A tiny sample of dust from asteroid Bennu is forcing a major reassessment of how the fundamental ingredients for life may have formed in our solar system. New research reveals that key amino acids, the building blocks of proteins, likely originated in the extreme cold and radiation of deep space, challenging the long-held belief that they required warm, liquid water to emerge.
The findings, based on material returned to Earth by NASA’s OSIRIS-REx mission in 2023, suggest that the conditions necessary for creating life's precursors are far more diverse and widespread throughout the cosmos than previously understood.
Key Takeaways
- Analysis of asteroid Bennu samples shows amino acids formed in icy, radiation-rich environments.
- This discovery contradicts the dominant theory that warm liquid water was essential for their creation.
- The findings suggest the building blocks of life could form in many different and harsh cosmic settings.
- A new chemical mystery has emerged from the unique isotopic signatures of the Bennu samples.
Challenging a Long-Held Theory
For decades, the prevailing scientific model for the formation of amino acids in space has been a process known as Strecker synthesis. This chemical reaction requires a mixture of compounds like hydrogen cyanide and ammonia reacting within liquid water.
However, a team of scientists at Penn State, analyzing a precious sample of Bennu's dust no larger than a teaspoon, found evidence that points to a completely different pathway. Their results indicate that several amino acids on Bennu did not form in a warm, wet environment.
“Our results flip the script on how we have typically thought amino acids formed in asteroids,” said Allison Baczynski, assistant research professor of geosciences at Penn State and a lead author on the study. “It now looks like there are many conditions where these building blocks of life can form, not just when there’s warm liquid water.”
Instead, the chemical fingerprints suggest these molecules were forged in frozen ice exposed to intense cosmic radiation, likely in the frigid outer reaches of the early solar system.
Unlocking Secrets at the Atomic Level
The research team used highly specialized instruments to perform an isotopic analysis on the asteroid material. This technique measures slight variations in the mass of atoms, which can reveal the environmental conditions under which a molecule was created.
Their focus was on glycine, the simplest known amino acid. Because of its simple two-carbon structure, glycine is an excellent marker for tracing the earliest prebiotic chemical processes that occurred long before life began.
What are Amino Acids?
Amino acids are organic compounds that combine to form proteins. Proteins are essential for nearly all biological functions, from building cellular structures to facilitating the chemical reactions that sustain life. The presence of amino acids in meteorites and asteroids supports the theory that some of life's foundational molecules were delivered to a young Earth from space.
The isotopic signatures of the glycine in the Bennu sample were inconsistent with formation in liquid water. According to Baczynski, advances in instrumentation were critical to this discovery, allowing the team to make precise measurements on extremely small amounts of organic material.
A Tale of Two Asteroids
To provide context for their findings, the researchers compared the Bennu samples with material from one of the most studied space rocks in history: the Murchison meteorite.
The Murchison meteorite, which landed in Australia in 1969, is also rich in carbon and contains a variety of amino acids. However, previous analysis showed that its amino acids likely formed under conditions that included liquid water and milder temperatures—conditions similar to those on early Earth.
The contrast between the two is stark and telling.
“What’s a real surprise is that the amino acids in Bennu show a much different isotopic pattern than those in Murchison,” explained Ophélie McIntosh, a postdoctoral researcher at Penn State and co-lead author. “These results suggest that Bennu and Murchison’s parent bodies likely originated in chemically distinct regions of the solar system.”
This comparison suggests there was no single, universal process for creating life's building blocks. Instead, they may have formed through multiple pathways in vastly different environments across the developing solar system.
New Questions Emerge from the Dust
While the study answers one major question, it has unexpectedly opened up another. Amino acids can exist in two forms that are mirror images of each other, often referred to as "left-handed" and "right-handed" versions.
A New Puzzle to Solve
Scientists had assumed that these two mirror-image forms would be created with identical isotopic characteristics. However, the team found that the two forms of another amino acid, glutamic acid, had dramatically different nitrogen isotope values in the Bennu sample. Why these chemically identical but structurally mirrored molecules carry different signatures is currently a mystery.
Solving this puzzle could provide even deeper insights into the chemical evolution of the solar system and the specific processes that create the molecules necessary for life.
“We have more questions now than answers,” Baczynski stated. The team hopes to continue its analysis on a wider range of meteorites to see if the patterns found in Bennu and Murchison represent two of many possible formation pathways for the building blocks of life.