Western Washington University   College of Sciences and Technology   Physics/Astronomy Dept.   Bellingham, WA USA
 
ASTRO 101

Analemma
Asteroids
Aurora
Big Bang
Black Holes
Bode Titius
Brightest Stars
Comets
Constellations
Coordinates
Cosmology
Cruithne
Dark Matter
Eclipses
Galaxies
Historical
HR Diagram
Hubble's Law
Intelligent Life
Kepler's Laws
Leap Year
Light Waves
Lunar Libration
Messier Objects
Meteors
Milky Way
Moon
Moon Phases
Planets
Precession
Rainbows
Redshift
Seasons
Stellar Evolution
Stardust
Sun & Fusion
Telescopes
Tides
Time of Day
Twilight
Zodiac
 
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 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 objectsTotal Volume (km3)
95014.49 x 108
40013.35 x 107
200134.19 x 106
100505.24 x 105
501306.55 x 104
255008.18 x 103
1032005.24 x 102
51800065.4
2.5960008.18
11000000.052

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.NameMean Oribit (Km)Radius (Km)Mass (Kg)DiscovererDate
2062Aten144,514,0000.5?Helin1976
3554Amun145,710,000??Shoemaker1986
1566Icarus161,269,0000.7?Baade1949
433Eros172,800,00033x13x13?Witt1898
1862Apollo220,061,0000.7?Reinmuth1932
2212Hephaistos323,884,0004.4?Chernykh1978
951Gaspra330,000,0008?Neujmin1916
4Vesta353,400,0002653.0x1020Olbers1807
3Juno399,400,000123?Harding1804
15Eunomia395,500,0001368.3x1018De Gasparis1851
1Ceres413,900,0004668.7x1020Piazzi1801
2Pallas414,500,0002613.18x1020Olbers1802
243Ida428,000,00035??1880?
52Europa463,300,000156?Goldschmidt1858
10Hygiea470,300,0002159.3x1019De Gasparis 1849
511Davida475,400,000168?Dugan1903
911Agamemnon778,100,00088?Reinmuth1919
2060Chiron2,051,900,00085?Kowal1977