Approximately 4 billion years ago, one of the most massive asteroids ever recorded in the Solar System collided with Ganymede, the largest moon of Jupiter. This event not only caused a shift in Ganymede's rotational axis but also permanently altered its geological structure. Research suggests that the asteroid, which had an estimated diameter of about 300 kilometers, was 20 times larger than the one that caused the extinction of the dinosaurs on Earth. Its impact created a crater with a diameter between 1400 and 1600 kilometers, drastically changing the surface of the moon.

On the surface of Ganymede, there are large grooves that form concentric circles around the impact point, which led scientists in the 1980s to hypothesize that this pattern was the result of a massive asteroid impact. However, it was only recent research by planetary scientist Naoyuki Hirate from Kobe University, which used computer simulations, that allowed a more detailed analysis of the event. Hirata discovered that the impact point was almost perfectly positioned on the meridian farthest from Jupiter, suggesting that Ganymede underwent a process of reorientation of its rotational axis.

This change was caused by a strong shift of mass within Ganymede due to the asteroid, and simulations showed that only an impact of this magnitude could cause such a drastic effect. The research results also point to potentially significant changes in the moon's internal structure, including changes in its subsurface ocean, which is more than 100 kilometers deep. Scientists believe that these oceans contain more water than all of Earth's oceans combined, making Ganymede an intriguing object in the search for possible life forms beyond Earth.

Despite the importance of this discovery, many details about the thermal and structural consequences of the impact on Ganymede's interior are still unknown. The European Space Agency (ESA) plans the JUICE (JUpiter ICy moons Explorer) mission, which will reach Ganymede's orbit in 2034. During the six-month mission, JUICE will collect data that will help scientists in further analyzing the effects of this ancient impact and its influence on the evolution of Jupiter's largest moon.

Thanks to this mission, scientists will gain new insights into the history of the Solar System and the process of shaping icy satellites like Ganymede, which will enable a better understanding of the dynamics of planets and moons over billions of years.

Source: Kobe University