A paper just published by a team of astronomers examines evidence for the idea that another major planet, nicknamed the New Planet, orbits the Sun far beyond Neptune. What they found calls into question the case to assume that the planet is there. At the same time, they cannot say that the evidence indicates the planet not existing.
[UPDATE (Feb. 16, 2021 at 20:30 UTC): Mike Brown, one of the astronomers looking for Planet Nine, weighed in on this paper not long after I posted this article. He shows that, broadly speaking, the paper is correct in its methodology, but (as I also say below) cannot disprove the orbital alignments of the objects observed. It adds some uncertainty to the observations but in fact the observations are still wholly consistent with the existence of Planet Nine.]
We know of eight major planets orbiting the Sun, Neptune being the farthest 4.5 billion kilometers, about 30 times farther than the Sun Earth. Beyond Neptune are several groups of frozen bodies, some of them of decent size, such as Pluto at almost 2,400 km wide. These are collectively called trans-Neptunian or TNO objects.
Some of these objects are extremely far, as the 2012 VP113, which never approaches the Sun 12 billion km and reaches up to 65 billion. This makes them very weak and hard to find. To date, only a few dozen of these extreme TNOs (or ETNOs) have been discovered.
A few years ago, it was found that a handful of them (those that were not even close enough to the Sun to be affected by Neptune’s gravity) seemed to have orbits that were strangely aligned. We would expect their orbits to be oriented in all directions, uncorrelated. But they are not. They seem to have similar characteristic orientations, as if something were aligned there.
This could be another planet, more massive than Earth and very far away, which interacts with them gravitationally in time, organizing its orbits. Its position in the sky can be roughly calculated using the orbits of these ETNOs as a guide, but so far nothing has been found.
The problem is that these ETNO observations may suffer from what is called a selection bias. Surveys that find these objects tend to show only in certain parts of the sky at certain times of the year and find them easier when they are closer to the Sun and therefore brighter. This means that surveys may tend to find them in orbits aligned in this way, selecting them from a much larger population of objects that are indeed randomly oriented.
If this is the case, then the reason for searching for the New Planet disappears in the first place. Obviously, it is important to realize how important this role can play.
So that’s what the team of astronomers did. They examined the investigations in question, observing how these observatories scanned the sky. Then they simulated a large population of objects from Neptune’s past using realistic features and asked how many of them would miss the polls and if they would find others that had aligned orbits.
What they found is that, statistically speaking, the observations of these ETNOs are consistent with them coming from a larger population of objects with randomly oriented orbits. So it is possible that the ETNOs are evenly distributed around the Sun, and the effects of the New Planet are an illusion. We just think we see its effects because of it way we observe these objects.
However, this does not conclusively prove that this is the case! You can match the data to a random population, but you can also frame them with a population affected by the New Planet. What I find, in essence, is that the latter is much less likely.
But I can’t rule it out. Also, even if the distribution is random, this does not prove that the New Planet does not exist. It could still be there, but one of the initial reasons for assuming it is has been weakened. I will notice that astronomers looking for it have other reasons to believe that it exists, because of the way it could affect other objects in the outer solar system.
I will also add that the whole thing is severely limited by the very small number of these objects discovered. All this is based on a few of them and you have to be extremely careful when dealing with small number statistics. It’s like turning a coin four times and it would appear the same way four times. Is the currency correct? May be; there is a 1 in 8 chance that this will happen randomly. You need to turn it over several times before the random chance plays a small enough role that you can be more sure of the currency itself.
The best thing to do here is to get more feedback. We need to find many more of these extreme objects and see what their orbits are like. New telescopes coming online soon, such as the Vera Rubin Observatory, hope to do just that, and other investigations are underway.
Scanning the sky for the New Planet in the most likely locations is a good idea anyway. At best, she finds the planet. Hatred! In the worst case, there is more data that can be used for many purposes, and if the New Planet is not found, we will learn something there.
I admit that I want the planet to be there, because it would be extremely great and I would learn a huge amount about the history of the solar system from it. But because I am so inclined, I myself must be skeptical of the statements made about it and critically examine them. I have my own biases*, just as we all do. We must remember not to overinterpret the results in any way and not to draw firm conclusions based on statistical data.
We hope we have a much better idea of the New Planet soon.
*Mike Brown, one of the astronomers actively searching for the New Planet, is an old friend of mine.