There's good news for those who were annoyed when Pluto was knocked off the list of planets. According to a pair of scientists at Caltech, there may actually be nine planets in the Solar System after all. Researchers Konstantin Batygin and Mike Brown say that a planet ten times the mass of Earth may be circling the Sun in a highly elliptical orbit 20 times the distance of Neptune or 36 billion mi (60 billion km), with a year of 10,000 to 20,000 Earth years.
Caltech says that the still-hypothetical planet has yet to be observed and that its existence is based on mathematical modeling and computer simulations derived from the orbits of six Kuiper Belt objects in the outer Solar System. These objects have very unusual orbits that are tilted 30º to the plane of the ecliptic, where the eight known planets reside, and all point in the same direction.
Batygin and Brown say that this could be due to the presence of a previously-unknown planet or a mass of Kuiper Belt objects. However, the latter was dismissed because it would require the belt to be a hundred times more massive that it's believed to be. In addition, the movements of the other planets could not explain the phenomenon because the planetary orbits are too irregular in relation to one another to cause the tilt and alignments.
To determine whether an unknown planet was involved, Batygin and Brown assumed that it has a perihelion (closest distance to the Sun) that was 180º out of synch with the other planets or other known objects. Their calculations indicated that a ninth planet would set up a state called a mean-motion resonance, that keeps the six Kuiper Belt Objects stable and prevents them from colliding with one another.
In addition to explaining the six Kuiper Belt objects, Batygin and Brown discovered that their hypothesis also explains orbital anomalies of Kuiper objects Sedna and 2012 VP113, and predicted the presence of Kuiper objects perpendicular to the ecliptic – four of which have been observed in the last three years.
The scientist believe that the presence of the ninth planet could shed light on the origin of the Solar System by indicating the existence of a fifth "core" to the theorized four around which the gas and dust of the early system may have condensed to form the planets Jupiter, Saturn, Uranus, and Neptune. They say that this fifth core could have been ejected by Jupiter or Saturn to form the ninth planet, which may explain its highly eccentric orbit.
The Caltech team says that despite its great distance, larger earthbound telescopes should be able to see the Neptune-like planet and they hope that their announcement will spur a hunt for it. In addition, Brown, who was instrumental in having Pluto downgraded to a dwarf planet, hopes that the news will help un-ruffle some feathers.
"All those people who are mad that Pluto is no longer a planet can be thrilled to know that there is a real planet out there still to be found," says Brown. "Now we can go and find this planet and make the solar system have nine planets once again."
The Caltech research was published in The Astronomical Journal.
In the video below, Batygin and Mike Brown discuss their findings.