Asteroid Bennu looks like a hard, wild world. It is covered with many big rocks, not smooth sand. When NASA’s OSIRIS-REx spacecraft arrived at Bennu in 2018, scientists were surprised. Earlier heat data from Earth had suggested a softer, smoother surface, more like a sandy beach. But Bennu was rough almost everywhere. OSIRIS-REx later took a sample in October 2020 and returned it to Earth on September 24, 2023, so scientists could study the rocks closely. (science.nasa.gov)

Now NASA says the mystery is finally clearer. In a March 17, 2026 report, scientists explained that Bennu’s rocks are not just porous, with many tiny empty spaces. They are also full of cracks inside. These cracks were the missing clue. Because of the pores and cracks, heat does not move well through the rocks. So even large boulders can heat up and cool down quickly. From far away, that quick heat change made Bennu look as if it had lots of fine sand, even though its surface is actually full of boulders. (science.nasa.gov)

This is why Bennu seems so “bumpy.” Its rocks are weak, broken, and easy to damage, not strong like one solid block. X-ray scans of the returned sample showed different kinds of crack patterns inside the particles. Computer models based on those scans finally matched the heat data seen by the spacecraft. In other words, Bennu’s rough face and its strange heat behavior can both be true at the same time. (science.nasa.gov)

That makes Bennu even more interesting. It is a small near-Earth asteroid, but it can teach us how asteroid surfaces change over time. NASA says this work also helps scientists understand telescope data better when they study other asteroids from far away. A rough asteroid may not always be made of strong rock. Sometimes, like Bennu, it is a pile of cracked, fragile stone with a very long story inside. (science.nasa.gov)