NH Arrokoth (formerly Ultima Thule) Encounter Observations & Results, post-flyby discussion as the data arrives Options

[nprev]

This will be where we talk about the data as it arrives over the next 20 months or so.

[Roman Tkachenko]

Just made it a little smoother

[Decepticon]

Can we expect more images by Friday 11th?

[Gladstoner]

Which areas of Ultima Thule got the highest resolution coverage?

[nprev]

Posts concerning the search for a new target after Ultima Thule moved to the KBO Encounters thread.

[hendric]

New Horizons is in solar conjunction, I think new data will be arriving next week

http://www.planetary.org/multimedia/space-...w-horizons.html

https://spacenews.com/new-horizons-complete...f-ultima-thule/

The science team will work with those data this week, then take a break next week when the spacecraft is in solar conjunction, with the sun blocking communications with the spacecraft. The science team will reconvene around Jan. 15, Stern said, after communications resume.

[MahFL]

Which areas of Ultima Thule got the highest resolution coverage?

They did not release that information. They took one stripe of images as they did the closest flyby. Assuming it was a horizontal shot across the "center" some of Ultima ( the big lobe ), might be imaged, bearing in mind when the load was sent up they did not fully know the shape or spin rate.

[john_s]

The LORRI field of view in the highest-resolution "CA06" LORRI images is just a bit bigger than the size of the target, so with luck we could get the whole thing. The relatively slow rotation means that we'll cover much the same face as seen in the images already down, though of course from a somewhat different angle.

John

[WTW]

New Horizons is in solar conjunction, I think new data will be arriving next week

There was one more DSN downlink from NH received right after the last news conference, but that may have been mostly engineering data -- hard to tell.
(DSN Now was being flakey during that - hopefully the DSN itself wasn't, and the download went OK.)

[Ron Hobbs]

Canberra is listening and talking to New Horizons according to DSN Now.

(Rubs his hands impatiently)

[Nafnlaus]

Canberra is listening and talking to New Horizons according to DSN Now.

(Rubs his hands impatiently)

Finally! Can't wait to get some new data

[vikingmars]

An excellent article was just posted by the NH team about Ultima-Thule :
"Overview of initial results from the reconnaissance flyby of a Kuiper Belt planetesimal: 2014 MU69"
https://arxiv.org/abs/1901.02578

CONGRATULATIONS again to the NH team ftr this incredible feat !

[pioneer]

Does anyone know when the next press conference will be or if it has been scheduled?

[wildespace]

An excellent article was just posted by the NH team about Ultima-Thule :
"Overview of initial results from the reconnaissance flyby of a Kuiper Belt planetesimal: 2014 MU69"
https://arxiv.org/abs/1901.02578

CONGRATULATIONS again to the NH team ftr this incredible feat !

Little significant color variegation across either lobe has been detected as of this writing

There's a new word I learned today - variegation.

Excited to hear all this information (however preliminary) coming in from the mission. Glad they picked up on the colour variation near the "neck".

[Guest_alex_k_*]

Trying to sharpen

[fredk]

It's hard to know without seeing the raw images how much noise we have in these views. To me they look noisy (and we were told to expect noisy images), so I'm suspicious of the fine, pixel-scale detail. But on the other hand, the abstract cited above refers to the "mottled appearance", and the team should know whether the amplitude of that fine detail is consistent with noise or not. Or maybe by the "mottling" they mean several-pixel-scale detail? It'll be really interesting to see the closer views.

And also interesting to see higher phase angle views, to break the degeneracy between topography and albedo variations...

[kenny]

The interesting light color at the "neck" might suggest there could be slight movement between the 2 component bodies, and "grinding" of relatively fresh ice in that area...

[HSchirmer]

The interesting light color at the "neck" might suggest there could be slight movement between the 2 component bodies, and "grinding" of relatively fresh ice in that area...

Anybody know which direction is "up" and which is "down" at the neck of a contact binary like UT?

How did / could that change as the binary spun-down?

[JTN]

Anybody know which direction "up" and which is "down" at the neck of a contact binary like UT?

This slide from the Jan 2 press conference slides sheds some light on the present situation. (It doesn't give a vector but I assume things roll toward the neck.)

[JTN]

Tidbit from Alan Stern on Twitter yesterday: "We’re plaiinong an inage release— in 10 days!" (I make that about 23 Jan).

https://twitter.com/AlanStern/status/1084661266159931393

[Guest_alex_k_*]

An animation about details. Quality of 4:22 LORRI image is lower, but still.

[Alan Stern]

Tidbit from Alan Stern on Twitter yesterday: "We’re plaiinong an inage release— in 10 days!" (I make that about 23 Jan).

https://twitter.com/AlanStern/status/1084661266159931393

Update: Now planning an image release for this week too.

Sorry for the typos above, was walking between flights in Doha; well, actually running between flights!

[peikojose]

Update: Now planning an image release for this week too.

Sorry for the typos above, was walking between flights in Doha; well, actually running between flights!

Nice!

[John Moore]

Update: Now planning an image release for this week too.

Sorry for the typos above, was walking between flights in Doha; well, actually running between flights!

Interviewed Alan many years' back...a wonderful experience: walking then, running still today to inspire.

[Marcin600]

A slightly more elongated and less round shape of UT from a slightly different perspective ? https://twitter.com/hashtag/UltimaThuleFlyby?src=hash

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[Marcin600]

New movie from 500000 km to 28000 km: http://pluto.jhuapl.edu/News-Center/News-A...p?page=20190115

[Øyvind G]

New movie from 500000 km to 28000 km: http://pluto.jhuapl.edu/News-Center/News-A...p?page=20190115

From the release:
"...rotation of Ultima Thule in the seven hours between 20:00 UT (3 p.m. ET) on Dec. 31, 2018, and 05:01 UT (12:01 a.m.) on Jan. 1, 2019..."

Isn't that nine hours?

[john_s]

Oops! Sorry about that.

John

[Ian R]

Wonderful images! Amazing how a slew of pictures at very moderate resolution can still be pretty insightful. I took one of the GIF animations and made an aligned and 'bouncy' version:



Looks as if the lobes are less spherical than they are hamburger shape!

[Ian R]

My speculation is that the two lobes were never individual objects in the first place, and that the original fast rotation of MU69 -- back when it was newly formed and more prone to deformation -- caused a 'blob' to begin to separate from the main body due to centripetal forces, which in the end weren't enough for the two components to part completely.

Just a stab in the dark from a layperson!

[Marcin600]

My speculation is that the two lobes were never individual objects in the first place, and that the original fast rotation of MU69 -- back when it was newly formed and more prone to deformation -- caused a 'blob' to begin to separate from the main body due to centripetal forces, which in the end weren't enough for the two components to part completely.

Just a stab in the dark from a layperson!

I think that this is one of many possibilities. In any case, things seem to be more complicated than they originally seemed

[Marcin600]

For example, two bodies could be originally separate and flattened independently as a result of rotation. More data from New Horizons is needed.

[stevesliva]

For example, two bodies could be originally separate and flattened independently as a result of rotation.

Or accretion.

This is definitely real? If I focus on just the neck/isthmus then it does appear real, but I worry it's just an artifact.

[pdalek]

Ultima Thule looks like a snowman. A big snowman is a good way to think about formation and properties.

Comets have density about that of handmade snowballs. U-T is probably similar.
Calculating gravitation and centrifugal acceleration will show it is gravitationally bound over the entire surface and so was not formed by stretching a sphere.

The escape velocity is about that of a human thrown snowball. Fall velocities would be similar. At such velocity, a small snowball acreating under gravity will splat. For a large falling snowball, self gravitation will keep the ball in shape. Higher impact velocity would change things, but without large nearby planets to shift orbits, this is unlikely.

The compressive strength ordinary packed snow is sufficient to prevent a 19km and a 14km balls from merging to a much more compact space. It is easy to estimate the contact area.

Modelling the gravitational field shows local down is up to about 30 degrees from surface normal near the neck. This is about the angle of repose of lightly packed snow.

[Marcin600]

As Stevesilva supposes, the slightly flattened shape of Ultima (and Thule?) - if it is not a low resolution artifact - may be the result of the specificity of the accretion process itself - in one plane, a bit like an accretion disc (?)

I think the wonderful New Horizons team is already working on the interpretations.

[john_s]

I took one of the GIF animations and made an aligned and 'bouncy' version:

Looks as if the lobes are less spherical than they are hamburger shape!

Hi Ian-

Thanks for that very revealing "de-rotated" animation. We on the science team had been planning to do the same thing, but you beat us to it. When I sent the team a link to your animation, it sparked quite an e-mail storm. UT continues to surprise!

Thanks again,
John

[Explorer1]

New post from Alan: http://pluto.jhuapl.edu/News-Center/PI-Per...tive_01_17_2019

In addition to data downlink from MU69, some distant observations of the unchosen flyby target in March, and some extra fuel for post 2020 maneuver to a more distant object.

[Roman Tkachenko]

I just played around with the sequence

https://www.youtube.com/watch?v=T_HGXKO9kus

[Guest_alex_k_*]

Looking for surface features. Strong Fourier-based processing performed, details are exaggerated if resolved properly.
05:01:47 (better res) vs 6 stacked 04:04

Focused on Ultima:


Focused on Thule:

[Ian R]

Thanks for that very revealing "de-rotated" animation. We on the science team had been planning to do the same thing, but you beat us to it. When I sent the team a link to your animation, it sparked quite an e-mail storm. UT continues to surprise!

Thanks again,
John

Hi John,

That's pretty amazing! Thanks for the feedback: it's an honor to be tangentially involved with the team as new discoveries are being made about UT.

Ian.

[alan]

What would happen when a body the size of one of UT's lobes was spun up if most of its mass was made up of a bunch of spheres a few km's in diameter instead of many smaller pieces? Would it end up hamburger shaped instead of football shaped as it shifted toward equilibrium?

[kenny]

Analysis of Ultima Thule comparing its morphology with those of previously-imaged comets....

Forbes Magazine on UT January 21

...by astrophysicist author Ethan Siegel.

[john_s]

The current best image (a big improvement over the earlier ones, due to lower noise and higher phase angle) has just been posted:

http://pluto.jhuapl.edu/News-Center/News-A...p?page=20190124

John

[Phil Stooke]

Wow, that is a fantastic image - I have just played with it slightly here by brightening the terminator to show faint features a bit better. Just don't ask me to interpret it! - well, OK, maybe the broader depressions near the terminator of the large lobe look a bit like they are bounded by scalloped scarps retreating due to volatile loss.

Phil

[Marcin600]

An amazing object!!! And it is becoming more and more fascinating. There are really a lot of these small hollows on almost the entire surface. I can not wait for more detailed pictures. Sadly, we'll never see the reverse side...

[Gladstoner]

This faint white ring is... interesting:



So far, it doesn't seem to be associated with topographical features.

I wonder if some Kuiper belt objects will display relic binary-contact collars, i.e. talus rings left over after the binary components separated by some process (impacts, gravitational interactions). I suppose they could be thought of as 'kiss marks'.

Since this ring is near the rotational pole, and rather thin, it probably isn't an example.

[Explorer1]

Amazing new image! It really does look more like the smaller lobe has massive impact on it (like Phobos' Stickney crater) or Damodar on Mathilde.....
This confirms the closest approach images were captured successfully? Big sigh of relief!

Any idea where exactly the rotation pole is? I'm assuming near the centre of mass, on the right side of the circle Gladstoner added.

[abalone]

I get the impression that its possibly evidence of been put together like a hailstone accretion and the lines and lumpy appearance might be an artifact of that. https://upload.wikimedia.org/wikipedia/comm.../94/Granizo.jpg Could also be the reason for the 'hamburger' shape if the individual lobe were slowly rotating during the accretion process before coming together.

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[hendric]

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.

[Ian R]

It's a jaw-dropping image: congratulations to the NH science team.

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

[Marcin600]

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

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[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]

It's a jaw-dropping image: congratulations to the NH science team.

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

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.

Attached thumbnail(s)

 

[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):

[Guest_Steve5304_*]

The two best views of UT thus far (courtesy of LORRI and MVIC):

Man...that ring...what the

The further out we get the stranger things are. It looks like a sad snowman! The media will jump all over this

[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!

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?

It's a jaw-dropping image: congratulations to the NH science team.

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

[Guest_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:

[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

[ronatu]

[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.

[PhilipTerryGraha...]

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 ...

[mcaplinger]

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]

• 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:

[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]

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:

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

[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]

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]

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.

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[alan]

J. I. Katz, Ultima Thule (486958; 2014 MU69): Necklace, Composition, Rotation, Formation

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

[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:

[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.


Here's some chords drawn in that help show the shape of the unlit side:

[monty python]

Bravo for the occultation fence photo. The movie of it was too hard to follow for me.

[HSchirmer]

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]

-A YORP/sYORP spin

MU69 is far from the Sun and large(ish). wouldn't YORP be negligible on such a body?

[HSchirmer]

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]

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 .

[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."

Attached thumbnail(s)

 

[peikojose]

Am I the only one that thinks that NH missed MU69 at the closest distance ?

[Explorer1]

Amazing new views!

Am I the only one that thinks that NH missed MU69 at the closest distance ?

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?