| Year,Mass,Notes | |
| 1931,1 Earth,Nicholson & Mayall | |
| 1942,0.91 Earth,Wylie | |
| 1948,0.1 (1/10 Earth),Kuiper | |
| 1973,0.025 (1/40 Earth),Rawlins | |
| 1976,0.01 (1/100 Earth),"Cruikshank, Pilcher, & Morrison" | |
| 1978,0.002 (1/500 Earth),Christy & Harrington | |
| 2006,0.00218 (1/459 Earth),Buie et al. | |