An Asteroid with Ancient Stardust and Interstellar Traces
The Bennu asteroid, known for its proximity to Earth, is a time capsule of sorts. It contains stardust that predates our solar system and carries organic materials and ices that originated from interstellar space. Analyses of samples from this asteroid have started to shed light on its composition.
These samples were obtained during an ambitious mission which involved a spacecraft flying close to Bennu, momentarily landing on its surface, and gathering samples. Scientists have been meticulously studying these samples since they made their way back to Earth.
The discoveries from these studies are offering unprecedented insights into the conditions that existed in the universe before the formation of our solar system around 4.6 billion years ago. They are also revealing more about the parent body that gave birth to the Bennu asteroid, which measures nearly 500 meters in diameter.
A Glimpse into a Turbulent Past
One of the studies suggests that Bennu's progenitor was a part of a violent cosmic collision. This ancient body, it seems, was a veritable mix of materials from a variety of environments, ranging from areas close to the sun to regions far from the sun within our solar system, and even beyond our solar system in interstellar space.
How do scientists know this? They were able to identify these different origins by studying isotopes, or variations of elements, present in the samples of Bennu's dust. Isotopes that originated in the solar system had a different composition than those that came from interstellar stardust.
These materials were transported over great distances to the region where Bennu's parent asteroid formed. The parent asteroid is believed to have formed in the outer solar system, possibly beyond the orbits of Jupiter and Saturn. However, a cataclysmic event disrupted this asteroid's existence. An incoming asteroid is believed to have struck it, shattering it into fragments. Over time, these fragments reassembled multiple times, with some of the surviving materials eventually forming Bennu.
Comparing Bennu with Other Celestial Bodies
Another study examined Bennu in comparison with primitive meteorites and another asteroid named Ryugu, from which samples were collected by a different space mission. The parent asteroids for Ryugu, Bennu, and the meteorites seem to have originated in a similar, distant region of the early solar system.
However, Bennu's composition shows some differences, suggesting that the region evolved over time or did not mix as thoroughly as previously thought. Particularly, materials from Bennu's parent asteroid underwent significant changes upon interacting with water.
Bennu's parent asteroid accumulated ice and dust. Over time, the ice melted, and the resulting liquid reacted with the dust, resulting in 80% of the sample being composed of water-containing minerals. This transformation likely occurred due to the parent asteroid accumulating icy material from the outer solar system and subsequent exposure to heat, which melted the ice and caused the liquids to react with solids.
Signs of Microscopic Collisions
The third study focused on the evidence of micrometeorites hitting Bennu. These tiny rocks left behind small craters and "impact melts" - fragments of rock that used to be molten - on the surfaces of the sample. Traces of the solar wind, a constant stream of particles emanating from the sun, were also found in the samples.
This suggests that Bennu's surface is weathering at a much faster rate than previously thought, with impact melting being the dominant mechanism. Despite Bennu not hosting life, these studies could potentially aid scientists in understanding how life emerged on our planet.
