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I realise that the planets are more or less part of the same orbital plane. But why is the orbit of Eris, or even Pluto, at such significant tilts of orbit (44 degrees and 17 degrees respectively)? I tried to find an answer but couldn't. What is the reason for this?

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    $\begingroup$ This was mostly addressed on this very website recently in astronomy.stackexchange.com/questions/57070/…. In short, objects that spend most of their time in the outskirts of the solar system haven't been subject to the forces that tend to bring orbits into the ecliptic that those in the "busier" parts of the solar system have. $\endgroup$ Commented Mar 18 at 13:08
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    $\begingroup$ @ScienceSnake: In your self-citation you haven't really answered this here question. Further you seem to be implying that there is selective inclination damping in the space between the gas giants, as opposed to no damping in the KBO's? How would that work? The gas disc is long gone and is surely not responsible for low(er) inclinations of stuff inside the orbit of Neptune. $\endgroup$ Commented Mar 18 at 21:41
  • $\begingroup$ Beyond Neptune, bodies are likely to become highly inclined, eccentric and detached from main solar system. The bodies are part of scattered disc, even beyond TNO. Have a read: ar5iv.labs.arxiv.org/html/1610.04992 $\endgroup$ Commented Mar 19 at 3:07
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    $\begingroup$ Pluto's tilted orbit is explained here. The explanation goes for Eris as well. I have explained in simple language and it is easy to grasp. $\endgroup$ Commented Mar 21 at 4:51

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Why is not always easy to answer, especially not for a specific object. We may seek a population-based answer, by having a look what population Eris is a part of, and hopefully having some simulations that let us understand where this population came from.

If we look at the inclination distributions of objects in the outer solar system, we see the following populations, and see that Eris is part of the 'scattered disc' population:

inclinations of TNOSs

What does the name 'scattered disc' indicate? Let's have a look at the eccentricity distribution of the same objects:

enter image description here

Here we see that there is a 'branch'-like feature in distance-eccentricity space (d-e space), on which Eris sits. At e=0, this branch emanates from close to Neptune, and in fact in typical planet formation simulations (also this), we see such branches generated by the scattering of objects by the giant planets. More specifically, an object can increase its eccentricity and semi-major axis during the scattering phase, as its angular momentum is conserved (the net exchange of angular momentum is zero) but the total energy of the scattered object is increased by exchange with the scatterer (Neptune).

In terms of mass, Eris is similar to Pluto, and it is plausible that they formed not far from each other in the vicinity of Neptune. Just that one got caught up in a resonance and the other one got scattered, as Neptune (presumably) migrated.

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  • $\begingroup$ Could you explain in somewhat simpler language? I cannot comprehend phrases like 'population', ' branch-like feature' and 'scattering phase'. Also, it is difficult for me to digest the stimulations (I haven't been too exposed to such things earlier. So if you can guide me through, it would be great help!) $\endgroup$
    – AstroByte
    Commented Mar 19 at 14:24
  • $\begingroup$ @AstroByte Well, those are a lot of concepts to explain. In brief, Eris has a high inclination because it got scattered by Neptunes gravity. $\endgroup$ Commented Mar 20 at 0:52

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