What is known about the ninth planet at the moment?

Last year two astronomers studied the farthest objects revolving around the Sun, which we found all the time, when suddenly we saw something interesting. These are ultra-long objects of the Kuiper belt, instead of having randomly oriented orbits, as if stretched out and bent in a certain direction. If one or two objects did this, it would be possible to write it off as a coincidence. But there were six of them. The chances of this being an accident were about 0.0001%. Instead, astronomers Konstantin Batygin and Mike Brown proposed a fundamentally new theory: somewhere there is a distant ninth planet, more massive than the Earth, but less than Uranus and Neptune. It is she who shifts all these objects. Since then, 16 months have passed, and that’s what we have in fact.

First, the idea is beautiful. Every time you try to find an explanation, other than this idea, nothing seems particularly convincing. But, like many brilliant ideas, it is also possible that it is simply incorrect. To see six ultra-long objects that do something unusual does not mean that there are no six million such objects, we just do not see them. Perhaps this is quite normal behavior.

Astronomers call this prejudice: in any data set, you only look at objects that are easiest to see / find / measure, and these objects will usually be outstanding in nature. If you look at the top of the tall grass and see only the giant elephants, you can conclude that the elephant does not exist, so your prejudice will be. But there is a way to get rid of it: ask what will happen if you collect new additional data, better and more accurate. What specific predictions can be made to confirm or disprove your theory? In the case of the ninth planet, there will be five.

If the ninth planet is real, it must spawn more distant objects with this strange unexpected alignment. If there was an ultra-long massive planet in the outer solar system, sometimes it would have to gravitationally collide with other objects in the Kuiper belt. Some will collide with the planet, some will be thrown out of the solar system, some will be thrown into orbit with the direction opposite to the ninth planet. We can verify this if we find more objects with large maximum orbital distances from the Sun: hundreds of times more distant from the Sun than the Earth.

The orbits of these objects should be inclined in the same direction as the original six. An unusual systematic shift for six objects has a chance of the order of 1 to 1000. If you find another dozen objects with a similar slope, the chance will be one per billion. Find more objects and measure their displacement – this is an excellent indirect test of the hypothesis of the ninth planet.

A small group of objects, contrary to the prediction # 1, will have orbits, displaced in the same direction as the ninth planet. This prediction was made by Batygin and Brown in the second work on this topic, and it has an interesting grain, because such objects have never been found.
Orbital planes of these objects should be inclined in one direction with a small spread. This is a refinement of the prediction # 2, which determines the distribution of systematic shifts. Additional modeling, conducted by the Brown team and presented at the conference in October, showed where the “north pole” of the orbital planes of these objects should be. If a large number of these ultra-long Kuiper belt objects are detected, their distributions can be compared with the predicted ones.

More importantly, the ninth planet should be there and it could be found from the ground. If there is a large massive planet, it should reflect enough sunlight to be able to catch it even from the ground, even with the help of our modern telescopes.

As for indirect evidence, the idea of ​​the existence of the ninth planet is pretty good. Forecasts one through four are indirect, and since the existence of the ninth planet was first predicted, four more objects were found: one by the OSSOS team and three by the Sheppard and Trujillo team. The green object whose orbit is moving to the right is the first example of prediction # 3, which is interesting. But it will be even more interesting if we arrange all the detected objects according to the modeling of their orbital planes. They will coincide with the models of Brown!

The more indirect evidence appears, the more you want to see the coincidences, given the limited availability of data. But here there are disadvantages:

All these data are not without prejudice; We found objects that fit relatively close to the Sun.

The total number of detected objects – ten – is too small to be considered significant.

The uncertainty of predictions # 3 and # 4 blurs the significance of the findings.

With all this, the ninth planet remains elusive.

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