Perspectives on the distribution of orbits of distant Trans-Neptunian objects

Looking at the orbits of small bodies with large semimajor axes, we are compelled to see patterns. Some of these patterns are noted as strong indicators of new or hidden processes in the outer solar system, others are substantially generated by observational biases, and still others may be completely overlooked. We can gain insight into the current and past structure of the outer solar system through a careful examination of these orbit patterns. In this chapter, we discuss the implications of the observed orbital distribution of distant Trans-Neptunian objects (TNOs). We start with some cautions on how observational biases must affect the known set of TNO orbits. Some of these biases are intrinsic to the process of discovering TNOs, while others can be reduced or eliminated through careful observational survey design. We discuss some orbital element correlations that have received considerable attention in the recent literature. We examine the known TNOs in the context of the gravitational processes that the known solar system induces in orbital distributions. We discuss proposed new elements of the outer solar system, posited ancient processes, and the types of TNO orbital element distributions that they predict to exist. We conclude with speculation.