78799 Xewioso

Discovery

Xewioso was discovered on 10 December 2002 by a team of astronomers at Palomar Observatory in California.^[1] The discovery team included Chad Trujillo, Michael E. Brown, Eleanor F. Helin, Steven Pravdo, Kenneth Lawrence, Michael D. Hicks, who were using Palomar's 1.22-meter (48 in) Samuel Oschin telescope.^[5] Follow-up observations were taken by Trujillo using Palomar's 1.52-meter (60 in) telescope on 4 and 5 January 2003, and results were reported to the Minor Planet Center.^{[5][6]: 101 } The team's discovery of Xewioso alongside the trans-Neptunian objects 2002 WC19 and 2002 XV93 was announced by the MPC on 5 January 2003.^[5] The discovery of Xewioso formed part of Trujillo and Brown's Caltech Wide Area Sky Survey at Palomar Observatory, which aimed to find bright, Pluto-sized Kuiper belt objects like Quaoar, Máni, and Aya.^{[6]: 103 }

In December 2003, the MPC published the first identified precovery observations of Xewioso, which included a pair of photographic plates from Palomar Observatory's Digitized Sky Survey.^[7] The earliest of these photographic plates came from 17 December 1989, which was found by Reiner M. Stoss.^[7] This 1989 plate remains as the earliest known precovery observation of Xewioso.^[1]

Name and number

The object is named after Xɛ̀vioso, a thunder god in the mythologies of the Tado (Fon and Ewe) peoples of West Africa.^{[8]: 6 } The naming of this object was announced by the International Astronomical Union's Working Group for Small Body Nomenclature on 1 September 2025.^[8] Before Xewioso was officially named, it was known by its provisional designation 2002 XW₉₃,^[1] which indicates the year and half-month of the object's discovery date.^[9] Xewioso's minor planet catalog number of 78799 was given by the MPC on 6 February 2004.^[10]

Size and albedo

Xewioso is a dark object with an extremely low geometric albedo of between 0.01 and 0.08 and an absolute magnitude of 5.4, which corresponds to a diameter of roughly 490 to 640 km (300 to 400 mi).^{[3]: 10, 12 } These measurements come from 2010 observations by the Herschel Space Observatory, which could determine Xewioso's size by detecting its far-infrared thermal emission.^{[3]: 4 } However the color and rotation period of Xewioso are unknown and its absolute magnitude also has significant uncertainty.^{[3]: 3 }

Density theory

Based on its size of 565+71
−73 km,^{[3]: 10 } it belongs to the proposed class of "mid-sized" TNOs between 400 and 1,000 km (250 and 620 mi) in diameter, which are believed to represent the transition between small, low-density TNOs and large, high-density dwarf planets.^{[11][12]: 1 } Planetary scientists have hypothesized that mid-sized TNOs should have highly porous and unheated interiors, because TNOs in this size range (namely Uni and Gǃkúnǁʼhòmdímà) have been found to have low densities around 1 g/cm³.^[11] However, Xewioso is not known to have any natural satellites or moons, which means there is currently no way to measure its mass and density.^{[13]: 1, 3 }