I want to share something I think is neat. 

See this? 

The geological map of Ganymede. The image I used as a critical guide to make Jovian Society in Sweet Sol System. 

Now check this out. 

This is from the current JUNO mission, June 8 2021. Neat picture huh? 

See that big white crater with the awesome bright star shaped ejecta? It's name is Tros. In "Sweet" Tros is a self-aware city burrowed into that crater basin. But that's not the super cool thing I'm writing about. 

Tros is located inside a sulcus. A sulcus in context of Ganymede is very likely a rift, with horst-graben tilt-block geomorphology. The sulcus Tros is impacted in is named Phrygia Sulcus. There's a lot of implications buried in that information alone, and planetary scientists are loath to read too much into them. But I'm free to ass-pull some creative freedom so here it goes. 

When water freezes it expands 11%. So it's implicit that the sulci popped open as Ganymede froze solid to some depth or another. The sulci of Ganymede occupy more than 11% of the surface area, so it sure as hell didn't happen on one go. But that's what gives planetary scientists pause. They cannot prove that the sulci rifted in accordance with that 11% rule. So they have to explore more. Some sulci are doubtless much older than others. And the temptation of invoking cryovolcanism mechanics is ever-present. Could be all that and more. More probes are needed. But that's not the super cool thing I'm writing about either.

Look up (not north, this image wasn't aligned so up is north,) from Tros, through Phrygia sulcus, to the "continent", only slightly darker in the black and white image. Ganymede's continents are different from Earths, don't read too much into the use of the word continent. But that dark pointy continent is named Perrine Regio. Perrine Regio is split by another sulcus. Both sides of that sulcus are Perrine Regio, and the sulci name is Sicyon Sulcus. The Regio continents are way older than the sulci, darker and higher. But that's also not the super cool thing I'm writing about. 

Look closer. Compare the two images. You should be able to see by comparing that there is another sulcus splitting Perrine Regio. It's name is Nineveh Sulcus. In Ninevah are craters. You can find their names on the map. You see Bau crater in Nineveh, and Enki Catena in Sicyon Sulcus. Enki Catena isn't a normal crater, it's a machine-gun impact. Something got busted up by mighty Jupiter and the bits shotgunned into moving Ganymede. But that's not the super cool thing I'm writing about. 

The cool thing I am writing about, you may have noticed by now. Not all the craters on the geological map are named, but one at the crossing between Ninevah and Phrygia is missing from the new image, and it's a big one. How cool is that? 

It looks like it has pale ejecta to the north and south of it. I can't see any newer small craters in the basin or on the ejecta, but there may be one down and to the right. Can it be this huge impact happened between the JUNO and Galileo missions? And everybody missed it? Unlikely, I must doubt. But I've gone looking and can't find an explanation. Could be the older images used to make the geological map were incomplete in the first place. Could be something else. Dunno. But that's a big neat crater and the idea that something that big could have hit Ganymede in the age of observation, and no one noticed, that has fun implications.  

Oh, and in my own self-interest I must mention. In Sweet Sol System, Sicyon Sulcus between Enki Catena and Sati Crater is where "Zarathustra" the self-aware Jovian city where the plot of the Jovian story mostly takes place, is located.