What are asteroids and how are they grouped?


  • On January 3, at around 6 a.m. IST, an asteroid darted past Earth. It travelled at a distance of 1.8 million km and was placed under the ‘Potentially Hazardous Asteroids’ category.
  • Continue reading to know more about asteroids and how they are classified.

What are asteroids?

  • Asteroids are rocky bodies in space, and they mostly originate between the orbits of Mars and Jupiter. This region is also known as the asteroid belt.
  • The following are also called as asteroids, though NASA prefers to call these “minor planets”
  • Trojans: these are rocky bodies that have the same orbit as a planet. There are Jupiter, Mars and Neptune trojans. In 2011, Nature published the discovery of the first Earth trojan, 2010 TK7.
  • Centaurs: these are rocky bodies between Jupiter and Neptune.
  • Trans-Neptunian objects: those ones beyond Neptune’s orbit.

What are asteroids composed of?

  • They could be composed of anything from clay and silicate rocks to metals. In fact, NASA classifies asteroids based on their composition. Here is the classification:
  • C-type (chondrite): such asteroids are made up of clay and silicate rocks
  • S-types (stony): these are composed of silicate materials and nickel-iron
  • M-types: such asteroids have a metallic composition

Why was today’s asteroid classified as ‘Potentially Hazardous’?

  • Any object that has its orbit near that of Earth is called as near-Earth asteroid.
  • The Near-Earth asteroids are further classified as:
  • Atiras: these are objects whose orbits are smaller than the Earth’s orbit, and they are within the Earth’s orbit as well.
  • Atens and Apollos: these are Earth-crossers (they cross the Earth’s orbit) with orbits near the Earth’s orbit.
  • Amors: these are asteroids with orbits outside the Earth’s but inside that of Mars’.

Potentially Hazardous Asteroids:

  • Any of the near-Earth asteroids can become potentially hazardous ones if their distance from the Earth is below 0.5 astronomical units or 7.5 million km. 1 astronomical unit is equal to 150 million km-the distance between Earth and the sun.
  • “There are thousands of Potentially Hazardous Asteroids. There is no need to panic as there is only an extremely small chance that they can be influenced by the Earth’s gravitation and we don’t see any collision with earth taking place anywhere in the near-future,


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