# Hydrothermal alteration of Ryugu from a disruptive impact recorded in a returned sample

## TL;DR

A sample from asteroid Ryugu shows signs of high-temperature hydrothermal alteration, suggesting it was affected by a major impact event.

## Contribution

The study identifies new sulfide minerals in a Ryugu sample, indicating high-temperature hydrothermal alteration under acidic conditions.

## Key findings

- Sulfides in the Ryugu sample show alteration between 230 to 400 °C under acidic and oxidizing conditions.
- The mineral composition of the sample suggests it was near the site of a large impact on Ryugu’s parent body.
- The findings link sample data to Hayabusa2 spectral observations, supporting a disruptive impact origin for Ryugu.

## Abstract

Samples returned from C-type asteroid (162173) Ryugu by JAXA’s Hayabusa2 spacecraft provide material free of terrestrial alteration for analysis. Previous work shows that Ryugu was aqueously altered below 100 °C under neutral to alkaline fluid conditions. Such low-temperature alteration was unexpected based on spacecraft observations which indicated that Ryugu’s surface may be thermally altered. Here we show that sulfides in a single particle (A0016) returned by the Hayabusa2 mission are unlike any previously described from Ryugu. The presence and compositions of violarite, pyrite, chalcopyrite, pentlandite, and Fe-depleted pyrrhotite grains provide direct evidence for hydrothermal alteration between 230 to 400 °C under highly oxidizing and acidic fluid conditions. We hypothesize that A0016 was near to the site of a large impact that disrupted Ryugu’s precursor parent body.

A Ryugu sample shows hydrothermal alteration (230–400 °C), linking returned material to Hayabusa2 spectral data and supporting Ryugu’s formation via a disruptive impact event, bridging spacecraft and sample observations.