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Posted by: HSchirmer Jan 4 2019, 05:08 AM

Topic moved to Chit-Chat from Pluto/KBO since it is not mission-specific- Admin



Is there any recent research into predicting the bulk properties of tholins on KBOs?
IIRC, Carl Sagan coined "tholin" as a better term for naturally-occurring-outer-solar-system-polymers, aka "star tar".
Tholins are naturally occurring polymers; in plain language, KBOs acquire a surface coating of "space plastic".

I'm curious for three reasons -

First, at Ultima Thule, we are seeing the first body where the bulk properties of surface tholins might have a significant or even dominant effect on surface morphology.
Gedanken experiment:
let's take Car Sagan's words at face value - tholins are "star tar" that builds up over time on outer solar system surfaces.
Well, when you add earth tar to earth dust, sand, gravel, and rock, you get asphalt pavement, which makes up the roads and parking lots and bike paths we are familiar with. It's sticky, coherent, and exhibits plastic deformation.
What if Ultima-Thule has a coating of "star asphault" (tar + regolith) on its surface?
Depending on the exact properties of the tholins (elasticity, plasticity, stress, strain, shear modulus)
a star-tar tholin skin could mean that Ultima and Thule are effectively giant bean bag chairs-
The outer "skin" of tholin-bound-regolith ascts like asphalt- it is a coherent surface, it deforms plastically under medium stress, but breaks under high stress.
The interior might be composed of loosely bound "goosebumps" or "dragon eggs" that are 10' / 3m diameter "accretion pebbles";
these would be functionally equivalent to the to the polystyrene beads in a bean bag chair.
In that case, Ultima Thule is, literally, a giant beanbag chair, with divots and ridges reflecting the effects of slow speed impacts.

Second, the bulk properties of a polymer (e.g. "plastic") and thus a tholin, could vary wildly depending on the specific composition and ratio of the polymer subunits you start with.
Make a polymer with vinylidene chloride and you get saran wrap (weak and stretchy), make the same polymer with vinyl chloride and you get PVC pipe (strong and tough), make it with carbonate, you get bulletproof glass (effectively impenetrable).
Getting some idea of the range of Tholin/polymer properties would really help to understand the bulk properties of "Tholin" on the surface of a KBO- does the Tholin coating act like tar and bind the surface regolith together in a sticky-flowing way, does it act like saran wrap and bind the surface regolith into a flexible sheet, or does it act like polycarbonate and bind the regolith into a hardened shell. Each is amazing in its own way.

Third, and most whimsically, there's a recent paper which notes that the dark-red tholin colored interstellar asteroid ‘Oumuamua accellerated away from the sun as if it were a thin sheet.
Perhaps it was: ever seen mud cracks or mud curls?
Imagine a sheet of tholin-reinforced-surface-regolith blasted off a distant exo-KBO by an impact, now fluttering through space.


Post Script- sometimes nature achieves "breakthroughts" without intelligence or civilizations-
https://www.scientificamerican.com/article/ancient-nuclear-reactor/
https://www.universetoday.com/140391/could-oumuamua-be-an-extra-terrestrial-solar-sail/#more-140391 but perhaps it's just a sheet of exo-tholin?

Posted by: vikingmars Jan 4 2019, 07:46 AM

[quote name='HSchirmer' date='Jan 4 2019, 06:08 AM' post='243160']
Post Script- sometimes nature achieves "breakthroughts" without intelligence or civilizations-
https://www.scientificamerican.com/article/ancient-nuclear-reactor/

Thanks a lot HSchirmer for taking an example such as Oklo in Gabon.
This incredible natural reactor is well known in France and, please, find herewith a paper that summarizes it all
 Radiation_1_OKLO_summary.pdf ( 366.87K ) : 616

Posted by: WTW Jan 4 2019, 12:22 PM

As mentioned in another topic, don't forget that the extremely low temperature of these tholins and any ices on which they are embedded is going to be a strong factor in their mechanical properties.

(Presumably at or below about 40 Kelvin, based on the longitudinal average at Pluto.)

[Which also means that temperature variations between the almost-continual daylight and shadow sides might also alter things such as plasticity/deformability, if present, depending on the thermal conductivity (heat disperson) of that surface.

Given Ultima and Thule's overall ovoid, almost spherical shape, such variation doesn't appear to be the case (so far) -- but it's unclear how much that temperature difference would actually matter.]

Will be interesting to see both what color(s) and what shape(s) are on the far (currently night) side.

Have there been studies of such properties of various tholin compounds at these low temperatures, that someone could reference?

Posted by: HSchirmer Jan 4 2019, 03:03 PM

Agreed, but thanks to a quirk of polymer chemistry, as long as you have some fraction of the tholin which remains "sticky" at low temperatures, the bulk material will remain sticky; as the long-chain tholins freeze into solid chunks, the remaining liquid is enriched in short-chain tholins will remain sticky. It's roughly analogous to how freezing saltwater results in a brine that gets more concentrated (and more resistant to freezing) the more you cool it.
Also, that "sticky" material might not need to arise from traditional "long chain polymer-goo", it could be side groups with polar charges, so it might be "sticky" like lunar dust.

IIRC, estimates are that UT's temperature should be around 35 Kelvin, which is similar to the colder areas of Pluto (average ~44 Kelvin) and there are some papers on https://arxiv.org/ftp/arxiv/papers/1503/1503.05315.pdf which suggest any initial surface N2 ice should be gone.

But, primordial N2 ices on the surface of UT might have actually developed some gas pressure if they mimic Triton's solid-ice-greenhouse effect (think of Mar's seasonal CO2 powered 'spiders', another solid-state greenhouse effect).

Basically, if Ultima Thule does have a thin coat of Tholin-mud on the surface, then there could be some wild mud curl structures...



mud-curls By Donna Catterick

stock image wikipedia


And since it's a micro-gravity environment, imagine them 10 meters or 100 meters tall...