International Space Agencies – Missions and Discoveries

Planet Nine


From UPSC perspective, the following things are important :

Prelims level : Planet IX

Mains level : Possiblities of a primordial black hole in the Milky way

Planet Nine

  • Hidden in the outer Solar System lurks a presence, believed to be a gigantic planet orbiting the same Sun and casting a visible influence on the behaviour of a number of other objects.
  • Although it has not yet been spotted, this behaviour would be difficult to explain if such a presence did not exist.
  • It is popularly referred to as Planet Nine, the presumed ninth planet of the Solar System, and occasionally as Planet X.

Planet of tiny black hole?

  • Scientists have proposed that this could be a tiny black hole instead.
  • They have shown that the behaviour of certain Trans-Neptunian Objects like a primordial black hole.

Primordial black hole

  • A primordial black hole is one that is believed to have formed immediately after the creation of the universe.
  • Like Planet Nine, primordial black holes too have been predicted to exist — including by the late Stephen Hawking — but none has been spotted as yet.

What do we know of Planet Nine so far?

  • Over the years, scientists have sought to explain several puzzling aspects of the Solar System by attributing these to the influence of Planet Nine.
  • In a 2016 paper made out a case for Planet Nine’s existence by arguing that it could be responsible for the peculiar alignment of icy objects on the outskirts of the Solar System.

What, then, is the basis of the new suggestion about a black hole?

  • Researchers based their theory proposed two gravitational anomalies.
  • One is the unusual orbits of asteroids beyond the orbit of Neptune, which have fed the prediction of Planet Nine, estimated to be somewhere between 5 and 20 times the mass of the Earth.
  • The other anomaly was observed thousands of light years away, by a project called the Optical Gravitational Lensing Experiment (OGLE).
  • In six observations, an object bent the light of a star like black holes do. This is called microlensing.
  • These six events correspond to objects whose masses are in the range 0.5 to 20 times the mass of Earth.

Can the black hole be found?

  • The catch is that it is much harder to look for a black hole than to look for a planet, especially when the black hole is predicted to be of small dimensions.
  • However, it is reasonable to expect a dark matter halo surrounds this black hole.
  • If dark matter can annihilate into particles we know, the halo surrounding the black hole would radiate high energy photons and the halo would be visible in X-rays and gamma rays.
  • Researchers propose to look through a gamma ray telescope dataset and try to find evidence of these annihilations.
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