GS8: Difference between Asteroid, Comet, Meteoroid, Meteor and Meteorite

The Earth has risen from its state of planetesimals to that of today by incorporating infinite, countless other planetesimals or other solid materials lying in its orbit around the sun during the early days of the Solar System. These collisions stopped nearly 4.0 Ga, but even today collisions with space objects continue which is splendidly observed as ‘Meteor Shower’. Over hundreds of tons of material in the form of dust, rock, and metal fall on Earth, every year. Period of Late Heavy Bombardment There was a period of Late Heavy Bombardment (also known as Lunar Cataclysm) which spanned during the Neoheadean to Eoarchean eras on Earth when the early terrestrial planets of the solar system encountered a large number of asteroids leftover from the accretion of planetesimals into planets. Several hypotheses are put forth to explain the soar of the flux of impactors in the Solar System, but no consensus yet exists. Due to the lack of atmosphere on Mars and Moon, these impactor sites are preserved with a little modification by seldom impacts suffered, later this event. However, similar facts cannot be traced with the same preciseness on the Earth as well as Venus. This question is for you, why is this so? Don’t worry as we will move forward we will answer every question that is in your mind. What are these objects which collide with the Earth? These are materials derived from the early protoplanets which either failed to rise, like ours, or collided with other protoplanets and turned into fragments. Mostly they are of asteroidal origin. They might also be fragments of materials ejected into space from Mars or Moon when large objects collided with them. The number of these materials strolls along the path of the Earth around the Sun. Asteroid: Space objects bigger than 10 m and orbiting the Sun. They are known to occur in a belt between Mars and Jupiter. Beyond this belt lies the snow line, after which the volatile materials are condensed into ice form. Remember we do not limit ice for solid forms of water. Comets: They are a cosmic ball of frozen gases having a core similar to that of Asteroid. When they approach the Sun from the outer space, certainly from Kuiper belt, the frozen gases sublimate and have a tail of vapors of gases and dust which is directed away from the Sun. What is the difference between Meteoroid, Meteor and Meteorite? Three names- Meteoroid, Meteors, and Meteorite; are the super twins or triplets which often confuse people. If not read or remembered in the sequence written you may commit a mistake. Meteoroid: Any object from space that will enter the Earth’s atmosphere to make a meteor is known as Meteoroid. Meteor: Objects which enter the atmosphere of the Earth are called Meteors. They leave a streak of bright, glowing, gas behind them as they fall through the atmosphere because of the friction offered by the atmospheric constituents which heat them up and vaporizes its material. They are often called ‘Falling Star’. Most visible meteors completely vaporize by an altitude of about 30 km. However, the dust size may slow down sufficiently to float down to Earth and larger ones can survive the heat from the friction during the entry and may crash on the surface. Meteorite: Objects which reach the surface, commonly crashing, are called Meteorite. They are not known to cause any significant damage to humans, although their service may be affected by their fall. Houses, cars, or buildings may get affected. However, there are known cases of a large meteor crashing into the Earth's surface leaving behind huge craters. How is Jupiter the guardian planet of Earth? When there are so many asteroids hurling between Mars and Jupiter, there is a great probability for one of these to collide amongst themselves and get deflected on a course of hitting the Earth every day. However, this is not the case as you already know, otherwise, we would be facing the asteroid massacre every then and now. The answer to this question is Jupiter. With the 70% leftover nebular mass accreted inside Jupiter after the Sun was formed, it ranks first in size as well as the proportion of mass when compared to other planets. Jupiter in its orbit is like a shepherd who guides all other asteroids in the belt because of its large gravitational force compared to the Sun (factor of distance also matters, remember!). Therefore, Jupiter diverts most of the asteroid from entering the terrestrial region and it either throws them in outer space or suffers the pain itself. Not only does it avoid asteroids to collide with Earth, but comets from the Kuiper belt are also deflected from the usual course because of Jupiter's gravitation. Sadly, nothing is perfect in this Universe, therefore some of these asteroids or comets which escape silently from the field of Jupiter. Don't forget to check the historical video of comet Shoemaker-Levy 9 collision with Jupiter by Science@Nasa. Jupiter is so big that 1300 Earth could comfortably fit inside it. This size is boon for Earthlings! Why are Geologists concerned with the Meteorite if they have astronomical values? I am sure this might have come into your mind. Well, they are important as many of the meteorites are believed to have formed during the early to intermediate stages of the development of solar nebula and have not gone any significant alteration or differentiation as the planetary bodies. They give colossal insights into the solar nebulas when no one was present to record what was going. Not only do they provide information about what happened 4.5 billion years ago, but they also provide us with information about what's beneath our feet i.e. the core of the Earth. How are do we identify the right meteorite? Meteorites are broadly classified as: Irons: Composed principally of metallic Fe-Ni alloy. Since they are significantly different from the terrestrial rocks, they are more likely to be observed as Museum specimens. Stone: Composed of silicate minerals. Since they are similar in appearance to the terrestrial rocks, they are not often recognized as meteorites. Stony-irons: contain a subequal amount of each. Irons and Stony-Irons are considered to be a part of chemically differentiated large space bodies. However, they are not all alike and display large variation depending upon which differentiated portions of a planet are they from. It is also based on the condensation temperature which is a function of the distance from the Sun, from which the meteorite was delivered on our planet. Stones are further subdivided on the basis of the spherical silicate inclusions between 0.1 and 3.0 mm in diameter, called Chondrules. Stones with chondrules are called Chondrites, whereas those without are called Achondrites. Achondrites are too considered to be differentiated meteorites like Stony-Iron and Iron meteorites. Chondrites are undifferentiated and are considered to be the most primitive type of meteorites because they represent the composition of the original solar nebula. Different simulation computer models are created to study these meteorites and to provide close speculations with how things happened at that time. They also explain the chemical composition of the planets or solar system if they represent them up to some extent. Check this video by Astronimate! References: 1. John D. Winter- Principle of Igneous and Metamorphic petrology 2. Stephen Marshak- Essentials of Geology 3. Asteroids, Comets and Meteors: NASA

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