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Originally Posted by djellison
Why would I make that assumption? To fit your model? Are you now stating our knowledge of the mass of the Earth and Moon could both wrong by 25% , but in opposite directions?
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That was supposed to be a thought experiment: Would you still stick with Newtonian dynamics if the density of the Earth were proven by other means to be less than the Newtonian density, (which is based upon both surface gravity and the Newtonian equivalence principle.
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The bulk density of Titan has been calculated via radio science of flybys. We now have a LOT of flybys, which have been used to shape the orbit of Cassini over nearly 4 years. If the bulk density of Titan as we understand is significantly wrong ( as you are now suggesting ) Cassini's mission wouldn't have worked.
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Once again, you are assuming that the equvalence principle is true; you are not allowing for any variability in the mass/inertia relationship. It is a fact that the apparent density of the Titan atmosphere did not thin near the poles (where there was expected to be a gradiant due to thermal condensation.) The atmospheric model did not work! The 'atmospheric drag' model had to be determined by trial-and-error, not using the expected thermodynamics of the Titan atmosphere; including an appropriate gravitational gradient. Remember the disagreement between the density of the upper atmosphere as measured by the INMS; and as experienced by Cassini? More apparent drag means either both the calibration of the INMS is off AND the atmosphere is thicker at altitude than Cassini mission planners had modeled, or the differiential in the gravitational field with respect to altitude is greater-than-expected.
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No debate. Accurate repeated flybys have changed the inclination of the orbit. Now - if you're going to argue that the flawed science of measuring the mass of Titan is the same flawed science used to then use that figure - feel free.
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You were not following the threads on the BA board when I was predicting that this would happen - the atmosphere would not appear to thin near the poles as modeled prior to the flybys.
Titan has proven not to be a good case for testing gravity; because if the calibration of the INMS is written off, whatever gradiant is necessary can be penciled in. I will be surprised if in the future, we do not learn than during the close pass of Enceladus, Cassini's momentum towards the moon increased more-than-expected at the moment of closest approach.
But what of the composition of the surface known to be Icy via observations from Cassini. Guess what - we get a density for Titan, and low and behind it appears to be made of the right sort of stuff for that density from observations. Quelle Suprise.
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How about an overview, from you, of all the major bodies in the Solar System ( Mercury, Venus, Earth, Moon, Mars, Phobos, Deimos, Ceres, Vesta, Jupiter, The Galileans, Saturn, Titan, Iap, Dione, Enceladus, Uranus, Neptune, Pluto ). How and why do these values : http://en.wikipedia.org/wiki/List_of...bjects_by_mass or other sites citing the known masses of the bodies in the solar system - vary from what YOU think they are. Give us your estimates for values on all those major bodies, citing why you believe their bulk composition to be different to that understood given the variations of density your values will incur.
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You will find my predictions in the same thread I referenced above:
Potential Threat to the Huygen Mission
The reason for these predictions is simple: I don't think that the Newtonian Equivalence principle is valid; very specifically I think there is a gradient in the path through space that is a function of the local mass; so the path of an orbiting body near the sun is longer (relative to the orbital distance) than the path of an orbiting body at a greater distance from the sun.
Further, I think that since it takes more momentum to complete an orbit nearer to the sun than one further from the sun; A probe such as Messenger to the inner solar system has to lose less energy than expected to park near the orbit of Mercury. I probe lifted to the outer solar system, such as Cassini requires slightly less energy. (In both cases the change in the inertial potential is obviously very small; and in the same direction as the correction for the solar wind.)
Finally, whenever a probe passes near a moon or planet, there is also an inertial gradient that is a function the mass moon or planet; and this very small, but very real gradient must effect the energy budget during a gravitational assist: Generally providing more energy than expected during gravitational boosts, and less gravitational braking than expected when trying to slow the probe down.
If Titan is much more dense than Newtonian physics predicts, the the density gradiant of atmospheric should be tighter: A thicker atmosphere near the surface; and less dispersion of light through the atmosphere than epected: Huygens proved this to be true.
Can you, or anyone else explain why the optical density of the atmosphere on the surface of Titan is only 1.5?