| Asteroids are known as minor planets because they are too small to be considered as planets. They range from the size of a grain of sand up to that of Texas. Some are found within the Earth's orbit to beyond Saturn's orbit. Most asteroids are found in the asteroid belt which is located between the orbit of Jupiter and Mars. Asteroids are rocky material left over from the formation of the Solar System. They may also be remains of planets destroyed in collision long ago. They are rather irregular in shape because most of them are not massive enough for their own gravity to force them into spherical shape. The total mass of all the minor planets put together is less than any of the major planets. There are mainly 4 types of compositional groups: silicon-rich (S type), nickel-iron-rich (M type), carbon-rich type (C type) and those rich in organic compounds (D type). Silicon-rich asteroids are reddish in color and reflect about 15 percent light. Carbon-rich asteroids are dark in color and reflect only about 3 percent light. Nickel-iron asteroids are only 5 percent the amount of all the existing asteroids. Although majority of asteroids are situated between Mars and Jupiter near the ecliptic plane, some like Hidalgo, has an elongated orbit which is inclined by over 40o to the ecliptic plane. Apollo asteroids are those few dozen asteroids whose orbits come close to the earth. The most important of these in history was Eros, which came within 26 million km of the Earth in 1901 and 1931. Another group of asteroids are called the "Trojans". They are located in Jupiter's orbit. These Trojan asteroids are an example of the important gravitational effects of Jupiter. |
| Number | Name | Radius (km) | Distance (106km) | Discoverer | Date |
|---|---|---|---|---|---|
| 1 | Ceres | 457 | 413.9 | G. Piazzi | 1801 |
| 511 | Davida | 168 | 475.4 | R. Dugan | 1903 |
| 15 | Eunomia | 136 | 395.5 | De Gasparis | 1851 |
| 52 | Europa | 156 | 463.3 | Goldschmidt | 1858 |
| 951 | Gaspra | 17x10 | 205.0 | Neujmin | 1916 |
| 10 | Hygiea | 215 | 470.3 | De Gasparis | 1849 |
| 243 | Ida | 58x23 | 270.0 | J. Palisa | 29 Sep 1884 |
| 704 | Interamnia | 167 | 458.1 | V. Cerulli | 1910 |
| 2 | Pallas | 261 | 414.5 | H. Olbers | 1802 |
| 16 | Psyche | 132 | 437.1 | De Gasparis | 1852 |
| 87 | Sylvia | 136 | 521.5 | N. Pogson | 1866 |
| 4 | Vesta | 262.5 | 353.4 | H. Olbers | 1807 |