Asteroid, the small planet

Did u ever watch "Deep Impact" ???Or "Armageddon" ??? I think u ever watched it...So exclaimed,right ???. The movie story about the asteroids that will hit earth...Could u imagine when an asteroid hit Earth ???It will be a  big big big disaster,the "dooms day"...Because of this ,the dinosaurs was extincted.

Asteroid Belt

Asteroid(planetoid also minor planet) is rock that orbiting the sun. Asteroid placed in the Asteroid belts,where between Mars and Jupiter. There are many asteroid with different size, beginning from 1 km diameter size until 1000km (Ceres,the biggest) . The asteroids amount in our solar are about 1million. Over 8,000 of these have been individually cataloged and named, and have well-determined orbits. Although it is common to depict the asteroid belt as a dense region, asteroids are actually quite well separated, rarely approaching within 1 million km of one another. (A few asteroids have moons of their own: these are certainly the exception to the rule.) All together, the asteroid belt contains about 0.1% of the mass of the Earth. Earth mass is about 5.98 x 10 ²⁴ kg. So it is 5.98 x x 10 ^{21 kg}

Asteroid Ida with ts satelitte(Dactyl)

Ceres

In addition to the asteroids in the belt, some asteroids share Jupiter’s orbit. Asteroids in this special group are called Trojan asteroids, and they orbit about 608 ahead or behind Jupiter. Their orbits are stabilized by the combined gravity of Jupiter and the Sun. Over 150 of these are known; the largest is about 300km in size.

Astronomers estimate that the asteroid was created the same time as our solar system. They are byproduct. As theory said that planets formed by the joining of the asteroids. Asteroids on the Asteroid belt is the rest of solar system material when was created. They have stable gravitional in there.

An asteroid approching erth

Finally, some asteroids are ‘‘Earth-crossing’’ and are potential impactors. These asteroids come from three different groups—the Apollo, Aten, and Amor asteroids. Most of these are small, less than 40km across, and so they are difficult to find in the sky. About 500 are known. Most of these will strike the Earth some time over the next 20–30 million years. Near-misses are common, and are often unpredicted. In 1990, an asteroid came closer to the Earth than the Moon. The asteroid was previously undiscovered, and was not noticed until after it had safely passed the
Earth.

Asteroids do not emit visible light, they only reflect it. Astronomers determinethe compositions of asteroids by comparing the spectrum of the light reflected by the asteroid and the spectrum of the Sun. Absorption lines that are present in the asteroid’s spectrum, but not in the solar spectrum, must be due to elements or minerals in the asteroid. Asteroids are classified in three major groups: carbonaceous (C), silicate (S), and metallic (M). Most asteroids are C-type asteroids, with very low albedo and no strong absorption lines. The rest are mainly S type, with an absorption feature due to a silicate mineral, olivine.


The amount of light reflected from an asteroid towards the Earth changes as the asteroid tumbles through space. We can use this information to determine how quickly the asteroids rotate. About 500 asteroids have been studied well enough to determine their rotation periods, which are generally between 3 and 30 hours.
Smaller asteroids have irregular shapes. The shape of small asteroids can be determined from analysis of the amount of radiation received over time (light curve).


Source : http://en.wikipedia.org/wiki/Asteroid
             Schaum's Outlines of Astronomy 

What's different between Meteoroid , Meteor, and Meteorite?

Confuse about Meteoroid , Meteor ,and Meteorite??? Same with me, at first i confuse about three kind of this word...but know i hadn't confuse again...want to know the different???Let's check it out...

When a small rock or bit of dust is floating in space, it is a meteoroid. As it falls through the atmosphere of the Earth, it produces a bright streak of light, and is called a meteor. When it actually makes it to the surface of a planet or moon, we call the rock a meteorite. The brightest meteors are called fireballs. Sometimes these are as bright as the full moon. Micrometeorites are meteorites that are as small as sand grains. These are so small that the atmosphere slows them without heating them, and they drift to the surface of the planet. Imagine,about 100 tons of micrometeorites accumulate on Earth every day.WOW!!!

Why on the moon there are so many crater???
On the Moon, however, there is no atmosphere. So, the meteors won't burn because there is no atmosphere. At last, the meteor will impact the moon surface and cause crater.

There are three basic types of meteorites: iron, stony, and stony-iron
1.  Iron Meteorites
Iron meteorites are the easiest to recognize. Why???Because this meteorites are overly heavy for their size, because they have a high proportion of iron. These meteorites come from planetesimal-sized chunks of rock

Iron meteorite

2.  Stony Meteorites
Stony meteorites resemble ordinary rocks. Consequently, stony meteorites are 

much less likely to be found, even though they are much more common than iron 

meteorites. Did u know that 95% of the meteorites that fall to Earth are stony meteorites???It's true. 

Stony 

meteorites have about the same density as ordinary rock,and hence are more difficult to find. Most of these stony meteorites are found in places like Antarctica, or the Sahara desert, where there are few ordinary rocks on the surface.Most stony meteorites contain rounded particles imbedded in the rest of the rock. These lumps are called chondrules and the entire stony meteorite isthen called a chondrite. Carbonaceous chondrites are a special kind of chondrite that contain high levels of carbon and often contain amino acids, the building blocks of proteins.

Stony Meteorite

3.  Stony - iron meteorite

Stony-iron meteorites, a hybrid in which pieces of metal are embedded in ordinary 

silicate rock, are less than 1% of the total number of meteorites that fall to Earth.

Stony-iron meteorite

The majority of meteorites probably come from the asteroid belt. Asteroids are

large enough to have held the heat of the early solar system for millions of years.

This allowed them to differentiate, so that the iron fell to the center, surrounded by

a thin stony-iron layer, and enveloped in a thick stone ‘‘crust.’’ When two such

objects collide, the fragments consist of lots of stony meteoroids, fewer iron

meteoroids, and a very small number of stony-iron meteoroids. These fragments

spray away from the collision site, and a few of them eventually find their way to

planets. Other sources of meteorites are comets, the Moon, and Mars.