Unexpected Discovery in NASA’s Asteroid Samples Suggests Bennu Originated from an Ocean World

Space

Scientists examining samples brought back by NASA from an asteroid have made a surprising discovery that suggests the space rock, Bennu, might have once been part of an ancient ocean world.

The researchers found water-soluble magnesium-sodium phosphate in the mottled stones from Bennu. This mineral was unexpected because it didn’t appear in any of the data collected by the spacecraft when it was at the asteroid. Phosphate compounds are crucial for all known life, as they form the backbone of DNA.

The findings, published in the journal Meteoritics & Planetary Science, add to the mystery of Bennu, which has puzzled scientists throughout the OSIRIS-Rex mission. The asteroid has been nicknamed the “trickster asteroid” for this reason.

“The presence and state of phosphates, along with other elements and compounds on Bennu, suggest a watery past for the asteroid,” said Dante Lauretta, the principal investigator, in a statement.

NASA’s OSIRIS-Rex mission, which stands for Origins, Spectral Interpretation, Resource Identification, and Security Regolith Explorer, was launched in 2016. The robotic spacecraft completed its 4-billion-mile journey when it dropped a capsule from 63,000 miles above Earth onto a patch of Utah desert last year. This mission marked the first time the U.S. has collected a sample from an asteroid. These samples are the most significant space souvenirs NASA has obtained since the Apollo moon rocks, gathered between 1969 and 1972.

NASA chose Bennu for the mission because it has a very slim chance of hitting Earth in the coming centuries. Understanding the asteroid could be useful for future efforts to redirect it if necessary.

Additionally, Bennu was selected because it is rich in carbon, which means it might contain the chemical building blocks of life. Some of its mineral fragments could be older than the 4.5 billion-year-old solar system. These grains of stardust might have come from dying stars or supernovas that eventually led to the formation of the sun and planets.

All forms of life on Earth have specific chemicals in their makeup, such as amino acids and sugars. Scientists have known that asteroids contain molecules believed to be the precursors to these chemicals. This is why many believe that space rocks brought these molecules to Earth through ancient collisions. By studying the Bennu samples, scientists hope to learn more about how these ingredients could have evolved.

“What I want to know is how you go from a simple carbon molecule, like methane, which is a natural gas, to something like amino acids, which make our proteins, or nucleic acid, which makes up our genetic material,” Lauretta said last year.

His ultimate goal is to find evidence of amino acids starting to link together through chemical bonds to form a chain, known as a peptide, which would signal the beginning of protein evolution.

The mission successfully brought back about a half-cup of crushed rocks and dirt. So far, researchers have been pleased with their findings.

The sample is rich in nitrogen and carbon, which are essential ingredients for life. Early analysis has found many clay minerals, particularly serpentine. This is similar to the type of rocks found at mid-ocean ridges on Earth, where geologists believe the recipe for life may have begun on our planet.

The magnesium-sodium phosphate in the Bennu sample is similar to sodium phosphates found on Enceladus, a moon of Saturn. Enceladus is covered by a saltwater ocean under ice and is known to shoot enormous geysers into space. Similar phosphate-enriched fluids are found in Earth’s soda lakes, such as Last Chance and Goodenough in Canada.

In the new OSIRIS-Rex paper, scientists suggest a “possible link” between Bennu and Enceladus, but more research is needed to prove this idea. The study of the sample has only just begun.

“These findings highlight the importance of collecting and studying material from asteroids like Bennu,” Lauretta said, “especially low-density material that would typically burn up if it were to enter Earth’s atmosphere.”