In 2023, NASA’s OSIRIS-REx mission delivered samples of the 4.6-billion-year-old asteroid Bennu to Earth.
Upon examining them, scientists discovered that the asteroid – which existed when the Solar System was in the earliest phase of its formation – contained amino acids, the fundamental building blocks of life as we know it.
These acids are responsible for the production of proteins and peptides found in DNA. Their retrieval from space confirmed what scientists had theorized decades ago: that the ingredients for life came from space.
On the other hand, the question of how these molecules formed in space was still a mystery. But new research led by Penn State scientists has offered some fresh insight into that unresolved question.
According to their study, which appeared in the Proceedings of the National Academy of Sciences, it’s possible that some of them may have originated in an icy, radioactive environment at the dawn of the Solar System.
This challenges previously-held assumptions about where and under what conditions amino acids can form in early stellar environments.
In addition to scientists from the Department of Geoscience at the University of Pennsylvania, the research team included astrophysicists and geologists from the Catholic University of America, the American Museum of Natural History, University of Arizona’s Lunar and Planetary Laboratory, Rowan University’s School of Earth and Environment, and the Solar System Exploration Division and Center for Research and Exploration in Space Science and Technology (CRESST II) at NASA’s Goddard Space Flight Center.
To analyze the tiny dust samples collected from the asteroid, the team used custom instruments capable of measuring subtle variations in atomic mass (isotopic ratios). Specifically, the researchers focused on the two-carbon amino acid glycine, the smallest of the amino acids.
Nevertheless, this amino acid plays an important function in cellular biology, linking with other acids to form proteins. These cells are responsible for most biological functions, ranging from cell-building to catalyzing chemical reactions.
“Here at Penn State, we have modified instrumentation that allows us to make isotopic measurements on really low abundances of organic compounds like glycine,” Allison Baczynski, an assistant research professor of geosciences at Penn State and co-lead author on the paper, explained in a Penn State release:. “Without advances in technology and investment in specialized instrumentation, we would have never made this discovery.”
The molecule can form under a wide range of conditions and is often considered a key indicator of early prebiotic chemistry. Locating it in comets and asteroids supports the theory that the basic building blocks of life formed in space and were distributed to a young Earth, thereby giving rise to life. Previously, scientists generally believed that glycine was formed only via the Strecker synthesis. During this process, hydrogen cyanide, ammonia, and aldehydes or ketones react in the presence of liquid water to form the molecule.
The new results suggest that Bennu’s glycine may not have formed in the presence of liquid water, but instead came together in ice exposed to radiation in the early outer 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 there are 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.
The team then compared their results with an analysis of amino acids from the famous Murchison meteorite, which landed in Australia in 1969. Their findings suggest that the Murchison molecules formed via Strecker synthesis in the presence of liquid water and at warmer temperatures. Such conditions could have existed on the parent bodies of similar meteorites, similar to conditions on a young Earth. Said Ophélie McIntosh, a postdoctoral researcher in Penn State’s Department of Geosciences and a co-lead author on the paper:
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.
While these results address some of the questions regarding how amino acids form in space, they also present many new mysteries for scientists. In particular, amino acids occur in mirror-image forms, which scientists previously thought had identical isotopic signatures. But in the Bennu asteroid, the two forms of glutamic acid that were also found have very different nitrogen values. Moving forward, the team aims to determine the reason for this.
“We have more questions now than answers,” Baczynski said. “We hope that we 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.”
Written by Matthew Williams/Universe Today.
