Ever since Neptune was discovered in 1846, astronomers have wondered about the possibility of the existence of another, far more distant planet in our solar system. Discrepancies in the orbits of the outer planets have even led some scientists to theorize about the existence of a "Planet X," a phantom planet with mass large enough to explain these gravitational deviations.

Now a new analysis of the orbits of our solar system's "extreme trans-Neptunian objects" or ETNOs — bodies that have been found to exist in the outskirts of our solar system — has revitalized the Planet X theory. In fact, scientists suspect there may be at least two more undiscovered planets in our solar system, planets larger than Earth but more distant than Pluto, reports NBC News.

"This excess of objects with unexpected orbital parameters makes us believe that some invisible forces are altering the distribution of the orbital elements of the ETNOs, and we consider that the most probable explanation is that other unknown planets exist beyond Neptune and Pluto," lead author Carlos de la Fuente Marcos, of the Complutense University of Madrid, said in a statement.

"The exact number is uncertain, given that the data that we have is limited, but our calculations suggest that there are at least two planets, and probably more, within the confines of our solar system," he added.

How is it possible that such large objects could remain undetected within our own solar system? Well, such planets would be so distant from the sun that they would be virtually undetectable with modern instruments. To put it in perspective, the distance from Earth to the sun is measured as 1 AU (astronomical units). Pluto, by comparison, is almost 50 AU at its furthest orbit. The distance between the proposed new planets and the sun would be a whopping 200 AU or more. That's four times the distance of Pluto from the sun at its furthest orbit! So it's unlikely that we'll be spying Planet X or Y anytime soon.

Even so, if the results are confirmed, they would represent one of the greatest astronomical discoveries in recent history. The research is published in the Monthly Notices of the Royal Astronomical Society.

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