From Comets to Pluto and Beyond: Kuiper Belt Objects and Investigations

The orbital structure of small bodies beyond Neptune (also known as trans-Neptunian objects – TNOs) was unknown until recently. In addition to Pluto, since the 90’s several TNOs have been found revealing a number of puzzling features in the trans-Neptunian region, now often called the Kuiper Belt. Remarkably, the steady analysis of the data collected during the flyby of Pluto by the New Horizons spacecraft in summer 2015, for the first time, is unveiling surprising and unprecedented physical characteristics of the body which for about seventy years was known as the farthest planet of the Solar System. Furthermore, the discovery of a growing number of objects in the Kuiper Belt has been providing several increasingly rich and unexpected treasures in terms of physical, chemical, and orbital/dynamical features over the past few years. To name a few, the discovery of dwarf planets in the Kuiper Belt (Eris, Makemake, Haumea) revealed that Pluto is a member of such objects and that other still undiscovered dwarf planets potentially lurk in the trans-Neptunian region. Also, the orbital structure in the Kuiper Belt is quite complex: TNOs have been identified in various dynamical classes such as the classical, resonant (in mean motion resonances with Neptune), scattered/ing, and detached populations. A number of correlations of physical properties with such dynamical classes have also been observed, which suggests the existence of strong ties between surface chemical properties/composition with dynamical origin and evolution during the history of the Solar System. In sum, the vast and still largely unexplored expanses of space beyond the orbit of Neptune holds the key to understand not only the Kuiper Belt, but also the origin and evolution of the Solar System as a whole. In particular, studies of TNOs can strongly constrain the orbital evolution of the giant planets, which then can provide important clues on terrestrial planet formation, formation of Trojan asteroids and satellite systems, among others.

Intriguingly, certain features of the orbital configuration of some TNOs may even bear the silent imprint of the existence of a true remote planet, primarily called Planet Nine or Telisto, whose gravitational pull would gradually sculpt the ensemble of those objects. We hope that the distinguished researchers who kindly wish to contribute to this Research Topic will provide the community of interested readers with the latest developments at the forefront of the research in this fascinating and rapidly evolving field. Contributions based on theory/modelling, observations, and experiments are highly welcomed.