Planet 9 representation: Bluish purple planet with some swirls.

New evidence for planet 9 on the edge of our solar system

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New evidence strongly suggests the existence of a Planet 9 on the edge of our solar system. Image via Solen Feyissa/Unsplash.

New evidence for Planet 9

Evidence is growing that a planet the size of Neptune – Planet 9 – is hiding deep in the outskirts of our solar system. Researchers from Caltech, Université Côte d’Azur and Southwest Research Institute shared a pre-print article on April 17, 2024. In it, they claim that a group of small bodies outside Neptune are converging due to the gravitational influence of Planet 9. These distant bodies in the Solar System are not evenly distributed in their orbit, like the boulders of the asteroid belt. Instead, they form clumpy groups. So the researchers think that a larger, more distant object is pushing them into this pattern due to gravity. And so, planet eight – Neptune – was essentially discovered. Neptune tugged at Uranus’ orbit.

Two of the four authors of the new paper, Konstantin Batygin and Mike Brown of Caltech, are the founders of the theory of Planet 9. Mike Brown even wrote a book about his life and research at the outer edges of our solar system, including its reclassification from Pluto. The book is titled How I Killed Pluto and Why It Had It Coming. But these researchers believe there is an object much larger than Pluto further out in our solar neighborhood. This planet would be the size of five Earths (about the size of Neptune) and 400 to 800 times further from the Sun than Earth.

The astrophysical diary letters has accepted the article for publication. It has not yet been peer-reviewed. A copy of the article is available on arXiv.

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Batygin on Event Horizon podcast

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

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

Batygin also said:

What we have been looking at in this article is a population of Trans-Neptunian objects that we had previously ignored. These are populations of long-period icy asteroid-like creatures that generally live outside Neptune’s orbit… but have orbits that pierce Neptune’s orbit. We also looked specifically 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 pushed around by the giant planet, they would have scattered if left alone. As Batygin said:

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

Batygin even said that a solar system without Planet 9 can be ruled out with five sigma certainty. This value is considered sufficient for areas such as particle physics to call it a discovery. It is a ‘gold standard’, equivalent to a one in a million chance that the result was random.

Planet 9, galactic tide or black hole?

Besides Planet 9, are there any other theories that could explain the clustering of the Trans-Neptunian objects? One of those theories concerns the galactic tide. And the researchers looked at this gravity of the galaxy itself. But they found that some features of object distribution cannot be reproduced with the galactic tide. However, the Planet 9 theory fit perfectly.

Another theory, not discussed in the article, is that Planet 9 could be a black hole instead. If black holes are roaming the distant solar system, Harvard astronomer Avi Loeb has proposed a way to look for them. They looked for flashes of light from encounters between black holes and small, distant objects.

The upcoming Vera Rubin Observatory could be the instrument to provide the crucial data to solve the mystery of Planet 9 or the solar system’s black holes. The telescope should be operational in early 2025.

Unfortunately, the new data from the recent research doesn’t help us figure out the direction in which to point our telescopes at Planet 9. So the hunt continues.

Social media announcement

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

Bottom line: Researchers said the buildup of small objects beyond Neptune’s orbit fits perfectly with the existence of a planet 9 hiding at the edge of our solar system.

Source: Generation of low-inclination Neptune-crossing TNOs by Planet Nine

Via Event Horizon

Kelly Kizer Whitt

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About the author:

Kelly Kizer Whitt has been a science writer specializing in astronomy for more than twenty years. She started her career at Astronomy Magazine and was a regular contributor to AstronomyToday and the Sierra Club, among others. Her children’s picture book, Solar System Forecast, was published in 2012. She has also written a dystopian novel for young adults titled A Different Sky. When she is not reading or writing about astronomy and gazing at the stars, she enjoys traveling to the national parks, doing crossword puzzles, running, tennis and paddle boarding. Kelly lives in Wisconsin.

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