Planet 9 Hypothesis

Planet 9 Hypothesis

In Today’s world, everyone is aware about the how the Solar System works. But still there are many unanswered questions which makes the Solar System. Most Important and most basic of them being, what are the boundaries of the Solar System. For decades, we used to think that the last planet that is the Neptune(or Pluto earlier) is the last end of the our Solar System.
But as the recent studies which includes the result of various new telescopes and many AI simulated models predicts that there’s a large part of our Solar System which is still not known.


What is the requirement of such theories and predictions?

The reason why the scientist community is working on more and more of such theories is that there are many irregularities in the present known and accepted models of our Solar System.
These include:-
The tilted axis of sun and most planets
 Planets revolving outside the solar plane
 Strange orbits of trans-neptue bodies
 Periodic meteor destruction on Earth over long history
 Strange wobbling of sun, noticed due to the movement of constellations over years
 Wierdness in our system when compared to the till known systems

Let’s discuss some theories about what is hidden from us in our own Solar system-

Summary of the theories of Planet 9

There are many models of the Planet 9, but the most discussions happen about the one predicted by Batygin, Brown and Betts. There simulations have shown the possibility of what is popularly called as 5-Planet Nice Model. It’s the possibility of our solar system to have 5 giant planets comprising 2 gas giants and 3 ice giants, rather than the regular 4 planet model of 2 gas giants and 2 ice giants.
In the simulations performed by the above mentioned, the Planet 9 is formed along with and in the same array as the other gas and ice giants. But during the initial years of the solar systems’ formation, it had a very close encounter with Jupiter or Saturn, which dramatically throws it out of the current boundaries of the solar system. But what stabilized it’s orbit is still a matter of mystery. Majorly the drag of the remnants of the solar nebula is considered the reason which reduced the eccentricity of the orbit of the Planet 9, thus stabilizing it. Some scientists even consider the possibility of the force of a nearby star to be the reason behind this gain of stability.This initial throwing of planet 9 made it devoid of the huge amount of matter of the proto-planetary disk.
There’s also a possibility that Planet 9 might have been captured from outside of the solar system during a close encounter between sun and another star. This theory assumes the other star has a very distant planet and this three body interaction altered the path of that Planet and with time gradually it came in a stable orbit of our Sun. For this to happen it is needed that the other star doesn’t have any super massive planets like Jupiter or Saturn which would have held that outer planet for their star.
There are also theories for the in situ formation of the planet 9 but these theories doesn’t appeal enough as for formation of planet at such a large distance from sun. The proto-planetary disk is needed to be huge, which was probably not the case.


Planet 9 is hypothesized to orbit around the sun in elliptical orbit having eccentricity ranging from 0.2 to 0.5 and it’s semi-major axis is estimated to be between 400-800AU. It’s proposed mass is estimated to be some where in between 5-10 Earth Masses and maybe up to 20 Earth masses for certain other simulations. As stated earlier, it was thrown out of the major part of the proto-planetary disk thus keeping it debarred from turning into more massive ice giants like Neptune or Uranus. If it had been thrown out of the disk after some considerably, it would might have turned into a gas giant located very far by capturing the planetesimals located in the outer orbits of the solar system near the proposed orbit of the planet 9.

There’s another theory that assumes the hypothetical and mysterious Planet 9 to be something that is called as PBH or a primordial black hole. PBHs are tiny black holes which are supposed to be created before the solar system and during the formation of our Universe. Going further in this theory Jakub Scholtz and James Unwin has claimed it’s mass to be around 5Earth Masses and thus relative to that, it’s radius can be estimated to be less than 5cms.

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Existence of such a possible planet or a hypothetical PBH can easily explain most anomalies related with our outer solar system and th
e objects related from the outer solar system. The paths of ETNOs(extreme trans-neptune objects), sednoids, kuiper belt and beyond objects can easily be explained.
According to the latest definitions of a planet, it is necessary for the object to be the dominating force in it’s area of influence.

Scientists try to explain the below phenomenons using the gravitational influence of the planet 9 if exists-
1.Clustering of eTNOs in collective orbits
2.Existence of large amount of objects collectively called Sednoids with perihelia as high as           70AU
3.Some TNOs have been observed moving perpendicular to the common planetary plane.


If the existence of the proposed Planet 9(or the hypothetical PBH) is proved, it will explain all these anomalies. It’s gravity can be considered the reason behind the irregualr movement of the TNOs, and while moving in it’s orbit for the past millions or billions of years it would have by now cleared and arranged the relatively small objects by either colliding(and then absorbing them) or by putting them in stable orbits thus, even the irregular clustering of the objects can be explained.