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Jupiter’s moon Ganymede may have shifted on its axis when a giant asteroid smashed into it about 4 billion years ago, according to a new study.
Ganymede, the largest moon in the solar system, is even larger than Mercury and the dwarf planet Pluto. And past research has found evidence to suggest that there is a salty ocean 10 times deeper than Earth’s oceans beneath its icy crust.
But many questions remain about the moon, and scientists need more high-resolution imagery of its surface to unravel the mysteries of Ganymede’s history and evolution.
Deep craters cover much of Ganymede’s surface, creating a pattern of concentric circles around a single spot that has led some astronomers to believe that the moon was heavily impacted in the past.
“Jupiter’s moons Io, Europa, Ganymede and Callisto all have interesting individual characteristics, but the one that caught my attention was these rings on Ganymede,” said Naoyuki Hirata, assistant professor of planetology at Kobe University in Japan, in statement. “We know that an asteroid impact created this feature about 4 billion years ago, but we weren’t sure how big this impact was and what effect it had on the moon.”
Hirata is the author of a new study, published Tuesday in the journal Scientific Reports, that explores what created Ganymede’s system of craters and what the impact was — which could be investigated more closely by the European Space Agency’s Juice spacecraft. . a way to study Jupiter and its moons.
Ancient influence
Ganymede has long held a fascination for Hirata, who said he believes it is “wise” to reveal its evolution. The surface of the moon is a study in contrasts, with bright regions of ridges alongside ridges that cut across darker areas.
Hirata looked at the system of cracks on Ganymede, which extend from a single point on the moon’s surface like the concentric cracks that form when a rock hits a car windshield, he said.
Hirata noted that the center point of the crater was along the moon’s axis of rotation, suggesting that the moon’s complete reorientation was due to a large impact event.
Previous research has suggested that a large planetary body collided with Pluto early in its history, which rearranged the distribution of ice on the dwarf planet and led to the formation of a distinctive “core” on the planet’s surface. Hirata said he believes a similar situation occurred on Ganymede, with its icy shell and subsurface ocean.
A sudden change in the way mass is distributed on a planet can change the position of its axis, or the imaginary line around which planetary bodies rotate. When a large asteroid slams into a planet, it creates a gravitational anomaly that changes the way a planet rotates. So Hirata calculated what kind of impact Ganymede’s current orientation could create.
His equations showed that an asteroid about 186 miles (300 kilometers) wide initially created a crater about 870 to 994 miles (1,400 to 1,600 kilometers) in diameter.
The asteroid was 20 times larger than the one that hit the Yucatan Peninsula in Chicxulub, Mexico, and as a result the dinosaurs fell to Earth 66 million years ago. The crater left on Ganymede was 25% the size of the moon, according to the study.
Up-close investigation juice mission
It’s still unclear how much Ganymede’s axis has shifted, Hirata said. But future data collected by the Juice mission, or Jupiter Icy Moons Explorer, could shed more light on Ganymede’s history and impact event.
The spacecraft, launched in April 2023, completed a historic flyby of Earth and the Moon on August 21 that put it on track to reach Jupiter and its moons in 2031.
It is difficult for researchers to determine whether an ancient impact created the craters on Ganymede without more data, which the Sun mission could provide, said Adeene Denton, a postdoctoral researcher in the Lunar and Planetary Laboratory at the University of Arizona. She was not involved in Hirata’s study.
“This paper presents an interesting premise, with a lot to think about, for the evolution of lunar and sea ice,” said Denton, who co-authored a study in April covering the impacts on Pluto and its large basin. , called Sputnik Planitia, makes up the left lobe. of the core element observed by astrologers.
“It’s worth noting that considering ancient, degraded geological features on planetary bodies and how they affect the planet’s orientation can be questioned,” she said. “With so little information on the large, old features, it is difficult to be confident that this feature will be identified as a basin, as well as a possible mass anomaly. Fortunately, unlike Pluto and (Sputnik Planitia), we are going back to Ganymede soon and can get the additional information needed to solve this.”
Researchers believe Ganymede’s interior may resemble a club sandwich, stacked with alternating layers of ice and ocean. He could understand how the influence of the moon has changed revealing insights into its interesting internal structure, said Hirata.
“I want to understand the origin and evolution of Ganymede and the other moons of Jupiter,” he said. “The giant must have had a significant impact on Ganymede’s early evolution, but the thermal and structural effects of the impact on Ganymede’s interior have not yet been investigated. I believe further research into the internal evolution of ice moons could be done afterwards.”
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