NASA Unravels Bennu's Rugged Surface Mystery

Asteroid's jagged surface explained by porous boulders and extensive crack networks

Mar. 18, 2026 at 12:12am

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NASA's OSIRIS-REx mission to the asteroid Bennu encountered a surprising landscape of large boulders and few smooth patches, contrary to earlier observations. Researchers analyzed samples from Bennu's surface using advanced techniques like X-ray computed tomography and found that the boulders are highly porous and riddled with extensive crack networks, explaining the asteroid's rapid heating and cooling.

Why it matters

Understanding the physical properties of asteroids like Bennu is crucial for future asteroid mining and deflection missions, as well as providing insights into the formation and evolution of our solar system. The unexpected findings from OSIRIS-REx challenge previous assumptions about asteroid surfaces and highlight the value of in-situ exploration.

The details

When the OSIRIS-REx spacecraft arrived at Bennu in 2018, scientists were surprised to find a surface covered in large boulders, rather than the smoother regions they had anticipated based on earlier observations. Measurements by NASA's Spitzer Space Telescope in 2007 had suggested Bennu had a low thermal inertia, indicating a sandy, beach-like surface. However, the boulders should have acted more like concrete, retaining heat longer. Analysis of samples returned to Earth revealed that the boulders are highly porous and contain extensive networks of cracks, which help explain the rapid heating and cooling observed on Bennu's surface.

  • NASA's OSIRIS-REx spacecraft arrived at asteroid Bennu in 2018.
  • NASA's Spitzer Space Telescope made observations of Bennu in 2007.

The players

Andrew Ryan

A scientist with the University of Arizona's Lunar and Planetary Laboratory in Tucson, who led the mission's sample physical and thermal analysis working group.

Scott Eckley

An X-ray scientist within NASA Johnson Space Center's Astromaterials Research and Exploration Science (ARES) division.

Nicole Lunning

The lead OSIRIS-REx sample curator within the Astromaterials Research and Exploration Science division at NASA Johnson.

OSIRIS-REx

NASA's asteroid sample return mission to the near-Earth asteroid Bennu.

Spitzer Space Telescope

A NASA infrared space observatory that made observations of asteroid Bennu in 2007.

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What they’re saying

“When OSIRIS-REx got to Bennu in 2018, we were surprised by what we saw. We expected some boulders, but we anticipated at least some large regions with smoother, finer regolith that would be easy to collect. Instead, it looked like it was all boulders, and we were scratching our heads for a while.”

— Andrew Ryan, Scientist, University of Arizona Lunar and Planetary Laboratory

“The sample goes into its own 'spacesuit,' gets a CT scan, and then comes back to its pristine environment, all without having any exposure to the terrestrial environment. We can image right through these airtight containers to visualize the shape and internal structure of the rock that's inside.”

— Nicole Lunning, Lead OSIRIS-REx Sample Curator, NASA Johnson Space Center

“X-ray computed tomography allows us to look at the inside of an object in three dimensions, without damaging it.”

— Scott Eckley, NASA Johnson X-ray Scientist

What’s next

Researchers will continue to analyze the Bennu samples returned by OSIRIS-REx to further understand the asteroid's composition and evolution.

The takeaway

The unexpected findings from the OSIRIS-REx mission to Bennu challenge previous assumptions about asteroid surfaces and highlight the value of in-situ exploration. The highly porous and cracked nature of Bennu's boulders provides new insights that will inform future asteroid mining, deflection, and solar system formation studies.