Answer: The idea of an alleged planet Nibiru (and a future catastrophic encounter with Earth) originated with Nancy Lieder, a Wisconsin woman who claimed that as a girl she was contacted by gray extraterrestrials called Zetas, who implanted a communications device in her brain. This claim alone would give pause to any rational person - even if not scientifically trained - that the whole Nibiru story is so much balderdash.
There is no such astronomical entity as Nibiru or "Planet X" as it's also been called, nor any potential for future collision with Earth. It really is all an elaborate fable that has been circulated among assorted gullible groups - who've also made empty collision claims.
The multiple collision forecasts are important because to actually know that would require knowing the alleged object's orbital elements. In fact there have never been any orbital elements computed for Nibiru which indicates it's merely a creation of overactive imaginations.
Let's grasp then that orbital elements ultimately determine whether a proposed (or hypothetical) planetary object is fact or fiction. These include a set of parameters used to define the properties of the orbit: a (semi-major axis), e (eccentricity), M, the mean anomaly, W the longitude of the ascending node, i, the inclination of the planet''s orbit, to the ecliptic and w the argument of the perihelion.
A typical diagram that may be used is shown below:
The diagram shows assorted orbital elements for a planet of mass m2 (the Sun is m1) and this can be used as a basis for orbital energy analysis and also to predict future positions. Energy constants in celestial mechanics are very useful for quickly coming to terms with specific properties of an orbit such as shown in the accompanying sketch- designating a generic orbit in x-y-z space .
The critical or key parameter here is h, the angular momentum vector for the orbiting system.
The fact none of these have ever been computed for Nibiru shows more than anything that it doesn't really exist. The relevance of orbital elements is because the "Niburians" keep making forecasts of collisions with Earth leading to calamity. One such impact was designated for May, 2003. According to a Wikipedia entry: "One week before the supposed arrival of Planet X in May 2003, Lieder appeared on KROQ-FM radio in Los Angeles, and advised listeners to euthanize their pets in anticipation of the event as she had done"
So she must have known the orbital elements to make such a forecast and even kill her pet, right? Nope! Never happened. Not to be denied, the Nibuirans made yet another doomsday forecast for Dec. 21, 2012, the supposed date for the "end of the world" by the Mayan calendar - which I'd already skewered, e.g.
If people were intelligent enough and genuinely curious they'd be more invested in a real "Planet X" which is actually Planet Nine for our solar system. "Planet Nine" is the name given to the newest potential member of our solar system by astronomers at Caltech. But don't call it "Planet X", because they are averse to having it conflated with the Nibiru baloney.
Artist's conception of 'Planet Nine' - predicted by Caltech astronomers
To be sure, Planet Nine has not technically been "discovered", as in actually training the Palomar telescope on it. No, its existence has been inferred from the marvelous science of celestial mechanics, based on the gravitational effects detected on smaller objects in the Kuiper Belt - and from mathematical modeling techniques and computer simulations.According to the Caltech site, the two scientists - Konstantin Batygin and Michael Brown describe their work in an issue of the Astronomical Journal. They show how Planet Nine helps explain a number of mysterious features of the field of icy objects and debris beyond Neptune known as the Kuiper Belt. Those who wish to access the actual paper can get the .pdf here:
Planet Nine is about 1 million times more probable than any Niburu, but sadly too many lack the curiosity to explore that because it entails mastering - learning actual scientific principles. By contrast, Niburu's existence has merely been based on recycled babble, phony forecasts (that have never materialized), and false claims of "experts" (unnamed astronomers and seismologists) who supposedly support this bunkum but haven't yet published anything in serious journals or even come to public light. Thus, as far as science can inform us - Nibiru simply does not exist. It is a figment of the imagination of millions of gullible folks who have probably never taken a science course in their lives.
This confirms again that the tragedy of humanity is that it's too often fascinated with mythical objects or catastrophes and not engaged or intelligent enough to deal with the real entities. OR real catastrophes, like global climate change.