Ganymede, the biggest moon in the solar system, was hit by an asteroid 20 times larger than the one that ended the age of the dinosaurs on Earth, according to new research.
The impact, reckoned to have taken place about four billion years ago, was so huge that the giant moon’s axis shifted—and the telltale signs are still there.
Unique Moon
Bigger than Mercury and only slightly smaller than Mars, Ganymede Ganymede has a diameter of 3,273 miles/5,268 kilometers. It’s the largest moon and the ninth-largest object in the solar system after the eight planets. It’s also the only moon planetary scientists know of with both an atmosphere and a magnetic field.
It’s also the only one of Jupiter’s four large Galilean moons (the others being Europa, Callisto and Io) whose surface is dominated by furrows that form concentric circles around one specific spot.
In May 2022, it was claimed that Ganymede’s pock-marked, grooved and patterned surface may have been caused by an asteroid up to 90 miles/150 kilometers wide. That’s now being revised up.
Ganymede’s Furrows
“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,” said Hirate Naoyuki, a planetologist at Kobe University and author of the paper published today in Scientific Reports. “We know that this feature was created by an asteroid impact about four billion years ago, but we were unsure how big this impact was and what effect it had on the moon.”
Massive Impact
A specialist in simulating impact events on moons and asteroids, Hirata calculated that the asteroid that struck Ganymede, shifting its rotational axis, likely had a diameter of around 186 miles (300 kilometers).
That’s about 20 times larger than the asteroid or comet that struck Earth 66 million years ago, causing the 110-mile (180 kilometers) wide Chicxulub crater close to Mexico’s Yucatán Peninsula. It likely resulted in an impact winter lasting decades that killed the dinosaurs.
Recent research revealed that the dinosaur-killing asteroid outside Jupiter’s orbit during the early development of our solar system.
Oxygen And Ice
According to NASA, astronomers using the Hubble Space Telescope found evidence of a thin oxygen atmosphere on Ganymede, which they believe is coming from its icy surface. Also using data from the Hubble Space Telescope, a study in 2021 announced that scientists had found the first evidence for water vapor in the atmosphere of Jupiter’s giant icy moon Ganymede. Ganymede is also thought to have an underground ocean beneath its icy surface.
Juno And JUICE
NASA’s Juno spacecraft visited Ganymede on a brief flyby in 2021 and imaged its pock-marked, grooved and patterned surface—clues to what happened to the moon four billion years ago. Data collected by Juno suggests that there are mineral salts and organic compounds on the surface of Jupiter’s giant moon Ganymede.
The European Space Agency’s JUpiter ICy moons Explorer (JUICE) spacecraft is currently on its way to Jupiter, where from 2034, it will go into orbit of Ganymede for six months. It will be the first-ever mission to the moon of another planet.
Wishing you clear skies and wide eyes.
