New Bennu Samples Shed Light on Water’s Role in Early Solar System Chemistry

NASA's OSIRIS-REx mission has returned asteroid Bennu samples that offer unprecedented clues about the early solar system and the history of extraterrestrial water.

The retrieved material, the largest asteroid sample ever brought to Earth, provides scientists with critical evidence about the solar system’s primordial environment and evolutionary processes billions of years ago.

Why Bennu and the OSIRIS-REx Mission Matter

Nearly a year after the OSIRIS-REx spacecraft delivered pieces of Bennu, researchers are uncovering unexpected insights about this carbon-rich asteroid’s story. Bennu was selected because of its near-Earth orbit, convenient size, and the presence of organic compounds.

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These traits make Bennu a prime subject for studying the solar system’s earliest components. Bringing samples back to Earth enables far more detailed examination than space-based instruments can achieve. As noted by Universe Today, “Returning samples to Earth is the best and most complete way to study asteroids.”

Bennu is classified as a B-type asteroid, abundant in carbonaceous substances critical for unraveling the solar system’s beginnings. These constituents help trace how our planetary neighborhood formed. OSIRIS-REx lead scientist Dante Lauretta emphasized the importance: “Bennu potentially could have once been part of a wetter world.”

What Bennu’s Material Reveals

Around 120 grams of material have undergone extensive evaluation with cutting-edge methods like plasma mass spectrometry, infrared spectroscopy, and X-ray CT scanning. The analyses uncovered a diverse mixture of minerals and organics, including some unexpected components. The samples’ unaltered condition means they preserve their original makeup from billions of years ago without melting or re-crystallization.

One standout discovery is the detection of serpentine and other clay minerals, resembling those found along Earth's mid-ocean ridges. This points to past water interactions on Bennu. Dante Lauretta highlighted this surprise: “The biggest surprise for me is that there are salty crusts coating a subset of the particles. We’re probably pretty familiar with this in Arizona. If you have hard water, and you build up those white, crusty salts that clog your shower head and your faucets, that’s the same kind of process that we’re seeing on these asteroid samples. You had a salty liquid and it evaporated away and left what we call evaporite minerals behind.”

Implications for Planetary Science

The presence of these minerals suggests Bennu went through hydrothermal activity, similar to processes occurring on Earth's ocean floors. This supports the idea that water—a key ingredient for life—may have been more common in early space environments than once believed. The similarity between Bennu’s clay minerals and terrestrial analogs provides valuable comparative data for studying planetary formation and evolution.

Moreover, discovering water-soluble phosphates in the samples is particularly important. These molecules play essential roles in biology on Earth and their existence on Bennu hints at a broader distribution of life-favorable chemistry across the solar system. According to research published in Meteoritics and Planetary Science, “The presence and state of phosphates, along with other elements and compounds on Bennu, suggest a watery past for the asteroid.”

The comprehensive analysis by Dante S. Lauretta's team has generated a detailed profile of the sample, now accessible to the scientific community for further exploration. Lauretta remarked, “Finally having the opportunity to delve into the OSIRIS-REx sample from Bennu after all these years is incredibly exciting. This breakthrough not only answers longstanding questions about the early solar system but also opens new avenues of inquiry into the formation of Earth as a habitable planet.”