In October of last year, I shared my insights on the significance of sample return missions, with a particular emphasis on the OSIRIS-REx mission, which had returned samples from Asteroid Bennu the previous month. After more than six months, a paper detailing the initial findings from the analysis of the Bennu sample has been published; what it reveals is fascinating.
For a start, the amount of carbonaceous regolith sampled and returned to Earth is approximately 120 grams, twice the amount needed to meet the mission's science goals leading to potentially more findings as further research will be possible. Again, this sample represents material in pristine condition which haven't been contaminated by Earth's atmosphere or biosphere, unlike meteorites.
Very dark in appearance, the regolith is composed of lighter material scattered throughout as veins, with particle sizes ranging from sub-micron dust to a stone about 3.5 cm long. Similar to what was found on asteroid Ryugu, which had samples returned by the Japanese Hayabusa 2 mission, Bennu is composed of the most chemically primitive materials known, showing very different alterations than what took place on planets and other large planetary bodies.
As anticipated from the remote sensing of Bennu's surface during the spacecraft's orbit around the asteroid, minerals formed in the presence of water (hydrated phyllosilicates) and carbon-rich materials (carbonates and organic compounds) were discovered. Again, this supports the idea that asteroids were directly involved in delivering water and the building blocks of life to Earth.
Magnesium-sodium phosphates might suggest further chemical alterations due to water—it has been suggested that transient pockets of water exist beneath Bennu's regolith—while trace minerals can provide insights into how the asteroid evolved since its creation in the early solar system; Bennu, which currently has a semi-major axis of 1.1 AU, may have originated from a different location within our Solar System.
What I find particularly exciting is the detection of presolar grains—material created before our Solar System existed—which can provide information about the life of the previous star from which we emerged.
These discoveries, along with others as further analyses of the Bennu sample are conducted, will enhance our understanding of the conditions that prevailed in the early solar system and ultimately bring us closer to answering some of the most profound questions in science: where do we come from, and are we alone in the universe?
These results support the need for more sample return missions as low-density material rarely survives atmospheric entry or is free from contamination. The OSIRIS-REx mission continues as the spacecraft is now en route to asteroid Apophis where it will study the physical changes of the asteroid after its rare close encounter with Earth in 2029. This new mission, named OSIRIS-APEX, will not involve a sample return, but it demonstrates the resilience of modern space exploration efforts.
As always, upwards and onwards.
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