Asteroid Itokawa … but when and how did it form exactly?OPEN ACCESS
Fred Jourdan, Nicholas E. Timms, Tomoki Nakamura, William D.A. Rickard, Celia Mayers
Geochimica et Cosmochimica Acta
Available online 14 September 2025
“Asteroid Itokawa is made of reassembled fragments from a monolithic parent asteroid which got shattered during a collision with a large object. Data are scarce regarding the metamorphic processes that occurred on the monolithic parent body and the age and nature of the catastrophic disruption event. Here, we investigate the timing of the metamorphism inside the parent body of Asteroid Itokawa and the age and nature of the catastrophic breakup event recorded in particles returned from Itokawa. We studied three regolith dust particles recovered by the Hayabusa space craft from the rubble pile asteroid 25,143 Itokawa using electron backscatter diffraction, time-of-flight secondary ion mass spectrometry, and 40Ar/39Ar dating techniques. Our results show that none of the particles show noticeable sign of shock metamorphism. Two of the particles yielded 40Ar/39Ar age of 4559 ± 61 and 4130 ± 33 million years (Ma), while a third particle returned a maximum error age of 703 ± 53 Ma. When combined with existing data, and diffusion models, these results show that ∼4.5 billion years (Ga) ago, Itokawa’s parent monolithic body cooled down from a peak metamorphism temperature ∼800 °C to ∼300 °C in less than 64 million years at a depth of >20 km. Then at ∼4.22 Ga, Itokawa’s parent body was shattered in a collisional process involving a heterogeneous temperature distribution during the impact, with some regions escaping shock metamorphism and experiencing less than a few hundred degrees Celsius. The fragments re-agglomerated in a larger rubble pile body where they subsequently cooled down over tens of millions of years. For the next 4 billion years, Asteroid Itokawa was regularly impacted and progressively shrunk by mass wasting.”
