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NH Ultima Thule Encounter Observations & Results, post-flyby discussion as the data arrives
HSchirmer
post Feb 9 2019, 11:39 PM
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QUOTE (JRehling @ Jan 28 2019, 08:41 PM) *
re: resurfacing, we're certainly looking at a world where geology doesn't apply in the usual sense, but there are still mechanisms at this scale that can blank the surface:

•The shaking that occurs with a straight-on impact could cause material to flow down slopes.
•An impact could shower the surface with material causing a new surface to overlie the old one.
• Porous portions of the body could collapse inward to a new configuration at higher density.
•Electrostatic accumulation of fine-grained material burying the old surface.

More?

Cohesion
• Tholin ("Sagan's star tar") surface weathering cementing sun-facing surfaces into a crust WITH sun-facing surface darkening over a wide spectral range.

ReDistribution
• YORP (natural photon drive) effects spinning the lobes up/down over time, depending on their current orientation and frost coverage/albedo patterns.
•sYORP (natural photon+cryovolatile gas drive) effects spinning the lobes up/down depending on their current orientation and frost coverge/albedo patterns.

Observation-
The patterns on the surface of Ultima Thule resembles the heat/flow patterns you get on a breakfast pancake-
a thin surface layer breaking and creeping as the interior slumps and spreads out.
Let's assume UT consists of unconsolidated material high in volatiles.
Apply heat (sunlight/hot pan) to form a crust/tholins, and you find that the bulk material spreads out (YORP, sYORP, heat driven sublimation to the limb) into a thin disk.

Hypothesis-
Tholin formation causes "browning" which forms a skin,then
-A YORP/sYORP spin or -B ammonia/volatile sublimation
push material towards the edge/shadowed limb of the dark side. This mass transfer to the edges results in a "pancake" shape where a tough tholin skin develops on two sides and sublimating material "squishes" out along the perimeter.
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Paolo
post Feb 10 2019, 07:49 AM
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QUOTE (HSchirmer @ Feb 10 2019, 12:39 AM) *
-A YORP/sYORP spin


MU69 is far from the Sun and large(ish). wouldn't YORP be negligible on such a body?
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HSchirmer
post Feb 10 2019, 03:54 PM
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QUOTE (Paolo @ Feb 10 2019, 07:49 AM) *
MU69 is far from the Sun and large(ish). wouldn't YORP be negligible on such a body?


Normally yes.
But, like raindrops wearing down a mountain range seems negligible, over geologic or astronomical timeframes it should add up.

A recent paper mentions ammonia sublimation and deposition as a resurfacing possibility, Ultima Thule (486958; 2014 MU69): Necklace, Composition, Rotation, Formation https://arxiv.org/abs/1902.00997 so if there is enough heat from photos to drive sublimation, there should be enough photons for YORP or sYORP.

And a hamburger shaped dark-red body is a pretty good candidate for YORP/sYORP effects, especially if there is a white frosty coating on one side.

So, it seems like we are looking at a pair of spheroids, resembling a "bag of oranges" or "bag of grapes".




Wait, I finally read the extended caption, -the blue dotted lines are the range of uncertainty!?!

"The dashed blue lines span the uncertainty in that hemisphere, which shows that Ultima Thule could be either flatter than, or not as flat as, depicted in this figure. "

So, these could be incredibly flattened!
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dudley
post Feb 11 2019, 04:51 PM
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Could it be that the problems of dissipating momentum, and the odd, flattened shapes of Ultima and Thule could be related? Could the momentum have been dissipated when the two objects encountered each other in space, in the process of pulling each other into the flattened shapes we observe today?
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stevesliva
post Feb 11 2019, 06:10 PM
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My notes on the press conference remind me that it was predicted that CA06 would be the potentially highest resolution images. These "crescent" images are CA07 and I see CA01 and CA04 in the raw images page. Still more coming!
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HSchirmer
post Feb 11 2019, 07:36 PM
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QUOTE (dudley @ Feb 11 2019, 05:51 PM) *
Could it be that the problems of dissipating momentum, and the odd, flattened shapes of Ultima and Thule could be related? Could the momentum have been dissipated when the two objects encountered each other in space, in the process of pulling each other into the flattened shapes we observe today?


There are a few ideas similar to that- usually dealing with a mostly vaporized rocky planet loses energy to reform a rocky planet or binary; of course, when you think of it, this is fundamentally the same process as gas and ice losing energy to form a KBO.

The structure of terrestrial bodies: Impact heating, corotation limits, and synestias
https://agupubs.onlinelibrary.wiley.com/doi...02/2016JE005239

The Origin of the Moon Within a Terrestrial Synestia
https://agupubs.onlinelibrary.wiley.com/doi...02/2017JE005333
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