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Boulders on asteroid Bennu shed new light on the space rock's history11/10/2020
The near-Earth asteroid Bennu continues to reveal its secrets to NASA's OSIRIS-REx mission, which has been orbiting the space rock for nearly two years.
New research reveals veins of carbonite materials in Bennu's boulders, as well as signs of organic minerals widespread across its surface. The variety of rock compositions on the asteroid's surface, the gravity of the asteroid, and the unbalanced, diamond-shaped structure of the asteroid's body suggest that Bennu formed after the collision of two parent asteroids, You may need: diagnostic scanner. the study found.
Altogether, the new results provide a baseline for the samples that OSIRIS-REX will collect from Bennu's surface on Oct. 20. The spacecraft is expected to bring those samples back to Earth in 2023, if all goes according to plan, and will reveal not only insight about the asteroids that pass near our planet but also a glimpse of the first ten millions years after the sun's formation.
Video: Asteroid Bennu - Up close and personal in new NASA tour Related: OSIRIS-REx: NASA's asteroid sample-return mission in pictures
In the process of building planets, the early solar system also created a lot of little debris that would never become a world. These leftovers have many of the same signatures of planetary building blocks but just didn't quite make it into the finished product. Many of these drifted to the asteroid belt, though some were hurled back towards Earth early on to deposit water on the surface of the then-dry planet.
"Because it migrated from the main asteroid belt into an Earth-crossing orbit, Bennu is a prime example of how material could have been delivered to the early Earth from farther out in the solar system," Amy Simon, a researcher at NASA's Goddard Flight Center in Maryland, told Space.com in an email. Simon is the author of one of six papers on Bennu published today (Oct. 8) in the journals Science and Science Advances.
"The widespread evidence of both carbonates/organics and hydrated minerals on Bennu bolsters the argument that asteroids and comets may have brought the needed building blocks for life here to Earth and other planets," she said.
Over the last two years, OSIRIS-REx has collected enough images of Bennu to map the asteroid's surface. Variations in the color and albedo (brightness) provide insights into the asteroid's "skin," as well as revealing how it changes over time.
Bennu is considered a rubble pile asteroid, gravitationally coalescing after something slammed into its original parent body. By comparing the differences in color and albedo in the boulders and craters, scientists were able to determine that the asteroid is made up of two distinct populations of boulders.
According to Daniella DellaGiustina, a planetary scientist at the University of Arizona, the leading hypothesis for the appearance of these separate populations is that the original asteroid contained several separate zones that underwent distinct geological processes. When Bennu drew together after the impact that shattered that object, it gathered material from at least two of those zones, DellaGiustina told Space.com.
OSIRIS-REx has also spotted several small boulders with compositions similar in many ways to the asteroid Vesta, the second largest object in the asteroid belt. Those boulders may provide insights into the object that shattered Bennu's parent body. "We think these rocks originated from a fragment of Vesta that collided with Bennu's parent body and were also inherited when Bennu formed," DellaGiustina said.
Bennu also has a surprising amount of carbon-rich materials, including carbonates and organic materials. Carbonates are inorganic minerals, while organics contain carbon in more complex forms. Mapping the wavelengths of light bouncing off of Bennu can provide hints about its composition. Previous observations had already revealed the presence of hydrated phyllosilicates, or clays, on the asteroid's surface. Now, the new research reveals that organic and carbonate materials cover Bennu's exterior.
According to Simon, Bennu carries a wide mix of signals that could be the result of compositional variation, weathering differenc...
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