Giant impact on early Ganymede and its subsequent reorientation

Abstract

The origin and early evolution of the Jovian moon Ganymede, known to have an internal ocean, have garnered considerable interest in the field of origin of satellites and life. Ganymede has an ancient impact structure, called a furrow system. The furrow system is the largest impact structures in the outer solar system and the impact should have significantly affected Ganymede's early history; however, its impact is poorly understood. Here we show that mass redistribution induced by the furrow-forming impact caused a reorientation (true polar wander) of Ganymede. The center of the furrow system is located close to the tidal axis, indicating that the impact created a positive 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 degree and 90 degree can reproduce the current location of the furrow system. Furthermore, this ejecta model is adoptable in Pluto's reorientation. Although it is proposed that Pluto's reorientation indicates the presence of a global ocean, our model indicates that it occurs even if no ocean.