Too cool, part 51: Enki Catena

I still routinely check out Astronomy Picture of the Day, even though I’ve come to personally call it the Photoshop of the Day because the number of edited images are now surpassing the unaltered ones – virtually all of those showing starfields over landscapes, certainly. But yesterday’s deserves a look at least. It’s a magnificent sharp image of Jupiter’s moon Ganymede, taken by the Juno spacecraft, and the detail is stunning – clicking on their image (linked within the one below) will take you to the full-resolution version, and it’s well worth it.

Jupiter's moon Ganymede from Juno
Image credit: JPL-Caltech, SwRI, MSSS. Processed by Kevin Gill

Just the textures and details revealed when viewed at full resolution are fascinating enough, but there’s a specific detail that jumps out when you find it, vaguely visible in the smaller version here. About one-third down from the top and just left of the center of the moon is a prominent white splash on the edge of a dark smear, and through the middle of that white region runs a connected string of smaller craters – thirteen, to be exact, in a remarkably straight line.

Turns out this is Enki Catena; ‘catena’ is the term for a line of craters, as if you didn’t know that. It is presumed that they were all formed either simultaneously or in quick succession from an object, likely a comet, that got close enough to Jupiter to be broken up by the gravitational forces. and later impacted on Ganymede. Recent investigations into the nature of comets has revealed that they are more loose collections of dust and boulders than they are a solid body, unsurprising to a degree because they’re too small to compact themselves tighter through their own gravity; more surprising is how the whole mass gets redirected into long-term orbits between the outer reaches of the solar system (the Kuiper Belt) and the sun or Jupiter. Yes, there are comets that orbit around Jupiter itself rather than the sun, because it’s big, you know. But it likely takes rather specific conditions to direct such a mass away from typical orbital profiles into the elongated ellipses that comets typically follow, without just tearing them apart. And Enki Catena, at least, indicates that this particular one didn’t begin with a much larger, solid body that gradually accumulated more dust and ice, because all of the craters are roughly the same size.

That dark smear that it crosses the boundary of, by the way, deserves a close look too, because it’s pretty specifically delineated, and the other image of Enki Catena, obtained in 1997 by the Galileo mission, clearly shows a boundary trench, which is also visible in other portions of this image away from Enki Catena. Is the whole region bounded by a trench, and moreover, what caused this? That’s something else to ponder. Makes me wonder if we’ll get a lander onto Ganymede within my lifetime.

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