The Moon probably was born when the young Earth was hit by another planet. That blasted a lot of debris into space. Much of it came together to form the Moon.

But Earth wasn’t the only world to get smacked around in the early solar system. One of the others might have been Ganymede, the largest moon of Jupiter. A recent study suggested that a giant asteroid slammed into it, making it wobble for a thousand years.

Ganymede is the largest moon in the solar system – bigger than the planet Mercury. It probably has an ocean of liquid water below its icy crust. The ocean might be 60 miles deep, and hold more water than all of Earth’s oceans combined.

The new study looked at some long ripples on the surface, the way Ganymede spins, and other evidence. Researchers then used computer models to simulate Ganymede’s history. Their work suggested that Ganymede was hit by an asteroid about four billion years ago. The asteroid was almost 200 miles in diameter, and hit near the north pole. That caused Ganymede to wobble. Eventually, it flipped over on its side. What had been the equator became the poles as Ganymede settled down after a massive impact.

Jupiter is close to our moon at nightfall. It looks like a brilliant star. Aldebaran, the brightest star of Taurus, is to the lower right of Jupiter. Binoculars reveal Jupiter’s four big moons, including Ganymede – a world that might have suffered a “big whack” billions of years ago.

Script by Damond Benningfield