Asteroid Bennu and the Ingredients for Life – S8, Episode 80

What Can Asteroid Dust Tell Us About Life?

A dark speck of asteroid material may not look like much, but to an astrochemist, it is a time capsule that can contain billions of years of history. 

Researchers at NASA want to understand whether some of life’s chemical ingredients were formed in space while Earth was still in its infancy. Discovering amino acids or other organic compounds on an asteroid does not mean scientists have discovered extraterrestrial life but rather demonstrates that important molecules can form beyond Earth.

Enter OSIRIS-REx

NASA’s OSIRIS-REx was the first U.S. mission to collect a sample from an asteroid and return it to Earth. Launched in 2016, the spacecraft traveled to the near-Earth asteroid Bennu, mapped and studied its surface, and then briefly touched down in 2020 using its robotic TAGSAM arm to collect rocks and dust before delivering the sample in 2023.  

By studying this ancient, carbon-rich material, scientists hope to better understand how the early solar system formed, investigate the organic compounds and other ingredients that may have contributed to life itself, and learn more about asteroids that could potentially threaten Earth. 

José works as part of the OSIRIS-REx sample analysis team at NASA’s Goddard Space Flight Center. His job is to study organic molecules in material returned from Bennu and compare them to Earth samples. 

Why NASA Chose Bennu

Fragments of asteroids already reach Earth as meteorites, so why send a spacecraft billions of miles to collect what we already have here? 

Every meteorite recovered on Earth is contaminated by the interactions it has with our atmosphere, soil, water, microorganisms or human hands. Weather can also destroy fragile compounds before scientists have a chance to detect them. 

OSIRIS-REx solved that problem by collecting material directly from an asteroid, protecting it during the journey and delivering it to Earth with a carefully documented history. 

Analyzing the Samples

José works as part of the OSIRIS-REx sample analysis team at NASA’s Goddard Space Flight Center. His job is to study organic molecules in the material returned from OSIRIS-REx. Aponte’s work began years before the samples were returned, as he and other researchers developed and tested the methods they would eventually use on the irreplaceable material. 

Analyzing Bennu requires extraordinary care, as a single fingertip may contain more organic material than the asteroid dust being examined. 

Researchers clean their solvents, glassware, equipment and workspaces while running control samples, called blanks, alongside the asteroid material. Those controls help establish whether a signal came from Bennu or from the laboratory environment. 

The team can detect some molecules at concentrations near one part per billion. One of the primary tools is a mass spectrometer, which Aponte describes as a highly sensitive balance. It breaks molecules into smaller, electrically charged pieces and measures them. Each molecule produces a distinctive pattern of pieces, and scientists can use that pattern like a fingerprint to determine what exactly is present. 

Before using a new method on Bennu, researchers may spend several years testing it on other materials. There is little room for error once a precious asteroid sample enters the laboratory. 

What We’ve Learned so Far

Analysis of Bennu material has revealed 14 of the 20 amino acids used in life to build proteins, along with all five nucleobases used in DNA and RNA. Scientists also found carboxylic acids, ammonia, formaldehyde-related chemistry and thousands of nitrogen-bearing compounds. The diversity of these molecules provides scientists with valuable insight into Bennu’s complex chemical history. 

Unlike biology, which uses enzymes to produce specific compounds, space chemistry unfolds through radiation, changing temperatures, interactions with water and many unpredictable reactions. The resulting chemical mixture shows the environment in which the asteroid’s material formed and changed. 

These findings support the idea that meteorite impacts delivered at least some water and organic material to early Earth. They do not establish asteroids as the only source, but they add another important piece to the puzzle. Chemistry occurring here at home also contributed to the inventory from which life eventually emerged. 

Why Life Is “Left-Handed”

Many amino acids can exist in two forms that mirror each other, much like a person’s left and right hands. Chemists call this property chirality. 

Although both versions can form, life on Earth builds proteins almost entirely from left-handed amino acids. Scientists still do not know why biology adopted one form so strongly. 

Some meteorites contain a small excess of left-handed amino acids. One hypothesis is that material delivered from space gave early chemistry a slight preference that biology later amplified. Bennu offers researchers an unusually clean opportunity to investigate that possibility. 

The team has also reported tentative evidence of tryptophan, one of the more complex amino acids used by life. Researchers detected fragments consistent with tryptophan at the expected point in their analysis, but not enough evidence to confirm the complete molecule. The result remains promising rather than conclusive and also provides a good example of the caution required in this work. 

Bennu the Time Capsule

Bennu contains minerals that are formed as salty water evaporates. Those salts indicate that its material once experienced conditions very different from those at the asteroid’s present location. 

Scientists think Bennu may be rubble left behind after the destruction of one or more larger parent bodies. Some of its material may have formed farther from the Sun before gravitational interactions and collisions carried it into the inner solar system. 

That makes Bennu a time capsule, but not a static one. Its chemistry records water, heat, radiation, migration and destruction across an immense span of time. 

The samples returned by OSIRIS-REx will continue to be studied for decades. Future instruments may detect compounds that today’s technology cannot see. José hopes later researchers will eventually assemble a more complete inventory of the molecules found in asteroids and meteorites. 

Bennu cannot yet tell us exactly how chemistry became biology. It does show that many of life’s ingredients were present beyond Earth and may have been widespread when the planets were young. 

Frequently Asked Questions

What is asteroid Bennu? 

Bennu is a small, carbon-rich near-Earth asteroid containing primitive material from the early solar system. NASA selected it for OSIRIS-REx because its composition, orbit and preserved chemistry make it scientifically valuable. 

What was the OSIRIS-REx mission? 

NASA’s OSIRIS-REx spacecraft traveled to Bennu, mapped its surface, collected a sample in 2020 and returned that material to Earth in 2023 for laboratory analysis. 

Why are Bennu samples more useful than ordinary meteorites? 

Meteorites are altered and contaminated after entering Earth’s atmosphere. Bennu material arrived with a documented history and was handled under controlled conditions, allowing scientists to study a much cleaner sample. 

Did scientists find life on Bennu? 

No, scientists found organic molecules associated with the chemistry of life. Organic molecules can form without biology, so their presence is evidence of prebiotic chemistry, not proof of living organisms. 

What are amino acids and nucleobases? 

Amino acids are molecules life uses to construct proteins. Nucleobases are components of DNA and RNA. Finding them in asteroid material shows that important biological building blocks can also form through nonbiological processes in space. 

What can students learn from Aponte’s career? 

Aponte did not begin his education with a plan to become an astrochemist. He studied in Peru, initially focused on medicinal chemistry and later found his way into space science. He advises students to develop what they are good at, remain open to unexpected paths and keep trying when the work becomes difficult.

Go Deeper:

• José C. Aponte’s Bio (NASA)
• The OSIRIS-REx Mission (NASA)
• The OSIRIS-REx Spacecraft Fact Sheet (Lockheed Martin)
• About Asteroid Bennu (NASA)

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