Theasteroid belt ormain belt is a ring of small and large rocks and dust between theorbits ofMars andJupiter. The biggest object in the asteroid belt isCeres, adwarf planet. TheKirkwood gaps separate the asteroid belt into several groups. The belt istoroidal in shape.
Mostasteroids orbit at 2 to 3 times the distance between Earth and the Sun. Planets that are "inside" - or before - the asteroid belt (which means they are closer to the sun) are calledinner planets. Planets that are "outside" - that is, after - the asteroid belt are calledouter planets: soMercury,Venus,Earth, andMars areinner planets, whileJupiter,Saturn,Uranus andNeptune are theouter planets.
In 1802, shortly after discovering2 Pallas,Heinrich Olbers suggested toWilliam Herschel thatCeres andPallas were fragments of a much larger planet that once occupied the Mars–Jupiter region, this planet having suffered an internal explosion or a cometary impact many million years before.[1] Thishypothesis has fallen from favor. The large amount of energy needed to destroy a planet, and with the belt's low combined mass (only about 4% of the mass of theMoon) do not support the hypothesis. Also, the significant chemical differences among the variousasteroid spectral types are difficult to explain if they come from the same planet.[2] Today, most scientists accept that the asteroids never formed a planet at all.
TheSolar System formed when a cloud of interstellar dust and gas collapsed under the influence ofgravity to form the Sun andplanetesimals, and eventually the planets.[3] This gravitational accretion led to the formation of the rocky planets and thegas giants.
Planetesimals in the region which would become the asteroid belt were too strongly disturbed by Jupiter's gravity to form a planet. Instead they continued to orbit the Sun as before, while occasionally colliding.[4] In regions where the velocity of the collisions was too high, the shattering of planetesimals was more common than accretion,[5] preventing the formation of planet-sized bodies.
↑Masetti, M.; and Mukai, K. (2005)."Origin of the Asteroid Belt". NASA Goddard Spaceflight Center. Retrieved2007-04-25.{{cite web}}: CS1 maint: multiple names: authors list (link)
