The largest moon in the solar system is Ganymede, which orbits the largest planet, Jupiter. New research suggests that an asteroid struck Ganymede four billion years ago, and the collision made the moon's tilt and texture what it is today.
According to Naoyuki Hirata, an assistant professor of planetology at Kobe University in Hyogo, Japan, the asteroid was around 20 times larger than the Chicxulub asteroid that caused the dinosaurs on Earth to go extinct 66 million years ago.
Ganymede is 50 percent larger than our own moon and is slightly bigger than the planet Mercury. It has an ocean beneath its icy surface. The ocean is up to 60 miles deep and is believed to possibly be able to harbor life. The moon also has other interesting features, including deep furrows that are visible on its surface.
The furrows resemble the cracks that spread outward from the spot where glass is struck and broken. They form concentric circles around the site of an asteroid impact, which altered the moon's topography and tilt forever.
What first caught Hirata's eye was that the crater left behind by the asteroid faces directly away from Jupiter. That clue pointed to the possibility that Ganymede had shifted on its rotational axis in the past.
Previous research conducted on Pluto with the New Horizons space probe supported the idea further, as Pluto was found to have shifted on its rotational axis due to an asteroid strike as well.
Hirata created computer simulations to determine what kind of event could have led to Ganymede's present-day position and figure out how big the asteroid was. He found that the asteroid probably had a radius of 93.2 miles.
In order to cause Ganymede to shift to its current position, the asteroid would have had to hit the moon at a 60 to 90-degree angle.
The resulting crater would have been between 870 miles and almost 1,000 miles in diameter, roughly equal to the size of the state of Alaska. During the aftermath of the collision, the crater filled up with dust and other materials, making its presence less obvious.
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