Massive asteroid impact may have shifted axis of solar system’s largest moon

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Jupiter’s moon Ganymede may have shifted on its axis when a massive asteroid hit it about 4 billion years ago, a new study suggests.

Ganymede, the largest moon in the solar systemis even larger than Mercury and the dwarf planet Pluto. And previous research has found evidence suggesting that beneath its thick, icy crust lies a salty ocean which is 10 times deeper than Earth’s oceans.

But many questions remain about the moon, and scientists need more high-resolution images of its surface to solve the mysteries surrounding Ganymede’s history and evolution.

Deep grooves cover large swaths of Ganymede’s surface, and they form a pattern of concentric circles around a point that has led some astronomers to believe the moon experienced a major impact event in its past.

“Jupiter’s moons Io, Europa, Ganymede and Callisto all have interesting individual features, but the one that caught my attention was these grooves on Ganymede,” Naoyuki Hirata, an assistant professor of planetary science at Kobe University in Japan, said in a statement. “We know this feature was created by an asteroid impact about 4 billion years ago, but we weren’t sure how big that impact was and what effect it had on the moon.”

Hirata is the author of a new study, published Tuesday in the journal Scientific reportswhich explores what created Ganymede’s groove system and the fallout from the impact – which could be studied in more detail by the European Space Agency’s Juice spacecraft, currently en route to study Jupiter and its moons.

An ancient impact

Ganymede has long intrigued Hirata, who calls the discovery of its evolution “significant.” The moon’s surface is a study in contrasts, with bright regions of ridges alongside grooves that cut through darker areas.

Hirata took a closer look at the system of grooves on Ganymede, which extend from a single point on the moon’s surface like the concentric cracks that form when a rock hits a car’s windshield, he said.

Hirata noticed that the center point of the groove lay along the moon’s rotation axis, implying that an event such as a large impact would have caused the moon to completely reorient itself.

Previous research has suggested that a a large planetary body collided with Pluto Early in its history, the dwarf planet was reorganized, resulting in a distinctive “core” on its surface. Hirata believes a similar scenario occurred on Ganymede, with its icy shell and subsurface ocean.

A sudden change in the way mass is…