TNOs

TNOs, or trans-Neptunian objects, are minor planets that orbit the Sun at distances beyond Neptune, typically beyond 30 astronomical units. They are remnants from the solar system’s formation and include a wide range of bodies, from small icy objects to dwarf planets such as Pluto, Eris, Haumea, Makemake, and Gonggong. Studying TNOs helps scientists understand the early solar system and planetary migration.

They are categorized by orbital dynamics. Kuiper belt objects form a disk beyond Neptune and include resonant bodies locked in Neptune’s mean-motion resonances and non-resonant classical KBOs. The scattered disc contains objects on highly eccentric orbits that extend far from the Sun; detached objects have orbits that are only weakly perturbed by Neptune. Some TNOs may belong to a distant inner Oort cloud.

Notable members include Pluto, Eris, Haumea, Makemake, Orcus, Quaoar, Sedna, and Gonggong. Several of the largest bodies have been classified as dwarf planets by the IAU, while others are commonly treated as such in scientific literature. TNOs range from kilometer-scale objects to large, multi-hundred-kilometer bodies often accompanied by moons.

Discovery and naming: The first TNO discovered after Pluto, 1992 QB1, was announced in 1992, marking the beginning of the modern era of trans-Neptunian studies. Since then, deep surveys have cataloged thousands of TNOs, enabling statistical and dynamical analyses. Names are assigned by the IAU, though many objects remain unnamed.

Significance: Studying TNOs informs models of solar system formation, Neptune’s migration, and the outer solar system’s structure, and provides insight into the composition of primordial material. Ongoing surveys and missions aim to map their orbits, sizes, and surfaces, deepening our understanding of the solar system’s frontier.