# Giant impact on early Ganymede and its subsequent reorientation

## TL;DR

A massive ancient impact on Ganymede likely caused the moon to reorient itself, shifting its position relative to Jupiter's gravity.

## Contribution

The paper links Ganymede's furrow system to true polar wander via a giant impact and mass redistribution.

## Key findings

- An impactor with a 150 km radius and a steep angle best explains the furrow system's location.
- The impact likely caused mass redistribution leading to Ganymede's reorientation toward its tidal axis.
- Future missions may detect topographic or gravity anomalies from the impact and reorientation.

## Abstract

Ganymede has an ancient impact structure called a furrow system. The furrow system is the largest impact structure in the outer solar system, and the impact should have significantly affected Ganymede’s early history; however, its effects are poorly understood. No attention has been given to the center of the furrow system coinciding with Ganymede's tidal axis, indicating that mass redistribution induced by the furrow-forming impact caused a reorientation (true polar wander) of Ganymede. We propose that the impact ejecta created a mass anomaly that reoriented the impact site toward the tidal axis. We found that an impactor with a radius of 150 km and an incidence angle between 60° and 90° most accurately reproduces the current location of the furrow system. We predict that future explorations would reveal remnant topographic profiles or gravity anomalies associated with the furrow-forming impact and reorientation. Additionally, various possible explanations for the reorientation of Ganymede, such as an impactor-origin mascon beneath the basin or a thickness variation in the lithosphere, should be studied.