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New Horizons: Near Encounter Phase
siravan
post Jul 16 2015, 02:52 PM
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Interesting possibility. I wonder whether it is also possible that relatively moderate size impacts may deliver enough torque to Charon to disrupt the tidal locking (which is probably tenuous anyway) for a while. The process of reestablishing the lock can be a source of heating.
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silylene
post Jul 16 2015, 02:52 PM
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QUOTE (Y Bar Ranch @ Jul 16 2015, 02:40 PM) *
That source of energy would be traced back to energy introduced by solar insolation, but rather than directly heating the surface it would be a kind of second order effect to the system. Still, any heat generated through that effect would have to be equal or less than just pure insolation?


Yes, exactly. But that is a lot of energy even at Pluto's distance.
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MarkG
post Jul 16 2015, 02:53 PM
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QUOTE (Y Bar Ranch @ Jul 16 2015, 06:40 AM) *
That source of energy would be traced back to energy introduced by solar insolation, but rather than directly heating the surface it would be a kind of second order effect to the system. Still, any heat generated through that effect would have to be equal or less than just pure insolation?

Internal mass re-distributions, like a mantle convection, would also lead to mutual tidal force transfer. One can speculate that if there was a large phase-change region internally, some sort of positive-feedback resonance could occur. and amplify the "churn". The point is, the mutual tidal lock generates interesting reactions to perturbations.

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alk3997
post Jul 16 2015, 02:59 PM
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QUOTE (silylene @ Jul 16 2015, 08:30 AM) *
Agreed too. I have been considering something very similar.

If large amounts of gases are subliming from one location on the planetary surface during the summer (for example, the equator), and re-freezing into cooler locations (for example the poles), then the mass distribution of the body will change significantly. If the gases re-freeze, especially in a non-spherically symmetric manner, then the planetary mass distribution will be non-symmetrical, and more importantly, lead to a unbalance in the idealized orientation of this tidally locked binary planet system. This will create torque and cause a shift of the planetary axis as Pluto re-orients is mass distribution to the gravitationally lowest energy mode, and a subtle rebalance of the dynamics of the binary planetary system. This re-orientation of the axis should cause flexation of the crust, generating heat, which could be the internal heat engine.

Same goes for Charon.


247 year cycles, or longer phase cycles?


Needs modeling.


That's what I was trying to say a few pages back by saying we are incorrectly treating the Pluto and Charon bodies as gravitational point sources rather than as wider bodies. You said it much better than I did. Thank you!

The effects are subtle but add time (lots of time), an occasional good ringing and material transport will result in the gravitational energy providing some heating. It can't take too much heating at these temperatures to change these icy materials into slush.

One other quick note: I know this is obvious to all of us but this is the only mutual-tidal locked system any of us have seen (assuming we haven't been out of our solar system). Some reworking of the models would not be surprising.

Andy
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EDG
post Jul 16 2015, 03:04 PM
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QUOTE (JRehling @ Jul 15 2015, 08:40 PM) *
A collision between an impactor and Pluto requires that two things be in the same place at the same time. A capture scenario would require that three things be in the same place at the same time. To a decent approximation, the probability of the latter would be the square of the probability of the former. Not very likely.



The third "thing" just has to be a moon of one of the other two things already in a capture scenario, doesn't it? Since it seems that a lot of small objects can have moons in the asteroid and kuiper belts, I don't think it's that much less likely that Pluto could pass close to a pair of small objects rather than just a single one.

You say it's not very likely, but don't we think it already happened with Neptune capturing Triton?


It seems to me that the team have already decided beforehand that Charon must have formed in a giant impact, and I'm not terribly comfortable with that since I think that kind of conclusion can only be reached after looking at all the data - I don't see how they can be so sure of that from distant observations alone. I think we're really looking at two hypotheses here:

1) Pluto was hit by another object and Charon (and the other small moons?) formed from the debris. This happened long enough ago that there is no evidence for the impact on the surfaces of Pluto or Charon. Tidal despinning circularised the orbit and altered the surfaces of the two worlds before they locked with eachother.

2) Pluto captured Charon from another body that it passed close to. This happened long enough ago that the orbit circularised and Charon locked to Pluto. Tidal despinning altered the surfaces of the two worlds before they locked with eachother.

I think the only major issue with the second hypothesis is how the other moons fit in. Are they leftovers from smaller impacts on Pluto that happened afterwards? Are they also captured bodies (Kerberos seems different from the other small moons at least). But either way, the trick now is to look at all the data and figure out which one is the more valid hypothesis.

Have they pinned down the exact orbital eccentricities and inclinations of all the moons? If not, they should be able to from the data they've got from the approach and flyby.
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Nafnlaus
post Jul 16 2015, 03:14 PM
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QUOTE (rasun @ Jul 16 2015, 01:34 PM) *
Water's peculiar property is that it expands when freezing. Isn't that necessary for pingo formation?


I don't know about neon, but freezing liquid nitrogen (due to pressure drop) likes to form a foam of far greater volume than the liquid, at least when not under pressure. It also undergoes a glassy ->crystalline phase change with a rapid change in volume.

The basic point, though, is that there could be some very dramatic frost heaving effects caused purely by orbital temperature/pressure changes. These mountains may be the height of the rockies, but they're only the weight of a <100-meter hill (per unit area)
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TheAnt
post Jul 16 2015, 03:15 PM
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QUOTE (MarkG @ Jul 16 2015, 04:10 PM) *
It is worth pointing out that with Pluto and Charon strongly tidally locked, any perturbation to one of them will quickly transfer some forces to the other. in a somewhat non-intuitive fashion. Even a seasonal sublimation/deposition mass transfer on Pluto would create a mass shift that would generate forces on Charon, which would cause different forces back on Pluto.
This could be modeled and tested....


Wonderful hypothesis, I have been wondering how Pluto could have this kind of cryogenic "geology" we're gotten hints of in the high resolution frames. And a thank you to JohnVV for the processing which give an idea of relative hights also. If your line of thinking is correct many phenomena might be possible, even Pluto quakes.
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silylene
post Jul 16 2015, 03:32 PM
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QUOTE (Nafnlaus @ Jul 16 2015, 02:26 PM) *
(nitrogen could do similar closer to the surface... though its freeze-thaw is rather energetic!)


I saw the Youtube video, and I do not think that it applies at all to Pluto.

In the Youtube experiment, the phase transitions being displayed was liquid N2 was being supercooled and flash frozen into a glass. The subsequent transition from glassy N2 to cystalline N2 was energetic, and caused disruption of the glass as crystals formed, and was fairly energetic.

However, in the case of Pluto on the surface, the phase transition would be gas to solid N2(g) -> N2(s), and this process would be layer-by-layer deposition. I would not expect this to deposit from gas to solid as a glass unless the deposition rate was extremely fast. Even then, if there were any crystalline N2 on the surface prior, then ongoing subsequent deposition onto an existing crystalline N2 would maintain crystallinity, and not form a glassy solid N2. Thus no opportunity for the energetic glassy - > crystalline N2 transition.

In the putative case of an underlying sea of N2(l) which putatively freezes, I also would not expect it to flash freeze as a lake of glassy N2. All it would take is one seed crystal of cystalline N2 somewhere to seed the freezing to go directly to crystalline N2. Presumably, the layer of frozen N2 over the putative lake would be in the crystalline form already, so any additional N2 freezing would continue to form additional crystalline N2, not glassy N2. Thus no opportunity for the later energetic glassy - > crystalline N2 transition.



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hendric
post Jul 16 2015, 03:38 PM
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From the Heart photo & fredk's placement of the frame on it, it looks like the hummocks are caused by an impact crater just off-screen in the frame, visible at the bottom of the full disk image. I don't think we've seen wavey ejecta like that before though, so it could the crater is just lying atop previously hummocky terrain...

http://www.nasa.gov/sites/default/files/th...frame_color.jpg

We should know more about crater morphology once we get the frames to the left of Tombaugh Regio, there's a few decent sized craters there.


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Blue Sky
post Jul 16 2015, 03:45 PM
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I am wondering if the crater-counting method of judging the age of a surface needs to be 'calibrated' for the far outer planets differently than it is for the inner ones.

The KBOs probably outnumber the Asteroid Belt objects, but they are so spread out, and without Jupiter stirring the pot so much during the Heavy Bombardment, maybe the density of collisions was less.

Hm, but on the other hand if Pluto/Charon had a past close encounter (and maybe even Pluto/Neptune) perhaps my hunch is wrong.
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mcaplinger
post Jul 16 2015, 04:04 PM
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QUOTE (Blue Sky @ Jul 16 2015, 08:45 AM) *
I am wondering if the crater-counting method of judging the age of a surface needs to be 'calibrated' for the far outer planets differently than it is for the inner ones.

See "Cratering rates in the outer Solar System", Zahnle et al.
http://adsabs.harvard.edu/abs/2003Icar..163..263Z


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Mr Valiant
post Jul 16 2015, 04:16 PM
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I feel that a Probe that visited Pluto during perihelion would have seen a very different Pluto.
Imagine, Summertime on Pluto? Again, imagine aphelion ???
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JRehling
post Jul 16 2015, 04:49 PM
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QUOTE (EDG @ Jul 16 2015, 08:04 AM) *
You say it's not very likely, but don't we think it already happened with Neptune capturing Triton?


Neptune has the largest Hill Sphere in the solar system, with a radius of 116 million km. It could potentially capture something due to an impact taking place inside that sphere.

Pluto's Hill Sphere is 1/3000th the volume of Neptune's.

It's not impossible, but it's a lot more likely for one thing to hit Pluto than it is for two things to hit, in just the right way, while near Pluto.
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lars_J
post Jul 16 2015, 04:50 PM
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QUOTE (EDG @ Jul 16 2015, 11:04 AM) *
It seems to me that the team have already decided beforehand that Charon must have formed in a giant impact, and I'm not terribly comfortable with that since I think that kind of conclusion can only be reached after looking at all the data - I don't see how they can be so sure of that from distant observations alone. I think we're really looking at two hypotheses here:

1) Pluto was hit by another object and Charon (and the other small moons?) formed from the debris. This happened long enough ago that there is no evidence for the impact on the surfaces of Pluto or Charon. Tidal despinning circularised the orbit and altered the surfaces of the two worlds before they locked with eachother.

2) Pluto captured Charon from another body that it passed close to. This happened long enough ago that the orbit circularised and Charon locked to Pluto. Tidal despinning altered the surfaces of the two worlds before they locked with eachother.

I think the only major issue with the second hypothesis is how the other moons fit in. Are they leftovers from smaller impacts on Pluto that happened afterwards? Are they also captured bodies (Kerberos seems different from the other small moons at least). But either way, the trick now is to look at all the data and figure out which one is the more valid hypothesis.

Have they pinned down the exact orbital eccentricities and inclinations of all the moons? If not, they should be able to from the data they've got from the approach and flyby.


Since the entire system with Charon and the other moons is in the same plane, it seems exceedingly unlikely (or impossible?) that Charon was captured as it is now. The entire system seems to be the result of one impact event. Any moons that existed before the impact would likely have been ejected from the system.

But I'm just an armchair amateur, so I could be very wrong.


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pioneer
post Jul 16 2015, 04:57 PM
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I just discovered Pluto ski T-shirts are available online. Do you all think those mountains we saw yesterday would be good for skiing? unsure.gif I'm sure there would be some black diamonds.
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