AN OUTER PLANET BEYOND PLUTO AND THE ORIGIN OF THE TRANS-NEPTUNIAN BELT ARCHITECTURE

Abstract

Trans-Neptunian objects (TNOs) are remnants of a collisionally and\ndynamically evolved planetesimal disk in the outer solar system. This complex\nstructure, known as the trans-Neptunian belt (or Edgeworth-Kuiper belt), can\nreveal important clues about disk properties, planet formation, and other\nevolutionary processes. In contrast to the predictions of accretion theory,\nTNOs exhibit surprisingly large eccentricities, e, and inclinations, i, which\ncan be grouped into distinct dynamical classes. Several models have addressed\nthe origin and orbital evolution of TNOs, but none have reproduced detailed\nobservations, e.g., all dynamical classes and peculiar objects, or provided\ninsightful predictions. Based on extensive simulations of planetesimal disks\nwith the presence of the four giant planets and massive planetesimals, we\npropose that the orbital history of an outer planet with tenths of Earth's mass\ncan explain the trans-Neptunian belt orbital structure. This massive body was\nlikely scattered by one of the giant planets, which then stirred the primordial\nplanetesimal disk to the levels observed at 40-50 AU and truncated it at about\n48 AU before planet migration. The outer planet later acquired an inclined\nstable orbit (>100 AU; 20-40 deg) because of a resonant interaction with\nNeptune (an r:1 or r:2 resonance possibly coupled with the Kozai mechanism),\nguaranteeing the stability of the trans-Neptunian belt. Our model consistently\nreproduces the main features of each dynamical class with unprecedented detail;\nit also satisfies other constraints such as the current small total mass of the\ntrans-Neptunian belt and Neptune's current orbit at 30.1 AU. We also provide\nobservationally testable predictions.\n