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Thread: Pluto!

  1. #1
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    Pluto!

    This just in:

    “There is no giant body that can be deforming Pluto on an ongoing regular basis to heat the interior,” he says, “so this is telling us you don’t need tidal heating to power” change on icy worlds –

    So how the hell is Pluto not pock marked with craters?!

    Mountains of water ice, eh?

    How is any of this possible??!?

    The New Horizons pics are insane.

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    Quote Originally Posted by ragasssd View Post
    ... So how ... is Pluto not pock marked with craters?! ...
    Just speculating because you asked, and nobody knows for sure, but it could be that Pluto has a Methane and Nitrogen ice surface covering a sea of Methane, Nitrogen, and maybe Hydrogen with harder ices forming mountain islands above the sea, and that any new large impacts melt the surface and erase the older smaller craters.
    Forming opinions as we speak

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    Phil speculates it could be radioactivity from subsurface rocks.

    Also, I think this would be a more suitable discussion for Astronomy rather than Q&A, since we don't really know of or have any straight answers to this issue yet.
    Last edited by Fiery Phoenix; 2015-Jul-15 at 09:10 PM.
    “Of all the sciences cultivated by mankind, Astronomy is acknowledged to be, and undoubtedly is, the most sublime, the most interesting, and the most useful. For, by knowledge derived from this science, not only the bulk of the Earth is discovered, but our very faculties are enlarged with the grandeur of the ideas it conveys, our minds exalted above their low contracted prejudices.” - James Ferguson

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    Could it be possible that the reason the surfaces of pluto and charon look young is because they have not experienced the late heavy bombardment? If the late heavy bombardment is caused by the interaction of the gas giants drawing icy bodies from the kuiper belt into the inner system this wouldn't affect remaining planetoids in the kuiper belt to the same extent as the moons of the gas giants and the inner rocky planets.

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    I've been looking at the images and thinking about the Pluto system. Would we really expect it to be as cratered as objects closer in? I know it is at closest approach but would we expect Kuiper belt objects to be as impacted as objects further in?

    The whole system seems very weird from what we would have expected even just a few years ago. I'm getting really interested on the explanations of how the system could have formed.

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    Quote Originally Posted by Fiery Phoenix View Post
    Also, I think this would be a more suitable discussion for Astronomy rather than Q&A, since we don't really know of or have any straight answers to this issue yet.
    As I've told many a technician, if I knew the answer now, I wouldn't need to do the research.

    And now with the Admin hat - thread moved from Q&A to Astronomy
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    I think it is likely the lack of craters denotes a young surface, and so some energy source like radioactive decay in the silicate core must still be at work. Also, with such a thin vernier, the nitrogen coating at the surface probably is due to either cryovolcanism or geysers, and this is outgassing now.

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    Quote Originally Posted by ragasssd View Post
    So how the hell is Pluto not pock marked with craters?!
    Here's another vote for interior radioactive heating:

    Radioactive heating from within Pluto may drive geological activity and resurface this region with fresh material, says team member Veronica Bray, a planetary scientist at the University of Arizona in Tucson.
    Everyone is entitled to his own opinion, but not his own facts.

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    Quote Originally Posted by Cougar View Post
    Here's another vote for interior radioactive heating:
    Radioactive heating from within Pluto may drive geological activity and resurface this region with fresh material, says team member Veronica Bray, a planetary scientist at the University of Arizona in Tucson.
    A very gratuitous supposition ,this scientific explanation ! Why the moon or Mars who are all silicate shows so little volcanic activity today if radioactive heating is the cause ?

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    In the Pluto image the sharp looking mountains are streaked with dark material that has eroded channels in the ice. The active process likely is the seasonal formation of a methane/nitrogen atmosphere which is then subject to UV dissociation to form tholins, that deposit as dark material. This is possibly a very gradual process if it has continued for billions of years could result in covering craters, submerging mountains, and peaks streaked with gullies.

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    Maybe answers will come from comparing to the surfaces of the smaller moons of Pluto-- they should have the same recent bombardment history but different resurfacing effects.

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    Also looks like the solar wind in blasting away at the thin nitrogen atmosphere.

    http://www.nasa.gov/nh/pluto-wags-its-tail

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    Quote Originally Posted by Ken G View Post
    Maybe answers will come from comparing to the surfaces of the smaller moons of Pluto-- they should have the same recent bombardment history but different resurfacing effects.
    Will we be seeing the smaller moons as anything but big pixels?

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    I'm expecting the better resolution images of the moons will be coming in September. I thought I heard Alan Stern say that
    Last edited by thoth II; 2015-Jul-17 at 11:33 PM.

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    Both Pluto and Charon appear to be only very lightly cratered. An explanation applicable to both seems to be called for. Is there any indication that Charon also has an atmosphere that could be involved in long-term obscuration of its surface?
    Then too, Charon would be an even unlikelier site of current radiogenic heat than Pluto.
    Perhaps the giant impact on Pluto, which is thought to have created its system of moons, was unexpectedly recent; recent enough that the reworked surfaces have not had time to be substantially cratered.

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    That seems like a possible explanation, but then we need to accept that such a very improbable event could have occurred recently. There doesn't seem to be a whole lot out there to collide with!

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    It's not clear that a relatively recent giant impact is less probable than a tidal or radiogenic heating scenario, in this setting. Pluto's eccentric orbit caries it through the most densely populated area of the Kuiper belt. An object of a mass sufficient to constitute a giant impact on Pluto could be much smaller, and so, much less improbable, than the giant impact thought to have affected Earth.

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    But the target is smaller too! I would expect the probability of a major collision is quite small, but of course I have no quantitative calculations to back that up. Since we expect Pluto to have been affected by a major collision, if that is our explanation of Charon for example, then the question moves to when did it happen. That's a probabilistic question, proportional to the timespan allowed, and the density of objects capable of making such a collision. Perhaps it is true that the late bombardment period is not relevant to the Kuiper belt, so we might not have such an early-weighted probability as we would for Mercury or Earth. But even so, if the solar system is 4.5 billion years old, one has at most a 1/5 chance a given collision would happen in the last billion years, and even less if you want to make it more recent than that. And then there's the problem of where are all the smaller objects that go along with a big one? In other words, anything one does to increase the probability of a recent major collision will also crank up the rate of recent minor collisions, such as would make craters. One has a problem with the ratio of big hits to small hits, unless one can fill in the small hits somehow.
    Last edited by Ken G; 2015-Jul-19 at 03:31 AM.

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    Given the discussed time frame of the last 100 million years, a simple probabilistic approach would suggest odds of a giant impact at Pluto of about 2 percent. It doesn't appear that we know enough about the long term dynamics of the Kuiper belt to rule out the possibility of something that could perturb those odds.
    If a giant impact rendered Pluto molten, many smaller impacts at that time could conceivably have been absorbed without leaving a trace on the surface.
    If it is finally conceded that radiogenic and tidal-frictional heating are inadequate explanations for Pluto's, and Charon's, relatively young surfaces, a relatively recent giant impact may turn out to be the most reasonable scenario.

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    Quote Originally Posted by galacsi View Post
    A very gratuitous supposition ,this scientific explanation ! Why the moon or Mars who are all silicate shows so little volcanic activity today if radioactive heating is the cause ?
    Because silicates have a much higher melting temperature?
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    The point was, I believe, that the radiogenic heating in a planet comes from the decay of radioactive elements in its crust and mantle. Both Mars and our Moon have much larger volumes of silicate crusts and mantles than does Pluto, yet they have shown no real evidence of current heat-driven geology. Expecting Pluto to have such activity seems unwarranted.

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    Quote Originally Posted by Ross 54 View Post
    ... Expecting Pluto to have such activity seems unwarranted.
    A couple of thoughts on this:
    1. It would take much less radiogenic heating on Pluto to have a noticeable effect than it would on Mars or the Moon. The average vibrational energy of atoms on its surface is much less than 1% of that on the Moon, and the materials on the surface are much closer to the solid-liquid transition temperature.
    2. I think the decay of radioisotopes anywhere crust, mantle, or core will all contribute equally to the heat flowing out of the celestial body.
    Forming opinions as we speak

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    I think your point 1 might be the crux of the issue here. Ross 54 is saying that the heat flux at the surface depends on the total volume of radioactives that have not yet decayed away, so relevant is the ratio of volume to surface area, and that shows up poorly on Pluto. But your point is that it's not just the heat flux that matters, but also what the heat flux does.
    Last edited by Ken G; 2015-Jul-19 at 08:21 PM.

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    It appears that Charon and Pluto have oddly young surfaces in common. Their close association suggests that this is not a coincidence. While Pluto appears to have some readily volatile substances on its surface, Charon's surface seems to be dominated by water ice. This is apparently expected to be rock stable at the available temperatures. It seem unlikely that a 750 mile (1200 km) -wide moon would have radiogenic heat sufficient to alter this situation significantly.

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    Is it possible that tidal heating has been dismissed too quickly? After all Pluto has the largest satellite relative to its size in the solar system.

    Is it also conceivable that the Pluto system has been perturbed by close encounters with Neptune in the past? Although the Pluto system has come back to equilibrium since, that would've lead to heat production.

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    Since Pluto and Charon are mutually tidally locked, there seems to be little flexing of the materials of either body, so very little heat evolved in this way. The tidal deformations on both Pluto and Charon appear to remain in a single shape in the same areas of each body. There are seemingly no significant changing or moving tides.
    With Pluto's orbit significantly inclined with respect to that of Neptune, a close encounter between the two in the past appears very unlikely.

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    Quote Originally Posted by kzb View Post
    Is it possible that tidal heating has been dismissed too quickly? After all Pluto has the largest satellite relative to its size in the solar system.
    They're tidally locked, so that eliminates nearly all the tidal heating.
    Conserve energy. Commute with the Hamiltonian.

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    Quote Originally Posted by Ross 54 View Post
    Since Pluto and Charon are mutually tidally locked, there seems to be little flexing of the materials of either body, so very little heat evolved in this way. The tidal deformations on both Pluto and Charon appear to remain in a single shape in the same areas of each body. There are seemingly no significant changing or moving tides.
    With Pluto's orbit significantly inclined with respect to that of Neptune, a close encounter between the two in the past appears very unlikely.
    I'm wondering about the past though. The fact that Pluto and Neptune are in resonant orbits surely means there has been a lot of interaction in the past in order to get them into this state. The Pluto satellite system would then have to relax into its current condition. Admittedly a bit of a stretch to think this only completed 100 million years ago, but I thought it was worth raising.

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    I would expect a modest amount of heat from radioactive heating could produce the resurfacing effects we see on Pluto and Charon because they have icy mantles and crusts. This heat on Mars and moon wouldn't be sufficient to melt and resurface their rocky crusts.

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    As far as I'm aware, no dynamical solutions were found that would allow past encounters between Neptune and Pluto, close enough to have a significant bearing on tidal friction. Apparently, eons ago, Neptune moved gradually outward toward the Kuiper belt and caused the stabilizing orbital resonances, and super-resonances with Pluto we still see today.
    The Pluto system has a maximum temperature of ~ 55 K. The surface temperature of Charon would have to be raised by over 200 Kelvin to allow the water ice that is thought to dominate there to melt, and resurface an otherwise cratered crust. I am having trouble seeing how a moon 750 miles in diameter could muster enough radiogenic heat to accomplish this.
    Last edited by Ross 54; 2015-Jul-20 at 11:05 PM.

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