Asteroid Larger Than The One That Wiped Out Dinosaurs Once Rocked Jupiter’s Moon

A Kobe University researcher has confirmed that an asteroid which struck Jupiter’s moon Ganymede was about 20 times larger than the one that ended the age of the dinosaurs on Earth. According to the new study, when the asteroid struck Ganymede, the largest moon in the solar system, its axis shifted because of the collision, and was one of the biggest impacts with clear traces in the solar system.

Ganymede, like Earth’s moon, is tidally locked, meaning it always shows the same side to the planet it is orbiting, and thus has a far side. The fact the moon is covered by furrows that form concentric circles around one specific spot, researchers concluded in the 1980s they were from the result of a major impact event.


“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,” remarked 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.”

Because there is so little data concerning Ganymede, research is very difficult. Hirata was able to draw comparisons of similarities with an impact event on Pluto, which caused the dwarf planet’s rotational axis to shift. Adding in what was learned from the New Horizons space probe, Hirata, a specialist in simulating impact events on moons and asteroids, deduced the similarities implied that Ganymede had also underwent a reorientation.

His realization allowed him to calculate what kind of impact could have generated the reorientation. In a study published in the journal Scientific Reports, Hirata explained the asteroid probably had a diameter of around 300 kilometers, or about 20 times as large as the one that is thought to have impacted Earth 65 million years ago and ended the age of the dinosaurs. The researcher concluded the impact created a transient crater between 1,400 and 1,600 kilometers in diameter. According to Hirata’s simulations, only an impact of this size could have caused the Ganymede’s rotational axis to shift into its current position.

“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,” explained Hirata.

More information will be collected in the coming years, as Ganymede is the European Space Agency’s JUICE space probe’s final destination. If all goes to plan, the spacecraft will enter orbit around Ganymede in 2034, making observations for six months.