Asteroid Bennu Samples Reveal Secrets of Early Solar System Formation
- Analysis of a half-gram sample of material from asteroid Bennu reveals that the carbon-rich body formed near the water-ice boundary in the early solar system, with the gas...
- Isotope geochemistry teams at ETH Zürich studied a half-gram portion of the roughly 120 grams of material returned by NASA's OSIRIS-REx mission.
- The data suggest Bennu, Ryugu, and the CI-meteorites originated in a transitional zone close to the water-ice line roughly 4,5 Milliarden Jahren ago.
Analysis of a half-gram sample of material from asteroid Bennu reveals that the carbon-rich body formed near the water-ice boundary in the early solar system, with the gas giant Jupiter playing a critical filtering role. Researchers at ETH Zürich examined isotopes of iron, titanium, and chromium from the sample, which was brought to Earth by NASA’s OSIRIS-REx spacecraft in September 2023. The findings provide new data on how raw materials mixed before planets took their current shape.
Isotope Analysis Yields a Chemical Fingerprint
Isotope geochemistry teams at ETH Zürich studied a half-gram portion of the roughly 120 grams of material returned by NASA’s OSIRIS-REx mission. Isotope ratios remain nearly unchanged over billions of years, creating a chemical fingerprint that reveals an object’s cosmic birthplace and age. According to the study published in Science Advances, titanium and iron are evenly distributed within Bennu. The isotopic pattern of Bennu matches that of asteroid Ryugu—sampled by Japan’s Hayabusa2 spacecraft—and rare, carbon-rich CI-meteorites. Isotope geochemist Maria Schönbächler notes that Bennu shares characteristics of both the inner and outer solar system, defying earlier theories that placed its origin entirely in the cold outer reaches where comets form.
Formation Near the Water-Ice Boundary
The data suggest Bennu, Ryugu, and the CI-meteorites originated in a transitional zone close to the water-ice line roughly 4,5 Milliarden Jahren ago. This boundary marks the distance from the young sun where water vapor freezes, allowing ice to act as a glue that binds fine dust particles. This setting explains why Bennu contains significant water, as vapor condensed locally during the asteroid’s formation. Researchers describe Bennu as a primitive body whose composition has remained largely unaltered since the birth of the solar system.
Jupiter’s Role in the Young Solar System
Schönbächler and her co-authors identify the gas giant Jupiter as a key player in shaping this dust reservoir. Jupiter formed rapidly within the first million years of the sun’s history and acted as a sieve that permitted only the finest dust to pass. Bennu orbits the sun once every 1.2 years and approaches close to Earth every six years. This proximity enabled the OSIRIS-REx mission to collect surface samples on September 23, 2023, in the Utah desert, paving the way for the laboratory analyses completed at ETH Zürich.
