The search for the origins of life on Earth has taken a significant leap forward with new analysis of samples returned from asteroid Bennu. In 2023, NASA’s OSIRIS-REx mission successfully delivered material from the 4.6-billion-year-classic asteroid to Earth, and scientists are now discovering that these ancient space rocks contain amino acids – the fundamental building blocks of proteins and, life as we know it. This discovery confirms long-held theories that the ingredients for life may have originated beyond our planet.
But pinpointing how these crucial molecules formed in space has remained a mystery. Recent research, led by scientists at Penn State University, suggests a surprising possibility: some of these amino acids may have originated in an icy, radioactive environment in the early solar system. This challenges previous assumptions about the conditions necessary for the formation of these vital compounds and opens new avenues for understanding the prebiotic chemistry that may have seeded life on Earth.
The research, published in the Proceedings of the National Academy of Sciences, focused on glycine, the simplest amino acid. Researchers used specialized instruments to measure subtle variations in atomic mass (isotopic ratios) within the Bennu samples. “Here at Penn State, we have modified instrumentation that allows us to make isotopic measurements on really low abundances of organic compounds like glycine,” explained Allison Baczynski, assistant research professor of geosciences at Penn State and co-lead author on the paper. “Without advances in technology and investment in specialized instrumentation, we would have never made this discovery.”
Previously, the prevailing theory held that glycine formed primarily through a process called Strecker synthesis, requiring liquid water, hydrogen cyanide, ammonia, and aldehydes or ketones. However, the new analysis suggests that Bennu’s glycine may have formed in a different way – within ice exposed to radiation in the frigid outer reaches of the early solar system. As Baczynski summarized, “Our results flip the script on how we have typically thought amino acids formed in asteroids. It now looks like You’ll see many conditions where these building blocks of life can form, not just when there’s warm liquid water. Our analysis showed that there’s much more diversity in the pathways and conditions in which these amino acids can be formed.”
Comparing Bennu to the Murchison Meteorite
To further understand the origins of these amino acids, the team compared their findings to data from the Murchison meteorite, a well-studied space rock that landed in Australia in 1969. Analysis of the Murchison meteorite’s amino acids indicated they likely formed via Strecker synthesis in the presence of liquid water and at warmer temperatures – conditions that could have existed on the parent bodies of similar meteorites, and potentially on early Earth. Ophélie McIntosh, a postdoctoral researcher at Penn State and co-lead author, noted, “One of the reasons why amino acids are so important is because we think that they played a big role in how life started on Earth. What’s a real surprise is that the amino acids in Bennu show a much different isotopic pattern than those in Murchison, and these results suggest that Bennu and Murchison’s parent bodies likely originated in chemically distinct regions of the solar system.”
The research team also observed an anomaly in the isotopic signatures of glutamic acid, another amino acid found in the Bennu sample. Unlike previous expectations, the two mirror-image forms of glutamic acid exhibited different nitrogen values, presenting a new puzzle for scientists to solve.
Implications for Understanding Life’s Origins
The discovery doesn’t just refine our understanding of amino acid formation; it broadens the potential environments where life’s building blocks could have arisen. The team’s findings suggest that the conditions necessary for prebiotic chemistry may be more common throughout the solar system – and beyond – than previously thought. This supports the theory of panspermia, the idea that life’s precursors are distributed throughout the universe by asteroids, comets, and other celestial bodies. NASA’s OSIRIS-REx mission, which initially delivered the Bennu sample, is now continuing as OSIRIS-APEX, heading towards asteroid Apophis for a 2029 encounter.
“We have more questions now than answers,” Baczynski said. “We hope that One can continue to analyze a range of different meteorites to look at their amino acids. We want to know if they continue to look like Murchison and Bennu, or maybe there is even more diversity in the conditions and pathways that can create the building blocks of life.” Future research will focus on analyzing additional meteorite samples to determine if the isotopic patterns observed in Bennu are unique or representative of a wider range of prebiotic environments.
The ongoing analysis of the Bennu samples promises to continue reshaping our understanding of the origins of life, offering a glimpse into the chemical conditions that may have existed in the early solar system and potentially paving the way for the discovery of life beyond Earth.
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