You don’t, it’s nonsense. The whole thing is BS - no such planet is even possible.

In “Planet X”, X stands for unknown. Pluto is so far the first and only confirmed planet X. We have had many “planet X” candidates since then, but none have been confirmed.

The conspiracy theorists treat them as if they are all the same planet, with an orbit of 360 (or 3600) years crossing the orbits of all four gas giants as well as Mars and Earth. Even “Nemeisis” - a now pretty much disproved hypothesis of a red dwarf star or possibly a brown dwarf, orbiting our sun at a distance of a 1.5 light years away, in an elliptical orbit that sometimes takes it a bit closer to the Sun but still over a light year away, with a period of 26 million years! With the next close approach predicted for 15 million years in the future.

They look at this hypothesis and say “Look, told you so, that’s Nibiru with a period of 3600 years due to hit Earth next year or month and this proves they have been tracking it all along”. From the point of view of an astronomer the whole thing is total bonkers.

However ,there could be extra planets in our solar system. Not hiding amongst the planets we already know. That is impossible, we know the solar system out to Neptune and a fair bit beyond, like the back of our hand. But beyond that, it rapidly gets harder to see what’s there. The thing is that when you double the distance from the sun, a planet gets sixteen times fainter (a quarter of the apparent size, and the sunlight hitting it is four times fainter, so the image in the telescope photograph is sixteen times fainter).

If so they have to orbit way beyond Neptune or we’d have seen them long ago. A “brown dwarf” or a “red dwarf” would be ven more conspicuous -a brown dwarf is a failed star that is hot by its internal heat - that doesn’t make it invisible. It’s as easy to see in visible light as any planet, if near a star or sun. But invisible in complete darkness in the depths of space light years from any star because it is visible only by reflected light, unlike a star that shines by its own light no matter where it is. So we can see brown dwarfs by their warmth even if too far to see easily by reflected light, and we see red dwarfs because they shine by their own dim but easy to spot red light.

Also, if there are extra planets - they could cross the orbit of Neptune - Pluto does. But they can’t also cross the orbit of Uranus, never mind Saturn and Jupiter as well.

It’s 4.6 billion years since our Moon formed. Any planet that was in an orbit crossing those four gas giants would have been deflected from its orbit soon after it first entered it, within a million years. For instance if it was still in the orbit when the Moon formed, a time when the solar system was still in process of settling down, it would have gone well over 4.5 billion years ago.

It can cross one of the orbits, the orbit of Neptune, by being in a resonance. This means that whenever it crosses the orbit, then a bit like a child skipping a rope, it misses every time. Pluto does that, though it crosses Neptune’s orbit, Neptune is never there because it is in a resonance with Neptune. But it can’t cross two or more of those gas giants so never can come near Saturn or Jupiter never mind Earth. That’s why astronomers when they hypothesize “planet X” never hypothesize planets that come into the inner solar system. Those orbits are impossible - were possible in the inner solar system, but aren’t any more.

It can’t be in an orbit within Neptune because we’d have known about it for centuries.

So, it’s just not possible to have an extra unknown planet in our solar system that passes by Earth.

That leaves rogue planets coming from interstellar space. But those are so rare that there is no real chance of that happening either.

So no, it can’t happen at all. For debunking of many of the conspiracy theories see my

• Nibiru Bullshit Tester - How to check if they know anything about astronomy
• Debunked: Nibiru is invisible because it is a brown dwarf or made of dark matter
• Debunked: Nibiru will hit Earth on [Insert Date here]
• Debunking: Planet 9 is Nibiru
• Debunked: Our Sun or Earth could be hit by a rogue planet, neutron star, black hole or star
• List of the articles in my Debunking Doomsday blog to date