The Asteroid Belt
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 pr^{3})
to estimate how many Ceressized 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 (km^{3}) 
950  1  4.49 x 10^{8} 
400  1  3.35 x 10^{7} 
200  13  4.19 x 10^{6} 
100  50  5.24 x 10^{5} 
50  130  6.55 x 10^{4} 
25  500  8.18 x 10^{3} 
10  3200  5.24 x 10^{2} 
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 10^{8} km^{3}
The volume of the Earth is roughly 1.0 x 10^{12} km^{3}. 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  3.0x10^{20}  Olbers  1807 
3  Juno  399,400,000  123  ?  Harding  1804 
15  Eunomia  395,500,000  136  8.3x10^{18}  De Gasparis  1851 
1  Ceres  413,900,000  466  8.7x10^{20}  Piazzi  1801 
2  Pallas  414,500,000  261  3.18x10^{20}  Olbers  1802 
243  Ida  428,000,000  35  ?  ?  1880? 
52  Europa  463,300,000  156  ?  Goldschmidt  1858 
10  Hygiea  470,300,000  215  9.3x10^{19}  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 
