Thread by @mike_malaska

This is one of the greatest images taken by humankind. It is the first (and only) time we ever landed on an Ocean World.

There is A LOT you can learn by looking a this image.

What did we see? What can we learn?
(thread)
🧵

https://twitter.com/tsplanets/status/1482023709259055116

Wow. Look at that sky. It's all orange. It's a moon that has an ATMOSPHERE. Orange stuff is from filtered, scattered light coming down through a chemical-laden atmosphere.

(No surprise, the probe came down through the atmosphere on a parachute.)
en.wikipedia.org/wiki/Atmospher…

The Huygens probe was not a lander. It was an atmospheric probe. It was, however, designed to survive a soft landing on the surface.
So it's primary goal was learning more about Titan's complex atmosphere. The landing was a really nice added bonus.
en.wikipedia.org/wiki/Huygens_(…

On Titan, organic molecules get built up high in atmosphere and eventually settle (or rain) out onto Titan surface.
Look at the surface pic again. It does NOT look like a uniform coating or blanket of organic snowfall on everything.
You see different things.
That's a big clue.

That tells you that geologic processing (making different things you see in that image) happens FASTER than simple burial. At least in this location.

When we talk about organic airfall and burial we point to this image a lot! And say, "Oh yeah, so how does that explain THAT?"

And, if you do the math of some of the Titan atmospheric models, it turns out that that organic airfall accumulation is pretty slow. Maybe about as fast as dust accumulates in your house if you have a clothes dryer inside your home.
But given time, tens of meters of organics.

In some places, (not here) those organics pile up to big thick stacks of hundred meter plateaux of organics. Think of Colorado Plateau, but all organics.
jpl.nasa.gov/videos/titan-c…

Gotta add some background info for that video. Except for the voiceover and text, it was entirely produced at the time through "amateur enthusiast" effort from publicly released data.
(two of those amateur enthusiasts later ended up working at JPL.)
THIS IS WHY YOU RELEASE DATA.

So...back to that Huygens image. Look at the topography. Pretty flat and boring, right?
How do you make things flat? Wind deposits, Lake deposits, stream deposits. Erosion or sublimation to things without a lot of strength. Something like that probably happened here. More clues.

And you've got those "lanes" of rounded things. Rock or cobble-sized if you want geology sizing.
How different are they....they are all almost the same size?
BIG CLUE.

Getting something all the same size is kinda hard. You either gotta build something up to same size and stop. Or break it down to same size and stop. Or....sort it somehow.

A few ways to sort things, wind, or liquid. Titan's atmosphere thick and cold. Dense. Can do work.

As "fluids" (yeah, a great weasel word, can use that word for flowing gases, mixtures in gases, liquids, and mixtures in liquids) carry stuff in suspension (or mix), as the turbulence flows, stuff can settle out. Big things first, then smaller as turbulence decreases.

Here's a fun easy home experiment you can do to show how things settle out.

DEMO TIME!!!!

soil-net.com/dev/page.cfm?p…

This is called (wait for it...) "sorting". Those rock- and cobble-sized things in the image have been sorted.

Great evidence for "fluids" doing the work and dropping stuff of a certain size out right here.

If we were there as a field geologist (oh I wish!!!) we could walk around, see how the size changes as we work outward. See where size bigger (closer to source) and see where size smaller (farther from source). But there could be local lanes where flow more or less turbulent.

Now, look at those things. What shape are they?
Rounded? or rough and angular? or even spiky?
Definitely rounded. Or at least sub-rounded.
Geology looooves classification. Is important to understanding processing.
Roundedness definition (with pix).
en.wikipedia.org/wiki/Roundness…

Soooo. Rounded. That means that if these things got transported, they probably got rounded from getting clacked together. Like rocks in a stream or a beach here on Earth.
Need to know how strong those things are to figure distance (how much clacking and rounding happened?)

If really weak (think candle wax) it may not need to travel be very far. Would round quickly. If really really strong, (like a metal spike, maybe) could be really really far. But we can say that it travelled long enough to become subrounded, maybe.

Geologists like to tell stories from rocks. But sometimes there's other options. Like:
Maybe those rocks got rounded in whatever river was moving them around.
Or maybe the rocks were already rounded in a cliff, and got retransported.
Or maybe rough rocks, then sublimed to smooth.

If you look close, there is another clue. Some of these rocks are leaning on each other in a certain direction. This is called imbrication. That indicates flow.
Here is an example pic of imbrication.

(Incidentally, I took that picture during a Cornell University "Titan lakefest" conference field trip where we were talking about Titan lakes and surface processes.)

So that sorting+rounding+imbrication gives even more evidence of fluid activity. This story is starting to really come together!

And there are fine sands too! They are darker. Maybe they are made of different stuff? Dunno!

Light colored things, and dark colored things. Sorta.
We gotta talk a little bit about contrast.....

This pic has been MASSIVELY stretched to bring out contrast. Data values close to the limit of differentiation. There was an article written about what it would look like if you were there. Pretty much uniform dark brown. No contrast your eyes could see.
sciencedirect.com/science/articl…

(Yes. I know. Paywall for that article. But..click on "show figures" and look at Figure 10 - the brown boring one. That is the representation of what you would see without contrast-stretching.)

That's another clue. Everything is very dark and low contrast. So...either everything started out close to same color or it got that way after maybe a little bit of dark dust settled on it. But there are subtle (very subtle) shading differences. Sand sized things darker.

So, we got a geology story. Stuff gets moved in, fluid flow, transporting, rounding, drops out and sorts, imbricates. Then dust covering (or maybe before?).

And now we come to THE BIG TITAN MYSTERY: what are those things made of? What did we land on.

WE DON'T KNOW!!!

If you read some articles, they may refer to those objects as "water ice cobbles and rocks". But...we can't prove that. There's no actual evidence for those particular rocks. It could also be big lumps of organic molecules.

When we mapped this particular area of Titan, we called it a "variable plains unit". Which could have water ice, or not. Or organic materials, or maybe not much. Is kinda "variable."

There are dark dunes nearby. We saw some in the near-surface images. Those we know for sure are made of organic materials. Spectra (which only looks at top coating) but also microwave emissivity, which probes deeper. Consistent with low dielectric constant organic molecules.

And overall, we get a pretty low dielectric constant right where Huygens landed, too. So it can't be all water ice.

So if I had to guess (and sometimes I do), I'd guess the dark stuff is probably organic sand stuff. and the cobbles and rocks are maybe-possibly water ice.

But if you also said "Oh, well, those are rocks made out of benzene or acetonitrile" I'd prolly go "yeah, OK, we can go with that too."

There are things nearby that look like water ice mountains. But even those seem to have organics mixed in a bit.

Returning to this very spot, or looking at it from orbit at high resolution, getting better context, seeing how things changed (Did Huygens get buried, covered in a later flood deposit?) would really help tie story together.
This is why this is such an awesome picture.
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