Scientists discovered that asteroid Bennu has a collection of salty minerals that formed in a specific order when brine evaporated, offering insights into the type of water that existed billions of years ago.
In the last year, an intriguing collection of samples from the 4.5-billion-year-old asteroid Bennu has been examined at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab). These materials were collected when Bennu was approximately 200 million miles from Earth.
Berkeley Lab is part of a collaborative effort involving over 40 institutions that are studying the chemical properties of Bennu to gain a better understanding of the evolution of our solar system and its planets. A new study released today in the journal Nature reveals that Bennu originated from a primordial wet environment, potentially from the coldest regions of the solar system, likely past Saturn’s orbit.
The asteroid showcases a set of salty mineral deposits that emerged in a precise sequence as the brine evaporated, which provides hints about the nature of water that existed billions of years prior. These brines may have served as a rich environment for creating vital ingredients for life, and similar minerals can be found in dried lake beds on Earth (like Searles Lake in California) as well as on Jupiter’s moon Europa and Saturn’s moon Enceladus.
Matthew Marcus, a scientist at Berkeley Lab who manages the Advanced Light Source (ALS) beamline where some of these samples were analyzed, expressed, “Studying asteroid materials directly from space is an incredible opportunity. We possess highly specialized tools that allow us to analyze the composition of Bennu and uncover its history.”
The samples were harvested by NASA’s OSIRIS-REx mission, the first U.S. endeavor to return asteroid samples. Approximately 122 grams of material was returned from Bennu, marking the largest sample ever gathered from an extraterrestrial object beyond the Moon.
To investigate the Bennu samples, Marcus collaborated with Scott Sandford from NASA Ames Research Center and Zack Gainsforth from UC Berkeley Space Sciences Laboratory. They utilized scanning transmission X-ray microscopy (STXM) at the ALS. By adjusting the X-ray energy, they could identify specific chemical bonds on the nano scale and create a map of the different chemicals present in the asteroid. The research team found that the last salts to evaporate from the brine had mixed into the rock at minute levels.
Sandford stated, “This type of information gives us crucial insights into the processes, environments, and timelines that led to the formation of these samples. Understanding these materials is vital, as they may represent components that contributed to the early conditions on Earth and could be significant in the origin and evolution of life.”
Researchers at Berkeley Lab’s Molecular Foundry also used electron beams to image the same Bennu samples via transmission electron microscopy (TEM). The Foundry was instrumental in preparing these samples for experiments conducted at the ALS, utilizing an ion beam to create microscopic slices of the material that are approximately a thousand times thinner than a sheet of paper.
Gainsforth remarked, “Examining the exact same atoms with both STXM and TEM eliminated many uncertainties in our data interpretation. We confirmed that what we observed was a common phase formed by evaporation. Extracting Bennu’s secrets required extensive effort, but we are thrilled with the outcome.”
This isn’t the first instance in which the ALS and Molecular Foundry have analyzed materials from space. They previously studied samples from the asteroid Ryugu, enhancing our understanding of the early solar system. More investigations of Bennu using the STXM and infrared beamlines at the ALS are also scheduled for the next year.
Additionally, Berkeley Lab researchers contributed to another paper released today in Nature Astronomy, which examined organic materials found on Bennu. Within the samples, the team detected 14 of the 20 amino acids essential for protein synthesis on Earth. They also identified all five nucleobases, the circular molecules found in DNA and RNA, alongside ammonia, which may have played a role in the emergence of primitive life on Earth.
The findings support the theory that asteroids like Bennu could have delivered water and critical chemical elements required for life to Earth in ancient times. Given the similarities between Bennu and the icy dwarf planets and moons in the outer solar system, these fundamental building blocks of life could potentially be abundant.
