Ancient Asteroid Impact Shifted Jupiter’s Largest Moon

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Kobe University researcher Naoyuki Hirata was the first to discover that an asteroid impact on Jupiter's moon Ganymede occurred almost exactly on the meridian farthest from Jupiter. This finding suggested that Ganymede had experienced a reorientation of its rotational axis, enabling Hirata to calculate the type of impact that could have caused this shift.

Kobe University researcher Naoyuki Hirata was the first to discover that an asteroid impact on Jupiter's moon Ganymede occurred almost exactly on the meridian farthest from Jupiter. This finding suggested that Ganymede had experienced a reorientation of its rotational axis, enabling Hirata to calculate the type of impact that could have caused this shift.

A massive asteroid struck Ganymede, Jupiter’s largest moon, about 4 billion years ago. This impact likely changed the moon’s tilt, according to new research by Hirata Naoyuki from Kobe University. The discovery offers fresh insights into our solar system’s early history.

Uncovering Ganymede’s Ancient Scars

Ganymede is bigger than Mercury and has unique features, including underground oceans and a pattern of grooves on its surface. Scientists have long wondered about these grooves, first seen in the 1980s. Now, we may have an answer.

HIRATA Naoyuki studies how impacts affect moons and asteroids. He noticed something others had missed: the likely impact site is almost exactly opposite Jupiter on Ganymede’s surface. This suggests the moon rotated after being hit.

“The Jupiter moons all have interesting features, but Ganymede’s grooves caught my attention,” Hirata explains. “We knew an asteroid impact created them about 4 billion years ago, but we weren’t sure how big it was or what it did to the moon.”

Simulating a Cosmic Collision

Hirata used computer simulations to figure out how big the impact must have been to turn Ganymede. His results, published in Scientific Reports, show it was an enormous event.

The asteroid was likely about 300 kilometers wide – 20 times larger than the one that killed the dinosaurs on Earth. It would have left a huge crater between 1,400 and 1,600 kilometers across, changing how Ganymede’s mass was spread out and causing it to tilt.

“I want to understand how Ganymede and other Jupiter moons formed and changed,” Hirata says. “This giant impact must have affected Ganymede’s early development, but we haven’t yet studied how it changed the moon’s interior. That’s what I’d like to research next.”

Why it matters: This research is important for several reasons:

  1. It helps us understand how big impacts shaped planets and moons long ago.
  2. It shows how computer models can teach us about distant objects we can’t easily study up close.
  3. It will help guide future missions to Ganymede, like the European Space Agency’s JUICE probe set to arrive in 2034.
  4. It might help us understand how similar impacts could affect Earth and other planets.

For most people, this study offers a glimpse into our solar system’s violent past. It shows that space is dynamic and ever-changing. It also highlights why we need to keep exploring space and developing new ways to study it.

As we wait for missions like JUICE to send back more information, Hirata’s work lays the groundwork for future studies. His research not only teaches us about Ganymede but also helps explain how our entire solar system formed over billions of years.

Quiz:

  1. How wide was the asteroid that hit Ganymede?
  2. About how long ago did this impact happen?
  3. What is the name of the future space mission that will study Ganymede?

Answer Key:

  1. About 300 kilometers
  2. Around 4 billion years ago
  3. JUICE (Jupiter Icy Moons Explorer)

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