Asteroids are known for their catastrophic potential, as seen with the one that wiped out the dinosaurs 65 million years ago. Now, a new study reveals that a much larger asteroid, approximately 20 times bigger, struck Ganymede, the largest moon in the solar system, around four billion years ago, altering its rotational axis.
Scientists have long known about the impact that left massive concentric circles on Ganymede’s surface. Planetologist Hirata Naoyuki from Kobe University explained that such giant impacts were frequent in the early solar system and significantly affected Ganymede’s internal structure, with the crater taking up 25% of the moon’s size.
Published in *Scientific Reports*, the study found that the impact site is nearly opposite Jupiter on Ganymede’s meridian, suggesting the asteroid strike was powerful enough to shift the moon’s axis. A similar reorientation was observed on Pluto after an asteroid impact, as revealed by NASA’s New Horizons probe.
Simulations suggest that the asteroid responsible for Ganymede’s dramatic shift was about 190 miles in diameter—20 times larger than the asteroid that struck Earth 65 million years ago.
Ganymede, which hosts a vast subsurface ocean, remains a key target in the search for habitable space bodies. The European Space Agency’s JUICE mission is set to explore Ganymede, along with Jupiter’s other moons, Callisto and Europa, upon its arrival in 2034.
