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NASA’s asteroid probe just found something unexpected

Published Sep 21st, 2020 7:26PM EDT
bennu asteroid
Image: NASA/Goddard/University of Arizona/Lockheed Martin

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  • Scientists studying the asteroid Bennu have discovered parts of a different asteroid on its surface.
  • Bennu has chunks of the asteroid Vesta on its surface, and researchers can only guess as to how they got there.
  • NASA’s OSIRIS-REx spacecraft has been orbiting Bennu for months.

NASA’s OSIRIS-REx asteroid probe has been orbiting the large space rock known as Bennu for many months now. It’s been studying its surface, planning and testing its ability to grab a sample of its surface material, and just generally enjoying its time with the big weird rock.

Now, in a somewhat unexpected discovery, it seems as though the asteroid Bennu has bits of another asteroid on its surface. How they got there is anyone’s guess, but the discovery is giving scientists a slightly better understanding of how certain asteroids form. Bennu, it seems, is a big old “rubble pile” according to NASA.

NASA scientists believe that Bennu is the end result of a massive collision between two objects. The loose material leftover from the crash collected into a ball, which then drew more and more debris thanks to the pull of gravity, eventually forming the asteroid we see today. Bennu’s incredibly dirty, debris-strewn surface is a great hint that the asteroid has messy insides as well.

NASA has studied the asteroid Vesta in depth. It’s a large rock in the asteroid belt between Mars and Jupiter, and parts of it have even fallen to Earth. The Bennu research team managed to find parts of Vesta on Bennu’s surface, but how exactly did they end up there? NASA has a theory.

“Our leading hypothesis is that Bennu inherited this material from its parent asteroid after a vestoid (a fragment from Vesta) struck the parent,” Hannah Kaplan of NASA’s Goddard Space Flight Center said in a statement. “Then, when the parent asteroid was catastrophically disrupted, a portion of its debris accumulated under its own gravity into Bennu, including some of the pyroxene from Vesta.”

Okay, so Bennu didn’t hit Vesta, but rather collected material from a collision between a chunk of Vesta and a separate body. That’s just a theory, of course, but it appears to be the most plausible one at the moment.

Apparently, this kind of cross-contamination is common across many different asteroids. As NASA explains:

Observations reveal it’s not unusual for an asteroid to have material from another asteroid splashed across its surface. Examples include dark material on crater walls seen by the Dawn spacecraft at Vesta, a black boulder seen by the Hayabusa spacecraft on Itokawa, and very recently, material from S-type asteroids observed by Hayabusa2 at Ryugu. This indicates many asteroids are participating in a complex orbital dance that sometimes results in cosmic mashups.

This begs the question as to whether surface samples from these asteroids will be entirely useful if they’re tainted with material from other space rocks. Still, having the material on Earth to study will surely yield some new discoveries.