the ecliptic was photographed and digitally evaluated for slowly moving objects. Hundreds of TNOs were found, with diameters in the range of 50 to 2,500 kilometers. Eris, the most massive TNO, was discovered in 2005, revisiting a long-running dispute within the scientific community over the classification of large TNOs, and whether objects like Pluto can be considered planets. Pluto and Eris were eventually classified as dwarf planets by the International Astronomical Union. In December 2018, the discovery of , nicknamed "Farout", was announced. Farout is the most distant solar system object so-far observed and is about 120 au away from the sun. It takes 738 years to complete one orbit. Classification According to their distance from the Sun and their orbital parameters, TNOs are classified in two large groups: the Kuiper belt objects (KBOs) and the scattered disc objects (SDOs). The diagram to the right illustrates the distribution of known trans-Neptunian objects (up to 70 au) in relation to the orbits of the planets and the centaurs for reference. Different classes are represented in different colours. Resonant objects (including Neptune trojans) are plotted in red, classical Kuiper belt objects in blue. The scattered disc extends to the right, far beyond the diagram, with known objects at mean distances beyond 500 au (Sedna) and aphelia beyond 1,000 (). KBOs The Edgeworth-Kuiper belt contains objects with an average distance to the Sun of 30 to about 55 au, usually having close-to-circular orbits with a small inclination from the ecliptic. Edgeworth-Kuiper belt objects are further classified into the resonant trans-Neptunian object, that are locked in an orbital resonance with Neptune, and the classical Kuiper belt objects, also called "cubewanos", that have no such resonance, moving on almost circular orbits, unperturbed by Neptune. There are a large number of resonant subgroups, the largest being the twotinos (1:2 resonance) and the plutinos (2:3 resonance), named after their most prominent member, Pluto. Members of the classical Edgeworth-Kuiper belt include 15760 Albion, 50000 Quaoar and Makemake. Another subclass of Kuiper belt objects is the so-called scattering objects (SO). These are non-resonant objects that come near enough to Neptune to have their orbits changed from time to time (such as causing changes in semi-major axis of at least 1.5 AU in 10 million years), and are thus undergoing gravitational scattering. Scattering objects are easier to detect than other trans-Neptunian objects of the same size because they come nearer