60-mile wide asteroid reshaped our solar system’s largest moon

A catastrophic event roughly 4 billion years ago shook our solar system to its core. Kobe University researcher Hirata Naoyuki discovered that a massive asteroid impact on Ganymede, Jupiter's largest moon, drastically reshaped its surface and altered its geological history.

Ganymede: Jupiter's largest moon

Bigger than the planet Mercury itself, Ganymede tops the charts as the largest moon in our solar system. But, it is not just the size that makes Ganymede intriguing.

Scientists have found that Ganymede's surface has two main types of terrain: bright, ridged areas and darker, older sections filled with impact craters.

Splits and furrows, that resemble concentric circles around a specific spot, mark Ganymede's surface. These furrows, first noticed back in the 1980s, hinted at a monumental impact event.

What's most fascinating about this mammoth moon is that underneath its icy crust, there’s a subsurface ocean that might hold more water than all of Earth's oceans combined, sparking exciting possibilities about the potential for life.

Beyond its sheer size, Ganymede has its own magnetic field, which is pretty unique for moons in our solar system. This magnetic field interacts with Jupiter’s strong magnetosphere, creating some amazing and dynamic auroras.

Researchers are still studying Ganymede’s atmosphere, which has a thin layer of oxygen, to get a better grasp of its geological and magnetic features.

Asteroid impact on Ganymede

“The Jupiter moons Io , Europa , Ganymede and Callisto all have interesting individual characteristics, but the one that caught my attention was these furrows on Ganymede,” says the Kobe University planetologist HIRATA Naoyuki.

“We know that this feature was created by an asteroid impact about 4 billion years ago, but we were unsure how big this impact was and what effect it had on the moon.”

To solve the puzzle, Hirata analyzed how the impact location almost perfectly aligned with Ganymede's meridian farthest away from Jupiter. This alignment indicated a pattern similar to an impact event on Pluto that triggered an axis shift.

Known for his expertise in simulating asteroid and moon impacts, Hirata leveraged his knowledge to decipher the kind of impact that could have caused Ganymede's dramatic reorientation.

Simulations of Ganymede asteroid impact

In the latest edition of Scientific Reports , Hirata revealed that the asteroid causing this colossal impact likely had a diameter of around 300 kilometers.

This figure is 20 times larger than the asteroid that ended the era of the dinosaurs on Earth by creating a transient crater between 1,400 and 1,600 kilometers in diameter.

Simulations pointed out that only an asteroid of this monstrous size could cause a shift in Ganymede's rotational axis.

Ganymede, asteroids, and the future

“I want to understand the origin and evolution of Ganymede and other Jupiter moons. The giant impact must have had a significant impact on the early evolution of Ganymede, but the thermal and structural effects of the impact on the interior of Ganymede have not yet been investigated at all. I believe that further research applying the internal evolution of ice moons could be carried out next,” explains Hirata.

Good news is on the horizon for Hirata and other researchers. Ganymede, famous for its subsurface oceans, is the final target for the ESA’s JUICE space probe .

The probe is expected to enter Ganymede's orbit by 2034, and will spend six months collecting data that might just answer Hirata's pressing questions.

Importance of liquid water

Liquid water is a critical element in the search for extraterrestrial life, and Ganymede's subsurface ocean places it firmly in the spotlight of astrobiological research. Beneath its thick icy crust, this ocean may provide the essential conditions for life as we know it.

The presence of liquid water, combined with the potential for chemical interactions between the ocean and rocky mantle, creates a compelling environment for biological processes.

This raises significant questions: Could extremophiles, organisms that thrive in harsh conditions, exist there? Investigating these possibilities not only enriches our understanding of Ganymede but also expands the parameters of habitability in the universe.

Collaborations on asteroid and Jupiter study

The study of Ganymede and its mysteries is not a solitary pursuit; rather, it underscores the importance of interdisciplinary collaborations.

Scientists across various fields -- including planetary science, geology, astrobiology, and even materials science -- are contributing to a holistic understanding of this moon.

By sharing insights and methodologies, researchers can tackle complex questions regarding the moon's formation, history, and the implications for life.

As the JUICE mission approaches, the integration of diverse scientific expertise will be paramount in analyzing the data and further unraveling Ganymede's enigmatic characteristics, showcasing the collaborative spirit that drives cosmic discovery.

Ongoing space odyssey

Hirata's groundbreaking research was supported by the Japan Society for the Promotion of Science and the Hyogo Science and Technology Association.

As we continue to unravel the enigmas of our universe, this remarkable finding takes us one step closer in understanding the mysteries of our solar system's largest moon , Ganymede.

The study is published in the journal Scientific Reports .

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