Leucus is planned to be visited by the Lucy spacecraft, which launched in 2021. The flyby is scheduled for 18 April 2028, and will approach the asteroid to a distance of 1,000 km (620 mi) at a relative velocity of 5.9 km/s (13,000 mph).[8]
During spring 2013, a rotational lightcurve of Leucus was obtained from photometric observations made by astronomers Robert Stephens and Daniel Coley at the Center for Solar System Studies (CS3), California, using a 0.35/0.4-meter Schmidt-Cassegrain telescope. The lightcurve showed an exceptionally slow rotation period of 513.7 hours with a brightness variation of 0.53 in magnitude (U=2+). No evidence of a non-principal axis rotation (NPAR) was found.[11] It is one of the slowest rotators known to exist.
In preparation for the planned visit by the Lucy spacecraft, Leucus was once again observed by astronomers Marc BuieatSwRI and Stefano MottolaatDLR in 2016. The obtained bimodal lightcurve gave a somewhat shorter period of 440 hours and an amplitude of 0.7 magnitude.[12]
According to the surveys carried out by the Infrared Astronomical Satellite IRAS, and NASA's Wide-field Infrared Survey Explorer with its subsequent NEOWISE mission, Leucus has a low albedo of 0.06 and 0.08, with a diameter of 42.1 and 34.2 kilometers, respectively.[13][14] The Collaborative Asteroid Lightcurve Link derives a lower albedo of 0.05 and a diameter of 42.1 kilometers, in accordance with the result obtained by IRAS.[15]
^French, Linda M.; Stephens, Robert, D.; Coley, Daniel R.; Wasserman, Lawrence H.; Vilas, Faith; La Rocca, Daniel (October 2013). "A Troop of Trojans: Photometry of 24 Jovian Trojan Asteroids". The Minor Planet Bulletin. 40 (4): 198–203. Bibcode:2013MPBu...40..198F. ISSN1052-8091.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^Buie, Marc W.; Zangari, Amanda Marie; Marchi, Simone; Mottola, Stefano; Levison, Harold F. (October 2016). "Ground-based characterization of Leucus and Polymele, two fly-by targets of the Lucy Discovery mission". American Astronomical Society. 48: 208.06. Bibcode:2016DPS....4820806B.
^Tedesco, E. F.; Noah, P. V.; Noah, M.; Price, S. D. (October 2004). "IRAS Minor Planet Survey V6.0". NASA Planetary Data System – IRAS-A-FPA-3-RDR-IMPS-V6.0: IRAS-A-FPA-3-RDR-IMPS-V6.0. Bibcode:2004PDSS...12.....T. Retrieved 15 June 2018.