78799 Xewioso

Lore & Background

Xewioso was discovered on 10 December 2002 by a team of astronomers using Palomar Observatory's 1.22-meter Samuel Oschin telescope. The discovery team included Chad Trujillo, Michael E. Brown, Eleanor F. Helin, Steven Pravdo, Kenneth Lawrence, and Michael D. Hicks. Follow-up observations were made on 4 and 5 January 2003 with Palomar's 1.52-meter telescope, and the discovery was announced by the Minor Planet Center on 5 January 2003, alongside two other trans-Neptunian objects. The earliest known precovery observation dates to 17 December 1989, found by Reiner M. Stoss on photographic plates from Palomar's Digitized Sky Survey.

The object was named after Xɛ̀vioso, a thunder god in the mythologies of the Tado (Fon and Ewe) peoples of West Africa. The naming was announced by the International Astronomical Union's Working Group for Small Body Nomenclature on 1 September 2025. Its minor planet catalog number 78799 was assigned by the MPC on 6 February 2004.

Xewioso orbits the Sun at a distance of 28–47 AU (average 38 AU) once every about 230 years. Its orbit has an eccentricity of 0.24 and an inclination of 14°, and it last passed perihelion in 1926. It is considered an inner classical Kuiper belt object of the dynamically 'hot' population, and because its orbit crosses Neptune's, it can technically be considered a centaur. Physically, Xewioso is dark with an extremely low geometric albedo (0.01–0.08) and an absolute magnitude of 5.4, yielding a diameter of 490–640 km. Its size was measured by the Herschel Space Observatory in 2010 via far-infrared thermal emission. Its color and rotation period are unknown, and it has no known natural satellites, so its mass and density cannot be measured.

Reader's Guide

Xewioso is significant as a mid-sized trans-Neptunian object (TNO) with a diameter of roughly 565 km, placing it in the proposed class of 'mid-sized' TNOs between 400 and 1,000 km. These objects are believed to represent the transition between small, low-density TNOs and large, high-density dwarf planets. Planetary scientists have hypothesized that mid-sized TNOs should have highly porous and unheated interiors, based on low densities (around 1 g/cm³) found in similar-sized objects like Uni and Gǃkúnǁʼhòmdímà. However, because Xewioso lacks any known moons, its mass and density remain unmeasured, leaving its internal structure uncertain. Its discovery was part of the Caltech Wide Area Sky Survey, which aimed to find bright, Pluto-sized Kuiper belt objects. The object's naming after a West African thunder god reflects the tradition of naming TNOs after mythological figures. Its orbit at the inner edge of the Kuiper belt and its high inclination make it a member of the dynamically 'hot' population, and its orbit-crossing with Neptune allows it to be technically classified as a centaur.

Did You Know?

• Its diameter is between 490 and 640 kilometers (300–400 mi), based on Herschel Space Observatory observations.
• The earliest known precovery observation of Xewioso dates to 17 December 1989.