Weywot (formal designation (50000) Quaoar I) is the only confirmed moon of the trans-Neptunian dwarf planet Quaoar. It was discovered by Michael Brown and Terry-Ann Suer using images taken by the Hubble Space Telescope on 14 February 2006. It is named after the Tongva sky god and son of Quaoar. Weywot is about 116–172 km (72–107 mi) in diameter and orbits Quaoar every 12.4 days at an average distance of 13,300 km (8,300 mi). Weywot is thought to play a role in maintaining Quaoar's outer ring by gravitationally influencing it in an orbital resonance.
Discovery Weywot was first imaged by the Hubble Space Telescope on 14 February 2006, during Michael Brown's survey for satellites around large trans-Neptunian objects (TNOs) using Hubble's high-resolution Advanced Camera for Surveys. Consecutive images from that date showed that Weywot appeared stationary relative to Quaoar and was visibly separated at an angular distance of 0.35 arcseconds. After Brown's Hubble survey concluded in late 2006, he and his colleague Terry-Ann Suer reported their newly discovered TNO satellites to the Central Bureau for Astronomical Telegrams, which published their discovery of Weywot alongside the three TNO satellites Vanth, Tinia, and the nameless moon of 208996 Achlys on 22 February 2007. To determine Weywot's orbit, Brown reobserved Weywot with Hubble in March 2007 and March 2008. Together with his colleague Wesley Fraser, Brown published the first preliminary orbit of Weywot in May 2010. Fraser and Brown were unable to precover Weywot in earlier ultraviolet Hubble images of Quaoar from 2002, either because the satellite was obscured by Quaoar or it was too faint in ultraviolet light.
Name Weywot was not assigned a provisional designation when its discovery was announced. Brown left the choice of a name up to the Tongva, whose creator-god Quaoar had been named after. The Tongva chose the sky god Weywot, son of Quaoar. The name of Weywot was officially announced by the Minor Planet Center in a notice published on 4 October 2009.
Orbit
Weywot orbits Quaoar at an average distance of 13,300 km (8,300 mi) and takes 12.4 days to complete one revolution. Its orbit is likely coplanar (orbital inclination close to zero) with respect to Quaoar's equator, although it appears to be inclined relative to Quaoar's outermost ring by 4.8°±1.6°. If Weywot orbits coplanar with Quaoar's equator, then its orbital inclination with respect to the ecliptic plane would be approximately the same as Quaoar's axial tilt of 15° with respect to the ecliptic. Weywot's orbit is nearly circular with an eccentricity of 0.0111+0.0044−0.0040. A circular orbit implies that Weywot may have formed out of a disk of material that orbited Quaoar within 100 million years after the Solar System's formation. Before 2019, Weywot's orbit was highly uncertain due to limited number of observations. Due to its great distance from Earth, Weywot's orbit shows little parallactic change in perspective when observed from Earth, which leads to mirror ambiguity where two possible inclinations could equally fit Weywot's orbit. That is, it could not be recognized whether Weywot orbited prograde or retrograde with respect to the ecliptic. The discontinuity of known observations of Weywot at the time also resulted in a 0.39-day alias in its orbital period, which allowed for even more possible orbit solutions with different orbital periods. Weywot's orbit was previously thought to have a high eccentricity of 0.14, which led astronomers to speculate that its apparently eccentric orbit could have been caused by collisions with other bodies, gravitational perturbations, slow tidal circularization, or an origin as a collisionally-ejected fragment of Quaoar. Uncertainties in Weywot's orbit were eliminated after astronomers obtained precise measurements of Weywot's positions from stellar occultations beginning on 4 August 2019, which allowed researchers to unambiguously settle on a prograde, 12.4-day circular orbit for Weywot.
Ring dynamics In February 2023, astronomers announced the discovery of a distant ring orbiting Quaoar at a distance of 4,148 km (2,577 mi), which nearly coincides with the 6:1 mean-motion orbital resonance with Weywot that lies slightly interior to the ring at 4,021 km (2,499 mi). This near-coincidence suggests Weywot could play a role in perturbing the ring by producing irregularities in the ring's width and density. Together with Quaoar's 1:3 spin-orbit resonance that lies slightly farther from the ring, the 6:1 Weywot mean-motion resonance is thought to help prevent the ring from accreting into a solid body. It is unknown which of these two resonances plays a more dominant role in maintaining the ring, as the underlying parameters necessary to calculate their effects are poorly known.
Physical characteristics Weywot is one of the darkest known satellites belonging to a trans-Neptunian object, with a low albedo of 0.024–0.078. It has a very dim apparent magnitude of 24.7, which is 5.6±0.2 magnitudes fainter than Quaoar in visible light. Combined with its close proximity to Quaoar, Weywot's faintness makes observations difficult, leaving it resolvable only to the most sensitive telescopes such as the Hubble Space Telescope and the Keck Telescopes. For these reasons, most of Weywot's physical properties such as its mass, color, and light curve have yet to be measured. As of 2025, Weywot is thought to be about 165 km (103 mi) in diameter, based on multiple observations of a stellar occultation by Weywot on 22 June 2023. Occultations by Weywot have been observed previously on 4 August 2019, 11 June 2022, and 26 May 2023, which all gave similar diameter estimates of about 170 km (110 mi). Given Weywot's magnitude difference from Quaoar, this occultation-derived diameter suggests Weywot has a low geometric albedo of about 0.04, considerably darker than Quaoar's albedo of 0.12. Weywot was previously thought to have a diameter of 81 ± 11 km (50 ± 7 mi), about half that of the occultation measurement, because researchers based this estimate only on Weywot's relative brightness and assumed it had a similar albedo as Quaoar. In 2026, Weywot's diameter is thought to be 116–172 km in diameter, with a 95% confidence.
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