Far away in the frozen outermost depths of our solar system, there might be a hidden planet four times the size of Jupiter. This secret companion to the Sun could be responsible for sending comets into the inner solar system.
This idea is an intriguing variation on the old Nemesis theory, which holds the Sun has a smaller companion star orbiting the outer reaches of the solar system. The Nemesis star was thought to be either a pint-sized red dwarf of a failed brown dwarf, and either way its movements through the Oort Cloud at the furthest edge of our solar system would cause comets to hurtle out of their obits. Some of these would hit Earth, leading to mass extinction events. The presence of Nemesis would explain why these extinctions occur in an apparently cyclical fashion.
That's the old theory, which fell apart because (among other things) it turns out Nemesis could not have a stable enough orbit to account for the regular mass extinctions, which is the main reason such an object was hypothesized in the first place. But now University of Louisiana-Lafayette astrophysicists John Matese and Daniel Whitmire have a new theory that holds a rather different kind of companion object is out in the Oort Cloud. Fittingly, they've named it Tyche, who in mythology is the good sister of the evil Nemesis.
So, why should Tyche exist? For one thing, two centuries worth of observation indicate a disproportionate amount of comets originate from the outer regions of the Oort Cloud as opposed to the areas closer to the Sun. A planet anywhere from one to four times the mass of Jupiter could be responsible for the gravitational influence that would create this imbalance. Matese points out that the probability that this effect is purely a statistical fluke is extremely small, which suggests there's something strange going on out there in the outer Oort. Tyche might also be responsible for the unusually elongated orbit of the dwarf planet Sedna.
Matese says such the discovery a planet would be a huge shock to planetary scientists:
"Most planetary scientists would not be surprised if the largest undiscovered companion was Neptune-sized or smaller, but a Jupiter-mass object would be a surprise. If the conjecture is indeed true, the important implications would relate to how it got there - touching on the early solar environment - and how it might have affected the subsequent distributions of comets and, to a lesser extent, the known planets."
If the planet exists, it would be located some 30,000 astronomical units away, meaning its distance from the Sun is 30,000 times that of Earth. It be extremely cold, with a temperature of about -73 degrees Celsius. At such a freezing temperature, Tyche would radiate no heat for us to detect, and its extreme distance would make it incredibly hard to spot. By comparison, Neptune is only 30 astronomical units away, and the Kuiper Belt is just 55 AU from the Sun.
There's some hope that we could find Tyche, however. NASA's WISE space telescope might have caught sight of Tyche before its mission ended in October. Actually, we need to hope it spotted the planet twice, as otherwise it would be impossible to corroborate its existence. If WISE, which is the most powerful infrared telescope yet built, could not detect Tyche, then it will be quite a few years before we've got a legitimate chance at seeing it again... assuming it's out there in the first place.