling 1.2 billion miles (2 billion kilometers) to Bennu, NASA’s OSIRIS-REx spacecraft arrived in December 2018 and began orbiting the asteroid. Until the spacecraft got to Bennu, we could only see the asteroid as a pixelated blob through Earth telescopes and radar measurements. Still, scientists had an idea of what they would find at Bennu by using years of radar and thermal measurements and computer models to predict its mass, shape, and surface features.  

On the left, a compilation of radar images of asteroid Bennu. On the right, a shape model based on radar imaging and visible light curves. CREDITS: Michael C. Nolan / Arecibo Observatory / CC BY-NC-ND 3.0

In early 2019, OSIRIS-REx began to study Bennu in detail. The spacecraft zigzagged Bennu in a trajectory that looked like a child’s sweeping crayon sketch. The first closeup images of the asteroid revealed surprises that would require scientists to update some of the fundamental assumptions used in their predictive computer models.  

Instead of there being a smooth, sandy beach on the surface that the mission team had expected to see, Bennu was littered with boulders and was spewing rock particles into space. It became clear that safely navigating to the surface would be an unexpected challenge. The mission team would spend most of the next year mapping Bennu in detail and looking for a relatively smooth area with the fewest hazards and the most opportunity to gather scientifically interesting samples. 

Learn more:

NASA’s OSIRIS-REx Spacecraft Arrives at Asteroid Bennu 

NASA’s OSIRIS-REx Spacecraft Enters Close Orbit Around Bennu, Breaking Record 

NASA Mission Reveals Asteroid Has Big Surprises 

Coming up tomorrow: “Choosing a Touchdown Site from a Sea of Hazards.” 

 — Lonnie Shekhtman