On January 14, 2005, the Huygens probe successfully landed on the surface of Saturn's moon #Titan
Here is a link to a video clip, as well as links to where you can download this video.
https://science.nasa.gov/resource/titan-descent-data-movie-with-bells-and-whistles/
This was one of the greatest of humankind's achievements....the first time we ever landed on an #OceanWorld.
But what did we learn? What do these images tell us?
Thread time!
(Full disclosure, I am currently leading a team of brilliant scientists funded by the Cassini Data Analysis Program to put the Huygens, and future Dragonfly landing sites into geological context of Titan.
We are still actively researching this, but can share background context of previously published work.)
Link to Wikipedia article for generahttps://en.wikipedia.org/wiki/Titan_(moon)
Image link: https://photojournal.jpl.nasa.gov/catalog/PIA14924
Huygens was an atmospheric probe. It was designed to profile the atmosphere measure chemistry with a GCMS, and, if it got super lucky, land on the surface.
As it came down, it got a peek at geology and a key surface image of the Titan.
(That surface image is incredibly important. there have been so many remote sensing-based theoretical ideas that got killed with "But hey, does that explain the Huygens image? No? Buh-bye!")
Planetary Photojournal image PIA08115: https://photojournal.jpl.nasa.gov/jpeg/PIA08115.jpg
Let's look at that image in detail...there is A LOT there!
We knew Titan had a lot of photochemistry stuff coming down. So maybe it would be like a big blanket of organic "snow" covering everything?
But look at the image, you see cobbles, sand grains, different things. It's not all buried in uniform snow!
That tells us that geology, and geological processing of Titan airfall stuff is faster than just airfall building up and piling up in a big blanket.
Titan is happening!
What else do we see? Look at the "rocks". They are rounded...AND uniform sized. How did that happen? Like on Earth, rocks can get rounded from clacking together in a stream. And as a stream loses power, different sized rocks get dropped out. They also seem to lean together as if they were dropped by a stream. (The fancy word for this is "imbricated".)
A good story for this scene is floods wash across, dropping rounded eroded sorted rocks in an imbricated deposit.
So that is a pretty good story. But there's some really parts too that don't get a lot of press.
The big geology story seems correct. (And our work seems to confirm it, too..) But...we actually don't know what those "rocks" and "sands" are made of. A lot of people assume the cobbles are ice (and you'll see that in literature), but the ugly truth is that we actually don't know.
It seems likely to be ice, but we don't have any actual analysis of those cobbles. It is a mystery!
(Mystery = fun.)
The other thing that is really wild, is that the Huygens scene has had the contrast massively stretched. Really massively. If you saw this with your own eyes, the entire scene would be a uniform dark muddy brown. (Karkoschka et al., Icarus 2016).
What does that tell us?
It tells us that Titan has some type of dusty coating that gets everywhere, or at least in this part of Titan. Probably optically thin (few hundred microns).
This could be reason why optical and radar see differences.
In fact, I'll go a bit farther and state that optical data may give you an idea of top coating, and might reveal some morphologies, but radar (and microwave emissivity) gives you a better idea about what is happening on Titan.
Optical (infrared) is only the top coating, the spray paint tagging by Titan. Radar (and microwave emissivity) interrogates the true beauty of Titan. Radar probes 10's of cm deep. Get you beyond just the surface coating paint.
That's a big lesson for Titan.
Huygens landed at a margin between and "infrared bright" area called Adiri and an "infrared dark" are called Adiri that we now know is a sand sea of organic sand dunes.
It did NOT land in the sand sea dunes, nor in an exposed mountain patch of ice. It landed in a type of plain.
We now know that Titan is a mostly sedimentary world with mostly plains. Is the Huygens Landing Site a typical scene? That is some of the research we are currently working on.
Global map of Titan. Plains are cyan.
This is an area of active research. We are hoping that we can put the images and discoveries of the Huygens landing site in context of other locations of Titan. And that we can learn about the Dragonfly landing site as well.
Dragonfly's target is Selk crater, the larger crater in red to north of the Huygens landing site in the global map in the previous post.
Here is a 2016 publication on Titan's Afekan region, that also described Selk crater: https://www.sciencedirect.com/science/article/abs/pii/S0019103516000889
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