The team's infrared scrutiny of Ryugu's anhydrous grains reveals that some are abundant in amorphous silicates, bearing a mineral composition akin to that of certain anhydrous primitive asteroids, comets, and interplanetary dust particles of cometary origin.
Recent infrared analysis of grains from the carbonaceous asteroid Ryugu points to a profound connection between the origins of Ryugu’s parent body and the formation sites of comets and primitive asteroids in the outer protoplanetary disk.
Asteroid Ryugu: A Second-Generation Asteroid
As a product of the reassembly of fragments from a larger body in the main asteroid belt, Ryugu stands as a second-generation carbonaceous asteroid. Late in 2020, the Japanese Hayabusa2 mission made a triumphant return to Earth, bringing with it 5.4 grams of material retrieved from Ryugu. These samples primarily comprise hydrated minerals originating from Ryugu’s parent asteroid, transforming via aqueous alteration of the initial anhydrous grains. These grains reveal the makeup of the protoplanetary dust that contributed to the formation of Ryugu’s parent asteroid.
Deducing Asteroid Ryugu’s Composition
Leading a new study, the teams from IAS (Orsay, France), Tohoku University (Japan), and the SMIS beamline of synchrotron SOLEIL (France) have focused on infrared hyperspectral imaging of two millimeter-sized Ryugu “stones”. The aim was to discern their mineral composition and compare the asteroid with other extraterrestrial substances – within the lab (meteorites and interplanetary dust) and beyond our planet (asteroids and comets). The research findings are published in The Astrophysical Journal Letters.
Unveiling Connections to Primitive Asteroids and Comets
The team’s infrared scrutiny of the asteroids anhydrous grains reveals that some are abundant in amorphous silicates, bearing a mineral composition akin to that of certain anhydrous primitive asteroids, comets, and interplanetary dust particles of cometary origin. These amorphous-rich grains were shaped by pre-accretion processes in the protoplanetary disk, which served as the nursery of our solar system.
Tracing Back to the Outer Solar System
In line with these findings, Ryugu’s parent asteroid appears to be a large planetesimal formed in the outer solar system, in a reservoir neighboring the comet accretion region. Planetary migrations subsequently relocated Ryugu’s parent asteroid to the main asteroid belt. Following these movements, aqueous alteration would have shaped the spectral diversity we observe today among the “primitive” asteroid classes.
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