Scientists analyzing samples from the asteroid Bennu have identified thousands of organic molecules, including the building blocks of proteins and genetic material. "This increases the likelihood of finding life elsewhere," researchers say.
Scientists Discover Organic Molecules in Asteroid Sample
Researchers analyzing samples collected from an asteroid and returned to Earth a year and a half ago were surprised to discover that it contains numerous organic molecules, including key building blocks of life as we know it. Scientists from NASA and several U.S. universities examined the composition of the samples retrieved by the OSIRIS-REx mission from the asteroid Bennu in 2020.
After the sample capsule landed on Earth, researchers initially struggled to open its container, but their efforts paid off. The 120-gram sample contained over 16,000 types of organic molecules, far exceeding initial estimates. Among these were 16 of the 20 amino acids that form all proteins in living organisms, as well as all five nucleobases that make up DNA and RNA—the genetic material of all life on Earth. “Our odds of finding life elsewhere are increasing,” NASA senior scientist for sample return at NASA’s Goddard Space Flight Center and co-author of the research, Daniel Glavin told The New York Times.
Some of these building blocks have been found before in meteorites that fell to Earth, but their extraterrestrial origin was uncertain due to exposure to our atmosphere. The Bennu samples, however, arrived in a sealed, airtight container, leaving no doubt that they authentically represent the asteroid’s composition.
The new findings indicate that much of the early solar system had the necessary conditions for the formation of life’s essential molecules. “It doesn’t take something like a planet or a big moon,” said Tim McCoy, curator of meteorites at the Smithsonian National Museum of Natural History and a co-author of the study, “These are run-of-the-mill, small bodies in the outer part of the solar system.”
The research findings have been published in two scientific papers—one in Nature and another in Nature Astronomy.
"NASA’s OSIRIS-REx mission already is rewriting the textbook on what we understand about the beginnings of our solar system," said Nicky Fox, associate administrator, Science Mission Directorate at NASA Headquarters in Washington. “Asteroids provide a time capsule into our home planet’s history, and Bennu’s samples are pivotal in our understanding of what ingredients in our solar system existed before life started on Earth.”
Surprising discoveries from the early solar system. The sealed sample capsule being retrieved from the Utah desert, September 2023. | Photo: NASA/Keegan Barber
Chemistry Within the Ice
Scientists analyzed the history of asteroid Bennu based on the composition of the minerals found in its samples. Their findings suggest that Bennu, which measures about 600 meters in length, is a remnant of a much larger celestial body, roughly 100 kilometers across, composed of a mix of ice and rock. Researchers believe this ancient body formed in the outer reaches of the solar system, beyond Jupiter’s orbit.
Despite its distance from the Sun, the massive object remained warm due to the presence of radioactive elements. According to the study, temperatures in its interior reached approximately 20°C (68°F), causing its icy components to melt into a salty water solution that circulated through its internal cavities as it drifted through space. The asteroid contained a high concentration of ammonia (NH₃), which, in this warm, watery environment, reacted with formaldehyde (CH₂O) and other compounds to form amino acids and nucleobases—the building blocks of genetic material.
According to researchers, this ancient body remained in this state for millions of years. Over time, as its radioactive material decayed, it gradually cooled down. However, the relatively high concentration of ammonia raised the freezing point, keeping its interior liquid. At some point, Jupiter’s gravity disrupted its orbit, sending it into the region between Mars and Earth. There, a collision with another celestial body shattered it into fragments. Over time, some of these fragments reaccumulated, forming the asteroid Bennu as we know it today.
16,000 types of molecules in a 120-gram sample. NASA researchers at Johnson Space Center collect soil samples from the capsule’s exterior before opening it. | Photo: NASA
The Questions of Life
Researchers continue to analyze the samples, hypothesizing that within the asteroid’s interior, some amino acids may have reacted to form simple proteins, or that certain nucleobases combined into a gene-like molecule. However, they do not believe that actual life could have emerged on the ancient asteroid within its limited timeframe of a few million years in a warm environment. “I don’t think it went that far,” concluded McCoy. “I think it went somewhere down the path towards life.”
Some of the study’s findings raise intriguing questions. Certain molecules exist in two chemically identical but structurally opposite forms—mirror images of each other, like our hands. On Earth, life exhibits a clear preference for left-handed amino acids. However, the samples from Bennu contained equal proportions of both forms. This suggests that in early Earth, both forms may have been equally abundant, leaving the question of when and why life "turned left" still unresolved.
The new discoveries only heighten researchers’ curiosity about planetary bodies believed to harbor liquid water beneath thick ice layers, much like the ancient body from which Bennu originated. Such subsurface oceans likely exist on Europa, one of Jupiter’s largest moons; Enceladus, a moon of Saturn; and the dwarf planet Ceres. If these environments contain similar materials and have undergone comparable chemical processes over much longer timescales, it could hint at the possibility of microbial life emerging there.
Marc Schneegurt, an astrobiologist at Wichita State University who was not involved in the study, emphasizes the significance of these findings. “There could hardly be any study more important to our understanding of the origins of life in the solar system.”