He is a prolific discoverer of asteroids. The Minor Planet Center (MPC) credits him with the discovery of 35 numbered minor planets between 1997–1999. As of March 2016, the MPC ranks him 204th in the all-time, top-astronomer chart by number of discovered bodies. Antonini is also credited with the discovery of the supernovae SN 2000B and SN 2001dd. In January 2004, he co-discovered S/2003 (1089) 1, a minor planet moon orbiting the main-belt asteroid 1089 Tama.
The 7-kilometer sized main-belt asteroid 12580 Antonini, discovered by Laurent Bernasconi in 1999, was named in his honour.