An evaporite sequence from ancient brine recorded in Bennu samples

Area of Science:

• Planetary Science
• Astrogeology
• Cosmochemistry

Background:

• Brines form from evaporating or freezing water-rich fluids.
• Mineralogical evolution of terrestrial brines is understood, but extraterrestrial brines remain poorly constrained due to lack of direct sampling.
• Remote sensing suggests brines exist on outer Solar System icy bodies.

Purpose of the Study:

• To analyze salt minerals in samples returned from asteroid (101955) Bennu.
• To understand the formation and evolution of late-stage brines on early asteroid parent bodies.
• To infer the potential presence of similar brines on icy Solar System bodies.

Main Methods:

• Analysis of returned asteroid samples from the OSIRIS-REx mission.
• Identification of mineralogical composition, including diverse salt types.
• Comparison of findings with terrestrial brine evolution and extraterrestrial observations.

Main Results:

• Discovery of diverse salt minerals in Bennu samples, including sodium-bearing phosphates, carbonates, sulfates, chlorides, and fluorides.
• These salts formed from the evaporation of a late-stage brine early in Bennu's parent body history.
• The salts are sensitive to atmospheric exposure, highlighting the importance of sample return and curation.

Conclusions:

• The presence of diverse salts confirms the existence of ancient brines on asteroid parent bodies.
• Findings support the hypothesis that similar brines may persist in the interiors of icy bodies like Ceres and Enceladus.
• Sample return missions are crucial for detailed analysis of volatile-rich extraterrestrial materials.