International Space Agencies – Missions and Discoveries

What is Planet Nine?


From UPSC perspective, the following things are important :

Prelims level: Planet Nine, Dwarf Planets

Mains level: NA

A new study’s “treasure map” suggests that a planet several times more massive than Earth could be hiding in our solar system, camouflaged by the bright strip of stars that make up the Milky Way.

Do not wonder. This too was a PYQ:

Q.Which planet was downgraded to dwarf planet status?

(a) Pluto

(b) Mars

(c) Earth

(d) Venus


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Planet 9

  • Planet Nine is a hypothetical planet in the outer region of the Solar System.
  • Its gravitational effects could explain the unlikely clustering of orbits for a group of extreme trans-Neptunian objects (ETNOs), bodies beyond Neptune that orbit the Sun at distances averaging more than 250 times that of the Earth.
  • Based on earlier considerations, this hypothetical super-Earth-sized planet would have had a predicted mass of five to ten times that of the Earth, and an elongated orbit 400 to 800 times as far from the Sun as the Earth.

Curiosity for the ninth Planet

  • In August 2006, the International Astronomical Union broke several hearts when it announced that it had reclassified Pluto as a dwarf planet. ‘
  • The decision was based on Pluto’s size and the fact that it resides within a zone of other similarly-sized objects.

Is everyone convinced that Planet Nine exists?

  • Researchers from across the globe have carried out several studies on Planet Nine and there are several theories about it, including one that stated Planet Nine could in fact be a black hole.
  • Another research has argued that the unknown object causing anomalous orbits of the trans-Neptunian objects could be a primordial black hole.
  • Yet another study noted that a trans-Neptunian object called 2015 BP519 had an unusual trajectory because it was affected by Planet Nine’s strong gravity.

Back2Basics: Dwarf Planet

  • A dwarf planet is a small planetary-mass object that is in direct orbit of the Sun – something smaller than any of the eight classical planets, but still a world in its own right.
  • As of today, there are officially five dwarf planets in our Solar System.
  • The most famous is Pluto, downgraded from the status of a planet in 2006.
  • The other four, in order of size, are Eris, Makemake, Haumea and Ceres. The sixth claimant for a dwarf planet is Hygiea, which so far has been taken to be an asteroid.
  • These four criteria are – that the body orbits around the Sun, it is not a moon, has not cleared the neighborhood around its orbit, and has enough mass for its gravity to pull it into a roughly spherical shape.

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