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13th February, 2023 Science and Technology

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What are 'Asteroids'?

  • Asteroids are actually minor planets that can neither be classified either as a planet or as a comet. These are generally in the direct orbit around the Sun, also known as the inner solar system.
  • The larger forms of asteroids are also known as planetoids. These are different from the minor planets in the outer solar system in their volatile-based surfaces much like comets. These are generally known as Asteroid Belt.


  • Asteroids are mainly the remnants of circumstellar disk of gas around newly-formed star and the debris disk together.
    Their remains together are known as planetesimals.
  • Mainly the known asteroids are present in the Jupiter Trojans or in the asteroid belt formed between the Mars’ orbit and that of Jupiter. Others are found in the solar system near Earth, termed as near-Earth asteroid. The size of asteroids can vary from 1000 km to 10 meters.
  • The 3 largest asteroids are almost spherical in shape like miniature planets, but with differentiated interiors. A majority of them, however, are small with irregular shapes.

      Depending on the chemical component, which is the carbon content, metal composition and silicate quantity, the asteroids are classified into 3 main groups:

      1. C-type – These are the most common type of asteroids, consisting 75% of known asteroid population, also dominating the outer part of asteroid belt. All carbonaceous asteroids fall under this category. C-type asteroids are extremely dark in their nature with their reflection coefficient ranging from 0.03 to 0.10.
      2. S-type – The moderately-bright asteroids (albedo/reflection co-efficient- 0.10-0.22) with component mainly including iron and magnesium silicates. These are mainly found in the inner asteroid belt.
      3. M-type– The asteroids with nickel and iron in its purest form are categorised under M-type. Sometimes these are also found with the presence of stones. Their brightness ranges from 0.1 to 0.2. All the asteroids are visible by binoculars except for one, 4 Vesta. This is the only asteroid that can be seen even without binoculars because of the relatively reflective surface. It is only rare that a passing asteroid becomes visible to naked eyes.