It was discovered on 2 December 1991, by American astronomer Carolyn Shoemaker at the Palomar Observatory in southern California, United States.
[1] The assumed C-type asteroid has a rotation period of 6 hours, a notably eccentric orbit of 0.27, and belongs to the 40 largest Jupiter trojans.
[4] Several rotational lightcurve of Achates have been obtained from photometric observations by Robert Stephens, Stefano Mottola and Lawrence Molnar since 1992.
[10][11][a] The best-rated measurement made at the robotic Calvin–Rehoboth Observatory in February 2007, gave a rotation period of 5.958 hours with a brightness amplitude of 0.32 magnitude (U=3).
[7][8][9] The Collaborative Asteroid Lightcurve Link derives an albedo of 0.0526 and a diameter of 91.82 kilometers based on an absolute magnitude of 9.0.