- Comets, Asteroids and Meteors are the part of Solar System. These celestial bodies revolve around the sun due to gravitational attraction between sun and these bodies.
- Asteroids:
- Asteroids lie in the space between Mars and Jupiter. They revolve around the sun in the same manner as the planets do in an elliptical orbit. This asteroid belt is also known as main asteroid belt.
- Scientists believe that these asteroids are part of a planet which is exploded and never unites again due to the strong gravitational force of the Jupiter.
- While some scientists believe that these asteroids are leftover of solar system formation, 4.6 billion years ago.
- They never get collide each other into a planet formation due to the strong gravitational force of Jupiter. Hence they remain in broken state of irregular shaped rock which revolves around the sun.
- These asteroids are irregular in shape and size; some of them are hundreds of km in radius while others are only of few meters in radius.
- Largest among these asteroids is Ceres which is 946 km in diameter after Ceres, Vesta is the second largest asteroids among them. It is also in round shape and occupies 25 % of the total mass of the asteroids.
- Composition of asteroids differs from each other; they are made up of different kinds of rocks however most of them also have metallic composition of nickel and iron.
- Trojan Asteroids: Trojan asteroids or simply Trojans are asteroids which share the orbit of a planet and located at leading (L4) and trailing (L5) Lagrangian point. It should be noted that Trojan asteroids are also discovered for different planets but the term Trojan asteroids generally refers to the Trojan asteroids of Jupiter.
- This Asteroid belt separates the inner planet region from the outer planet region of the solar system.
- Uses: These asteroids are formed at the same time during the formation of solar system. Scientists can discover a lot of thing from these rocks like formation process of sun and planets. Scientists can do research on asteroids through meteorites which some time falls on the earth surface without burning to ashes.
- Exploration: NASA’s spacecraft the NEAR shoemaker landed on Eros which lies near the earth for exploration. The DAWN space probe of NASA has orbited and studied the second largest asteroid Vesta. After studying Vesta DAWN went to largest asteroid Ceres for studying and exploration. NASA has also launched spacecraft OSIRIS-Rex for exploring asteroid BENNU which is near to the earth. BENNU has also brought a rock sample for further study on asteroids.
- Meteoroids:
- Meteoroids are small celestial bodies moving around the Sun whose diameter differs from few millimetres to several kilometres.
- They are generally smaller than asteroids.
- According to their composition they can be categorised into rocky and metallic meteoroids.
- Iron and nickel occupies 90 % in the total composition of metallic meteoroids whereas rocky meteoroids are composed of several elements like oxygen, iron, nickel, silicon, magnesium etc.
- Meteors:
- When meteoroids come closer to the earth they were attracted by the earth’s gravitational force and enters into to the earth’s atmosphere.
- When they enters in to the earth’s atmosphere they encounters friction with the atmosphere and hence they heated up and burns causing a flash of light.
- This light produced by burning of meteoroids can be seen from a large area on the surface of the earth.
- This streak of light produced by burning of meteoroids in the atmosphere of earth is known as meteors.
- Meteors are informally known as falling stars or shooting stars.
- Fireballs: These are the meteors which are brighter than usual meteors.
- Bolide: They are synonymous to the fireballs. They are generally brighter meteors which generally explode in the atmosphere.
- Meteor Shower: Whenever earth catches up or passes through debris of broken comets showers of lights produced due to burning of this debris into the atmosphere of the earth. This process is called meteor showers. Some meteor shower occurs in a fixed interval in a year.
- Meteorites:
- Sometimes meteors which are slightly big in size do not burn completely into the atmosphere of the earth and strikes the surface of the earth. These meteors in astronomy are known as meteorites.
- Metallic meteorites contains large proportion of iron and nickel as there composition and stony meteorites contains rocky material in large proportion and also few percentage of iron and nickel.
- In India Lonar lake in Maharastra is form by the meteorites strike.
- Hoba Meteorites: It strikes the earth’s surface in Namibia. It is composed of 84 % iron, 16 % nickel and small amount of cobalt. Its mass is about 60 tonnes and is largest meteorite on the earth.
- Barringer Meteor Crater: This crater is having a diameter more than a kilometre lies in Arizona. Scientists believe that this crater was formed about 49000 years ago.
- Comets:
- Comets are having rocky composition and are surrounded by easily vaporising materials like ice, water, ammonia, methane.
- They revolve around the sun and their orbit is highly elliptical with a very high time period of revolution around the sun.
- When the comets approaches the sun, easily vaporising materials surrounding the comets vaporises and forms a cloud known as comma.
- Materials from the comma moves away due to the force exerted by solar radiation and produce a tail which glows in the suns light. This process is called as out-gassing.
- Comets have a bright head and a long tail. This tail of comet increases as it approaches towards Sun and its tail is always away from the sun. This are nothing but out-gassing of easily vapourising materials which shines in the Sun light and appears from the earth like a glowing torch.
- Periodic comets are often written with a prefix ‘P’ which indicates the comet is periodic.
- Halley, Encke, Tempel-Tuttle, swift Tuttle are few of the comets which are popular.
- Dead Comets: When a comet is out-gassed with no volatile material left around it no comma and tail appears when it approaches towards Sun. Such comets are known as dead comets.
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