471325 Taowu

471325 Taowu (provisional designation 2011 KT₁₉, formerly nicknamed Niku (/ˈniːkuː/)) is a trans-Neptunian object whose orbit is tilted 110° with respect to the ecliptic. Thus, it has a nearly polar retrograde orbit around the Sun from the reference point of Earth's orbital plane.^[5]

471325 Taowu

Taowu imaged by the Canada–France–Hawaii Telescope on 22 May 2014
Discovery[1]
Discovered by	Mount Lemmon Survey
Discovery site	Mount Lemmon Obs.
Discovery date	31 May 2011
Designations
MPC designation	(471325) Taowu
Named after	Taowu
Alternative designations	2011 KT19 "Niku" (nickname)
Minor planet category	TNO[2] · centaur[3][4] distant[1]
Orbital characteristics
Epoch 17 October 2024 (JD 2460600.5)
Uncertainty parameter 2
Observation arc	14.05 yr (5,131 d)
Earliest precovery date	10 May 2010
Aphelion	47.588 AU
Perihelion	23.839 AU
Semi-major axis	35.713 AU
Eccentricity	0.3325
Orbital period (sidereal)	213.43 yr (77,955 d)
Mean anomaly	42.884°
Mean motion	0° 0m 16.625s / day
Inclination	110.311°
Longitude of ascending node	243.903°
Time of perihelion	≈ 15 May 1999 ±0.13 days[2]
Argument of perihelion	322.913°
Physical characteristics
Mean diameter	177 km (assumed albedo 0.058)[4]
Apparent magnitude	22[1]
Absolute magnitude (H)	7.45[2][1]

Discovery

Taowu was discovered on 31 May 2011 by the Mount Lemmon Survey in Arizona. It was announced by the Minor Planet Center on 2 June 2011, after other telescopes confirmed the object with additional observations.^[6] The object was given the minor planet provisional designation 2011 KT₁₉, which reflects its discovery date.^[6] Initial calculations of Taowu's orbit using these few observations suggested it was a centaur on a prograde elliptical orbit (semi-major axis 28 AU, eccentricity 0.41, inclination 38°).^[6][5]: 2 However, Taowu was only observed for up to 8 days before being lost, due to large uncertainties in its orbit.^[5]: 2

In 2016, a team of astronomers led by Ying-Tung Chen performed a search for outer Solar System objects in observations by the Pan-STARRS 1 survey.^{[7][8][5]: 1} They rediscovered Taowu in Pan-STARRS observations from 2013–2016 and recognized it had an unusual retrograde polar orbit. Chen's team made follow-up observations at Lulin Observatory in Taiwan and found additional observations of the object in archival images from the Dark Energy Survey and Canada–France–Hawaii Telescope.^[8][5]: 2 After Chen's team submitted their observations of Taowu to the Minor Planet Center, it was recognized that Taowu had been previously observed by the Mount Lemmon Survey in 2011.^[5]: 2 Taowu received its permanent minor planet catalog number 471325 in 18 August 2016 and the Minor Planet Center declared Mount Lemmon Survey as the object's official discoverer.^[9]: 512

Name

The object is named after Taowu, one of the Four Perils in Chinese mythology. The name follows the International Astronomical Union's naming conventions for centaurs on Neptune-crossing orbits (perihelion <30 AU), which are named after mythological chimeras.^[10]: 8 The name was announced by the International Astronomical Union on 3 February 2025.^[11]

The object was previously nicknamed "Niku" by Ying-Tung Chen, who was involved with rediscovering the object and studying its orbit in 2016. The nickname comes from the Chinese adjective meaning "rebellious", in reference to the object's unusual retrograde orbit.^[8][7]

Orbit

Taowu is in a 7:9 resonance with Neptune. Currently it is the only object with a nearly polar orbit that is in resonance with a planet.^[12] Notably, it is part of a group of objects that orbit the Sun in a highly inclined orbit; the reasons for this unusual orbit are unknown as of August 2016.^[5] Taowu's orbital characteristics have been compared to those of 2008 KV42 (nicknamed "Drac"). The orbits of Taowu, 2008 KV₄₂, 2002 XU93, 2010 WG9, 2007 BP102, 2011 MM4, appear to occupy a common plane, with three in prograde and three in retrograde orbits. The probability of this alignment occurring by chance is 0.016%. These orbits should leave a common plane in a few million years because the precession of prograde and retrograde orbits are in opposite directions. Simulations including the hypothetical Planet Nine did not maintain a common orbital plane and the plane does not coincide with the plane of the predicted high-inclination large semi-major axis objects of that model. Other simulations with a few Earth-mass dwarf planet on a high-inclination orbit also failed to reproduce the alignment.^[5]

The orbit of Taowu (white) in relation to Pluto and the planets of the Solar System

The orbit of Taowu (purple), is shown with another steep retrograde TNO, 2008 KV42 (yellow), and the other planets. Pluto's orbit is in red.

Physical characteristics

The diameter of Taowu has not been measured, but it can be estimated from its brightness (absolute magnitude) using a range of plausible values for its surface reflectivity (geometric albedo). If Taowu reflects between 5% and 25% of visible light, then its diameter is between 100 and 200 km (62 and 124 mi).^[13] Taowu's rotation period had been measured as part of a 2023 study, but results have not yet been published.^[14]