Key takeaways

  • Scientists have found new evidence suggesting a large, hidden planet, about the size of Neptune, exists far beyond our solar system.
  • The unusual grouping of small objects beyond Neptune might be due to the gravitational pull of Planet 9, similar to how Neptune was discovered by its influence on Uranus.
  • The latest research provides the most statistically significant evidence yet for Planet 9’s existence, with a high level of certainty.
  • Other theories, like the gravitational influence of the galaxy or a potential black hole, have been considered but do not match the observed data as well as the Planet 9 hypothesis.
  • Despite the new findings, the exact location of Planet 9 remains unknown. Future observations, like those from the upcoming Vera Rubin Observatory, could be crucial in confirming its existence.

New evidence for Planet 9

There is mounting evidence that Planet 9, which is roughly the size of Neptune, is hidden far outside of our solar system. On April 17, 2024, researchers from Southwest Research Institute, Université Côte d’Azur, and Caltech shared a pre-print study. They contend in it that the gravitational pull of Planet 9 causes a collection of minor planets orbiting beyond Neptune to gather together. Unlike the stony pebbles of the asteroid belt, these far-off solar system asteroids are not uniformly dispersed throughout their orbit. Rather, they cluster together. Therefore, the researchers believe that they are being gravitationally drawn into this pattern by a bigger, farther-off object. In actuality, this is how Neptune, planet eight, was found. Pulling on Uranus’ orbit was Neptune.

The notion of Planet 9 was first proposed by Caltech’s Mike Brown and Konstantin Batygin, two of the paper’s four authors. Actually, Mike Brown authored a book detailing his life and work studying the furthest regions of our solar system, which included Pluto’s reclassification. How I Killed Pluto and Why It Had It Coming is the title of the book. However, these scientists think that somewhere farther out in our solar system, there is an object far larger than Pluto. This planet would be 400–800 times farther from the sun than Earth and the size of five Earths, or roughly the size of Neptune.

The Astrophysical Journal Letters has accepted the paper for publication. It is not yet peer-reviewed. A copy of the paper is available on arXiv.

Batygin on Event Horizon podcast

Batygin said on John Michael Godier’s podcast Event Horizon that this is:

… the fifth and most statistically significant evidence we have to date for the existence of Planet 9.

Batygin also said:

What we looked at in this paper is a population of Trans-Neptunian Objects that we had ignored up until now. These are populations of long-period icy asteroid-like things that typically live beyond the orbit of Neptune … but have orbits that pierce the orbit of Neptune. We also specifically looked at the population of Neptune-crossers that live close to the plane of the solar system.

So, because the objects cross Neptune’s orbit and are getting pushed around by the giant planet, if left alone they would have dispersed. As Batygin said:

The fact that we see them at all necessitates some form of gravitational influence. … What we show in this paper is that not only is Planet 9 up to the task, moreover it’s that the orbital distribution that Planet 9 predicts is perfectly consistent with what we see in the data.

According to Batygin, a solar system devoid of a Planet 9 may be excluded with a five sigma degree of certainty. In domains like particle physics, this value is deemed sufficient to announce a finding. A “gold standard” would be around one in a million chances that the outcome was arbitrary.

Planet 9, galactic tide or black hole?

What other ideas, besides Planet 9, may account for the Trans-Neptunian Objects’ clustering? Among them hypotheses is the one about the cosmic tide. Additionally, the gravitational attraction of the galaxy itself was examined by the astronomers. However, they discovered that the galactic tide is unable to replicate several aspects of the item distribution. But the Planet 9 idea made perfect sense.

An alternative hypothesis that isn’t included in the study is that Planet 9 could actually be a black hole. Harvard astronomer Avi Loeb has suggested a method for looking for black holes that could be wandering around in the furthest reaches of the solar system. They would search for flares left over from interactions between tiny, far-off objects and black holes.

Soon to be built Vera Rubin Observatory may hold the key to unlocking the secrets of Planet 9 and solar system black holes. The telescope is scheduled to be operational by early 2025.

Sadly, the new information from the most recent research does not assist us in determining which way to aim our telescopes in order to detect Planet 9. Thus, the search goes on.

Announcement on social media

Here’s how lead author Konstantin Batygin announced the discovery on social media:

Bottom line: Researchers said the bunching of small objects beyond Neptune’s orbit fits perfectly with the existence of a Planet 9 hiding on the outskirts of our solar system.

Source: Generation of Low-Inclination, Neptune-Crossing TNOs by Planet Nine

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