Asteroid pair

In 1993, Andrea Milani suggested that Antilochus forms an asteroid pair with 3801 Thrasymedes, using the hierarchical clustering method (HCM), which looks for groupings of neighboring asteroids based on the smallest distances between them in the proper orbital element space.^[15] The astronomer describes the finding as statistically significant though difficult to account for by a regular collisional event.^[15] The Antilochus–Thrasymedes pair is not listed at the Johnston's archive.^[16]

Rotation period

In December 2009 and June 2016, rotational lightcurves of Antilochus were obtained from photometric observations by American astronomer Robert Stephens at the Santana Observatory (646) and at the Center for Solar System Studies (CS3) in California. Lightcurve analysis gave a rotation period of 31.52 and 31.54 hours with an amplitude of 0.09 and 0.11 magnitude, respectively (U=2/2).^[18][19] Follow-up observations over a total of 11 nights by Stephens in August 2017 gave the so-far best-rated lightcurve with a period of 15.889±0.005 hours – which corresponds to half the period solution of the former results – and a slightly higher brightness variation of 0.12 magnitude (U=2+).^{[11][lower-alpha 1]}

Stephen's period determination supersedes previously reported results by Vincenzo Zappalà (1985; 12 h), Federico Manzini (2007; 12 h) and René Roy (2009; 22.5 h) (U=3−/3).^[5][20][21]

Diameter and albedo

According to the surveys carried out by the Infrared Astronomical Satellite IRAS, the Japanese Akari satellite, and NASA's Wide-field Infrared Survey Explorer with its subsequent NEOWISE mission, Antilochus measures between 101.62 and 111.69 kilometers in diameter and its surface has an albedo between 0.053 and 0.063.^[8][9][10] The Collaborative Asteroid Lightcurve Link adopts the results obtained by IRAS, that is, an albedo of 0.0633 and a diameter of 101.62 kilometers, with Pravec's revised absolute magnitude of 8.59.^[5]