Latest Research Reveals The Complex History Of Asteroid Bennu

Image of Asteroid Bennu superimposed to artist's impression of OSIRIS-REx. NASA/Goddard Space Flight Center/University of Arizona/IFLScience

NASA’s OSIRIS-REx is gearing up for its historical touchdown on Asteroid Bennu in a few weeks. Now, researchers have released six new papers, providing the most comprehensive understanding of the space rock to date.

On October 20, the OSIRIS-REx spacecraft will fly down to the surface of the asteroid to grab a sample in a crater nicknamed Nightingale. As reported in one of the three Science papers, scientists have discovered bright veins of minerals with a distinct infrared absorption in the crater, which the team believe are carbonate minerals.

If confirmed, this idea implies that the parent body of Bennu had flowing water and hydrothermal activity, since that’s how carbonates form. This could have lasted for thousands to millions of years. In addition, these minerals are likely common to other minor bodies in the solar system. It's possible many planetoids in the early solar system produced these hydrothermal alterations.

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Map of Bennu's surface (+/- 80 deg of latitude and 360 deg of latitude). The map shows the absorption attributable to carbon-bearing material from blue (little absorption) to red (deeper absorption features). Simon et al., Science (2020)]

And it’s not just carbonates, there are many other carbon-bearing materials across the surface of Bennu. In a second paper, researchers have shown that organic substances as well as carbonates are the rule rather than the exception on Bennu. In a third paper, researchers describe just how much the asteroid has changed, undergoing a complex evolution over billions of years.

Three other papers were also released in Science Advances and focus on Bennu as a whole. Researchers produced the most accurate 3D model of the asteroid with a resolution down to 20 centimeters (7.8 inches), as well as false-color images that highlight the subtle differences in the surface. They also show the location of the material that probably originated on the asteroid Vesta, the second-largest body in the asteroid belt. The map shows that the southern hemisphere is rounder and smoother, while the northern hemisphere is slopier and more irregular.

Another paper looked at the properties of Bennu's surface boulders. The asteroid is, after all, a big pile of rubble held together by very weak gravity. The data shows there are two main types of boulders that look different but have roughly the same composition.

False-color Red-Green-Blue (RGB) composites of asteroid Bennu in 3D. Bluer than average terrain looks blue, surfaces that are redder than average appear red. Bright green areas correspond to the instances of pyroxene, which likely came from a Vesta. Black areas near the poles indicate no data. NASA/Goddard/University of Arizona

Gravity is the subject of the final paper. By tracking small particles moving around Bennu, the team was able to map its gravitational pull with great precision and found that the asteroid's rubble is not evenly distributed. Bennu is less dense at the equator and in its center. This could be due to a very fast original rotation or due to its surface being disrupted in a dramatic fashion.

Next for this asteroid is OSIRIS-REx's sample collection and then another year of observations. The NASA spacecraft will then fly back towards Earth, where it will deliver its precious cargo in 2023. This will be the third asteroid sample after the two Japanese Hayabusa missions.

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