<P> Asteroids are given a unique sequential identifying number once their orbit is precisely determined . Prior to this, they are known only by their systematic name or provisional designation, such as 1950 DA . </P> <P> Estimating the sizes of asteroids from observations is difficult due to their irregular shapes, varying albedo, and small angular diameter . For example, pure C - type asteroids are much darker than most . Asteroids with only one or two axes measured may have a falsely inflated geometric mean diameter if the unknown second or third axis is significantly smaller than the primary axis . Asteroid 16 Psyche has an IRAS diameter of 253 km, yet has a more recent and accurate geometric mean of only 186 km . </P> <Table> <Tr> <Th> Name </Th> <Th> Diameter (km) (geometric mean) </Th> <Th> Dimensions (km) </Th> <Th> Mean distance from Sun (in AU) </Th> <Th> Date discovered </Th> <Th> Discoverer </Th> <Th> Class </Th> </Tr> <Tr> <Td> 1 Ceres </Td> <Td> 7002946000000000000 ♠ 946 ± 2 </Td> <Td> 965 × 962 × 891 </Td> <Td> 2.766 </Td> <Td> January 1, 1801 </Td> <Td> Piazzi, G . </Td> <Td> </Td> </Tr> <Tr> <Td> 4 Vesta </Td> <Td> 7002525400000000000 ♠ 525.4 ± 0.2 </Td> <Td> 572.6 × 557.2 × 446.4 ± 0.2 </Td> <Td> 2.362 </Td> <Td> March 29, 1807 </Td> <Td> Olbers, H.W. </Td> <Td> V </Td> </Tr> <Tr> <Td> 2 Pallas </Td> <Td> 7002512000000000000 ♠ 512 ± 3 </Td> <Td> 7002550000000000000 ♠ 550 ± 4 × 7002516000000000000 ♠ 516 ± 3 × 7005476000000000000 ♠ 476 ± 3 km </Td> <Td> 2.773 </Td> <Td> March 28, 1802 </Td> <Td> Olbers, H.W. </Td> <Td> </Td> </Tr> <Tr> <Td> 10 Hygiea </Td> <Td> 7002431000000000000 ♠ 431 ± 7 </Td> <Td> 530 × 407 × 370 </Td> <Td> 3.139 </Td> <Td> April 12, 1849 </Td> <Td> de Gasparis, A . </Td> <Td> </Td> </Tr> <Tr> <Td> 704 Interamnia </Td> <Td> 326 </Td> <Td> 350 × 304 </Td> <Td> 3.062 </Td> <Td> October 2, 1910 </Td> <Td> Cerulli, V . </Td> <Td> </Td> </Tr> <Tr> <Td> 52 Europa </Td> <Td> 315 </Td> <Td> 380 × 330 × 250 </Td> <Td> 3.095 </Td> <Td> February 4, 1858 </Td> <Td> Goldschmidt, H . </Td> <Td> </Td> </Tr> <Tr> <Td> 511 Davida </Td> <Td> 289 </Td> <Td> 357 × 294 × 231 </Td> <Td> 3.168 </Td> <Td> May 30, 1903 </Td> <Td> Dugan, R.S. </Td> <Td> </Td> </Tr> <Tr> <Td> 87 Sylvia </Td> <Td> 286 </Td> <Td> 385 × 265 × 230 </Td> <Td> 3.485 </Td> <Td> May 16, 1866 </Td> <Td> Pogson, N.R. </Td> <Td> X </Td> </Tr> <Tr> <Td> 65 Cybele </Td> <Td> 273 </Td> <Td> 302 × 290 × 232 </Td> <Td> 3.439 </Td> <Td> March 8, 1861 </Td> <Td> Tempel, E.W. </Td> <Td> </Td> </Tr> <Tr> <Td> 15 Eunomia </Td> <Td> 268 </Td> <Td> 357 × 255 × 212 </Td> <Td> 2.643 </Td> <Td> July 29, 1851 </Td> <Td> de Gasparis, A . </Td> <Td> </Td> </Tr> <Tr> <Td> 3 Juno </Td> <Td> 258 </Td> <Td> 320 × 267 × 200 </Td> <Td> 2.672 </Td> <Td> September 1, 1804 </Td> <Td> Harding, K.L. </Td> <Td> </Td> </Tr> <Tr> <Td> 31 Euphrosyne </Td> <Td> 256 </Td> <Td> 255.9 ± 5.8 km </Td> <Td> 3.149 </Td> <Td> September 1, 1854 </Td> <Td> Ferguson, J . </Td> <Td> </Td> </Tr> <Tr> <Td> 624 Hektor </Td> <Td> 241 </Td> <Td> 370 × 195 (× 195) </Td> <Td> 5.235 </Td> <Td> February 10, 1907 </Td> <Td> Kopff, A . </Td> <Td> </Td> </Tr> <Tr> <Td> 88 Thisbe </Td> <Td> 232 </Td> <Td> 221 × 201 × 168 </Td> <Td> 2.769 </Td> <Td> June 15, 1866 </Td> <Td> Peters, C.H.F. </Td> <Td> </Td> </Tr> <Tr> <Td> 324 Bamberga </Td> <Td> 229 </Td> <Td> 229 × 235 × 229 </Td> <Td> 2.684 </Td> <Td> February 25, 1892 </Td> <Td> Palisa, J . </Td> <Td> </Td> </Tr> <Tr> <Td> 451 Patientia </Td> <Td> 225 </Td> <Td> 225 × 234 </Td> <Td> 3.059 </Td> <Td> December 4, 1899 </Td> <Td> Charlois, A . </Td> <Td> </Td> </Tr> <Tr> <Td> 532 Herculina </Td> <Td> 222 </Td> <Td> 260 × 220 × 215 </Td> <Td> 2.772 </Td> <Td> April 20, 1904 </Td> <Td> Wolf, M . </Td> <Td> </Td> </Tr> <Tr> <Td> 48 Doris </Td> <Td> 222 </Td> <Td> 278 × 142 </Td> <Td> 3.108 </Td> <Td> September 19, 1857 </Td> <Td> Goldschmidt, H . </Td> <Td> </Td> </Tr> <Tr> <Td> 375 Ursula </Td> <Td> 216 </Td> <Td> 189 × 192 × 194 </Td> <Td> 3.126 </Td> <Td> September 18, 1893 </Td> <Td> Charlois, A . </Td> <Td> </Td> </Tr> <Tr> <Td> 107 Camilla </Td> <Td> 215 </Td> <Td> 285 × 205 × 170 </Td> <Td> 3.476 </Td> <Td> November 17, 1868 </Td> <Td> Pogson, N.R. </Td> <Td> </Td> </Tr> <Tr> <Td> 45 Eugenia </Td> <Td> 213 </Td> <Td> 305 × 220 × 145 </Td> <Td> 2.720 </Td> <Td> June 27, 1857 </Td> <Td> Goldschmidt, H . </Td> <Td> </Td> </Tr> <Tr> <Td> 7 Iris </Td> <Td> 213 </Td> <Td> 240 × 200 × 200 </Td> <Td> 2.386 </Td> <Td> August 13, 1847 </Td> <Td> Hind, J.R. </Td> <Td> </Td> </Tr> <Tr> <Td> 29 Amphitrite </Td> <Td> 212 </Td> <Td> 233 × 212 × 193 </Td> <Td> 2.554 </Td> <Td> March 1, 1854 </Td> <Td> Marth, A . </Td> <Td> </Td> </Tr> <Tr> <Td> 423 Diotima </Td> <Td> 209 </Td> <Td> 171 × 138 </Td> <Td> 3.065 </Td> <Td> December 7, 1896 </Td> <Td> Charlois, A . </Td> <Td> </Td> </Tr> <Tr> <Td> 19 Fortuna </Td> <Td> 208 </Td> <Td> 225 × 205 × 195 </Td> <Td> 2.442 </Td> <Td> August 22, 1852 </Td> <Td> Hind, J.R. </Td> <Td> </Td> </Tr> <Tr> <Td> 13 Egeria </Td> <Td> 206 </Td> <Td> 217 × 196 </Td> <Td> 2.576 </Td> <Td> November 2, 1850 </Td> <Td> de Gasparis, A . </Td> <Td> </Td> </Tr> <Tr> <Td> 24 Themis </Td> <Td> 198 </Td> <Td> spheroid 198 </Td> <Td> 3.136 </Td> <Td> April 5, 1853 </Td> <Td> de Gasparis, A . </Td> <Td> </Td> </Tr> <Tr> <Td> 94 Aurora </Td> <Td> 197 </Td> <Td> 225 × 173 </Td> <Td> 3.160 </Td> <Td> September 6, 1867 </Td> <Td> Watson, J.C. </Td> <Td> </Td> </Tr> <Tr> <Td> 702 Alauda </Td> <Td> 195 </Td> <Td> 97.365 ± 1.6 km </Td> <Td> 3.195 </Td> <Td> July 16, 1910 </Td> <Td> Helffrich, J . </Td> <Td> C / B </Td> </Tr> <Tr> <Td> 121 Hermione </Td> <Td> 190 </Td> <Td> 268 × 186 × 183 </Td> <Td> 3.457 </Td> <Td> May 12, 1872 </Td> <Td> Watson, J.C. </Td> <Td> </Td> </Tr> <Tr> <Td> 259 Aletheia </Td> <Td> 190 </Td> <Td> 178 × 190 </Td> <Td> 3.135 </Td> <Td> June 28, 1886 </Td> <Td> Peters, C.H.F. </Td> <Td> C / P / X </Td> </Tr> <Tr> <Td> 372 Palma </Td> <Td> 189 </Td> <Td> 188 </Td> <Td> 3.149 </Td> <Td> August 19, 1893 </Td> <Td> Charlois, A . </Td> <Td> </Td> </Tr> <Tr> <Td> 128 Nemesis </Td> <Td> 188 </Td> <Td> 188 </Td> <Td> 2.751 </Td> <Td> November 25, 1872 </Td> <Td> Watson, J.C. </Td> <Td> </Td> </Tr> <Tr> <Td> 6 Hebe </Td> <Td> 186 </Td> <Td> 205x185x170 </Td> <Td> 2.426 </Td> <Td> July 1, 1847 </Td> <Td> Hencke, K.L. </Td> <Td> </Td> </Tr> <Tr> <Td> 16 Psyche </Td> <Td> 186 </Td> <Td> 240 × 185 × 145 </Td> <Td> 2.924 </Td> <Td> March 17, 1852 </Td> <Td> de Gasparis, A . </Td> <Td> </Td> </Tr> <Tr> <Td> 120 Lachesis </Td> <Td> 174 </Td> <Td> 184x144 </Td> <Td> 3.301 </Td> <Td> April 10, 1872 </Td> <Td> Borrelly, A . </Td> <Td> </Td> </Tr> <Tr> <Td> 41 Daphne </Td> <Td> 174 </Td> <Td> 213x160 </Td> <Td> 2.765 </Td> <Td> May 22, 1856 </Td> <Td> Goldschmidt, H . </Td> <Td> </Td> </Tr> <Tr> <Td> 9 Metis </Td> <Td> 174 </Td> <Td> 222x182x130 </Td> <Td> 2.385 </Td> <Td> April 25, 1848 </Td> <Td> Graham, A . </Td> <Td> </Td> </Tr> </Table> <Tr> <Th> Name </Th> <Th> Diameter (km) (geometric mean) </Th> <Th> Dimensions (km) </Th> <Th> Mean distance from Sun (in AU) </Th> <Th> Date discovered </Th> <Th> Discoverer </Th> <Th> Class </Th> </Tr>

What is the biggest asteroid in the solar system