The asteroid belt is a term used to refer to a circumstellar disc that is considered to be part of the solar system. The asteroid belt also goes by other names such as the main belt or main asteroid belt, to differentiate it from other asteroids in the solar system including the Trojan asteroids. The asteroid belt had puzzled scientists for decades from the time when Johannes Kepler implied the presence of a planet between Mars and Jupiter in his 1596 Mysterium Cosmographicum. Giuseppe Piazzi was the first astronomer to observe an object in the belt which he named "Ceres" on January 1, 1801. Fifteen months later, another astronomer named Heinrich Olbers sighted another object in the same region which he dubbed "Pallas." The expression "asteroids" was suggested by William Herschel in 1802 after the Greek term asteroeides which means "star-like". On July 16, 1972, Pioneer 10 became the first spacecraft to explore the asteroid belt. 12 spacecrafts have transversed the region since then and collected useful data.
Asteroid Belt: Definition
Most of the asteroids orbiting in the solar system are congregated in a region beyond Mars. Together, these asteroids make up the asteroid belt. Other asteroids orbit in regions near the Earth's space while others shift or are displaced to the outer system via gravitational forces. Asteroids can measure a few feet or several hundred miles in width. The asteroid belt is thought to have millions of asteroids that are over 0.5 miles in diameter. The largest of the asteroids in the belt is Ceres which is about 945 miles in diameter followed by Vesta whose diameter is about 326 miles. Ceres ranks as the only sigle dwarf planet within Neptune’s orbit. These two asteroids in addition to Pallas and Hygiea contain half of the mass of the entire belt. The mass of all of the asteroids when combined is less than that of the mass of the Moon. About one-third of the belt's asteroids are part of an asteroid family where members exhibit similar spectral characteristics. Examples of these families are Eos, Flora, and Themis.
Where Is The Asteroid Belt Located?
A frequent question asked is: The Asteroid Belt Is Found Between Which Two Planets? The belt lies in a region between the orbits of Jupiter and Mars. The belt can be subdivided into the inner and outer belts. The asteroids orbiting near Mars constitute an inner asteroid belt while those orbiting nearer to Jupiter constitute the outer asteroid belt.
How Did The Asteroid Belt Form?
Initially, scientists thought that the components of the asteroid belt were once part of a bigger planet that had previously occupied the area between Jupiter and Mars. This hypothesis is no longer popular due to several reasons. The vast quantity of energy necessary to destroy a planet as well as the low mass of the belt, which is just about 4% of the mass of the Moon do not give credence to the explanation. Further, the notable chemical distinctions between the asteroids suggest they were never part of one planet. The hypothesis that is generally accepted today suggests that the fragments never formed a planet. As the solar system was forming, rock and dust in the sun's vicinity were pulled and clumped together by gravity pull to create planetesimals and subsequently planets. Within the territory of the Asteroid Belt planetesimals were greatly perturbed by Jupiter's gravity to successfully form a planet. The asteroids thus continued to orbit the sun with the occasional collisions. In areas where the collisions had high average velocity, the fragmenting of planetesimals dominated over accretion. The asteroids melted to some level during the Solar System's early history, and thus the elements within them were either wholly or partially differentiated by mass. The asteroids have undergone significant evolution from the time of their formation including bombardment by micrometeorites and surface melting from impacts of collisions.
What Is The Asteroid Belt Made Of?
A large number of asteroids are made up of rocks while some of them contain metals elements such as nickel and iron. Other asteroids contain a mixture of these elements together with carbon-rich elements. Distant asteroids may contain more volatiles elements and ice. The belt has three major groups of asteroids. Carbonaceous asteroids which account for more than 75% of the visible asteroids are rich in carbon, and they populate the outer regions of the belt. S-type asteroids are rich in silicate, and they are mainly located towards the belt's inner region. These asteroids contain no significant levels of carbonaceous materials which suggest that they have been altered significantly over time. M-type asteroids constitute about 10% of the belt's asteroids, and they contain iron-nickel and silicate materials. There is also the V-type of asteroids which are rare and are made of basaltic elements. Contrary to popular imagery, the region occupied by the Asteroid Belt is largely empty, and the asteroids are spread over a vast volume of space. Currently, hundreds of thousands of the belt's asteroids have been identified while the total number is projected to be in the millions or even more.
How Far Is The Asteroid Belt From The Sun?The belt’s distance ranges between 2.2 to 3.2 AU away from the Sun. The core cluster of the belt can be subdivided into three zones according to Kirkwood gaps. The gaps are named in honor of Daniel Kirkwood who in 1886 explained the existence of gaps in the asteroids’ distance. Zone I falls between the 4.2 resonance (2.06 AU) to the 3.1 resonance (2.5 AU) Kirkwood gaps. Zone II extends from the edge of the first zone all the way to the 5.2 resonance gap that is 2.82 AU away from the Sun. Zone III continues at the end of the second zone all the way to the 2.1 resonance gap whose distance from the sun is 3.28 AU. The belt's inner boundary consists of asteroids with a radius of 2.06 Au away from the Sun. The temperature of the belt fluctuates with the varying distance from the Sun. The dust elements close to the belt at 2.2 AU have a temperature of -73 degrees Celsius while that of the particles at 3.2 AU is -108 degrees Celsius.
What Is An Asteroid Belt?
Most of the asteroids orbiting in the solar system are congregated in a region between the orbits of Mars and Jupiter. Together, these millions of asteroids make up the asteroid belt.
About the Author
Benjamin Elisha Sawe holds a Bachelor of Arts in Economics and Statistics and an MBA in Strategic Management. He is a frequent World Atlas contributor.
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