Here's a related question (which I don't know the answer to - someone must have modeled this): If an impact on Pluto created the smaller moons and they initially were out of Charon's orbital plane - would Charon's gravity eventually cause them to migrate co-planar (or get ejected), such that any long duration surviving moon by definition has to be coplanar? This would help add weight to the impact vs initial formation theories of Charon and the smaller moons.

Looks like it's been taken down.

Edit: fullres of that version: https://pbs.twimg.com/media/CKDXE5iUkAACzu9.jpg:large

Here it is: http://www.nasa.gov/image-feature/new-hori...ntain-in-a-moat

More mountains.

Click to view attachment
Now that is just weird. I don't recall ever seeing a mountain coming up out of the center of a canyon, rift, chasm, or whatever.

I thought I would take a closer look at that suspicious dark blob that Xflare and others mentioned. I've up sampled and zoomed the image so its a bit fuzzy.

https://www.flickr.com/photos/124013840@N06...eposted-public/

Conclusion, probably not Cryovolcanic in origin, but there is lots of evidence of sublimation. A string of dark pits along the top edge and the right half seems to be shadow from higher ground in the centre. Although there are also dark pits on these peaks, they don't give me the impression of being Calderas or cones, just more sublimation hollows. Just a localised difference in dust/organics deposition I think, reflecting local differences in surface composition perhaps.

Top left of the image the light grey of the flatter terrain just intrudes and it can be seen to only partially cover the lumpy, pitted terrain, giving a "dune like" appearance. Many have commented about the "dunes" in the flatter grey areas. This is evidence that this is just the pre resurface terrain showing through the resurfacing layer. Being right at the edge of the tip of the Tombaugh Region, which is mainly Carbon Monoxide we are told, I suspect this is what has flowed over and resurfaced large parts of the area. By what process, is another story.

This extreme, though blurry close up does show how convoluted and pitted the surface is, much like the surface of a glacier on Earth, with differential sublimation, replacing the differential melting on a glacier. In places this forms long crevices and ridges, others mounds and pits. Next I am going to have a close look at that ropey looking terrain.

The fact we see craters on Charon reinforces the youth of Pluto's surface seen so far at high res.

First thing that struck me re moat mountain: deep sublimation pit/similar providing the path of least resistance to cryolava?

Nice to see a good example of flexure...

https://en.wikipedia.org/wiki/Lithospheric_flexure

My thought was an upwelling of heat that hasn't reached the surface, but softened it enough that the mountain pressed down, pulling down the area around it. Wouldn't have called that in a million years.

I suppose it could be a volcano, piling up and pushing down the area around it, but the borders look to well defined to me.

An exaggerated case of isostatic adjustment, like the depression of the seafloor around the Hawaiian Islands? What pushed up the mountain went away, or we have volcanism. Definitely weird.

Resemble a "sinking mount"...

It looks like a chunk of material has landed in soft putty. Ejecta from a nearby impact maybe, there is a huge crater just over the rim. Also notice the cracks all over the surface, some smaller craters straddle these cracks. It smacks of an ejecta, of impact or Cryovolcanic origin, debris field to me, as mentioned in an earlier post.

people were pointing out this plateau yesterday


moving around it at 45 Deg intervals

How about Hydra's sister in a close orbit got pulled in by Charon and made a relatively gentle impact?

that sunken spot on Charon looks a bit like the plateau i posted above

the mountain on Pluto is also a bit sunken

You can't say that without proper stereo data. Your renderings are nice, but they are only approximations that assume a consistent surface reflectivity.

On the sinking mountain in the trench: Maybe there is also an enhanced rate of volatiles sublimation in proximity to the mountain due to compressive forces, and/or greater solar insolation from reflection off the mountain sides? Could this add to the rate of sinking (in addition to isostatic adjustment) ?

Suppose the central mountain is a piece of ejecta. its shard like angular shape suggests it is. Whatever its source it would be "hot" compared to the icy surface. In Charon's tiny gravity, such a large lump would still hit the surface quite slowly and rather than a crater, it would "melt" its way into the surface. The area around the base of the object would sublimate away. It being so cold on Charon this might only occur for a limited time, the piece of "hot" ejecta rapidly cooling and freezing again. Result object sitting in an empty moat.

The smaller circular "craters" have no lips or their own ejecta, so I suspect smaller bits of debris have "melted" their way into the surface to create these cone shaped indentations.

I have to say I had the same thought. What would be the impact velocity of a fellow satellite on Charon?

Far too large to leave a nice fairly intact chunk sticking up from Charon's surface.

It could be the other way around, a frozen crust grew to that height and the mountain is just warm or conductive enough to melt volatiles around it.

This is an all-new map of Charon that includes all of the relevant global images from July 9 to July 14. Longitude 0 is at the left edge of the map.

Click to view attachment

Due to the low resolution of the images covering the anti-Pluto hemisphere it is not easy to determine if the chasm/cliff/trough extends around Charon. I think I see some hints that it might do so but I'm not sure. Examining the original images might reveal if this is the case.

The crater "over the rim" I am referring to is this one that dominates this image, which also has a suggestion of a plume of darker debris. The "smoking gun".

http://www.nasa.gov/sites/default/files/th...jhuapl-swri.png

The straight, bright line from this huge crater, at about 10 O'Clock, ends in a dark blob, the shadow of that sunken mountain perhaps. It would be in about the right place.

Very nice, Bjorn!

There are elliptical trajectories that have a body on the outbound leg encounter an object(Charon in the is case) just so the outbound velocity counteracts the gravitational pull of Charon and you get an (almost) zero velocity impact. it requires luck though.

True about the Hill Sphere, but as far as I'm aware two things don't need to "hit, in just the right way, while near Pluto" - they just need to pass close by. There doesn't need to be a collision for a planet to capture something.

(though I guess it just shifts the problem - if a KBO has a moon and one of those ends up being captured, then how did the KBO get its moon in the first place?).

I suppose a Giant Impact is an easier explanation in some ways - everything ends up in the same plane (though why didn't it all accrete into Charon? why are there little bits - the other moons - left over?). The assumption that it happened a long time ago is questionable at this stage though, I think. Once we get an idea of the history of the system through looking at the rest of the images then we'll be able to figure out things a bit better.

I think Triton's believed to be a captured KBO, and IIRC the other minor moons of Neptune (except Nereid, but that's always been weird and is probably captured too) are in the same plane too.

I think it's a stretch to claim that the entire system is the result of a single event. Why do the other small moons still exist? Why didn't they coalesced into Charon or get ejected from the system or fall back onto Pluto?

I'm all for speculating and conjecture, I'm just a little uncomfortable with people just assuming it's all caused by a single giant impact and can't be anything else (much that I'm concerned that the team seem to have ruled out tidal heating as the reason why the surfaces are still young). Let's bounce around ideas and have open minds and look at the data before jumping to conclusions! It's still the very early days, if all the other missions are anything to go by then anything people come up with now - no matter how certain they think they are - is almost certainly going to be superseded later after more analysis.

Two remarks Re the mountain in a hole on Charon.
1- the shadow doesn't match exactely and I can't figure out what is what
2- if you look outside the inset, there is another bigger mountain in a hole visible on the global view but in the shadow when the Closer view has been taken.

Occam is rolling over in his grave.

A relevant soundbite from that 2003 paper:

Something I'm too lazy / don't know how to try to work out: is there anywhere in the solar system where a fairly primordial flat surface would not have ended up saturated with impact craters? (I realise there's a lot of vagueness in that question.)

One explanation for the mountain-in-a-hole could be steam venting. The warmth radiated by the escaping steam would sublime the surrounding low temperature ices, creating the hole. As the escaping steam cools, some of it turns into ice crystals which fall back to the surface, creating the mound.

I would love to see such trajectories - because I'm quite doubtful they exist. Because if they did - the reverse would be possible - that you would under certain situations be able to just leap off Charon into such an elliptical trajectory.

could the mountain on Charon be something like the craters with oversize central mounds on Enceladus? I am thinking of craters Sindbad, Dunyazad, Aladdin...

JTN - Think about this with a bit of a mind-flip. Planets and other worlds form by accretion - zillions of bits coming together. As the world grows, every incoming object makes a crater. In the last 1 percent (volume) of growth, the entire surface is impacted so many times (to add that remaining mass and volume) that the entire surface is bound to be a saturated mass of craters. You can't add tens of km of material to a planet's crust without fully saturating it.

If you want an unsaturated surface you have to do something else to it - cover it with ejecta from one of the last large impacts (e.g. Orientale ejecta blanket on the Moon), or lava flows, or sediments or ice deposits, or erode it away as at Mars's dichotomy. Then that new surface starts accululating craters, but at the much lower rate typical of post-accretion times.

Even if Charon formed after a big impact on Pluto, it accreted from orbiting debris and would be saturated by that accretion. Something else happened to it later to make it look different.

Phil

True. The discovered exo planets - and now Pluto/Charon - does show that our existing models for solar and planetary system development are very lacking. A lot of assumptions are rightly being thrown out the window.

If pluto-charon and Triton They had the same orbit? In different point ..and Triton subsequently captured from Neptune gravity. .. :-/

The ropey terrain.

https://www.flickr.com/photos/124013840@N06...eposted-public/

I have waxed lyrical in the image description, so a brief summary. The large ropes are aligned like dunes in the prevailing pole to pole heat and atmosphere flow. The deposition of ices shows the falling ice crystals alignment twisted by the Coriolis effect. Diurnal, differential deposition followed by the reverse differential sublimation leaves a diagonal pattern of ridges and hollows, making the lines of hills/mountains look like rope. Simple when you see it, but there is no way I would have thought of it beforehand.

In a completely non-scientific view of that boulder in a hole image, my immediate first impression was a small asteroid hit Charon at a very slow speed and just happened to land in or roll into an existing hole. Since that time all evidence to its origin and possible path have smoothed over. What other solar system body (that we have more knowledge of) would have a similar or equivalent gravitational pull of Charon? Do we see things on their surfaces that indicate that large objects have hit slow enough to not cause large craters, remain on the surface and not burst apart?

That's what I don't like. It's waaaay too early to throw assumptions out of the window here - usually the existing models end up being fine generally, and there's just a tweak to do to accommodate the new data.

I can certainly appreciate the urge for scientists to look at new data and say "OMG THIS CHANGES EVERYTHING", but usually a more measured approach is needed to make progress .

Possibly. But if they data doesn't fit your existing hypothesis, sometimes a re-think *IS* in order. And stubbornly clinging on to your dear favorite theory (whatever it may be) does no one any favors. It is so tempting to think that we have it all figured out, and we are just missing that small final piece of the puzzle. But perhaps we are missing more than just one piece here.

you do not need that
it is visible in the original image from the nh site


it is not as pronounced as on Charon ,but it is visible

The isolated mountain on Ceres

I really don't think physics allows for the kinds of low-speed impacts that are being discussed here. It is much better to think in terms of deposition and removal of materials - simple geological processes - than to try to do physics without the math.

There are analogs to moats around mountains. Thousands of them on Mars, concentrated in mid-latitudes where temperatures conspire to allow ice-rich material to come and go. And several on Ariel, the satellite of Uranus which also has big rift structures.

The best understood would be Mars. A rock surface containing frozen water. In some places it's stable - it stays frozen In other places it melts and floods out of the subsurface in giant floods. But in some zones in the mid-latitudes the ice flows out from the sides of hills like glaciers (check out the Centauri Montes). And in a few places just equatorward of those kinds of flows (check out northern Kasei Valles) hills are surrounded by moats. Almost certainly they were produced by glacier-like flows out from the hills, which were later partly covered by other deposits (e.g. Kasei Valles sediment), and during a warm period the ice melted, leaving the moat. On Charon, we can speculate about the kind of 'ice' which could duplicate the process. Start there with geological speculation, it's much more likely to be productive.

Phil

No, that could be explained by smaller mounds surrounding the mountain. Much of the darker area around the mountain on the left side may just be darker deposits, some by product of the erosion process.

That does sound intriguing, and would be possible if Charon had significant non-H2O on it, but I thought its surface spectra was mostly H2O? If it had an H2O mantle with N2 or CO crust, I could see a warm (to the N2 or CO crust) H2O batholith push up and clear away the local crust - similar to the lava dome at Mount St. Helens melting away the glacier around it. But its spectra shows mostly H2O.

Curiouser and curiouser!

I was thinking that Neptune's moon, Proteus, would be a good example of the cratering record for the outer outer solar system. But, it doesn't have many craters either based on the Voyage 2 images. But, Proteus is protected by Neptune, which also draws impactors towards it.

Space is very big in the inner solar system but the amount of surface area in the Kuiper Belt is much bigger. Maybe the odds of an impact are just much smaller. Having said that there are still places on Pluto and Charon and are remarkably fresh so I don't think a diminished impact rate accounts for everything we are seeing.

Andy

Well, that's not me. If they're not delayed, better for me, I can see them earlier. If they are delayed, again better for me, the scientists will have more time to understand everything and I'll have my questions answered earlier.

Sorry to bust in on the Mountain with a Moat discussion....
Here is Hydra (from the released blocky image) Can any one point me to the actual Lorri image that this Hydra is in?
Click to view attachment

(its obviously a derelict Miner, XKCD Class, with that older type of Bussard Ramjet...)

Charon, while "small" still has an escape velocity of 580 m/s, or 2,100 km/hr. So very unlikely any impactor would survive. Even if the impactor was a solid body vs the rubble piles we've seen, that's fast enough to shatter it into a low pile at minimum - that mountain doesn't look like a rubble pile, it looks structural. It's hard to judge the cliff angles with that pic, but they look much higher than a normal angle of repose.

I'd be interested in any papers that talk about a low speed impact, I thought it wasn't possible to impact at less than escape velocity on an airless world.

Emily's not-planets picture has all the observed objects near Pluto/Charon size

http://www.planetary.org/blogs/emily-lakda...ot-planets.html

Ceres is probably our best analog with close up data, Tethys and Dione are closer in size, but with Saturn's gravity accelerating any inbound objects they'll have pretty high impact speed. It is interesting that Ceres has that one high mountain, but that doesn't look like an impactor, slow or otherwise. Iapetus could also work, being further out from Saturn's gravity well.

While everyone are focusing on that nervous mountain that has taken defensive measures, let's not forget that there appears to be more mountains on Charon in that picture:

Click to view attachment

Something interesting is going on to the lower right there as well.