NASA's OSIRIS-REx Mission Reveals Surprising Structure of Asteroid Bennu

NASA's OSIRIS-REx mission has unveiled unexpected findings about the asteroid Bennu, which was initially thought to have smoother regions based on Earth-based observations. Upon arrival in 2018, scientists discovered a rugged landscape dominated by large boulders. Andrew Ryan, a scientist at the University of Arizona’s Lunar and Planetary Laboratory, noted, “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.”

NASA

The initial observations were perplexing, particularly when compared to data from NASA’s Spitzer Space Telescope, which indicated low thermal inertia, suggesting a surface that heats and cools rapidly. However, the presence of large boulders, which should retain heat longer, contradicted this expectation. To investigate further, Ryan's team analyzed rock samples collected from Bennu using various laboratory techniques. Their findings, published in *Nature Communications*, revealed that while the boulders are porous, they also contain extensive networks of cracks that contribute to heat loss.

NASA

To explore the thermal properties of these samples, researchers at Nagoya University employed lock-in thermography, a laser-based method that measures heat diffusion. Ryan remarked, “The thermal inertia measured in the lab samples turned out to be much higher than what the spacecraft's instruments had recorded.” This discrepancy prompted the team to scale their findings from small samples to larger boulders, utilizing X-ray computed tomography (XCT) scans conducted at NASA’s Johnson Space Center. These scans allowed scientists to visualize the internal structure of the samples without damaging them.

NASA

The analysis revealed that the boulders of Bennu are not only porous but also significantly cracked, providing a crucial piece of the puzzle regarding the asteroid's thermal behavior. Ron Ballouz, a scientist at the Johns Hopkins University Applied Physics Laboratory, emphasized the importance of these findings, stating, “We can finally ground our understanding of telescope observations of the thermal properties of an asteroid through analyzing these samples from that very same asteroid.”

NASA

The OSIRIS-REx mission has fundamentally altered the understanding of Bennu's structure and thermal properties, highlighting the complexity of asteroid surfaces. As researchers continue to analyze the samples returned to Earth, these insights may reshape future interpretations of asteroid characteristics based on remote observations.

NASA