Fig. 5: Schematic diagram showing the progression of the impact-heating and disruption of the CI chondrite parent asteroid, to the accretion of Ryugu with unheated and heated material.
From: Hydrothermal alteration of Ryugu from a disruptive impact recorded in a returned sample
a, b Ivuna-like carbonaceous (CI) chondrite parent asteroid experiences aqueous alteration <100 °C. About 1 billion years ago, asteroid with CI chondrite mineralogy experiences a large disruptive impact, heating material up to 700 °C3. c Impact-disrupted material accretes into multiple CI chondrite rubble pile bodies, including bodies only of unheated material (i.e., <100 °C), mixtures of unheated and heated material, and those entirely composed of thermally altered CI material. d Ryugu accretes from mostly unheated material, but also accretes material heated by the impact. Buried and insulated heated material sustained temperatures between 230 and 400 °C on the order of a month, forming hydrothermally altered material like A0016. Regolith gardening later distributes this hydrothermally altered material across Ryugu, contributing to the weak 2.72 µm hydroxyl (-OH) band observed by Hayabusa2. Heated material is red. Unheated CI material is black. Sizes between stages b to c, and c to d are not to scale.
