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What is Planet?

Three conditions for a celestial object to be called a ‘planet’ –

  1. it must orbit the Sun
  2. it should be massive enough to acquire an approximately spherical shape
  3. it has to ‘clear its orbit’ i.e. be the object that exerts the maximum gravitational pull within its orbit


‘Dwarf planets’, on the other hand, need to only satisfy the first two conditions.

  • As per the third condition, if an object ventures close to a planet’s orbit, it will either collide with it and be accreted, or be ejected out.
  • But, in case of Pluto, it is affected by Neptune’s gravity.
  • It also shares its orbit with the frozen objects in the Kuiper belt.
  • Based on this, the IAU deemed that Pluto did not ‘clear its orbit’ (the third rule).

What is Ploonets?

  • Astronomers have defined a new class of celestial objects called “Ploonets,” which are orphaned moons that have escaped the bonds of their planetary parents.
  • Planet + moon = Ploonet.
  • The researchers explain that the angular momentum between the planet and its moon results in the moon escaping the gravitational pull of its parent.
Ploonet by Legacy IAS Academy
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September 2022
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