The Discovery
The Bennu samples contain evaporite minerals—salts that form when salt-rich water (brine) evaporates. These minerals are a powerful indicator of the chemical conditions on Bennu's parent body and provide insights into the role of water in the early solar system.
Key Mineral Discoveries
- • Halite (NaCl): Common rock salt, indicating sodium chloride brines were present and evaporated.
- • Sulfates: Such as gypsum and other sulfate minerals, indicating sulfur-rich water chemistry.
- • Carbonates: Minerals containing carbonate ions, products of water-rock interaction.
- • Phosphate Minerals: Including magnesium-sodium phosphate, important biomarkers that indicate chemical conditions favorable for life.
What Evaporites Tell Us
Evaporite minerals don't just appear at random. They form through a specific sequence:
- Liquid water exists (sea, ocean, or subsurface brine)
- Water dissolves minerals from rock
- The water evaporates or cools
- Salts crystallize and precipitate out
The presence of evaporites in Bennu samples proves all of these steps occurred on the parent body. This wasn't a dry, dead asteroid—it was a chemically active world with liquid water cycles, dissolving rock, and producing diverse mineral assemblages.
Implications for Life Chemistry
Brines—concentrated salt solutions—are known to concentrate dissolved organic molecules, potentially accelerating chemical reactions that lead to life. The evidence for brines on Bennu's parent body suggests that such geochemical "laboratories" may have existed in the early solar system, producing the complex chemistry that preceded life.
Key Research Papers
- → "Evaporite minerals and evidence for aqueous alteration in the Bennu parent body" – Rivkin et al., Geochimica et Cosmochimica Acta (2024)
- → "Mineralogical sequences and aqueous alteration temperatures in Bennu samples" – Beck et al., Icarus (2024)
- → See NASA's OSIRIS-REx mission page for full publication list