Jupiter's huge moon Ganymede may have the largest impact scar in the solar system

An artist's depiction of Jupiter, at left, and its massive moon Ganymede in the foreground.
An artist's depiction of Jupiter, at left, and its massive moon Ganymede in the foreground. (Image credit: Tsunehiko Kato, 4D2U Project, NAOJ)

Scientists have discovered what they believe may be the largest impact crater in the entire solar system, with scars covering a vast portion of Jupiter's biggest moon, Ganymede.

The scientists behind the new research wanted to revisit observations from a host of past NASA missions that studied the massive moon, which is larger than Mercury, the smallest planet in our neighborhood. In particular, they were intrigued by a set of features dubbed furrows, which appear on some of the moon's oldest terrain.

Previous researchers had pointed to these furrows as evidence of a large impact powerful enough to leave scars across an entire side of Ganymede. But on revisiting the structures, the scientists behind the new research believe that's an underestimate, and that the furrows represent an impact so large as to affect the entire moon.

Related: Photos of Ganymede, Jupiter's largest moon

The researchers began by gathering data collected by NASA's twin Voyager missions, which each flew past the Jupiter system in 1979, and by NASA's Galileo mission, which spent eight years over the late 1990s and early 2000s studying the massive planet and its neighbors.

The scientists then reanalyzed observations that covered what's called the Dark Terrain, which includes the oldest surfaces on Ganymede. Throughout the Dark Terrain, according to the new modelling, the furrows all ripple out from one point — even those on the opposite side of the moon.

The researchers suggest that makes the furrows indicators of an impact event that affected all of Ganymede, not just the one hemisphere previously identified as reshaped in such an event, although positively identifying an impact site takes more than suspicious rings.

Photos: NASA Jupiter probe images huge moon Ganymede like never before

But if an impact was to blame, quite a large asteroid — at least 30 miles (50 kilometers) across and possibly more like 90 miles (150 km) across — could have been involved in that collision, leaving a bullseye series of rings and fractures across the moon that, after millennia of geological processes, have become the furrows and troughs scientists see now, according to a statement about the new research.

If that modeling is correct, the scientists say, they have found the largest impact scar in the solar system, with a radius as large as 4,800 miles (7,800 km) — that's a radius about twice the length of the Mississippi River. The current largest known impact system, called Valhalla Crater and found on another Jupiter moon, Callisto, pales in comparison, with a radius of 1,200 miles (1,900 km).

The scientists behind the new research hope that new data will help them better interpret the furrows of Ganymede and understand precisely what formed them. The European Space Agency is at work building a spacecraft called the Jupiter Icy Moons Explorer (JUICE), which it intends to launch in 2022. The mission will focus on Ganymede, Callisto and Europa, arriving in the neighborhood in 2029 and operating there for at least three years.

The research is described in a study published July 15 in the journal Icarus.

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Meghan Bartels
Senior Writer

Meghan is a senior writer at Space.com and has more than five years' experience as a science journalist based in New York City. She joined Space.com in July 2018, with previous writing published in outlets including Newsweek and Audubon. Meghan earned an MA in science journalism from New York University and a BA in classics from Georgetown University, and in her free time she enjoys reading and visiting museums. Follow her on Twitter at @meghanbartels.

  • Don M
    Hmmm, according to this article and the statement from Kobe University, the impact on Ganymede precedes the formation of both our Solar System and our Universe: 40 billion years(!). Need some better editors.
  • rod
    FYI, I checked another report on this. The 40 billion years is there too. 'Huge ring-like structure on Ganymede's surface may have been caused by violent impact', https://phys.org/news/2020-08-huge-ring-like-ganymede-surface-violent.html, "It is believed that such an impact occurred around 40 billion years ago."

    Okay, this is easy to explain. We have another object and event dated older than the universe age in the BB model, the Hubble time :) This happens from time to time in dating methods :)
  • Mercury 3488
    Not only the 40 billion year gaff, but also I thought that the Utopia Planitia on Mars was the previously largest known impact basin in the solar system????

    Within the Jovian system, yes the Valhalla Basin on Callisto was the previously known largest or even among any of the moons in our Solar System.
  • RRG
    Maybe it was from a impact like an impact in your windshield and over time keeps getting bigger and bigger. Flexing vibrations and definitely gravity from that enormous planet Jupiter just continued to make it longer over many years. That would make it appear like the initial impact made it. Just a thought.
  • Larry L
    The diameter of Ganymede is 5,270 km, so its circumference is 16,500 km. How can you have a crater on it with a radius of 7,800 km (diameter of 15,600 km), their largest estimate? Also, the "usual" ratio of crater diameter to impactor diameter is 10 or 20 to 1 and is very velocity-dependent. With their biggest impactor being 150 km in diameter, that gives you a maximum crater diameter of 3,000 km. You would expect impacts at the distance of Jupiter to be lower than near Earth, but I guess they can be higher if the impactor got a velocity boost by Jupiter (slingshot effect). I am adding this a few minutes later, They have the RADIUS of the impactor being 150 km, so the maximum crater diameter would be 6,000 km or so, depending on the velocity of the impactor (20 km/sec seems high for this distance from the Sun.).
  • Catastrophe
    Here is the (previous) list:

  • rod
    FYI. The 40 billion years problem is 40 million years ago according to this report. That somewhat aligns with Saturn ring system ages said to be perhaps 100 million years old (according to some sources). 40 million years ago shows a younger age for some large impacts still taking place in the solar system. "The research team conducted a simulation to estimate the scale of the impact that formed this giant crater. This was carried out using the "PC Cluster" at the National Astronomical Observatory of Japan (NAOJ). The results indicated that an asteroid with a radius of 150km impacting Ganymede at a speed of 20km/s would be sufficient to form the observed structures on the satellite's surface. It is believed that such an impact occurred around 40 million years ago.", Huge ring-like structure on Ganymede's surface may have been caused by violent impact, https://www.sciencedaily.com/releases/2020/08/200807102339.htm
  • Mercury 3488
    rod. Ganymede orbits Jupiter, not Saturn. I think the article meant 4 billion years old.

    I am not so sure that impacts necessarily explains Ganymede's internal differentiaton as opposed to Callisto's homogeny. Ganymede certainly formed closer to Jupiter than Callisto, where there would be a greater abundance of heavier elements. Ganymede certainly has more iron internaly than Callisto.

    There appears to have been enough iron to form an inner iron rich core and an outer iron sulphide outer core like the Earth and Mercury (Ganymede is unique among the solar system moons to have a dual layered core). This separation would have generated enough heat for the layers to form within Ganymede.

    Europa and Io are also very heavily differentiated, though they both appear to have singular layered cores, so this makes sense.

    Does not mean though Ganymede did not have enormous impacts though.
  • rod
    FYI. The sciencedaily.com report says very clearly 40 million years ago and I see no other sources claiming to correct the time of impact to 4 billion years ago. I pointed out Saturn ring age here for thought and comparison with impact(s) at Ganymede dated much younger. if the Ganymede impact took place 40 million years ago and Saturn's rings are indeed quite young relative to geologic ages, that indicates there was recent catastrophism in our solar system. If there is evidence in our solar system for recent catastrophism that took place <= 100 million years ago, that should be clearly documented and pointed out to the public.
  • Catastrophe
    The rings of Saturn lie inside Saturn's Roche limit and may be the debris of a demolished moon. Would you necessarily include this as catastrophism (which would include impact)?