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Unmanned Spaceflight.com > Outer Solar System > Pluto / KBO > New Horizons
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Marcin600
QUOTE (hendric @ Jan 25 2019, 12:15 AM) *
Yeah that's my thought too, kinda like a kid with a snowball that keeps packing more snowballs onto it. Maybe the Thule lobe is just large enough to hold itself together, while the smaller objects just slumped.


a bit like a flattened hail https://ljkrakauer.com/LJK/00s/weirdhail.htm


covered with a tholin shell
dudley
One side of that dim ring on Ultima appears to be made up of two slightly separated arcs, on the side nearest Thule. The ring looks lopsided at first glance, but appears to have bilateral symmetry, on either side of a line running across it diagonally toward the dark cleft on one side of the 'neck' region.
HSchirmer
QUOTE (Ian R @ Jan 25 2019, 12:32 AM) *
It's a jaw-dropping image: congratulations to the NH science team. blink.gif

Here's a colorized version, purely for aesthetic purposes:

Click to view attachment


Very interesting how there's a scarp where the surface crust appears to end at the lower right,
and the highly defined craters are only on the area where there is no scarp.

There was a paper that calculated that the grooves on the Martian moon Phobos could be caused by low velocity impact with boulders that rolled along the surface.

Sorta looks like Thule and Ultima made contact around 5 o'clock, and rolled along ripping up the crust until it settled at 1 o'clock.


Soo, basically, it looks like a Bert the Turtle from 1950s civil defense films.
serpens
The news article comments on differences in the geologic character of the two lobes of Ultima Thule. Whether the suspected difference is compositional or textural this could imply the lobes developed separately. If so then when Ultima and Thule came together there would potentially have been a few scrapes, bounces and heat as linear and angular momentum was sorted out. In this respect the light ring Gladstoner refers to seems to fit the crater in the smaller lobe. Bit of a stretch but not beyond the bounds of possibility.
Ian R
The two best views of UT thus far (courtesy of LORRI and MVIC):

Click to view attachment
Steve5304
QUOTE (Ian R @ Jan 25 2019, 11:23 AM) *
The two best views of UT thus far (courtesy of LORRI and MVIC):

Click to view attachment



Man...that ring...what the blink.gif

The further out we get the stranger things are. It looks like a sad snowman! The media will jump all over this laugh.gif
stevesliva
If we think back to the fact that they're more hamburgers than spheres that ring might be circumpolar (well, the pre-merger rotational pole) and Ultima might've looked like Saturn's moon Atlas or Pan before getting a remora.
Gladstoner
The sparse cratering is intriguing. So far, the bodies don’t seem to be crater-saturated as one would expect for small, primitive bodies. Either they were resurfaced, or we are seeing a barely altered primordial surface. I don’t know of any other body in the solar system where this is close to being the case. Of course, forthcoming images will provide more details.

Plus, the crater size distribution seems to be one large depression on Thule and a few pits near the limit of resolution. So far, there appears to be a dearth of intermediate sizes. It’ll be interesting to find out what this says — if anything— about object distribution in this part of the solar system, assuming these are impact craters.

Also, there seem to be a number of concave scarps that are outward facing. Could these be slumping that occurred on an earlier, rapidly-rotating Ultima?
Webscientist
Very nice work!
Some "scientific artists" of the past had anticipated the shape of that new type of solar system object. Really remarkable! blink.gif

At first sight, I would bet that the density of Thule is higher than the density of the external blanket of Ultima since Ultima seems to have been more distorted by the relatively soft impact wheras Thule seems more uniform (or less distorted).

Can the gravitational interactions between the two parts in the rotation process engender landslides or resurfacing events erasing some craters?


QUOTE (Ian R @ Jan 25 2019, 12:32 AM) *
It's a jaw-dropping image: congratulations to the NH science team. blink.gif

Here's a colorized version, purely for aesthetic purposes:

Click to view attachment

Steve5304



I would think that you just don't have that much out that far...it unlikely to be any sort of resurfacing...how would that even happen that far out on a dead object like this?? Accretion over millions of years??

tty
It seems to me that an impact as large as the one on Thule would create enough momentum to separate the lobes, at least temporarily. Could the "ring" be a previous "attachment point"?
Marcin600
Small round pits are not necessarily impact craters. They are best seen at the terminator, but they seem to cover large surfaces - they appear as white dots. They can be "internal" and not "external" origin. They have similar size and lack of size distribution typical of craters. (I'm not talking about a big hole at Thule - it can be a crater, but it does not have to be!)
Rittmann
Some speculation based on the last image two-frame rotating image...

In the rotational image it seems as if there was not one, but two rings of bright material: the central one, and another one to the lower left side of the image. If this is a remnant of an ancient contact point between Ultima and Thule, I speculate that one of them was an earlier contact point and a later impact made Thule roll over Ultima creating the second ring. The exact place where the rolling happened could be the bright patch of material that is where both possible rings find each other. Since the lower left area apparently has two small craters / sinkholes, it would be the most ancient area.

In Thule there appears to be two different types of terrain. Right on the top we see some possible cratering, as well as on the right side of the depression / crater. But the central left side of the depression / crater appears smooth to a certain degree. This may be due to lightning conditions, but I think that an impact has enough kinetic energy as to melt partially the material in Thule and make it flow over older terrain. With such a low gravity, most of the splash would be lost but the melting could flow that way. The "melting" also seems to hide a bright line, that could be the ancient contact point between Ultima and Thule: it appears to be an arc of roughly the same size of the other rings in the current contact area and in Ultima. If so, stretching the hypothesis the V in Thule could correspond to the marking of the rolling: in Ultima we see two well-defined arcs touching, and the V in Thule would be the remnant of one of the sides of the touching arc. Also, the crater / depression has no clean border which could be explained by the melting hypothesis.

So the story of these bodies, according to these speculations, would be:

1. Formation of both bodies and for some unknown mechanism they eventually enter in contact. Original contact point is the central circle on Ultima.

2. Some moderate impact causes Thule to roll over Ultima, possibly from a not strong contact equilibrium position. This creates a second neck, the lower-left circle that seems more visible in the rotation image.

3. A bigger impact creates the crater / depression seen in Thule, splitting the contact binary and causing both bodies to change rotation axis. Eventually both bodies came into contact again, in the position we see nowadays. Impact creates enough cynetic energy as to partially melt the surface of the bodies, causing the flows we see and partially erasing the original contact rings in Thule, as well as melting the crater borders. Ejecta orbits the plane of the impact until collisioning with both bodies, littering the craters we see near the border of both bodies. Since ejecta impactors are small, melting is on a smaller scale and don't cause flows.

Against these hypothesis: there appears to be some sort of flow on Ultima, or at least similarities in the surface features, yet the rings are dimmed but not erased. This could mean that the flow is not such, but the rain of fine debris from the impact. The original impactor would then be the source of most impact craters we see in the border: we can see in the high-resolution image at least a couple of craters of a similar size in the (2) ancient neck, so at least from current data it seems that craters have a clear distribution over both surfaces.

As for the mechanism of making both bodies end up contacting, the only idea that comes into my mind is that since both bodies are fairly irregular in shape, the micro-gravity field should be far from homogeneous causing losses over time as mutual rotations cause shifts in the gravity field, so orbit would degrade over time. But I have no expertise in orbital mechanics, so I don't know if I just said something stupid here.
wildespace
Exciting!

Here's a version with some colours plugged in from a reprocessed colour image:

Click to view attachment

tty
As for the mechanism bringing the bodies back together after a major impact, tidal dissipation immediately comes to mind. If the impact energy was enough to make one body at least partially plastic the dissipation would be greatly increased.

However explicitly calculating the effect on two highly irregular (and possibly inhomogenous) rotating bodies in probably very eccentric orbits would be quite challenging. Qualitatively I would guess that the tidal effects would first slow down rotation of both bodies until they became tidally locked, and probably simultaneously decrease eccentricity of the orbits. Once tidal rotational lock is reached any further dissipation would very slowly bring the bodies together.

Of course they could also have re-collided physically long before this. It all depends on the orbits.
Spock1108
An attempt to add colors ...

Roman Tkachenko
My attempt to improve the image.
Not the best way to do such things when you have no raw image, but anyway rolleyes.gif
ronatu
Click to view attachment
jasedm
Following on from discussions about the surface geology, some of the shapes seem to be somewhat reminiscent of 'patterned ground' - polygonal structures caused by freeze/thaw and subsequent differentiation of surface material. I'm not sure if UT has enough of an eccentric orbit to cause these processes, but it seems a possibility.
PhilipTerryGraham
I'm assuming the raw MVIC data downlinked thus far hasn't been thrown up onto the PDS or any other place just yet?
Spock1108
It reminds me of someone ...

Click to view attachment
mcaplinger
QUOTE (PhilipTerryGraham @ Jan 26 2019, 02:03 PM) *
I'm assuming the raw MVIC data downlinked thus far hasn't been thrown up onto the PDS...

One does not simply "throw stuff" onto the PDS. https://pds-smallbodies.astro.umd.edu/data_...AP-01_R0_C0.pdf doesn't describe the schedule for the extended mission but Table 3 says the first delivery of Pluto encounter data took about 9 months from encounter.
JRehling
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?
Gladstoner
QUOTE (JRehling @ Jan 28 2019, 01:41 PM) *
• Porous portions of the body could collapse inward to a new configuration at higher density.


The feature marked here does resemble a line of collapse pits along a fracture:

Click to view attachment
Rittmann
Another mechanism comes to my mind for the white lines we see. If these bodies are made of lesser balls of aggregated material, which originally may have clumped before being added to Última and Thule, they would have boundaries. Any energetic impact that could have partially melted the surrounding material of the impact area could cause a melting, which would naturally flow through these discrete boundaries filling them up and causing contrast of materials.

As a result, even if there was a full melting of the clump surface, boundary would still differentiate. And the big circle in Última seems exactly that: melted surface which slightly seems a done with a surrounding ring, but the flowing material escapes this boundary - this seems apparent on the right side.

Against this, is where would be the impact crater causing any such melting. Thule has a crater, but Ultima seems devoid of any such originator in the area.
ngunn
QUOTE (Rittmann @ Jan 29 2019, 06:11 AM) *
If these bodies are made of lesser balls of aggregated material, which originally may have clumped before being added to Última and Thule, they would have boundaries.


I have one observation I haven't seen mentioned explicitly here. The constituent lumps of the larger lobe Ultima all seem to be about the same size, causing it to resemble a bag of oranges. I have absolutely no suggestions as to why that might be.
Gerald
During Rosetta's 67/P mission, there have been lots of speculations about cometesimals as building blocks. This paper appears to contain some of the according discussion, especially subsection 4.3 about their hierarchical agglomeration.
The paper is referencing a paper about simulations of this mechanism. Here an excerpt of the abstract:
QUOTE
The size distribution of cometesimals growing by drag-induced collisions develops a narrow peak in the range tens to hundreds of meters.

So, there seem to exist size-dependent agglomeration mechanisms with prefered grain sizes. Above some size, gravity between cometesimals should come into relevant play, and we are getting into a rubble pile model.

This is just some clue, where to start with.
Fran Ontanaya
Ultima resembles a bit Atlas too, which would imply it accreted within a ring of particles

Click to view attachment
alan
This model assumes gravitational instabilities formed 1 km planeteseimals which them accreted leftover cm-sized pebbles. It includes a period when similar sized planetesimals accrete each other:

Forming the Cold Classical Kuiper Belt in a Light Disk
http://adsabs.harvard.edu/abs/2016ApJ...818..175S

There are also some LPSC abstracts discussing formation mchanisms:
https://www.hou.usra.edu/meetings/lpsc2019/pdf/2809.pdf
https://www.hou.usra.edu/meetings/lpsc2019/pdf/3044.pdf
HSchirmer
QUOTE (Steve5304 @ Jan 25 2019, 05:59 PM) *
I would think that you just don't have that much out that far...it unlikely to be any sort of resurfacing...how would that even happen that far out on a dead object like this?? Accretion over millions of years??


IIRC, there is a "Stria" paper The Formation of Striae within Cometary Dust Tails by a Sublimation Driven YORP like Effect
about cryo-ice sublimation torques, which estimated that CO could still exert some pressure out to 40-50AU.

Also, "think fluffy", like aerogels (solid smoke), shuttle tiles, and pink fiberglass insulation, these objects should be exceedingly bad at heat conduction, and a large internal surface area should suppress convection by any internal gasses.

I'm really curious about the results from the "radar ping" experiments, billions of years with a surface dominated by sublimation, I'll guess there may be some ice pinnacles or other "twists" that are responsible for the appearance at this resolution.
Formation of metre-scale bladed roughness on Europa’s surface by ablation of ice
Roman Tkachenko
Interpolated animation derived from CA04 LORRI and CA06 MVIC frames
HSchirmer
QUOTE (ngunn @ Jan 29 2019, 11:05 AM) *
I have one observation I haven't seen mentioned explicitly here. The constituent lumps of the larger lobe Ultima all seem to be about the same size, causing it to resemble a bag of oranges. I have absolutely no suggestions as to why that might be.


A binary KBO goes splat. It generates fragments and a gravitationally bound exosphere.
Disruption leaves 2 primaries and 6 fragments.
Thanks to the laws of orbital mechanics, all 6 fragments accrete onto one fragment, creating "the hamburger", and kicking the "the meatball" into a more eccentric orbit.
Tides and the angular momentum transfer via the exosphere lock meatball and hamburger into a spiraling synchronous orbit, tidal heating cause the crater on the meatball and the scarps on the hamburger which replenish the exosphere. They end up tidally locked, and eventually dock.

-edit- Or, you've got a situation with "snow white and the 7 dwarfs" where seven small chunks accrete and capture one larger chunk.
alan
J. I. Katz, Ultima Thule (486958; 2014 MU69): Necklace, Composition, Rotation, Formation

QUOTE
Flyby images of Ultima Thule (486958; 2014 MU69) show a comparatively bright ``necklace'' between its two lobes, in contrast to its generally low albedo. The necklace is found in the most shaded, and therefore coolest, part of its surface. It may be clean, high albedo, ``hoarfrost'' condensed from vapor evaporated from the low albedo dirty ice elsewhere. Ammonia, the likely major constituent of Ultima Thule, has the necessary vapor pressure. The rotation period of 15±1h is at least twice its breakup period, indicating either that its formation was not limited by angular momentum or that half its angular momentum was lost after formation, perhaps to surrounding gas in the proto-Solar System. The lobes of Ultima Thule must have spherized under conditions different than those encountered by its present, post-contact, configuration.
AJAW
Will our estimate of the rotation rate ever become good enough to look back at the occultation results from last year and work out exactly how many rotations have happened since?
alan
New Horizons' Evocative Farewell Glance at Ultima Thule
Images Confirm the Kuiper Belt Object's Highly Unusual, Flatter Shape

http://pluto.jhuapl.edu/News-Center/News-A...p?page=20190208

Click to view attachment
marsbug
I usually read with fascination but don't contribute for fear of denting the signal to noise ratio. However, it seems worth noting that my very un-expert brain immediately drew a connection between the weird shape of Ultima Thule and the weird shape of Omuamua. A flat, sail like, shape has been put forwards as an explanation for Omuamua's light curve I believe, and now it seems we have proof that nature can indeed craft such a flattened shape. Is it rediculous to suggest that the interstellar object could have formed in the same region of it's original solar system that Ultima Thule occupies in ours, and the two formed along approximately parallel lines under similar forces - acting in a bizarrely
pro pancake shape fashion?
Explorer1
Absolutely bizarre! A bit like the tiny moons of Saturn... but no rings anywhere nearby.

At the very least, this is good confirmation of two separate bodies being formed.
Gladstoner
A little bit of Ultima-shine is visible on Thule:

Click to view attachment
jccwrt
I realigned the MU69 departure movie on MU69 itself to make an occultation fence. It looks like the small lobe is relatively well-constrained by stellar occultations. The larger lobe is a little more difficult to pin down, with fewer stars along the occulation path.
Click to view attachment

Here's some chords drawn in that help show the shape of the unlit side:
Click to view attachment
monty python
Bravo for the occultation fence photo. The movie of it was too hard to follow for me.
HSchirmer
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.
Paolo
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?
HSchirmer
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!
dudley
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?
stevesliva
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!
HSchirmer
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
MahFL
Alan Stern tweeted, new pics tomorrow smile.gif.
Marcin600
Sharpest view of Ultima Thule: http://pluto.jhuapl.edu/News-Center/News-A...p?page=20190222


"...The most detailed images of Ultima Thule -- obtained just minutes before the spacecraft's closest approach at 12:33 a.m. EST on Jan. 1 -- have a resolution of about 110 feet (33 meters) per pixel..."

"... The higher resolution brings out a many surface features that weren't readily apparent in earlier images. Among them are several bright, enigmatic, roughly circular patches of terrain. In addition, many small, dark pits near the terminator (the boundary between the sunlit and dark sides of the body) are better resolved. "Whether these features are craters produced by impactors, sublimation pits, collapse pits, or something entirely different, is being debated in our science team," said John Spencer, deputy project scientist from SwRI."
peikojose
Am I the only one that thinks that NH missed MU69 at the closest distance ? sad.gif
Explorer1
Amazing new views!


QUOTE (peikojose @ Feb 22 2019, 02:46 PM) *
Am I the only one that thinks that NH missed MU69 at the closest distance ? sad.gif


As Alan, said, these were the 'stretch goal' images, just a few minutes before closest approach. I don't think there will be much higher detail than this to come. Will there?
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