Asteroids are small heavenly bodies, which move around the sun like the planets. Thus they also called planetoids. Most of them go around the sun in the asteroid belt. There are millions of asteroids. They called also Minor Planets. Total mass of all asteroids is less than mass of the earth’s moon. But in size they can be dangerous. in past, many asteroids has crash into earth and in future will be hit into Earth. So that’s one reason why scientists study them. In asteroid belt, which is lie between the orbits of Mars and Jupiter, there are more than 200 asteroids which diameter larger than 100 km and scientists also estimated more than 7,50,000 asteroids in asteroid belt which diameter is larger than 1 km.
Comets are small heavenly bodies which has been sighted many times in the sky like Halley’s comet. They are characterized by a different orbit and a bright glowing tail. Comets are icy bodies that releases gas and dust. Some scientists believe that some comets have life like earth because some comets have life organic molecules and water.As a comet gets closer to the sun, the ice on the surface of the nucleus begins turning into gas, forming a cloud known as the coma. Radiation from the sun pushes dust particles away from the coma, forming a dust tail, while charged particles from the sun convert some of the comet’s gases into ions, forming an ion tail. Since comet tails are shaped by sunlight and the solar wind, they always point away from the sun. At first glance, comets and asteroids may appear very similar.
The nuclei of most comets are thought to measure 10 miles (16 kilometers) or less. Some comets have comas that can reach nearly 1 million miles (1.6 million km) wide, and some have tails reaching 100 million miles (160 million km) long.
We can see a number of comets with the naked eye when they pass close to the sun because their comas and tails reflect sunlight or even glow because of energy they absorb from the sun. However, most comets are too small or too faint to be seen without a telescope.
Meteorites are cosmic chunks of rock. When they enter in the atmosphere, impact pressure causes the body to heat up and emit light, thus forming a fireball, also known as a meteor or shooting/falling star. They may occur very frequently. A meteorite may range in size from less than a gram to more than 60 tons. They are exist in asteroid belt. Meteorites land at random everywhere on Earth. Most land in the oceans and are not at present recovered from the water. Of those that fall on the land many are also not recovered. Meteorites often arrive in a very dramatic display with blinding light, smoke trails and thunderous detonations. The meteoroid exploding into many fragments high in the air. Meteorites can also arrive as individual pieces with less notice. In the past when there were no detection methods available many meteorites would go unrecovered.
We can make estimates based on the meteorites found about how often large events occur. A handful of larger objects strike the Earth everyday. So many thousands of small ones hit the Earth that it grows heavier by tons of weight each day.