Bennu Surprise! The Asteroid Is Not What It Seems

Scientists are rarely surprised to learn that asteroids are not as they seem from a distance. The asteroid called Bennu, though, has handed them some soft, fluffy surprises.

By analyzing data gathered when NASA’s OSIRIS-REx spacecraft collected a sample from asteroid Bennu in October 2020, it turns out that the particles making up Bennu’s exterior are so loosely packed the spacecraft could have sunk deep into the asteroid if it had tried for a stable landing. Fortunately the thrusters were fired immediately as the sample was taken, backing the craft away.

“If Bennu was completely packed, that would imply nearly solid rock, but we found a lot of void space in the surface,” said Kevin Walsh, a member of the OSIRIS-REx science team.

Mission scientists have described the dramatic sample retrieval, which led to surprising discoveries about the asteroid’s nature, in two new studies. And the results aren’t just intriguing: The researchers say that the findings might have implications for a possible future deflection mission, should the 1,640-feet-wide (500 meters) Bennu (one of the riskiest known near-Earth asteroids) ever threaten to impact the planet.

The impact aftermath was so unexpected that Dante Lauretta, lead author of one of the two studies, campaigned for the spacecraft to revisit the area to understand what happened. Six months after sample collection, in April 2021, the researchers got another glimpse of the OSIRIS-REx touchdown site. They saw a 65 foot impact crater from a 15 second soft touchdown.

Now we understand the object is like a kids ball pit, soft and slippery, and not solid as it seems from distance.

Bennu’s soft, fluffy nature may complicate possible future deflections attempt, should astronomers ever determine the rock threatens to hit Earth. Currently its 200 million miles from Earth, and not a hazard at all. It’s also possible that asteroids like Bennu are so fragile that they will disintegrate in an atmosphere.

Asteroids can be made of solid metal, or in Bennu’s case, carbon compounds and water. Objects like Bennu may have brought amino acids and other life precursors to Earth.

OSIRIS-REx followed in the footsteps of Japan’s Hayabusa, which, in 2010, became the first spacecraft to bring a bit of an asteroid back to Earth. OSIRIS will return to Earth in 2023. Then head out again on a new mission to Apophis.

Bennu was discovered by the Lincoln Near-Earth Asteroid Research (LINEAR) project, which detects and tracks near-Earth objects, in 1999. It is named after the Bennu, the ancient Egyptian mythological bird associated with the Sun.

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David Raiklen

David Raiklen wrote, directed and scored his first film at age 9. He began studying keyboard and composing at age 5. He attended, then taught at UCLA, USC and CalArts. Among his teachers are John Williams and Mel Powel.
He has worked for Fox, Disney and Sprint. David has received numerous awards for his work, including the 2004 American Music Center Award. Dr. Raiklen has composed music and sound design for theater (Death and the Maiden), dance (Russian Ballet), television (Sing Me a Story), cell phone (Spacey Movie), museums (Museum of Tolerance), concert (Violin Sonata ), and film (Appalachian Trail).
His compositions have been performed at the Hollywood Bowl and the first Disney Hall. David Raiken is also host of a successful radio program, Classical Fan Club.