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Illustration of how the fact that resonant TNOs come to perihelion at preferred longitudes relative to Neptune translates into a non-uniformity in the observed distribution of their longitudes of perihelion (despite having an intrinsically uniform distribution!).

The plot on the right shows the projected positions of a large simulated population of particles in the asymmetric island of Neptune's 20:1 mean motion resonance. These objects spend most of their time very far from the sun. For the sake of illustration, I am labeling only those particles at heliocentric distances less than 55 au as "visible" to us (the blue dots). Neptune is shown as a green dot. As time moves forward (I started in 1990 near the dawn of Kuiper belt observations), Neptune moves forward and so do the resonant TNOs that are at perihelion. The "observable" distributions of the longitude of ascending node (top left) and longitude of perihelion (bottom left) are shown in blue for the currently displayed year and in red for all years from 1990 to the currently displayed year. The intrinsic distributions for the population are in black. It's clear that it takes an entire Neptune orbit (>160 years!) before we have a uniform observable distribution of the longitude of perihelion. Thus resonances with Neptune can create apparent "clusterings" in the longitude of perihelion in our sample of observed TNOs. (And this is separate from the cluterings also created by the survey pointing biases! These plots assume we see everything in blue!)

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