About 4 billion years ago, an asteroid struck Jupiter’s moon Ganymede, shifting its axis, confirming that the object was 20 times larger than the one that ended the age of the dinosaurs on Earth, according to the discovery published Tuesday in the journal Scientific Reports.
Ganymede is the largest moon in the solar system, larger even than the planet Mercury, and has oceans of liquid water beneath its icy surface.
Like Earth’s Moon, it always shows the same side to the planet it orbits and therefore also has a far side.
Ganymede is covered in much of its surface in concentric circles around a single point, leading researchers to conclude that they are the result of a large impact in the 1980s.
“We knew that this feature was created by an asteroid impact about 4 billion years ago, but we weren’t sure how large the impact was or what effect it had on the moon,” said one of the authors, Hirata Naoyuki of Japan’s Kobe University.
Data on the remote object are scarce, making research very difficult, so the researcher was the first to realize that the supposed impact location lies almost exactly on Jupiter’s farthest meridian.
Asteroid with a diameter of hundreds of kilometers
The Kobe University researcher now reports that the asteroid was probably about 300 kilometers in diameter, about 20 times larger than the one that hit Earth 65 million years ago and ended the age of the dinosaurs, and created a transient crater between 1,400 and 1,600 kilometers in diameter.
According to their simulations, only an impact of this size would make it likely that the change in mass distribution could cause the Moon’s rotation axis to shift to its current position.
Its result is valid regardless of where on the surface the impact occurred.
“I want to understand the origin and evolution of Ganymede and other moons of Jupiter. The giant impact must have had a significant effect on the early evolution of Ganymede, but the thermal and structural effects of the impact on Ganymede’s interior have not yet been investigated,” Hirata said in a statement.
Ganymede is the final destination for the European Space Agency’s JUICE spacecraft, which is scheduled to enter orbit around the moon in 2034 and conduct observations for six months.
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