78799 Xewioso

Lore & Background

Xewioso was discovered on 10 December 2002 by a team of astronomers at Palomar Observatory in California, using the 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 taken by Trujillo using Palomar's 1.52-meter telescope on 4 and 5 January 2003, and the discovery was announced by the Minor Planet Center on 5 January 2003 alongside the trans-Neptunian objects 2002 WC19 and 2002 XV93. The discovery formed part of Trujillo and Brown's Caltech Wide Area Sky Survey, which aimed to find bright, Pluto-sized Kuiper belt objects. The first identified precovery observations were published in December 2003, including a photographic plate from 17 December 1989 found by Reiner M. Stoss, which remains the earliest known precovery observation.

The object was named after Xɛ̀vioso, a thunder god in the mythologies of the Tado (Fon and Ewe) peoples of West Africa, with the naming 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 Minor Planet Center on 6 February 2004.

Xewioso orbits the Sun at a distance of 28–47 AU (average 38 AU) once about every 230 years. Its orbit has an eccentricity of 0.24 and an inclination of 14° with respect to the ecliptic. It previously passed perihelion in 1926. Because its orbit crosses Neptune's orbit, it can be technically considered a centaur according to the Deep Ecliptic Survey's definition. Physically, Xewioso is a dark object with an extremely low geometric albedo between 0.01 and 0.08 and an absolute magnitude of 5.4, corresponding to a diameter of roughly 490 to 640 km. These measurements come from 2010 observations by the Herschel Space Observatory. Its color and rotation period are unknown, and its absolute magnitude has significant uncertainty.

Reader's Guide

Xewioso's significance lies in its size and classification as a mid-sized trans-Neptunian object, between 400 and 1,000 km in diameter, which planetary scientists believe represents a transition between small, low-density TNOs and large, high-density dwarf planets. Based on its size of 565+71−73 km, it is hypothesized that mid-sized TNOs like Xewioso should have highly porous and unheated interiors, as similar-sized objects such as Uni and Gǃkúnǁʼhòmdímà have been found to have low densities around 1 g/cm³. However, Xewioso is not known to have any natural satellites or moons, so there is currently no way to measure its mass and density. Its discovery as part of the Caltech Wide Area Sky Survey contributed to the search for bright, Pluto-sized Kuiper belt objects. The object's high orbital inclination places it in the dynamically 'hot' population of inner classical Kuiper belt objects, and its orbit crossing Neptune's allows it to be technically classified as a centaur. The naming after a West African thunder god reflects the cultural diversity in minor planet nomenclature.

Did You Know?

• Xewioso was discovered on 10 December 2002 at Palomar Observatory in California.
• Its diameter is between 490 and 640 kilometers (300 and 400 mi).
• The earliest known precovery observation of Xewioso is from a photographic plate taken on 17 December 1989.