 Quaoar and Weywot (left of Quaoar) imaged by theHubble Space Telescope in 2006 | |
| Discovery[1][2] | |
|---|---|
| Discovered by |
|
| Discovery date | 14 February 2006 |
| Designations | |
Designation | (50000) Quaoar I[4]: 134 |
| Pronunciation | /ˈweɪwɒt/ |
| Orbital characteristics[5]: 8 | |
| Epoch 21 September 2006 (JD 2454000) | |
| 13329±19 km | |
| Eccentricity | 0.01111+0.0044 −0.0040 |
| 12.42727±0.00003 d | |
| 79°+39° −27° | |
| Inclination | 13.62°+0.32° −0.33° (toecliptic) |
| 353.3°+0.83° −0.85° | |
| 97°+28° −37° | |
| Satellite of | 50000 Quaoar |
| Physical characteristics | |
| ≈165 km[5] | |
| Mass | 2.4+1.2 −1.1×1018 kg[5][a] |
Meandensity | 0.5 to 1.5g/cm3[5] |
| Albedo | ≈ 0.04[6] |
| 24.7[7][b] | |
| ≈ 8.3[b] | |
 |
Weywot (formal designation(50000) Quaoar I) is anatural satellite or moon of thetrans-Neptuniandwarf planetQuaoar. It was discovered byMichael Brown and Terry-Ann Suer using images taken by theHubble Space Telescope on 14 February 2006. It is named after theTongva sky god and son ofQuaoar. Weywot is about 165 km (103 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 outerring bygravitationally influencing it in anorbital resonance.
Weywot was first imaged by theHubble Space Telescope on 14 February 2006, duringMichael Brown's survey forsatellites around largetrans-Neptunian objects (TNOs) usingHubble's high-resolutionAdvanced Camera for Surveys.[1][8] Consecutive images from that date showed that Weywot appeared stationary relative to Quaoar and was visibly separated at anangular distance of 0.35arcseconds.[1][9]: 1547 After Brown's Hubble survey concluded in late 2006, he and his colleague Terry-Ann Suer reported their newly discovered TNO satellites to theCentral Bureau for Astronomical Telegrams, which published their discovery of Weywot alongside the three TNO satellitesVanth,Tinia, and thenameless moon of 208996 Achlys on 22 February 2007.[8][1]
To determine Weywot's orbit, Brown reobserved Weywot with Hubble in March 2007 and March 2008.[10][11][7] Together with his colleague Wesley Fraser, Brown published the first preliminary orbit of Weywot in May 2010. Fraser and Brown were unable toprecover Weywot in earlierultraviolet Hubble images of Quaoar from 2002, either because the satellite was obscured by Quaoar or it was too faint in ultraviolet light.[9]: 1548
Weywot was not assigned aprovisional designation when its discovery was announced.[1] Brown left the choice of a name up to theTongva, whose creator-god Quaoar had been named after. The Tongva chose the sky godWeywot, son of Quaoar.[12] The name of Weywot was officially announced by theMinor Planet Center in a notice published on 4 October 2009.[4]: 134
Weywot orbits Quaoar at an average distance of 13,300 km (8,300 mi) and takes 12.4 days to complete one revolution.[5]: 8 Its orbit is likely coplanar (orbital inclination close to zero) with respect to Quaoar's equator,[13]: 1 although it appears to be inclined relative to Quaoar's outermost ring by4.8°±1.6°.[14]: 13 If Weywot orbits coplanar with Quaoar's equator, then its orbital inclination with respect to theecliptic plane would be approximately the same as Quaoar'saxial tilt of 15° with respect to the ecliptic.[13]: 1 Weywot's orbit is nearlycircular with aneccentricity of0.0111+0.0044
−0.0040.[5]: 8 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.[15]: 362
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 littleparallactic change in perspective when observed from Earth, which leads to mirror ambiguity where two possible inclinations could equally fit Weywot's orbit.[15]: 359 [9]: 1548–1549 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-dayalias in its orbital period, which allowed for even more possible orbit solutions with different orbital periods.[15]: 359 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 bycollisions with other bodies, gravitationalperturbations, slowtidal circularization, or an origin as a collisionally-ejected fragment of Quaoar.[16][15] Uncertainties in Weywot's orbit were eliminated after astronomers obtained precise measurements of Weywot's positions fromstellar occultations beginning on 4 August 2019, which allowed researchers to unambiguously settle on a prograde, 12.4-day circular orbit for Weywot.[17]: 6 [14]: 13 [5]: 8
In February 2023, astronomers announced the discovery of a distantring orbiting Quaoar at a distance of 4,148 km (2,577 mi), which nearly coincides with the 6:1mean-motion orbital resonance with Weywot that lies slightly interior to the ring at 4,021 km (2,499 mi).[17]: 3 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.[17]: 6 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.[17]: 6
Weywot is one of the darkest known satellites belonging to a trans-Neptunian object, with a lowalbedo of 0.04.[6] It has a very dimapparent magnitude of 24.7, which is5.6±0.2magnitudes fainter than Quaoar invisible light.[7] Combined with its close proximity to Quaoar, Weywot's faintness makes observations difficult, leaving it resolvable only to the most sensitive telescopes such as theHubble Space Telescope and theKeck Telescopes.[8] For these reasons, most of Weywot's physical properties such as its mass,color, andlight curve have yet to be measured.[9]: 1547
As of 2025[update], 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.[6][5] 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).[14] Given Weywot's magnitude difference from Quaoar, this occultation-derived diameter suggests Weywot has a lowgeometric albedo of about 0.04, considerably darker than Quaoar's albedo of 0.12.[6] 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.[18]: 15 [9]: 1547 [6]