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comets and asteroids

The gases and debris left over after the creation of the Sun eventually became the planets through the force of gravity. 

The four inner planets are rocky and the outer planets are gaseous.

Not all of the matter from a nebula becomes stars. In the case of our Solar System, some of the matter was further away from the Sun and produced  planets, asteroids and moons. Near the Sun the temperature is too high for gas to be more attracted to the planet than to the Sun so rocky planets are formed. Further away from the Sun it is colder and planets can have liquid and gas surrounding them, held in place by gravity.


Asteroids are a group of small rocky bodies that form a belt between the planets Mars and Jupiter in our Solar System. Comets are large masses of ice and dust that circle outside the orbit of known planets. Sometimes an outer planet comes near enough to cause one of them to be diverted towards the Sun. It then follows an elliptical orbit.


Asteroids are rocky objects, smaller than planets. Most of them are found in an 'asteroid belt', in orbit around the Sun between Mars and Jupiter. The asteroid belt or orbit is fairly circular.

 Asteroids can crash into each other. When they do, they may break apart and their orbit may change.

The orbits of some asteroids cross the Earth's orbit. At various times during the Earth's history,   asteroids have hit the Earth. 


It is thought that it was the collision of an asteroid with the Earth that helped to drive the dinosaurs to extinction. 

Scientists worry that an asteroid could still hit the Earth and cause a global catastrophe


Comets are balls of ice and dust that orbit the Sun, probably formed in the outer solar system.  Their orbits are different to those of planets: they are highly elliptical (an oval).

A comet’s orbit takes it very close to the Sun, then far away, beyond the planets.

The time to complete an orbit varies. Some comets take a few years, others millions of years.

Comets are often visible from Earth when they get close to the Sun. This is because the Sun’s heat vaporizes material from their surface, forming a tail of debris.


The speed of a comet increases as it approaches the Sun. This is because the strength of gravity increases.

      The dangerous of comets and asteroids 

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