NASA's OSIRIS-REx mission is rewriting our story of how life might have emerged beyond Earth. Recent analyses of regolith samples returned from the asteroid Bennu are shedding light on the cosmic origins of life's building blocks.
After collecting samples from the asteroid Bennu, approximately 168 million kilometers from Earth, the OSIRIS-REx spacecraft parachuted back to Earth on September 24, 2023, landing safely in the Utah desert. The discoveries made from the samples have revealed significant insights, showing the presence of numerous organic molecules and minerals believed to be integral to the genesis of life.
The samples yielded 33 known amino acids, including 14 of the 20 protein-building amino acids utilized by life on Earth, and all five nucleobases—adenine, guanine, cytosine, thymine, and uracil—that make up DNA and RNA. "We have discovered the next step on the path to life," stated Tim McCoy, curator of meteorites at the Smithsonian National Museum of Natural History.
Dr. Daniel Glavin, senior scientist at NASA’s Goddard Space Flight Center, noted, "Having studied meteorites for 35 years, I thought we were going to learn about the earliest geologic history of our solar system. What we ended up finding was... about the earliest biologic history of our solar system, which is remarkable.”
The composition of the Bennu samples showed high concentrations of ammonia, about 75 times more than what was found on samples returned from the Japanese Hayabusa2 mission. This high concentration indicates the possibility of Bennu's parent body being formed under colder environments, allowing the ammonia ice to persist before moving closer to the sun where it sublimated.
The mission’s team took precautionary measures to preserve the asteroid material’s pristine state, ensuring minimal exposure to Earth's atmosphere or any terrestrial contaminants. They prepared what they called 'Bennu tea,' boiling the samples to extract organic compounds for analysis through mass spectrometry techniques.
Scientific analysis revealed the existence of sodium-rich brine involved with the formation of mineral salts, which hinted at the presence of ancient watery environments on Bennu. McCoy explained, "It was within those cracks [of Bennu’s parent body]... where the evaporation occurred. Water was lost to the surface, and these minerals were left behind.”
Reflecting on the significance of these findings, Nicky Fox, NASA's associate administrator for the Science Mission Directorate, stated, "This really is a groundbreaking scientific discovery,” emphasizing the ancient brines' role in holding organic molecules. He also cautioned against jumping to conclusions; the findings, fantastic as they are, do not prove life existed on Bennu itself.
Interestingly, results indicated the amino acids found have left- and right-handed forms, equally represented. This unexpected finding raises questions about the origin of molecular homochirality integral to life on Earth. "I felt like this had invalidated 20 years of research... but this is exactly why we explore,” said Glavin. The implication here is significant—while Earth relies predominantly on left-handed amino acids, primordial processes on other bodies could lead to different outcomes.
The similarities between the compounds of Bennu and those found on bodies like Ceres and Enceladus suggest the widespread nature of life's building blocks across the solar system. Mahjoub, planetary scientist at the Jet Propulsion Laboratory, remarked, “Salt-rich evaporites create environments ideal for preserving and concentrating organic molecules,” underscoring the astrobiological significance of such materials.
These findings are but the beginning. Approximately 70% of the Bennu samples are being preserved for future study, hinting at new discoveries and insights scientists may reveal with advanced techniques not yet available.
The more researchers dig, the closer they get to some long-standing questions: If Bennu held all the pieces for life, why did life not arise there? Jason Dworkin, project scientist for OSIRIS-REx, wonders, “What did Bennu not have...that the Earth did have?” The answers to these questions could redefine our theories of life's origin.
Overall, the samples from Bennu provide compelling evidence of how potentially rich the solar system is with life's building blocks. Every new study could enlighten our quest to understand both our origins and the possibility of life existing beyond Earth, reiterates the importance of continued exploration.