Scientists find fragments of one asteroid on the surface of another

Scientists have found pieces of asteroid Vesta on asteroid Bennu's surface.

Why it matters: The new finding — detailed in the journal Nature Astronomy — gives researchers some insight into the origins of Bennu, a space rock that's actually a collection of rubble that came together after a huge collision, NASA said.

How it works: Scientists found evidence of the rocks from Vesta in photos taken by OSIRIS-REx, a spacecraft in orbit around Bennu now.

• The Vesta boulders contain a mineral known as pyroxene that's produced in high heat and likely didn't come from Bennu.
• "Our leading hypothesis is that Bennu inherited this material from its parent asteroid after a vestoid (a fragment from Vesta) struck the parent," NASA's Hannah Kaplan said in a statement.
• That parent asteroid was then broken apart and eventually some of its material — including those bits of Vesta — coalesced into Bennu, Kaplan added.

The big picture: The asteroid belt is a messy place. Asteroids often show signs of interactions with one another. Vesta, for example, has dark material on the walls of its craters that is thought to come from another object.

• Scientists think Bennu — which now has an orbit similar to Earth's — came from the inner part of the main belt of asteroids between Jupiter and Mars.
• "There are two inner Main Belt asteroid families (Polana and Eulalia) that look like Bennu: dark and rich in carbon, making them likely candidates for Bennu's parent," NASA said.

What's next: OSIRIS-REx is expected to touch down on Bennu next month to collect a sample that will be delivered back to Earth in 2023.