Is there a real planet called Planet X?

Answer 1

Planet X is just the temporary name used for a planet that hasn't been named yet. For example, Pluto was called Planet X before it got its official name. There isn't currently any unnamed planet being called Planet X.

Answer 2

Percival Lowell hypothesized that an undiscovered planet caused discrepancies in the orbits of Uranus and Neptune. He called it "Planet X" and the name has stuck. When Pluto was first discovered it was thought to be Planet X, but further examination showed that it could not be the cause of the orbital discrepancies (which were later shown to never have existed in the first place; the apparent problems were caused by some inaccurate observations).

The reasoning for the name "Planet X" is that X is traditionally used for an unknown quantity. Lowell certainly didn't believe that, when found, it would turn out to have a gigantic X on it.

Answer 3

Short answer: no.

Here's the long version.

"Planet X" was the hypothetical name given to an as-yet-undiscovered planet about a hundred years ago. The planet Neptune was discovered because mathematicians analyzing the orbit of the planet Uranus found that its orbit didn't quite match theory. This was kind of upsetting, because the theory was working so well for all the other planets, so they decided that there must be another planet out there past Uranus, and a couple of them did all the calculations required to tell astronomers where to look for this additional planet, and a couple of astronomers did exactly that, and lo and behold they found Neptune.

So, a bit after that, they did the same kind of analysis of Neptune's orbit, and said "Hey, there's another one, we'll call it Planet X as a placeholder." Figuring out where Planet X needed to be turned out to be more complicated, and it took a couple of decades before Clyde Tombaugh noticed a tiny point of light that moved (very slowly) and dubbed it Pluto.

Now comes the problem. Pluto was way too dim. To account for the discrepancies in Neptune's orbit, Planet X/Pluto needed to be fairly massive, which meant fairly big, and Pluto was just too dim to be as big as it needed to be, unless it was really, really dark (a lot darker than the Moon, which, despite how bright it looks in the sky, is actually about the color of old asphalt). So maybe there was Pluto, and another Planet X out beyond that...

Except there wasn't. There wasn't anything out there large enough to be Planet X. And the more we learned about Pluto, the smaller it seemed to get. When I was a child in the 1960s, it was thought that Pluto might be as large as Earth. Then it was revised downward to maybe about the size of Mars in the 1970s, then maybe as big as Mercury, and we now know it's considerably smaller than the Moon and not actually a "planet" by the modern definition.

So what explains the discrepancies in Neptune's orbit, then? It turns out that later, more careful observations showed that Neptune is moving precisely as it should be, and there's no need to invoke any mysterious Planet X to explain its orbit.

So, not only is there not a planet named Planet X, there never really was one, and it's now considered unlikely that there could be (because if there was, it would show up by affecting Neptune's orbit in predictable ways, and we've measured Neptune's orbit accurately enough to pretty much rule that out).

One other time the term "Planet X" has been used is in explaining the orbit of Mercury. Mercury's orbit precesses (wobbles, if you like) around the Sun, and the reason is that it's affected by the other planets. However, after taking them all into account, it wasn't quite enough to explain Mercury's precession, so there was some talk of a "Planet X" inside the orbit of Mercury (though a more common name for this hypothetical planet was "Vulcan"). Relativity shot that one down; when you take relativistic effects into account, it explains Mercury's orbit extremely well.

Finally, "Nabiru". Nabiru is a term that appears in some ancient mesopotamian texts. It's pretty vague, and no one's quite sure what it means. One thing it definitely does not mean is some mysterious planet that's coming to smash into the world or anything like that. It's likely that it's either an alternative name referring to one of the known planets (probably Jupiter), or it might be a word to describe a conjunction of a planet and a star, or two (or more) planets ... the ancients were pretty loose with what they called "stars". Planets? Wandering stars. Comets? Hairy stars. (The words "planet" and "comet" literally come from the Greek words for "wander" and "hair" respectively.)

Answer 4

No. Planet X is just a name for a planet that is not yet proven to exist. Before Pluto was discovered, back when it was just a theory, it was called Planet X. So there is no Planet X that will hit us in the future

Answer 5

No. Pluto is still called Pluto and is no longer considered a planet. Planet X was a planet once believed to orbit beyond Neptune based on the orbit of Uranus deviating from the expected values. When Pluto was first discovered it was believed to be Planet X, but it was later found that Pluto is not massive enough to account for the discrepancy in Uranus' orbit. The Planet X hypothesis was dismissed when we found we had made a small error in calculating the mass of Neptune, which accounted for the deviation in the orbit of Uranus.

Answer 6

Yes. Planet X is the one we haven't discovered yet.

Since we haven't actually discovered it, we know nothing about it. Once Planet X is actually discovered, it will be given a real name, freeing up "Planet X" for the _next_ undiscovered planet.

Planet X is also the name of the planet used in many old-time "space Opera" Science Fiction movies.

Answer 7

No. There was a hypothetical planet called Planet X a hundred years or so ago, but it was later discovered to not exist.