It was discovered on 15 April 1996, by Belgian astronomer Eric Elst at the La Silla Observatory in northern Chile.
[1] The assumed C-type asteroid is one of the 60 largest Jupiter trojans and has a rotation period of 15.82 hours.
[3] In August 2011, a rotational lightcurve of Prothoon was obtained from photometric observations by Robert Stephens at the Goat Mountain Astronomical Research Station (G79) in California.
[3][9] According to the surveys carried out by the Japanese Akari satellite, the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer, and the Infrared Astronomical Satellite IRAS, Prothoon measures between 62.41 and 64.31 kilometers in diameter and its surface has an albedo between 0.039 and 0.052.
[6][7][8] The Collaborative Asteroid Lightcurve Link derives an albedo of 0.0467 and a diameter of 64.41 kilometers based on an absolute magnitude of 9.9.