NASA's OSIRIS-REx mission has made history by returning samples from asteroid Bennu, shedding light on the potential building blocks of life beyond Earth. Collected from the ancient asteroid on October 20, 2020, and returned to Earth on September 24, 2023, the analysis of these samples has revealed the presence of amino acids, nucleobases, and various minerals known as evaporites, which are all key elements necessary for life.
According to Nicky Fox, associate administrator of NASA's Science Mission Directorate, "NASA's OSIRIS-REx mission already is rewriting the textbook on what we understand about the beginnings of our solar system." The mission aimed to explore the origins of life and how the early Earth might have shared conditions suitable for life, emphasizing the significance of the asteroid's samples.
The findings hinge significantly on the types of organic compounds and minerals found within the Bennu samples, which scientists from institutions like the Smithsonian's National Museum of Natural History and NASA's Goddard Space Flight Center have been studying rigorously. Among the discoveries, the researchers identified 14 different amino acids out of the 20 known to contribute to protein structure on Earth, alongside all five nucleobases—essential components for storing and transmitting genetic information. Daniel Glavin, co-lead author from NASA, acknowledged, "The clues we're looking for are so minuscule and so easily destroyed or altered from exposure to Earth's environment." Therefore, the pristine nature of these samples from space has been invaluable.
Another remarkable aspect of the analysis has been the detection of evaporite minerals, which suggest there were once water-rich environments on Bennu, conditions potentially conducive to the chemistry of life. Tim McCoy, curator of meteorites and another key researcher, remarked, "These papers really go hand in hand to explain how life’s ingredients actually came together to make what we see on this aqueously altered asteroid." The presence of salt minerals formed when water evaporated opens the discussion on how asteroids like Bennu could serve as delivery vehicles for life-sustaining compounds, possibly leading to the emergence of life elsewhere.
This past environment of Bennu is also worth exploring. Scientists believe the asteroid originated from a larger parent body formed during the early solar system billions of years ago. The floating dust and rock, unperturbed by significant changes for eons, has allowed surface materials to remain intact, providing insight no earthbound meteorite could. This historical perspective of the asteroid’s formation circles back to its rich chemistry, including high levels of ammonia—a compound known to play important roles in biological processes—alongside evidence of ancient brine solutions.
These recent discoveries are not just significant for Bennu. They stir questions about the potential for life elsewhere. Sean McMahon of the UK Centre for Astrobiology pointedly asked, "If these blocks of life on Earth came from extraterrestrial material, they could have also landed elsewhere in the Solar System." This aligns with the many theories surrounding the transfer of organic material across the cosmos, offering tantalizing possibilities about the origins of life on Mars or other moons.
Yet, with all the excitement of what has been learned, there remain mysteries. The presence of equal amounts of left- and right-handed amino acids within Bennu's samples raises questions about how life on Earth came to favor left-handedness exclusively. Jason Dworkin of NASA's Goddard remarked, "Why we, so far, only see life on Earth and not elsewhere, that's the truly tantalizing question."
With the samples analyzed and theories swirling, the OSIRIS-REx mission has set the stage for renewed exploration of life’s potential throughout the solar system. Having completed its first mission, OSIRIS-REx now transitions to the OSIRIS-APEX mission, which will visit asteroid Apophis after the close encounter with Earth expected in 2029.
The remarkable findings from Bennu continue to inspire both awe and curiosity, propelling humanity's quest to understand its own origins and the universe beyond.