21785 Méchain is a main belt asteroid with an orbital period of 1691.95 days (4.63 a). The asteroid was discovered by Milos Tichý at Kleť Observatory on 21 September 1999, and provisionally designated as 1999 SS2. On 24 June 2002, It was named in honor of a French astronomer and surveyor Pierre Méchain who with Charles Messier, was a major contributor to the early study of deep sky objects and comets.