NASA puts asteroid Bennu under the microscope | Space photo of the day for Aug. 29, 2025

Since its discovery in 1999, the near-Earth asteroid Bennu has captivated scientists as a time capsule from the early solar system — and also as a key to possibly understanding the origins of life.

To study the asteroid in depth, NASA launched the OSIRIS-REx spacecraft to Bennu. The probe collected samples in 2020 and returned them to Earth in 2023.

What is it?

Around a third of a mile (or 500 meters) wide at its middle, Bennu is full of carbon-bearing compounds and minerals that formed over 4.6 billion years ago. According to NASA, Bennu may have formed in the main asteroid belt between Mars and Jupiter before drifting closer to Earth.

Approximately every six years, Bennu is at its closest point to Earth in its orbit, around 186,000 miles (299,000 kilometers) from our planet. This accessible orbit made it the target of the OSIRIS-REx mission, which allowed scientists to study the chemistry, geology and history of the asteroid up close.

Where is it?

This scanning electron microscope image was taken at NASA’s Johnson Space Center in Houston, where some of the asteroid samples are being studied.

Why is it amazing?

Using scanning electron microscopes and other instruments, scientists have started to map out Bennu’s composition in detail. From their analyses, Bennu seems to be a blend of pre-solar stardust along with organic compounds likely forged in space. This suggests that Bennu’s parent body was composed of material sourced from various regions, possibly even beyond our solar system, before being assembled in the asteroid belt between Mars and Jupiter.

By microscopically studying Bennu, researchers have also been able to find that the asteroid’s geology has changed over the years due to interactions with water and ice. Bennu’s ancestor is believed to have contained significant amounts of ice, which melted and created chemical reactions that changed its minerals, resulting in a chemical composition in the asteroid sample with 80% water-containing minerals. These processes help astronomers understand how asteroids form and how their materials — including possible ingredients for life — may change over time before being delivered to Earth via impacts.

Want to learn more?

You can read more about the asteroid Bennu and NASA’s missions to study asteroids.