Ganymede, the largest moon in the solar system, has signs of an enormous ancient impact that would have redistributed its mass, changing its orientation in relation to Jupiter
By Jacklin Kwan
3 September 2024
The solar system’s largest moon, Ganymede, alongside Jupiter in a picture taken by NASA’s Cassini spacecraft
NASA/JPL/University of Arizona
A massive collision billions of years ago may have dramatically reoriented Ganymede, Jupiter’s largest moon.
Naoyuki Hirata at Kobe University, Japan, and his colleagues studied Ganymede’s extensive furrow system, a series of concentric troughs believed to be remnants of the largest impact structure in the outer solar system.
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The centre of the furrow system aligns closely with Ganymede’s tidal axis – the imaginary line running to Jupiter from the centre of the moon’s 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.
Through simulations, the researchers determined that the impactor responsible probably had a diameter of about 150 kilometres – 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.
Andrew Dombard at the University of Illinois Chicago says that if an asteroid like that hit Earth, “it would be a global sterilising event, a bad day”.