Formation and evolution of carbonaceous asteroid Ryugu: Direct evidence from returned samples

Area of Science:

• * Planetary Science
• * Astrogeology
• * Cosmochemistry

Background:

• * The Hayabusa2 mission successfully returned samples from the carbonaceous asteroid Ryugu to Earth.
• * Asteroid Ryugu is a C-type asteroid, believed to hold clues about the early Solar System.

Purpose of the Study:

• * To analyze the mineralogical and chemical composition of Ryugu samples.
• * To determine the formation location and timeline of Ryugu's parent body.
• * To understand the aqueous alteration processes Ryugu experienced.

Main Methods:

• * Microscopic and spectroscopic analysis of 17 Ryugu samples (1-8 mm).
• * Identification of mineral phases, including phyllosilicates, carbonates, olivine, and pyroxene.
• * Numerical simulations incorporating mineralogical and physical sample properties.

Main Results:

• * Discovery of carbon dioxide-bearing water inclusions in pyrrhotite, indicating outer Solar System origin.
• * Low abundance of high-temperature materials (chondrules, CAIs); high abundance of phyllosilicates and carbonates.
• * Evidence of low-temperature, high-pH aqueous alteration with low water/rock ratios (<1).

Conclusions:

• * Ryugu's parent body formed in the outer Solar System through aqueous alteration.
• * Formation occurred approximately 2 million years after the start of Solar System formation.
• * Ryugu samples provide insights into the composition and evolution of early Solar System materials.