New research shows that on an incredibly small scale, the components inside asteroid Bennu are not evenly mixed. Instead, organic matter and minerals are divided into three distinct chemical realms. These discoveries will help scientists understand how liquid water once changed the asteroid’s composition over time.
Bennu is known as a carbonaceous asteroid and is rich in carbon-based materials, including organic compounds. These compounds are important because they resemble chemical components necessary for life. The asteroid itself is made up of fragments of a much larger parent body that broke apart long ago. Bennu orbits relatively close to Earth, making it a prime target for NASA’s Osiris-Rex mission.
Primitive samples taken from the early solar system
One of the most valuable aspects of Bennu’s samples is that they remain unaffected by Earth’s atmosphere and environment. This makes it especially useful for scientists studying conditions in the early solar system. By examining these samples, researchers can learn how water, minerals, and organic matter first formed and interacted billions of years ago.
In this study, Mehmet Yesiltas and his team focused on a specific sample labeled OREX-800066-3. The material was collected directly from Bennu by the Osiris-Rex spacecraft and returned to Earth in September 2023. The samples were carefully sealed and protected, providing a rare and reliable record of Bennu’s original chemical reaction.
Bennu research at the nanoscale
To examine the samples, the researchers used advanced techniques called nanoscale infrared spectroscopy and Raman spectroscopy. These methods allow scientists to identify compounds by measuring how they interact with light. Importantly, this can be done at very small scales, down to about 20 nanometers. For comparison, a nanometer is one billionth of a meter, which is much smaller than what the human eye can see.
This level of detail reveals that Bennu’s internal chemistry is not homogeneous. Instead, the material forms three repeating types of organo-mineral domains, each with its own distinct composition.
3 different chemical domains
This study identified three main types of regions within the sample. One type contains large amounts of aliphatic organic compounds, which are simple carbon-based molecules made of carbon and hydrogen chains. Other regions are rich in carbonate minerals, which often form in the presence of water and can provide clues about past water environments. The third region contains organic compounds containing nitrogen, an element that plays an important role in biomolecules such as amino acids.
These differences indicate that the chemical properties of benne vary greatly from place to place, even on very small scales.
Uneven effects of water on Bennu
The uneven distribution of these chemical regions suggests that water did not affect Bennu in a single, uniform manner. Instead, liquid water likely interacted with different parts of the asteroid under different conditions, creating a patchwork chemical environment. This process is known as nanoscale heterogeneity, meaning that the composition changes depending on the exact location of the object being studied.
Despite this history of water interactions, the researchers found that the fragile organic molecules were still preserved. This is an important discovery because it shows that key chemical components can survive exposure to water-related changes.
Insights into the origins of life’s components
Overall, the findings provide new insight into how water, minerals, and organic matter interacted on primitive asteroids like Bennu. These interactions are thought to have played a major role in the formation of the early solar system and may have helped deliver the building blocks of life to Earth.
Studying Bennu at such a fine scale has allowed scientists to more clearly understand how complex chemistry developed in the universe long before planets like ours were fully formed.
