Little pieces of the 4.5 billion-year-old Asteroid Bennu are saying a whole lot about the history of the solar system. As the first asteroid samples to return to the U.S. for research, particles from Bennu have begun to paint a sweeping picture of the circumstances surrounding the asteroid’s formation while our solar system was still taking shape.
A trio of studies, published in Nature Astronomy and Nature Geoscience, on the Bennu samples have revealed new details about the asteroid, chronicling its action-packed past full of collisions and chemical reactions. Each of the three studies builds upon a different facet of Bennu’s history: where and how it formed, why it’s so water-rich, and what has caused its battered surface.
Bringing Bennu’s Samples Back to Earth Asteroid Bennu, more formally known as 101955 Bennu, is a near-Earth asteroid that just so happened to have the perfect conditions for sample collection. According to NASA, three factors made Bennu the ideal target: proximity to Earth, the right size and spin rate, and a carbon-rich composition.
NASA set out to retrieve samples from Bennu — which makes a close approach to Earth every six years — with its OSIRIS-REx mission, launched in 2016. After arriving on Bennu in 2018 and successfully collecting a sample in 2020, the spacecraft delivered the sample to Earth in 2023. Since then, scientists have been hard at work scrutinizing Bennu’s particles.
Read More: NASA Finally Gets At Its Bits of Bennu
Splitting From a Parent Asteroid The first of the three new studies has an answer to explain where Bennu came from. Bennu actually consists of fragments that split from a larger “parent” asteroid following its collision with another asteroid, likely in the asteroid belt between the orbits of Mars and Jupiter. The parent asteroid itself was a patchwork of materials from all across space: some were sourced near the Sun, while others came from faraway stars.
“Bennu’s parent asteroid may have formed in the outer parts of the solar system, possibly beyond the giant planets, Jupiter and Saturn,” said lead author Jessica Barnes, a professor at the University of Arizona’s Lunar and Planetary Laboratory, in a statement. “We think this parent body was struck by an incoming asteroid and smashed apart. Then the fragments re-assembled and this might have repeated several times.”
Researchers identified various materials by analyzing the samples’ isotopes. This allowed them to find an abundance of stardust, material predating the Solar System. The materials also suggest that Bennu may have emerged in the same region of space as Ryugu, a similar asteroid that has also been the subject of sample-return missions.
Chemical Reactions and Constant Collisions The second study, published in Nature Geoscience, determined that the minerals in Bennu’s parent asteroid were largely impacted by interactions with water.
The parent asteroid may have gathered a lot of icy material from the outer Solar System, which eventually melted. Silicate minerals then would have reacted with the water, a process driven by heat that either stemmed from the asteroid’s initial formation or a combination of later collisions and the decay of radioactive elements inside it.
“Now you have a liquid in contact with a solid and heat — everything you need to start doing chemistry,” said lead author Tom Zega, director of the Kuiper-Arizona Laboratory at U of A, in the press release. “The water reacted with the minerals and formed what we see today: samples in which 80% of minerals contain water in their interior, created billions of years ago when the solar system was still forming.”
The third study, also published in Nature Geoscience, concluded that Bennu has been facing a sustained session of space weathering.
The researchers observed microscopic craters and signs of once-molten rock on the surfaces of Bennu’s particles, suggesting that the asteroid has endured many micrometeorite impacts while also being whittled by solar wind. And unfortunately for Bennu, the lack of a protective atmosphere leaves it defenseless against space weathering.
The three studies demonstrate that Bennu offers a window into the early Solar System, helping scientists reach back billions of years in the past.
Read More: Basic Building Blocks of Life Found on Asteroid Bennu
Article Sources Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
NASA. Bennu Nature Astronomy. The variety and origin of materials accreted by Bennu’s parent asteroid Nature Geoscience. Mineralogical evidence for hydrothermal alteration of Bennu samples Nature Geoscience. Space weathering effects in Bennu asteroid samples
https://www.discovermagazine.com/tiny-particles-reveal-asteroid-bennu-s-origin-story-from-the-beginning-of-the-solar-system-47959
