Why didn't the asteroids form a planet?

Answer 1

A solar system starts out as a star surrounded by a "proto-planetary disk", a huge flat disk of gas, dust and rock, all attracted to the stars large gravity.

Over time, large objects in the disk attract dust and rock to themselves. They get bigger and bigger and... eventually you get a planet. Objects that attracted mostly gas formed gas giants like Jupiter and Saturn, objects that attracted mostly rock formed rocky planets like Earth and Mars.

Asteroids are basically what was left over, what didn't form planets. The asteroid belt between Mars and Jupiter is actually the remains of a "proto-planet" that didn't quite stick together in the formation of the solar system. It got ripped apart by Jupiter's gravity.

Answer 2

Scientists believe that the material in the asteroid belt was never a planet, that the asteroids formed in place as asteroids.

Some early theories of the formation of the solar system suggested that there should have been a planet between the orbits of Mars and Jupiter, and near the end of the 1700's, a number of astronomers searched for one there. The discovery of Ceres seemed to confirm their ideas, but the rapid discoveries of dozens of other similar objects gave rise to the idea that there had once been a planet there, that tidal stresses between this planet and Jupiter had caused it to be destroyed, and than the asteroid belt was the remnants of this destroyed planet. Ceres, Vesta, Juno and Pallas, then, become the largest remnants.

As fascinating as this concept is, there is no evidence that the asteroids were ever part of a planet. It is believed that planetesimals in the main asteroid belt evolved much like the rest of the Solar Nebula until Jupiter neared its current mass, at which point excitation from orbital resonances with Jupiter ejected over 99% of planetesimals in the belt. Both simulations and a discontinuity in spin rate and spectral properties suggest that asteroids larger than approximately 120 km in diameter accreted during that early era, whereas smaller bodies are fragments from collisions between asteroids during or after the Jovian disruption. At least two asteroids, Ceres and Vesta, grew large enough to melt and differentiate, with heavy metallic elements sinking to the core, leaving rocky minerals in the crust.

Answer 3

The gravitational forces within the asteroid belt were too weak to allow the asteroids to coalesce into a planet. Instead, the asteroids remained separate due to the disruptive effects of Jupiter's gravity, preventing them from merging into a larger body.

Answer 4

The amount of gravity was too little to hold the fragments into the air

Answer 5

No it was not.