Occultations suggest it is a compact or contact binary equivalent to a sphere 400 to 500 km in diameter.[7] On 20 November 2020, Chaos occulted a magnitude 16.8 star. Three observers detected the occultation, finding that the object is likely smaller than 600 km in diameter.[11] Another occultation was recorded on 14 January 2022; full results on size, shape, geometric albedo, and the spin-axis orientation have not been released[needs update].[12] A further occultation occurred on 28 September 2023, with a shadow crossing most of North America. This occultation was observed by over 30 observers;[13]
preliminary analysis suggests that Chaos is a binary (possibly a contact binary).[14]
Planetary symbols are no longer much used in astronomy, so Chaos never received a symbol in the astronomical literature. There is no standard symbol for Chaos used by astrologers either. Michael Moorcock's Symbol of Chaos () has been used.[15]
Orbit
19521 Chaos has an orbital period of approximately 309 years. Its orbit is longer, but less eccentric than the orbit of Pluto. 19521 Chaos's orbit is inclined approximately 12° to the ecliptic. Its orbit never crosses the orbit of Neptune. Currently, the closest approach possible to Neptune (MOID) is 12.5 AU (1.87 billionkm).[6]
Chaos will come to perihelion at around December 2033,[5] coming as close as 40 AUs from Earth. Its brightest magnitude will be 20.8.
^ ab"19521 Chaos (1998 WH24)". JPL Small-Body Database Browser (2007-12-14 last obs). Retrieved 11 April 2016.
^ abJPL Horizons Observer Location: @sun (Perihelion occurs when deldot changes from negative to positive. Uncertainty in time of perihelion is 3-sigma.)
^Gómez-Limón Gallardo, José María; Leiva, R.; Ortiz, J. L.; Desmars, J.; Kilic, Y.; Vara-Lubiano, M.; Santos-Sanz, P.; Kretlow, M.; Rommel, F. L.; Morales, N.; Fernandez-Valenzuela, E.; Souami, D.; Lucky Star Team; Observers of Nov. 2020, Jan 2022, Dec 2022; Mar 2023 Occultations (2023). "Chaos: Stellar Occultations Reveal a Binary Tno?". Seventh Edition of the Spanish Meeting of Planetary Sciences and Exploration of the Solar System (7Th Cpess. Bibcode:2023pses.conf80462G.{{cite journal}}: CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link)