The Bennu sample represents a remarkable achievement in space exploration. This material, collected from a carbon-rich asteroid, provides an unprecedented opportunity to investigate the origins of our solar system and the potential building blocks of life. It is the largest carbon-rich asteroid sample ever delivered to Earth by the U.S.
The OSIRIS-REx Mission
The OSIRIS-REx mission began its journey on September 8, 2016. Its primary objective was to collect a sample from the near-Earth asteroid Bennu. Bennu was selected as the target due to its classification as a B-type asteroid, a primitive sub-type of carbonaceous asteroids, meaning it has undergone minimal geological changes since its formation 4.5 billion years ago. This makes Bennu a “time capsule” from the early solar system.
The spacecraft arrived at Bennu on December 3, 2018, and spent nearly two years surveying its surface to identify a suitable sample collection site. The “Touch-And-Go” (TAG) maneuver occurred on October 20, 2020. During this maneuver, the OSIRIS-REx spacecraft briefly touched down on Bennu’s surface, using its robotic arm, the Touch-and-Go Sample Acquisition Mechanism (TAGSAM), to collect dust and pebbles. A burst of nitrogen gas helped capture the surface material.
The spacecraft departed Bennu on May 10, 2021, embarking on a 2.5-year journey back to Earth. On September 24, 2023, the sample return capsule separated from the main spacecraft and entered Earth’s atmosphere. The capsule parachuted down to the Utah Test and Training Range, where it was retrieved by NASA. The mission collected approximately 121.6 grams of material, exceeding the initial goal of 60 grams.
Initial Discoveries from the Sample
Preliminary analyses of the Bennu sample have yielded significant findings. Scientists quickly confirmed the presence of high-carbon content and water within the asteroid material. The water was found in the form of hydrated clay minerals. This discovery supports the hypothesis that water may have been delivered to our planet billions of years ago by asteroids like Bennu.
The sample also revealed carbon-rich organic compounds, including amino acids and nucleobases, which are fundamental components for DNA and RNA. Scientists identified 14 of the 20 amino acids used by life on Earth to build proteins, along with all five nucleobases. The presence of nitrogen, including ammonia, was also discovered, as nitrogen compounds are integral to biological processes. These findings indicate that the asteroid’s parent body once hosted liquid water and environments conducive to the formation of complex organic molecules.
The discovery of water-soluble phosphates, such as magnesium sodium phosphate, was also made. These compounds are components of biochemistry for all known life on Earth today. While similar phosphates have been found in other asteroid samples, the Bennu sample’s magnesium sodium phosphate is notable for its lack of inclusions and the size of its grains, suggesting a potentially “wetter past” for the asteroid or its parent body. The analysis of these materials provides a detailed glimpse into the asteroid’s composition at a microscopic level.
Scientific Significance and Future Research
The Bennu sample is important for understanding the formation and evolution of our solar system. Its material has remained relatively unchanged since the solar system’s early days, offering a direct window into the conditions present 4.5 billion years ago. The elemental composition of the sample closely resembles that of the Sun. Studying these “original ingredients” helps scientists piece together how planets like Earth formed.
The discovery of water and organic molecules in the sample reinforces the theory that asteroids played a role in delivering these ingredients to early Earth, which may have contributed to the emergence of life. The presence of salts suggests that the conditions necessary for complex organic chemistry were widespread across the early solar system, increasing the likelihood that life could have formed elsewhere. Scientists are investigating why life did not form on Bennu itself, despite having the necessary ingredients and environment.
Research on the Bennu sample is ongoing, with more than 200 scientists worldwide involved in its analysis. NASA plans to preserve at least 70% of the sample at the Johnson Space Center for future research by generations of scientists. The continued study of the Bennu sample will enhance our understanding of the solar system and may guide future missions to other celestial bodies to explore the potential for life beyond Earth.