Asteroids

The majority of asteroids are rocky planetoids orbiting the Sun between the orbits of Mars and Jupiter. This region is known as the Asteroid Belt. There are also groups of asteroids both 60 degrees ahead and 60 degrees behind Jupiter in its orbit. These are called Jupiter Trojan Asteroids. Another two groups ahead and behind Mars are called Martian Trojans. Asteroids have been found elsewhere in the solar system, including inside Earth's orbit of the Sun. Some, like Cruithne, have very odd orbits.

Most asteroids are the size of gravel but 16 asteroids have a diameter of 240 km or more. Ceres is the largest asteroid. It has a diameter of about about 914 km which is roughly the size of Texas.

Since the orbital radius of the average asteroid in the asteroid belt closely satisfies the prediction of the Bode Titius Rule, it seems reasonable (at first) to speculate about asteroids in terms of a "failed planet." In view of this hypothesis, consider the following observations.

This graph shows the number of discovered asteroids and their size. The data are more complete for the larger objects because they are easier to see in telescopes.

Ceres, the largest of all the asteroids, was first found by the Italian astronomer Giuseppe Piazzi who discovered it by chance in 1801. It was in fact the first asteroid ever discovered.

The diameter of Ceres is about 1000 km. The diameter of Mars is a little less than 7000 km. Although neither is a perfect sphere (especially Ceres), use the volume of a sphere (4/3 pr3) to estimate how many Ceres-sized asteroids would fit into a volume the size of Mars: 343


Here is a table that shows the number of asteroids in groups according to size, and the total volume of material in each group.

Diameter (km) Number of objects Total Volume (km3)
950 1 4.49 x 108
400 1 3.35 x 107
200 13 4.19 x 106
100 50 5.24 x 105
50 130 6.55 x 104
25 500 8.18 x 103
10 3200 5.24 x 102
5 18000 65.4
2.5 96000 8.18
1 1000000 .052


Add up the values in the last column to estimate the total volume of material that is contained within the asteroid belt: 4.87 x 108 km3 The volume of the Earth is roughly 1.0 x 1012 km3. What approximate percentage of the Earth's volume does the sum of all the asteroid volume represent? 0.0487%, an extremely small fraction of the volume of the Earth!

The Largest Asteroids
No. Name Mean Oribit (Km) Radius (Km) Mass (Kg) Discoverer Date
2062 Aten 144,514,000 0.5 ? Helin 1976
3554 Amun 145,710,000 ? ? Shoemaker 1986
1566 Icarus 161,269,000 0.7 ? Baade 1949
433 Eros 172,800,000 33x13x13 ? Witt 1898
1862 Apollo 220,061,000 0.7 ? Reinmuth 1932
2212 Hephaistos 323,884,000 4.4 ? Chernykh 1978
951 Gaspra 330,000,000 8 ? Neujmin 1916
4 Vesta 353,400,000 265 3.0x1020 Olbers 1807
3 Juno 399,400,000 123 ? Harding 1804
15 Eunomia 395,500,000 136 8.3x1018 De Gasparis 1851
1 Ceres 413,900,000 466 8.7x1020 Piazzi 1801
2 Pallas 414,500,000 261 3.18x1020 Olbers 1802
243 Ida 428,000,000 35 ? ? 1880?
52 Europa 463,300,000 156 ? Goldschmidt 1858
10 Hygiea 470,300,000 215 9.3x1019 De Gasparis 1849
511 Davida 475,400,000 168 ? Dugan 1903
911 Agamemnon 778,100,000 88 ? Reinmuth 1919
2060 Chiron 2,051,900,000 85 ? Kowal 1977