"A planet four times the size of Earth may be skirting the edges of the solar system beyond Pluto, according to new research. Too distant to be easily spotted by Earth-based telescopes, the unseen planet could be gravitationally tugging on small icy objects past Neptune, helping explain the mystery of those objects' peculiar orbits."
"For several years, astronomers have observed that a handful of the small icy bodies that lie in the so-called "scattered disc" beyond the orbit of the planet Neptune, including the dwarf planet Sedna, deviate from the paths around the sun that would be expected based on the gravitational pulls of all the known objects in the solar system."
"However, when Gomes ran the same calculations with the addition of the gravitational pull of a massive planet at the outskirts of the solar system, Sedna and the other anomalous objects' expected orbits fell in line with observations. The unseen planet would be too far away to perceptibly perturb the motions of Earth and the other inner planets, but close enough to the scattered disc objects to sway them."
"Several planet types could fit the disturbances seen in Gomes' calculations. For example, a Neptune-size planet, about four times bigger than Earth, orbiting 140 billion miles (225 billion kilometers) away from the sun would influence the anomalous objects in the observed manner. Or, a Mars-size planet with a highly elongated orbit — but one that always kept it well beyond the orbit of Pluto — could yield similar results. As for how it got there, the planet could have been born in and expelled from a distant star system and later captured by our sun's gravity, Gomes said, or it could have formed near our sun and gradually been thrust outward through gravitational interactions with the other planets."
"This would not be the first time a planet was revealed by way of its gravitational effects on other celestial bodies. The existence of Neptune was hypothesized at the turn of the 19th century — long before the gas giant was actually seen through a telescope in 1846 — because of the way it was perturbing the orbit of Uranus.
On the other hand, many astronomers spent much of the 1900s searching for an extra planet, dubbed Planet X, beyond the orbit of Neptune, because they believed there were anomalies in the orbits of Neptune and the other gas giants. "But it turned out that anomaly in Neptune's orbit was the result of bad observation," Levison said. The search for Planet X was called off (though some conspiracy theorists believe this was a cover up of the planet Nibiru, which they say is on a collision course for Earth.)"
So ok, of course a healthy dose of skepticism here is greatly warranted. Still, it is fun to speculate! Imagine, Planet X really exists! This is also the first time I'm hearing about planet Nibiru. The universe is a surprising place, it's fun to think about this stuff.