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Scientists spot hints of flowing water on asteroid’s surface

Published Oct 12th, 2020 10:11PM EDT
bennu rivers
Image: NASA/Goddard/University of Arizona/Lockheed Martin

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  • The asteroid known as Bennu has revealed some tantalizing secrets to NASA’s OSIRIS-REx spacecraft.
  • Some rocks and surface features of the asteroid appear to indicate that water once flowed on its surface or that of its parent asteroid.
  • NASA’s asteroid probe will begin its return journey to Earth in December and arrive back to Earth in 2023.

Water is precious in the universe. It’s a vital ingredient for life as we know it, so discovering where it comes from, what kind of planets and other bodies have it, and how so much of it made its way to Earth is incredibly important if we’re to understand the origins of life on Earth.

Now, researchers studying the nearby asteroid Bennu have come to a rather startling conclusion: The massive space rock that NASA’s OSIRIS-REx spacecraft has been studying for a couple of years now may have once had rivers on it. Yes, rivers on an asteroid. That’s some seriously wild stuff.

Several new research papers that focus on Bennu and its history were recently published in both Science and Science Advances. They examine the discoveries that OSIRIS-REx has made thus far and attempt to paint a clearer picture of the space rock’s incredibly interesting history.

The discovery that water was likely present on the asteroid’s surface — or at least on the surface of Bennu’s larger parent asteroid that Bennu was a part of — was made thanks to the identification of minerals on its surface.

“Our recent studies show that organics and minerals associated with the presence of water are scattered broadly around Bennu’s surface, so any sample returned to Earth should contain these compounds and minerals,” Dr. Vicky Hamilton, a co-author of several of the new papers, said in a statement. “We will compare the sample’s relative abundances of organics, carbonates, silicates, and other minerals to those in meteorites to help determine the scenarios that best explain Bennu’s surface composition.”

Bennu has been called a “rubble pile” due to its incredibly rocky surface. The asteroid, which scientists thought might be somewhat smooth, turned out to be covered in debris and rocks of all sizes. Some of the larger rocks show evidence of minerals that hint at flowing water in the asteroid’s past.

“Boulders strewn about near the Nightingale site have bright carbonate veins,” Hamilton explains. “Bennu shares this compositional trait with aqueously altered meteorites. This correlation suggests that at least some carbonaceous asteroids were altered by percolating water in the early Solar System.”

The OSIRIS-REx mission isn’t quite done yet, as the spacecraft’s ultimate goal is to collect a sample of the asteroid’s surface and then return it all the way back to Earth. The spacecraft will depart Bennu in December of this year and will carry the material to Earth where it will arrive in late 2023.