Cosmic collision: Massive asteroid once struck Jupiter’s largest moon

By Stephen Beech via SWNS

A "gigantic" asteroid impact shifted the axis of the Solar System's biggest moon, according to new research.

The 190-mile wide space rock that smashed into Jupiter's satellite Ganymede around four billion years ago was 20 times bigger than the one that killed off dinosaurs on Earth, say scientists.

Ganymede is the largest moon in the Solar System, even bigger than the planet Mercury.

Like the Earth’s moon, it is "tidally locked" - meaning that it always shows the same side to the planet it is orbiting.

On large parts of its surface, Ganymede is covered by furrows that form concentric circles around one specific spot, which led researchers in the 1980s to conclude that they are the results of a major impact event.

Dr. Naoyuki Hrata, of Kobe University in Japan, said: “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.

“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.”

He explained that data from the remote object is scarce, making research very difficult.

Dr. Hirata was the first to realize that the purported location of the impact is almost precisely on the meridian farthest away from Jupiter.

Drawing from similarities with an impact event on Pluto that caused the dwarf planet’s rotational axis to shift, he believed that Ganymede had also undergone such a reorientation.

Dr. Hirata is a specialist in simulating impact events on moons and asteroids, so the realization allowed him to calculate what kind of impact could have caused such a reorientation to happen.

He calculated that the asteroid probably had a diameter of around 300 kilometers (186 miles) - making it about 20 times as large as the one that hit the Earth 65 million years ago and ended the age of the dinosaurs.

The impact created a transient crater between 1,400 km and 1,600 km (870 and 995 miles) in diameter, according to the findings published in the journal Scientific Reports .

Transient craters, widely used in the lab and computational simulations, are the cavities produced directly after the crater excavation and before material settles in and around the crater.

Dr. Hirata said that only an impact of that size would make it likely that the change in the distribution of mass could cause the moon’s rotational axis to shift into its current position.

He says the result holds true, irrespective of where on the surface the impact occurred.

Dr. Hirata said: “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."

He added: "I believe that further research applying the internal evolution of ice moons could be carried out next."

Ganymede is the final destination of the European Space Agency's Juice probe which is due to enter orbit around the moon in 2034. It is scheduled to make observations for six months.

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