A massive collision billions of years ago may have dramatically reoriented Ganymede, Jupiter鈥檚 largest moon.
at Kobe University, Japan, and his colleagues studied Ganymede鈥檚 extensive furrow system, a series of concentric troughs believed to be remnants of the largest impact structure in the outer solar system.
The centre of the furrow system aligns closely with Ganymede鈥檚 tidal axis 鈥� the imaginary line running to Jupiter from the centre of the moon鈥檚 side that always faces its planet. This led the researchers to suggest that the impact that formed the furrows caused a significant redistribution of mass that reoriented the moon.
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Through simulations, the researchers determined that the impactor responsible probably had a diameter of about 150 kilometres 颅鈥� significantly larger than the one that caused the extinction of the dinosaurs on Earth, which is estimated to have had a diameter of about 10 kilometres.
at the University of Illinois Chicago says that if an asteroid like that hit Earth, 鈥渋t would be a global sterilising event, a bad day鈥�.
Upon impact, this asteroid would have breached Ganymede鈥檚 icy crust into the liquid oceans below, creating a transient crater and hurling vast amounts of material across the moon鈥檚 surface.
As this settled, it would have formed a thick blanket of ejecta around the impact site, creating a region where gravity is stronger due to the extra mass. Over time, this anomaly would cause Ganymede to reorient, aligning the impact site with its tidal axis, the simulation showed.
Hirata鈥檚 team compared this process with an event on Pluto, where a large impact created a basin called Sputnik Planitia, leading to a reorientation of the dwarf planet.
However, although it is likely that the Ganymede impact significantly affected the moon鈥檚 early history, estimating the size of the object that hit it is complicated because we lack good data on the gravity and topography of this frigid world, says Hirata.
Dombard says the model used in the paper doesn鈥檛 account for some of the complexities of Ganymede鈥檚 unique icy structure. 鈥淚 think it is very good for establishing that this process could occur, but I don鈥檛 necessarily trust the numbers,鈥� he says.
Scientific Reports
