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UBC Theses and Dissertations

A carefully characterised trans-neptunian survey Alexandersen, Mike


The Trans-Neptunian objects (TNOs) preserve evidence of planet building processes in their orbital and size distributions. While all populations show steep size distributions for large objects, recently a relative deficit of Neptunian Trojans and scattering objects with diameters D<100 km was detected. We have investigated this deficit with a 32 square degree survey, in which we detected 77 TNOs brighter than a limiting r-band magnitude of 24.6. Our Plutino sample (18 objects in 3:2 mean motion resonance with Neptune) also shows a deficit of D<100 km objects. We reject a single power-law size distribution at >99% confidence. The fact that three independent samples of three different populations show this trend suggests that it is a real feature, possibly shared by all hot TNO populations as a remnant of ''born big'' planetesimal formation processes. We surmise the existence of 9000 ± 3000 Plutinos with absolute magnitude Hr ≤ 8.66 and estimate 37000 +12000/-10000 Plutinos with Hr ≤ 10.0 (95% confidence ranges). Our survey also discovered one temporary Uranian Trojan, one temporary Neptunian Trojan and one stable Neptunian Trojan. With these discoveries, combined with our survey characteristics, we derive populations of 110 +500/-100, 210 +900/-200 and 150 +600/-140 for these populations, respectively, with Hr ≤ 10.0. With such approximately equal numbers, the temporary Neptunian Trojans cannot be previously stable Trojans that happen to be escaping the resonance now; they must be captured from another reservoir. Our population estimate also reveals that the Neptunian Trojans are less numerous than the main belt asteroids (semi-major axis 2.06<a<3.65), which has 592 asteroids with Hr ≤ 10.0. As the bias against detection of objects grows with larger semi-major axis, our discovery of three 3:1 resonators and one 4:1 resonator adds to the growing evidence that the high-order resonances are far more populated than can currently be explained theoretically.

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