CAPE CANAVERAL, FLA. -- A NASA spacecraft left a mess at an asteroid when it grabbed a load of rubble last year for return to Earth, new pictures revealed Thursday.

The Osiris-Rex spacecraft made one final flyby of asteroid Bennu on April 7 to take photos of the disturbance left by October's sample collection.

A depression is visible where Osiris-Rex penetrated the asteroid's surface. Boulders were hurled by the pressurized nitrogen gas that was fired at the ground to churn up material for vacuuming, and by the spacecraft's getaway thruster. One 1-ton boulder was flung an estimated 40 feet (12 metres).

The Osiris-Rex team meticulously plotted the final flyover to ensure the best shots. The pictures were taken around noontime to avoid shadows and better see the changes on Bennu's rocky surface.

"These observations were not in the original mission plan, so we were excited to go back and document what we did," the University of Arizona's Dathon Golish said in a statement.

Osiris-Rex will depart Bennu's vicinity next month and head back toward Earth with its precious 2-pound (1-kilogram) sample load. It's due to arrive in 2023.

The solar-orbiting, carbon-rich asteroid is 182 million miles (293 million kilometres) from Earth. By studying pieces of it, scientists hope to better understand how our solar system's planets formed and how people should react if an asteroid endangers Earth.

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