An ancient asteroid 20 times larger than the one that wiped out the dinosaurs could hit Jupiter’s moon Ganymede
New research suggests that Jupiter’s moon Ganymede may have shifted on its axis when a massive asteroid struck it about 4 billion years ago. Ganymede, the largest moon in the solar system, is even larger than Mercury and the dwarf planet Pluto. And previous studies have found evidence that beneath its thick icy crust is a salty ocean 10 times deeper than Earth’s oceans. But many questions remain about the moon, and scientists need higher-resolution images of its surface to solve the mysteries surrounding Ganymede’s history and evolution. Most of Ganymede’s surface is covered with deep grooves.
They form a pattern of concentric circles around a point, which has led some astronomers to believe that the moon has experienced a major impact event in the past. “Jupiter’s moons Io, Europa, Ganymede and Callisto all have interesting individual features, but it was Ganymede’s grooves that caught my attention,” Naoyuki Hirata, an assistant professor of planetary science at Kobe University in Japan, said in a statement. “We know that this structure was formed by an asteroid impact about 4 billion years ago, but it was unclear how large this impact was and how it affected the moon.”
Hirata is the author of a new study published Tuesday in the journal Scientific Reports. The study investigates how Ganymede’s groove system formed and the effects of that impact. The study may be studied in more detail by the European Space Agency’s Juice spacecraft, which is currently studying Jupiter and its moons. Ganymede has long fascinated Hirata, and he thinks it is “important” to uncover its evolution. The moon’s surface is a constellation of contrasts, with grooves running through dark areas next to bright ridges.
Hirata took a closer look at Ganymede’s groove system. It starts at a single point on the moon’s surface and resembles the concentric cracks that form when a rock hits a car windshield, he said. Hirata noticed that the center of the groove is aligned with the moon’s rotation axis, suggesting that some kind of big impact event caused the moon’s complete rearrangement.
Previous studies have suggested that a large planetary body collided with Pluto at an early stage, changing the distribution of ice on the dwarf planet and resulting in the formation of a characteristic “heart” on the planet’s surface. Hirata believes a similar scenario played out on Ganymede, which has an ice shell and ocean beneath its surface. A sudden change in the distribution of mass on the planet can change the position of its axis – the imaginary line around which the planetary body rotates. If a large asteroid collides with the planet, it will create a gravitational anomaly, changing the planet’s rotation. Hirata then calculated what kind of impact could have caused Ganymede’s current orientation.
The researchers believe that Ganymede’s interior looks like a club sandwich, composed of alternating layers of ice and ocean. Understanding how the impact changed the moon will provide insight into its intriguing internal structure, Hirata said.
“I want to understand the origin and evolution of Ganymede and other Jupiter moons,” he said. “The large impact must have had a significant impact on Ganymede’s early development, but the thermal and structural effects of the impact on Ganymede’s interior have not been studied at all. I think that next, further research on the internal evolution of icy moons could be carried out.”