(303775) 2005 QU182

Lore & Background

2005 QU182 was discovered on 30 August 2005 by American astronomers Mike Brown, David Rabinowitz and Chad Trujillo at the Palomar Observatory in California, using the 1.2-meter Samuel Oschin telescope. Precovery images date back to 1974, and as of 2026 it has been observed 626 times over 52 years. Its provisional designation was assigned on 1 September 2007, and it received its permanent number 303775 in 2014.

The object orbits the Sun at a distance of 36.8–189.1 AU with a semi-major axis of 113.0 AU, taking about 1201 years to complete one orbit. Its orbit has a high eccentricity of 0.674 and an inclination of 14.05°. It came to perihelion in 1971 and is currently 51.8 AU from the Sun. It belongs to the scattered disc, a population influenced by Neptune's gravitational perturbations. A 2021 study found its orbit is unstable over one billion years due to Neptune's influence, though none of the simulation tracks were completely lost from the Solar System.

Physically, 2005 QU182 has a diameter of 584+155−144 km, based on 2020 reanalysis of Herschel Space Telescope data. Its surface shows medium reddening (spectral slope 16 ± 2%/100 nm) and a composition rich in carbon dioxide ice, placing it among the CO2-type trans-Neptunian objects. Its rotation period is 9.61 hours, with a brightness variation of 0.12 magnitudes suggesting an approximately spherical shape. The Hubble Space Telescope is scheduled to observe it in 2026 to search for potential moons, which could allow direct measurement of its mass and density.

Reader's Guide

2005 QU182 is significant as a large scattered-disc object whose size (584+155−144 km) ranks it among the top 34 largest known trans-Neptunian objects. Its surface composition, dominated by carbon dioxide ice, places it in the CO2-type spectral class common among dynamically excited TNOs. The object's orbital instability over a billion-year timeframe, as shown in simulations, highlights the influence of Neptune's gravity on scattered-disc populations. Its rotation period of 9.61 hours and low brightness variation suggest a nearly spherical shape. The scheduled 2026 Hubble Space Telescope observations could discover a moon, enabling direct mass and density measurements—currently impossible due to the lack of known satellites. As a possible dwarf planet according to Mike Brown's classification, it represents a mid-sized TNO between 400 and 1,000 km, believed to have highly porous interiors. The object's discovery by a team of American astronomers at Palomar Observatory and its extensive observation arc of 52 years underscore its importance in understanding the outer Solar System's dynamics and composition.