The surface of Ganymede is covered with a mysterious groove system. In the 1980s, scientists assumed that these were traces of the largest astroblem. According to calculations, they were left by an asteroid with a diameter of about 300 kilometers. The author of a new scientific study showed that the collision had much more serious consequences.

Ganymede is one of the Galilean moons of Jupiter, the largest in the Solar System. Even the planet Mercury is smaller. It is claimed that an ocean hides its surface. The Voyager 1 and Galileo space probes discovered wonderful tectonic structures on Ganymede: depressions or, as they are also called, grooves. They often pass through the ancient dark regions of Galileo and Marius.

In 2020, Japanese scientists showed that the trough system, which stretches for 7,800 kilometers, forms concentric circles radiating from a single center, confirming the previous assumption about the origin of the effect.

The grooves are the oldest structures on Ganymede’s surface, dating back four billion years, and if so, they are an invaluable source of information about the moon’s geological history. One of the authors of the discovery of the giant astroblem on Ganymede, planetary scientist Naoyuki Hirata of Kobe University (Japan), modeled the effects of the impact. His paper was published in the journal Scientific Reports.

The scientist suggested that the material ejected by the collision with the asteroid created a positive gravity anomaly around the center of the crater. This changed the orientation of Ganymede, meaning its spin axis changed.

Ganymede, like many of the Solar System’s natural satellites, lies in a tidal capture zone, so it always has one side facing Jupiter, like the Moon does with respect to Earth.

Hirata noticed that the center of the groove system coincides with the longitude of the axis. According to the scientist, this indicates that the moon’s orientation has changed. Moreover, this situation is similar to what was observed in the Sputnik plain, the largest impact crater on Pluto, which suspected a positive gravitational anomaly and caused the orientation change. The center of the negative gravitational anomaly would gravitate towards the rotation axis in the opposite direction.

The author of the study calculated the probability that the center of the trough system would be where it is now after the satellite was reoriented. The model worked best with an asteroid radius of 150 kilometers and a transition crater radius of 700-800 kilometers (before the collapse).

“I am interested in the origin and evolution of Jupiter’s moons. This powerful impact had a significant impact on the early history of Ganymede. The thermal and structural consequences of the collision on its bowels have not yet been studied,” Hirata said in an interview with the university’s press service. The planetary scientist plans to devote his next work to the study of the evolution of the bowels of the largest moon.

Ganymede is the final destination of the JUICE mission launched by the European Space Agency more than a year ago. The probe is expected to enter orbit around the moon in 2034 and will crash into its surface after six months of observations.