In 2023, NASA’s OSIRIS-REx mission delivered samples from the 4.6 billion-year-old asteroid Bennu to Earth. When scientists examined them, they discovered that asteroids that were present during the early stages of the formation of the solar system contained amino acids, the basic building blocks of life as we know it. These acids are involved in the production of proteins and peptides found in DNA. Their recovery from space confirmed what scientists had theorized decades ago: that the ingredients of life came from outer space.
Meanwhile, the question of how these molecules formed in the universe remained a mystery. But a new study led by scientists at Penn State University provides new insight into that unanswered question. According to their study published in Proceedings of the National Academy of Sciencessome of them may have originated in the radioactive environment of the solar system’s dawn ice. This challenges previous assumptions about where and under what conditions amino acids form in early stellar environments.
The research team includes scientists from the University of Pennsylvania’s Department of Earth Sciences, as well as researchers from The Catholic University of America, American Museum of Natural History, University of Arizona Lunar and Planetary Institute, Rowan University School of Earth and Environmental Sciences, and Solar System Exploration Division and Space Science and Technology Research and Development Center (CREST II) At NASA Goddard Space Flight Center.
*Alison Budzinski (left), assistant professor of geosciences at Penn State, led the study along with Ophelie McIntosh, a postdoctoral fellow in Penn State’s geosciences department. Credit: Jaydyn Isiminger/Pennsylvania State University, CC*
To analyze small dust samples collected from the asteroid, the team used custom equipment that can measure subtle changes in atomic weight (isotope ratio). Specifically, the researchers focused on glycine, the smallest of the amino acids with two carbons. Nevertheless, this amino acid plays an important function in cell biology, combining with other acids to form proteins. These cells are responsible for most biological functions, from building cells to catalyzing chemical reactions.
“Here at Penn State, we have developed an instrument that allows us to make isotopic measurements of very small amounts of organic compounds, such as glycine,” explained Alison Baczynski, assistant professor of earth sciences at Penn State and co-lead author of the paper. Pennsylvania release:. “Without advances in technology and investment in specialized equipment, this discovery would never have been possible.”
This molecule can be formed under a wide range of conditions and is often considered an important indicator of early prebiotic chemistry. Its discovery in comets and asteroids supports the theory that the basic building blocks of life were formed in space and distributed to young Earth, where life originated. Previously, scientists generally believed that glycine was formed only through Strecker synthesis. In this process, hydrogen cyanide, ammonia, aldehydes or ketones react in the presence of liquid water to form molecules.
The new results suggest that Bennu’s glycine did not form in the presence of liquid water, but may have assembled in ice exposed to radiation in the early outer solar system. Budzynski summed it up as follows:
Our results overturn the general idea that amino acids are formed on asteroids. It now appears that there are many conditions under which the building blocks of life can form, not just when there is warm liquid water. Our analysis showed that there is much more diversity in the routes and conditions under which these amino acids are formed.
The researchers then compared their results with an amino acid analysis of the famous Murchison meteorite, which fell in Australia in 1969. Their findings suggest that the Murchison molecule was formed by Strecker synthesis at higher temperatures in the presence of liquid water. Such conditions, similar to conditions on young Earth, may have existed in similar meteorite parent bodies. “We’re excited to be able to explore new ways to explore the world’s most powerful planets,” said Ophelie McIntosh, a postdoctoral fellow in the Department of Geosciences at Penn State University and co-lead author of the paper.
One reason amino acids are so important is that they are thought to have played a major role in the beginning of life on Earth. What is truly surprising is that Bennu’s amino acids exhibit a significantly different isotopic pattern than Murchison’s, and these results suggest that Bennu’s and Murchison’s parent bodies likely originated in chemically distinct regions of the solar system.
These results address several questions about how amino acids form in the universe, but they also present scientists with many new mysteries. In particular, amino acids exist in mirror-image forms, which scientists previously thought had identical isotopic signatures. However, in the Bennu asteroid, the two similarly discovered forms of glutamate have significantly different nitrogen values. In the future, the team aims to understand why this is the case.
“Right now, we have more questions than answers,” Budzynski said. “We hope to be able to continue analyzing a variety of different meteorites for amino acids. We want to know whether they continue to look like Murchison and Bennu, or whether there is more diversity in the conditions and pathways that give rise to the building blocks of life.”
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