Is there a hidden massive planet in the outskirts of the Solar System? Scientists recently questioned the planet nine hypothesis. Credit: ESO/Tom Ruen/nagualdesign

Elusive World Dubbed Planet Nine Likely Isn’t Real After All

A new study claims that the original Planet Nine hypothesis could be untrue.

The hypothetical invisible ninth planet, which alters the orbits of the most distant objects in the solar system, again came under fire. And this time it might not be able to withstand the attack.

A new, more extensive analysis of the motion of distant objects showed that the hypothesis of a ninth planet could have been generated by sampling error.

Birth of the Planet Nine hypothesis

The ninth planet hypothesis appeared in 2016 in an article by Caltech astronomers Konstantin Batygin and Michael Brown, published in The Astronomical Journal (DOI: 10.3847 / 0004-6256 / 151/2/22 )The presence of another large body in the solar system was indicated by the orbits of small objects beyond Neptune.

These small objects are usually called extreme trans-Neptunian objects (ETNOs). They never fly closer to the Sun than 30 astronomical units but can fly away further than 150 AU.

Batygin and Brown found that all such known objects have orbits at perihelion at the same angle. Computer simulations showed that such an equal angle can be explained by the presence of a large planet – it could “pull” their orbits into a group. And this is how the hypothesis of planet nine appeared.

The supposed orbit of the ninth planet (highlighted in red) along with some anomalous orbits of trans-Neptunian objects (purple). Credit: MagentaGreen, Wikimedia
The supposed orbit of the ninth planet (highlighted in red) along with some anomalous orbits of trans-Neptunian objects (purple). Credit: MagentaGreen, Wikimedia

Sampling error

Calculations have shown that the mass of planet nine should be 5-10 times larger than the Earth. And it should fly at about 400-800 AU from the sun.

With such indicators, it is almost impossible to find it in the sky using the tools available to us.

And if you think about it, it’s even more difficult to catch these extreme trans-Neptunian objects. We get a chance to detect them only for a couple of decades while they pass perihelion – the point of the orbit closest to the Sun.

This is what caused the sampling error, according to the authors of the new study.

The authors of the hypothesis about the ninth planet, Batygin and Brown, built models for the orbits of only six objects. They took data on these orbits from several studies that did not describe the selection criteria.

In recent studies, the selection criteria have been approached more closely. And, although so far no study has been able to find enough ETNO objects to draw conclusions about all such objects, it makes sense to combine the research results.

This is exactly what the authors of the new study did – a team of scientists led by physicist Kevin Napier from the University of Michigan.

Planet Nine: New research 

The team selected five objects from OSSOS (which showed no signs of grouping objects), five objects from the Dark Energy Survey, and four more objects found by astronomers Scott Sheppard and David Tholen, who, by the way, we’re looking for exactly the ninth planet.

In these three studies, different goals were pursued, therefore, the criteria for selecting objects were different. The most important task was to bring all this data into a single format. For this, the authors have created an “observation simulator”.

If the ETNO grouping was explained by the attraction of a large body, then this effect would be noticeable in a larger sample. But, according to the authors, they did not see it.

Of course, this does not deny the existence of a ninth planet. Simply to prove its existence it will not be possible to use the orbits of extreme-Neptunian objects. We just don’t have enough information. Based on the data collected, it is impossible to either confirm or deny the existence of the ninth planet.

Brown’s answer

Last week, Michael Brown, one of the authors of the planet nine hypothesis, posted a detailed analysis of the new contradicting article on his blog.

He put new points on the main graph from his work, on which the main conclusion was drawn. And the new dots seem to support the hypothesis, why then didn’t the new study find clustering? Brown suggests that they got a result that really isn’t good enough to detect grouping. But a conclusion could only be drawn if they published the uncertainties. And they didn’t publish them.

And the problem, according to Brown, is not only in the interpretation of the result but also in the data from the Dark Energy Survey, which he considers completely biased. And the authors of the study themselves admit in their conclusions that if the grouping occurs exactly where the Dark Energy Survey collected data from, then the results will be biased. That’s where he looked, says Brown.

In his opinion, this conclusion should be correct: Dark Energy Survey data is in fact the same as previous conclusions about grouping, but Dark Energy Survey data is so biased that this should not surprise anyone.

Brown compares this to watching sunsets. Imagine that you happen to notice several times that the sun is setting in the west. And we decided to conduct a scientific study, whether this is always the case. But instead of watching the whole sky, you are looking at this one point in the west. Statistically, you conclude that you cannot confirm that the sun sets only in the west because perhaps it sets in all directions in the same way as in the direction of observation. The study is biased.

It just so happened that the Dark Energy Survey, Brown explains, was looking in the direction of grouping. And from this, he concluded that in all other directions everything should be identical.

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Clery, D., Mervis, J., Cho, A., O’Grady, C., Voosen, P., Casassus, B., . . . Moutinho, S. (2021, February 16). Claim for giant ‘Planet NINE’ at solar SYSTEM’S edge takes a hit.
Letzter, R. (2021, February 18). Planet 9 probably doesn’t exist, new paper argues.
Napier, K. J. (n.d.). No Evidence for Orbital Clustering in the Extreme Trans-Neptunian Objects [PDF].

Written by Vladislav Tchakarov

Hello, my name is Vladislav and I am glad to have you here on Curiosmos. As a history student, I have a strong passion for history and science, and the opportunity to research and write in this field on a daily basis is a dream come true.

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