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Thread: Pluto!

  1. #31
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    Mike Brown, self-described @plutokiller, implies it might just be redistibuted frost that's hiding a more battered surface.

    https://mobile.twitter.com/plutokiller

    @cosmos4u @StarzanPlanets covered in frost. frost redistribution is not the same as internal geological activity.
    But, wisely, he's mostly awaiting further data.
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    Skepticism enables us to distinguish fancy from fact, to test our speculations. --Carl Sagan

  2. #32
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    Volatile nitrogen and carbon monoxide frosts don't seem to account for kilometers-high mountains of rock-stable water ice. These mountains are apparently judged to be quite young, so internal geological activity, and the difficulties this suggests still seem to be in play.

  3. #33
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    Brian May posted a nice stereo pair of a look back at Pluto. The left image has enough resolution to show some of the probably more expected cratering on the left limb:

    https://twitter.com/DrBrianMay/statu...97960558735360
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    Skepticism enables us to distinguish fancy from fact, to test our speculations. --Carl Sagan

  4. #34
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    Quote Originally Posted by 01101001 View Post
    Brian May posted a nice stereo pair of a look back at Pluto.
    Odd, when I look at it the 3D sense is exaggerated in my direction so it makes Pluto seem very long and I'm looking the short way. It makes the white spray going under it look very long.
    Forming opinions as we speak

  5. #35
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    Excellent! Wide-eyed stereo, not cross-eyed!

    -- Jeff, in Minneapolis

  6. #36
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    Quote Originally Posted by Ross 54 View Post
    Apparently, eons ago, Neptune moved gradually outward
    toward the Kuiper belt
    I'm pretty sure I asked this before, and got an answer,
    but I have no memory of what the answer was.

    How could Neptune -- or any planet -- move outward?
    I can see how a planet could move inward if it ejects huge
    masses of dust and gas or asteroids that do not fall back
    to the planet's orbit. (Either by escaping the Solar System
    or by their orbits getting circularized in the Oort Cloud.)

    -- Jeff, in Minneapolis

  7. #37
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    A new image of 2 of pluto's moons:

    https://www.nasa.gov/image-feature/n...-smaller-moons

  8. #38
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    Quote Originally Posted by Jeff Root View Post
    I'm pretty sure I asked this before, and got an answer,
    but I have no memory of what the answer was.

    How could Neptune -- or any planet -- move outward?
    I can see how a planet could move inward if it ejects huge
    masses of dust and gas or asteroids that do not fall back
    to the planet's orbit. (Either by escaping the Solar System
    or by their orbits getting circularized in the Oort Cloud.)

    -- Jeff, in Minneapolis
    In the very early solar system, the planets tended to jostle one another with their gravity fields. The current thinking seems to be that Jupiter moved inward, by interacting with interplanetary debris. It swept up some of these, the Sun blasted others away. It then became possible for Saturn to stop Jupiter's inward migration, and eventually pull it outward again. Jupiter and Saturn established a 1:2 orbital period resonance. This apparently caused Uranus and Neptune to be pushed outward. The latter planet eventually established the stable resonances with Pluto, referred to in a previous post. It is also though to have captured its largest moon Triton, formerly a Kuiper belt object.
    Last edited by Ross 54; 2015-Jul-22 at 01:03 AM.

  9. #39
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    Quote Originally Posted by Ross 54 View Post
    It then became possible for Saturn to stop Jupiter's
    inward migration, and eventually pull it outward again.
    How? If Saturn was outside Jupiter's orbit, and Jupiter
    moved inward due to flinging out a huge amount of
    small stuff, then Jupiter and Saturn ended up farther
    apart than they started out, where they would have
    even less influence on each other.

    Quote Originally Posted by Ross 54 View Post
    Jupiter and Saturn established a 1:2 orbital period
    resonance. This apparently caused Uranus and Neptune
    to be pushed outward.
    How? What is the mechanism?

    -- Jeff, in Minneapolis

  10. #40
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    New pic from Pluto's Pluto region...err I mean, Tombaugh region. This time showing border of between two regions. And this is very interesting: dark region is heavily cratered, very old, whereas light area again does not display a single impact crater. Some craters have been partially filled with light stuff. It looks like someone poured milk on the poor planet which then froze. Again there are mountains. It'll be interesting to see whether the dark areas also have mountains.

    In last week's presser, there was some gentleman who remembered initial Mariner 4 results and described how disappointed people where that Mars turned out to be quite dead, cratered world like Moon (though in retrospect we were bit unlucky as Mariner 4 happened to see oldest regions of Mars). It seems after that, the expectation has always been that the worlds are dead & inactive and we're surprised when they're not (Io, Triton etc). However, now Pluto demonstrates much younger surface than expected, Saturnian moons have so much stuff going on we've managed to grasp only tiny portion of it, even Ceres shows hints of some kind of activity...the new default actually is that these worlds are "cryotectonically" (is that a real word?) active, and exception are those bodies which are not. So maybe we should rephrase the question "why are these worlds active?" to "why are those worlds not active?". Why are Callisto and Ganymede so inactive? Why the Uranian system appears so dead?

    Tidal energy has been dismissed as source of energy for Pluto's activity, however is it actually possible that librations could nevertheless transfer some energy between the bodies? Do we know what kind of librations Pluto & Charon have and is it theoretically possible it might have some effect...but now when I check, apparently Charon's orbit is almost completely circular so I guess even that is out.
    One last straw: Pluto and Charon are tidally locked to each other, so Charon always hangs over exact same spot of Pluto. Where precisely is that?

  11. #41
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    Wouldn't the sub-Charon point be logically chosen for Pluto's "Prime Meridian" when they draw up the maps?

  12. #42
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    Quote Originally Posted by Jeff Root View Post
    How? If Saturn was outside Jupiter's orbit, and Jupiter
    moved inward due to flinging out a huge amount of
    small stuff, then Jupiter and Saturn ended up farther
    apart than they started out, where they would have
    even less influence on each other.


    How? What is the mechanism?

    -- Jeff, in Minneapolis
    The latest theory is that there must have been at least one large planet ejected from the early solar system to explain the current configuration. Don't ask me about the details though.

    Pluto has a low average density (about 2g/cu cm) and has a lower proportion of heavy elements than the terrestrial planets. The radiogenic heating per unit volume of planet (if I can call it that) must be much lower because of this.

  13. #43
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    Quote Originally Posted by Jeff Root View Post
    How? If Saturn was outside Jupiter's orbit, and Jupiter
    moved inward due to flinging out a huge amount of
    small stuff, then Jupiter and Saturn ended up farther
    apart than they started out, where they would have
    even less influence on each other.


    How? What is the mechanism?

    -- Jeff, in Minneapolis
    I'm no expert in orbital mechanics, but I interpret what i read, as follows: Close gravitational interactions with planetesimals caused Jupiter to gain momentum from them. Jupiter's increased velocity made it assume an orbit nearer the Sun. Once such interactions decreased in frequency, Saturn's gravity was now sufficient pull Jupiter back outward. It no longer had to compete with the effect of near encounters of Jupiter with planetesimals.

    The 1:2 orbital resonance of Jupiter and Saturn presumably slowed Uranus, Neptune, and the Kuiper belt objects, whenever they were in conjunction from the point of view of the affected object, via their gravitational pull. This slowing would, it appears, force them into orbits further from the Sun.

  14. #44
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    This sounds all wrong. There might be nuggets of truth
    in it, but overall it makes no sense to me.

    Quote Originally Posted by Ross 54 View Post
    Close gravitational interactions with planetesimals caused
    Jupiter to gain momentum from them. Jupiter's increased
    velocity made it assume an orbit nearer the Sun.
    Jupiter should lose momentum (relative to the Sun) from
    such interactions, causing it to fall closer to the Sun and
    gain speed. This depends on the planetesimals or other
    stuff being thrown permanently out of Jupiter's orbit, so
    that it does not interact with Jupiter again. Jupiter can do
    that because it is the only planet massive enough to give
    stuff escape speed, and also because stuff it throws out to
    the Oort Cloud can have its perihelion raised by tidal force
    from the galaxy as a whole. That provides a mechanism
    for Jupiter to move closer to the Sun.

    Quote Originally Posted by Ross 54 View Post
    Once such interactions decreased in frequency, Saturn's
    gravity was now sufficient pull Jupiter back outward.
    I don't believe it. It sounds totally loopy.

    Quote Originally Posted by Ross 54 View Post
    It no longer had to compete with the effect of near
    encounters of Jupiter with planetesimals.
    Sounds fishy to me.

    Quote Originally Posted by Ross 54 View Post
    The 1:2 orbital resonance of Jupiter and Saturn
    presumably slowed Uranus, Neptune, and the Kuiper
    belt objects, whenever they were in conjunction from
    the point of view of the affected object, via their
    gravitational pull. This slowing would, it appears,
    force them into orbits further from the Sun.
    That sounds like you've mixed up cause and effect.

    If the immediate effect was to slow them, then they
    would fall closer to the Sun where they would move
    faster. If the immediate effect was instead to raise
    their orbits away from the Sun, then they would be
    moving more slowly in those new orbits. But maybe
    you meant that the immediate effect was to speed
    them up at each conjunction, which would raise their
    orbits, so their overall speeds would then be slower.

    I guess that sounds plausible. But if Jupiter pushed
    Uranus, Neptune, and the Kuiper belt objects farther
    from the Sun, then Jupiter had to fall closer to the
    Sun at the same time.

    -- Jeff, in Minneapolis
    .
    Last edited by Jeff Root; 2015-Jul-25 at 07:27 PM. Reason: tiny typo

  15. #45
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    What is needed here is some valid citations to solve the issue. It sounds strange to me also, but if there is good scientific backing I'll accept it.

    Eta: one huge question I have is this, I accept that an object under gravity would speed up, this also will tend to increase its orbit not decrease it surely?? The momentum of the object should tend to counteract the gravitational pull upon it's course, finding an equilibrium for its mass at a greater distance from the gravitational center of force.
    Last edited by malaidas; 2015-Jul-22 at 11:17 PM.
    You're really not going to like it, the meaning of life the universe and everything is.... is.... 42!
    What??????
    is that all you have to show for 7.5 million years of work?????
    it was a tricky assignment.

    "Live Long and Prosper" in memory of Leonard Nimoy
    "I think I'll change my name to Cliff. "Cliff, I can't see anyone lasting in this industry with a name like Cliff" in memory of Terry Pratchett

  16. #46
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    Well yes, as it turns out, my interpretation of what I read about solar system evolution went badly wrong. I respectfully suggest that no one try to make any sense out of what I wrote, and consult more reliable sources of information, instead. I'm sorry for any confusion I caused.

  17. #47
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    That's okay. I've been wanting to complain about that idea
    for quite a while.

    -- Jeff, in Minneapolis

  18. #48
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    malaidas,

    When a small body is in a circular orbit around a larger one,
    and you give the small body a shove so that it is momentarily
    moving faster in the direction of its orbit, then it will rise away
    from the larger body, slowing as it rises. Just like an object
    you throw up in the air slows as it rises. When it reaches
    apoapsis, it will be moving more slowly than it was originally.
    It will be moving too slowly to remain at that altitude, and
    begins falling back down, gaining speed again as it falls.
    It falls and gains speed until it reaches periapsis, when it is
    at the same altitude and moving at the same speed it had
    just after it was given the shove.

    The small body has been put into an elliptical orbit.

    If instead of giving the small body a single big shove at one
    point in its initial circular orbit, you shove on it very gently,
    all along the orbit for many orbits, the body will gradually
    spiral out to a higher circular orbit, moving more and more
    slowly all the time.

    While you are actually shoving it, the body will be moving
    faster than the speed for a circular orbit at that altitude,
    even though it keeps moving more and more slowly.

    So going faster makes you go slower, and vice-versa.

    -- Jeff, in Minneapolis

  19. #49
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    Cheers Jeff.

    I can understand the elliptical explanation, there's a minor question I have about the circular one. When we say slower is it actually slower locally, or are we simply talking the time taken for an orbit? If the former I need to go back and study angular momentum more closely.
    You're really not going to like it, the meaning of life the universe and everything is.... is.... 42!
    What??????
    is that all you have to show for 7.5 million years of work?????
    it was a tricky assignment.

    "Live Long and Prosper" in memory of Leonard Nimoy
    "I think I'll change my name to Cliff. "Cliff, I can't see anyone lasting in this industry with a name like Cliff" in memory of Terry Pratchett

  20. #50
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    It's faster locally, like Jeff said its speed would always be very slightly above the circular orbit speed. But the speed would be dropping with time because it is fighting gravity more than it is getting helped by your gradual push. Since it is spiraling gradually outward, the circular orbit speed is also dropping with time, so that's how the actual speed can be dropping yet still stay above the circular speed (by a very small margin).

  21. #51
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    Cheers Ken.
    You're really not going to like it, the meaning of life the universe and everything is.... is.... 42!
    What??????
    is that all you have to show for 7.5 million years of work?????
    it was a tricky assignment.

    "Live Long and Prosper" in memory of Leonard Nimoy
    "I think I'll change my name to Cliff. "Cliff, I can't see anyone lasting in this industry with a name like Cliff" in memory of Terry Pratchett

  22. #52
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    A graph of how orbital speed varies with distance from Earth
    is at http://www.freemars.org/jeff/speed/index.htm .

    Orbital period isn't shown on the graph but is in the table.

    The shape of the curve is odd because I wanted to show detail
    in low Earth orbit but also include the relatively distant Moon,
    so I put the origin of the logarithmic scale in a funny place,
    15 km below Earth's surface. There may be a better way to
    do it which doesn't result in the odd curve.

    -- Jeff, in Minneapolis

  23. #53
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    Cheers Jeff, had a brief look, but will view properly tomorrow, when I am fresher.
    You're really not going to like it, the meaning of life the universe and everything is.... is.... 42!
    What??????
    is that all you have to show for 7.5 million years of work?????
    it was a tricky assignment.

    "Live Long and Prosper" in memory of Leonard Nimoy
    "I think I'll change my name to Cliff. "Cliff, I can't see anyone lasting in this industry with a name like Cliff" in memory of Terry Pratchett

  24. #54
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    https://www.nasa.gov/feature/new-hor...-ices-on-pluto

    I would expect the flowing glaciers and polygon cells indicate some degree of heating is coming up from the interior. It will take them some time to find the origin of this heat.

  25. #55
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    Some radial lines extending across the left side of the 'heart' feature on Pluto suggest the possibility of a large impact; they look rather like lightly coated crater rays. Such an impact could have been a considerable source of heat. It still seems difficult to connect this with the raising of kilometers-high mountains of ice, though.

  26. #56
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    Quote Originally Posted by thoth II View Post
    I would expect the flowing glaciers and polygon cells indicate some degree of heating is coming up from the interior. It will take them some time to find the origin of this heat.
    It's certainly interesting. I've read that since there's no tidal heating, internal natural radioactivity was promptly mentioned. (It seems related that one receives measurably more millirems of radioactivity if you live in a house on a cement foundation. This is pretty negligible, but seeping radon gas is not!)

    But then there's this: "Pluto's atmosphere is replenished by ices that sublimate off its surface." And its atmosphere is detected out to 80 miles?! I guess if you never knew all that much about an object, you'd get surprise after surprise with a flyby. Major congratulations to all the team members that helped make happen and continue to make happen such an incredible achievement!
    Everyone is entitled to his own opinion, but not his own facts.

  27. #57
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    Some of that atmosphere might then escape from Pluto, and end up accreting onto other moons of the system. Charons red spot?

  28. #58
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    Quote Originally Posted by transreality View Post
    Some of that atmosphere might then escape from Pluto, and end up accreting onto other moons of the system. Charons red spot?
    And the contrary is also possible ,some volatiles escape from Charon , end on Pluto and resurface the (dwarf) planet.

  29. #59
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    Quote Originally Posted by malaidas View Post
    Cheers Jeff.

    I can understand the elliptical explanation, there's a minor question I have about the circular one. When we say slower is it actually slower locally, or are we simply talking the time taken for an orbit? If the former I need to go back and study angular momentum more closely.
    I think they mean a slower orbit; but at greater radial distance, so the angular momentum is greater. It is a 2pi verses r thing - so each increase of one in radius increases the angular velocity by 2pi; and the momentum has that ^2 multiplier as well. Jupiter could eject the Earth from the solar system with a loss of less than 4% of her momentum.

    A body nearing another body can provide either gravitational acceleration or braking, relative to a third body; and since all planetary bodies are in elliptical orbits the net effects can move another planet nearer to, or further away from the sun; and as always, the 'third body' will accelerate opposite the second body.
    Last edited by Jerry; 2015-Jul-26 at 11:22 PM.
    “It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts.” ― Arthur Conan Doyle, Sherlock Holmes

  30. #60
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    Quote Originally Posted by Jerry View Post
    A body nearing another body can provide either
    gravitational acceleration or braking, relative to a
    third body; and since all planetary bodies are in
    elliptical orbits the net effects can move another
    planet nearer to, or further away from the sun;
    If Jupiter reduces the perihelion of a smaller body,
    that smaller body will still have an aphelion at or
    beyond Jupiter's orbit. So unless the smaller body
    has its orbit changed by hitting some other planet
    or the Sun or by the galaxy's gravity gradient, it
    will continue to interact with Jupiter and will either
    hit Jupiter or be kicked out of the Solar system.

    I interpret that to imply that Jupiter gets a net
    push inward, with a larger mass of small bodies
    being thrown out and never returning than being
    thrown in and never returning.

    -- Jeff, in Minneapolis

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