This Asteroid Wasn’t Just a Rock, It Was Once a Salty, Watery World Holding Clues to Life

The samples that have been returned from the asteroid Bennu are forcing scientists to revise their understanding of the early solar system because they have revealed clear evidence that the asteroid once had liquid water in the form of mineral-rich brines.

The scientists have found evaporite minerals such as sodium-bearing phosphates, carbonates, sulfates, chlorides, and fluorides, which are normally formed when salty water evaporates slowly, and crystals are left behind.

According to a study published in PubMed and highlighted by the Smithsonian National Museum of Natural History, these minerals are clear evidence that the asteroid that Bennu came from had liquid water that existed for a long period of time and changed the rocks chemically.


Scientists have explained that the evaporite minerals serve as chemical fingerprints that retain information about the environments in which they were formed billions of years ago, which enables scientists to determine the history of water in the early solar system with surprising accuracy.

As highlighted in the PubMed study, these mineral sequences were formed during the late-stage evaporation of brines that trapped valuable chemical information from the primitive solar system inside the rocks that formed the asteroid Bennu.

Evidence of water-driven chemistry in space

The fact that these salts exist tells scientists that a process called aqueous alteration occurred. This is where water interacts with minerals and changes their structure and composition over time. This is a common process on Earth, but it was not always thought to have occurred on small asteroids.

According to research that was published on ScienceDaily, the mineral composition of Bennu tells scientists that liquid water flowed through its parent asteroid, altering its chemistry.

This finding supports a theory that has been around for a long time: that asteroids that were rich in water played a huge part in providing Earth with both water and organic compounds that may have been necessary for life to exist in the first place.

Instead of being dry objects that were created a long time ago, asteroids are now considered to be environments that are chemically active and played a part in creating life.

Strong parallels with Earth’s evaporated lakes

One of the most fascinating facts about the Bennu discovery is that the patterns of minerals on Bennu are similar to the patterns of minerals on Earth in dry lake beds and closed basins, which are also known as evaporites.

On Earth, these are formed due to the evaporation of water over thousands of years, which leads to the formation of layers of salt deposits. As mentioned in the study published in PubMed, Bennu also follows a similar pattern of mineral formation, which indicates that evaporation patterns are not exclusive to Earth and are a normal phenomenon on other planets as well.

This also gives scientists a sense of understanding about other planets because they can relate the environment on other planets with the environment on Earth, which they are already familiar with. In other words, Bennu was a miniature version of a salt lake, except that it was formed in space billions of years ago.

Rare minerals point to long-lived brines

Some of the most significant discoveries in the samples collected from Bennu are the presence of sodium carbonate minerals, including trona, which are rare in meteorites but common in the evaporated environments of lakes on Earth.

As stated in the press release by the Smithsonian Institution, the presence of these minerals indicates that the parent body of Bennu likely had stable, long-lasting brines that were subject to cycles of evaporation and chemical concentration.

This is important to scientists because it indicates that the presence of water was not just temporary but was present in a way that was chemically active, meaning that complex reactions were more likely to have occurred.

Organic molecules strengthen the case for life’s ingredients

Besides minerals, Bennu samples also include organic compounds such as amino acids and nucleobases. These are fundamental compounds of life. In a release by NASA, it was noted that the presence of organics and evaporite minerals together indicated that a water-rich environment on asteroids could have supported the presence of pre-biotic chemistry.

Scientists believe that impacts from such asteroids could have delivered the necessary ingredients to early Earth, which could have led to the chemistry necessary for life. The presence of both water-related minerals and organics within the same samples further supports the theory of asteroids as deliverers of life.

Advanced tools uncover microscopic details

To obtain this data, the researchers employed advanced technologies, including scanning electron microscopy and X-ray spectroscopy, which enabled them to analyze the sample from Bennu on a very small scale without damaging it. As the Smithsonian Institution puts it, “these technologies allowed for precise detection of the intricate structures of minerals and chemical compositions within the sample.”

This technology is very useful in the field of planetary studies, as it enables planetary researchers to analyze the samples that come from space, which was not possible even a few decades ago.

A new view of asteroids and early history

These Bennu samples indicate that the asteroids were not just lifeless rocks but were dynamic environments influenced by water and chemistry over long periods.

As emphasized by NASA and ScienceDaily, the discoveries change the way scientists think about the early solar system.

Ultimately, Bennu is more than just a rock because it is a time capsule that holds the evidence of ancient brines and complex chemistry that may have been responsible for making life possible on the planet.