Mike Malaska
On January 14, 2005 just over 20 years ago today, the Huygens probe touched down on the organic-rich surface of Saturn's moon Titan.
Here is the scene from Titan's surface. https://photojournal.jpl.nasa.gov/catalog/PIA07232
Scientists (I'm one of those) have been analyzing this image and the other descent images from the probe for 2 decades. What have we learned from the probe images about the surface of enigmatic moon?
[Thread]
ploum
@mike_malaska : I remember following this in real time from my student room.
I had visited ESTEC multiple times and had a huge Huygens poster next to my bed.
It was mindblowing. I remember watching and rewatching this picture while listening to the MP3 of the descent.
Incredible stuff.
ploum
@mike_malaska : for the record, the older friend who left me that room in 2000 to start working at ESA was assigned to work on Cassini/Huygens. He worked on solving the "bug" where it was discovered that doppler effect could mess communication between Cassini and Huygens.
Mike Malaska
Adding credits:
The Cassini-Huygens mission was a mission by NASA (National Aeronautics and Space Administration), ESA (European Space Agency), and ASI (Agenzia Spaziale Italiana).
Funding for my work on the Huygens landing site came from the Cassini Data Analysis Program (CDAP) from NASA.
For more info on the Cassini-Huygens mission see: https://en.wikipedia.org/wiki/Cassini%E2%80%93Huygens
Mike Malaska
So for me, the Huygens landing site was one of our (royal big "we") achievements. And we can use it to learn about another world, how that world operates, how different worlds can be, and then contrast with our own fascinating world.
I hope you enjoyed this thread!
[end thread]...see credits next post...
Mike Malaska
Today, as you drive around or walk around. Think to yourself: If I had just three or four single frame images of this scene, how would I describe it? what could I figure out?
And what would I NOT know about?
So this is one of the really fun things about planetary exploration. Trying to take all sorts of clues to fit together a story, then compare and put into big context.
Mike Malaska
Think of it like a single mission to Earth. If you could pick only ONE location on Earth and try to figure everything out where would you land?
In the middle of the ocean? You won't learn about mountains or dunes.
Land in a dune field? You won't learn about water, lakes, or canyons.
Mike Malaska
With Huygens landing site, we got incredibly super lucky. We landed right at margin of mountains, in a channel, way off some plains, and even further off some dunes.
I mean, if you had to land one place on Titan, we got a great diversity of features. Eventually could piece out the story.
Mike Malaska
There were winds moving organics around on Titan. Those mountains protected some areas, by creating wind shadows. So there were some places that were deposited, some places stripped.
That seems to be a general story at least in equator/mid-latitudes of Titan.
But in some special areas, you have river networks and channels. and big alluvial fans, massive bajadas, and ginormous water ice rich plains.
Mike Malaska
A big part of that story is that Titan may have looked like Europa with organics for a large part of it's history.
About a billion or so years ago, something happened, and the deep subsurface ocean shrank and the ice shell thickened. That big change may have cause icy mountains to uplift basins to drop, and labyrinth organic layers to uplift. The entire Adiri area may be a big uplifted area. With mountains on top of that too.
Mike Malaska
Those weird bright features near where Huygens landed? We think those are a key part of the story.
They are not river deposits. They could be organics or they could be ice.
We think the whole area was uplifted with a lot of organic cover and then eroded down by fluvial activity.
We still working on this, but submitted an abstract to present some of our story so far at the upcoming Lunar and Planetary Science Conference.
Mike Malaska
That channel is HUGE. Maybe several km across. The little river networks coming off the bright highlands likely did not contribute those rounded rocks, they came from somewhere else.
The big wide channel seems to originate to the SW (in foreground of the second movie) and go to the NE (to the background in the second movie).
The rocks came somewhere from the E Adiri bright area to the SW of where Huygens landed. Maybe from pretty far away.
Mike Malaska
Part of our work was painstakingly lining up radar images. You can get incredibly nice correspondence and start teasing out more information.
A lot of the really cool stuff seen at Huygens is sub-resolution to SAR radar data. But you can actually see a few hints of "something" in SAR.
Huygens plopped down in that dark region between the large bright uplands.
Mike Malaska
In the second descent movie, off to the left you see a brightish mountainous area with dark dendritic fluvial channels and another set with short stubby channels.
The two channel styles tell you about the geology. Overland flow where the dendritic channel, and subsurface flow with the short stubby channels.
Surprisingly, we actually just barely see these subtle differences in terrain when we carefully line up the SAR images.
Mike Malaska
If Huygens landed there, it would have been really boring. Just gravels or fine sands, and maybe a rare dune or two way out on the horizon.
Mike Malaska
As we dropped down, waaaay off the distance to the north left (which is up in the "bells and whistles" movie, but way off to the left in the second movie) we saw some dark lines that are linear dunes. This is the margin of the great Shangri-la sand sea.
We are calling that location with the dunes a "water-ice rich plain" which is a mix of water ice fluvial deposited sediments, but then dark organic longitudinal dunes.
If you go further north deeper into Shangri-La then it is a big sand sea.
Mike Malaska
Here is a new updated version of the images from that descent. This has some better blending of all the scenes. Still some data glitches and gaps that had to be filled and warped. but a pretty good idea (for now) of what it looked like as Huygens approached the surface.
Mike Malaska
I mean, think about this. You've got one chance to get all the information you can during this event. You want to capture everything so you can piece it together later to figure it out.
You know enough that is alien and that you don't know enough.
You also have limited bandwidth so you have to prioritize everything.
The more I learn, the more I untangle, the more impressed I am about the genius of that planning.
Mike Malaska
As the Huygens probe descended, it took lots of pictures on its way down to the surface. Those are just a gold mine of information.
Here is a really fun movie that we call the "bells and whistles" version. It is incredibly information rich. I love watching this over and over. You can see little cartoons showing probe orientation spin, telemetry data, instrument sequences, and images. I love to marvel at the planning that made this happen.
https://science.nasa.gov/resource/titan-descent-data-movie-with-bells-and-whistles/
Mike Malaska
Ahhhhh. That's still a mystery! You will read in Wikpedia or some of the literature that it is water ice.
But actually, we don't know. It could be ice, or other things: frozen benzene, solid HCN, mixed solid organics. We do not have detailed spectra or other chemical analysis of those rocks vs the sands.
(Personally, I think it's probably ice, but I want better proof.)
(The dark sands I'd lean my guess towards probably organics.)
It is good to have mysteries! Fun! Explore!
Mike Malaska
So. Streams or floods, rocks eroding, sorting. Faster than getting covered by atmospheric organic molecules. Got it.
But what are those rounded rocks made of?
Mike Malaska
And also what you DON'T SEE. We don't see a uniform snowscape blanket of organic molecules everywhere.
That tells us that whatever geological processes happen are faster than covering by organic molecule fallout.
That fallout happens at a rate of about same as dust builds up in your house if you have a clothes dryer in your house. Max 100 m per Gyr: 0.1 m per Myr, 0.1 mm per kyr or 0.1 microns per year. Give or take an order of magnitude.
So geology happens on Titan. It's not boring.
Mike Malaska
Just from this surface image, you can figure stuff out. All those rocks (whatever they are made of - that is still a mystery), are all rounded, and the same size.
Rounding suggests erosion, those "rocks" banged together repeatedly. Likes rocks in a river or shore (hint-hint-hint).
And sorting by some type of process where bigger rocks dropped out somewhere else, and smaller rocks or pieces dropped somewhere else.
Either a flood deposit or a stream deposit.
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