]Possible asteroid impact caused largest moon of Jupiter to topple

A massive impact billions of years ago may have dramatically changed the orientation of Jupiter's largest moon, Ganymede.

Takayuki Hirata The researcher from Kobe University in Japan and his colleagues studied Ganymede's vast groove system, a series of concentric grooves that are thought to be the remnants of the largest impact structure in the outer solar system.

The centre of the groove system is nearly aligned with Ganymede's tidal axis (an imaginary line that runs from the centre of the side of the moon that always faces the planet towards Jupiter), which leads the researchers to speculate that the impact that created the grooves may have caused a massive redistribution of mass, reorienting the moon.

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But while the Ganymede impact likely had a major impact on the moon's early history, a lack of good data on the frigid world's gravity and topography complicates estimating the size of the impacting object, Hirata says.

Dombard says the model used in the paper doesn't take into account some of the complexities of Ganymede's unique ice structure. “I think it's a pretty good model to prove that this process can happen, but I don't necessarily trust the numbers,” he says.