471325 Taowu

Lore & Background

Taowu was discovered on 31 May 2011 by the Mount Lemmon Survey in Arizona and announced on 2 June 2011 after confirmation by other telescopes. Initial calculations suggested it was a centaur on a prograde elliptical orbit (semi-major axis 28 AU, eccentricity 0.41, inclination 38°), but it was observed for only 8 days before being lost due to large orbital uncertainties. In 2016, a team led by Ying-Tung Chen rediscovered Taowu in Pan-STARRS 1 observations from 2013–2016, recognizing its unusual retrograde polar orbit. Follow-up observations at Lulin Observatory and archival images from the Dark Energy Survey and Canada–France–Hawaii Telescope confirmed the object. The Minor Planet Center declared Mount Lemmon Survey as the official discoverer. The object is named after Taowu, one of the Four Perils in Chinese mythology, following IAU naming conventions for centaurs on Neptune-crossing orbits. The nickname Niku, a Mandarin adjective meaning 'rebellious', was given by Chen in reference to the unusual orbit. Taowu is near, but likely not in a 7:9 resonance with Neptune; more accurate measurements indicate it will leave temporary libration within 500,000 years. It is part of a group of objects with highly inclined orbits, including 2008 KV42, 2002 XU93, 2010 WG9, 2007 BP102, and 2011 MM4, which appear to occupy a common plane—three in prograde and three in retrograde orbits—with a 0.016% probability of chance alignment. Simulations including the hypothetical Planet Nine or a high-inclination dwarf planet failed to reproduce this alignment. The diameter is estimated between 100 and 200 km based on an assumed albedo of 5% to 25%. A 2023 study attempted to check brightness variability due to rotation, but results have not been published.

Reader's Guide

Taowu's significance lies in its extreme retrograde polar orbit and its membership in a puzzling group of objects sharing a common orbital plane, despite having opposite orbital directions. The alignment of six objects—three prograde and three retrograde—has a 0.016% probability of occurring by chance, yet simulations with Planet Nine or a high-inclination dwarf planet could not reproduce it. This suggests unknown dynamical processes in the outer Solar System. Taowu's orbit is near a 7:9 resonance with Neptune but is not stable, as it will leave temporary libration within 500,000 years. Its rediscovery in 2016 by Chen's team highlighted the limitations of initial orbital calculations and the value of archival surveys. The object's name, from Chinese mythology, and its nickname Niku ('rebellious') reflect its unusual behavior. As of the article, the reasons for its orbit remain unknown, and no rotational light curve has been published. Taowu thus serves as a key object for studying the dynamics of high-inclination trans-Neptunian populations.

Did You Know?

• Taowu was initially thought to be a prograde centaur before its rediscovery revealed a retrograde polar orbit.
• The object's nickname Niku means 'rebellious' in Mandarin, referencing its unusual orbit.
• Taowu is part of a group of six objects whose orbital plane alignment has only a 0.016% probability of being random.