We have a new neighbour. Astronomers Scott Shephered of the Carnegie Institute of Sciences and Chad Trujillo of the Gemini Observatory in Hawaii have published a study in Nature detailing the discovery of 2012 VP113, a dwarf planet-sized nicknamed "Biden" after the current US vice-president. There's more to this discovery than a novelty name, however - it's the furthest object yet spotted orbiting our Sun, never getting closer than 11.9 billion kilometres, and has an orbital shape that indicates the possible presence of an even larger Earth-sized planet somewhere in the farthest reaches of the Solar System.
The most distant bodies orbiting the Sun, out beyond Neptune and the Kuiper Belt, lie in the Oort Cloud - this is where Biden is, along with Sedna (a probable dwarf planet candidate, which was spotted in 2001). Biden is estimated to be roughly 450km wide, but its orbit is absolutely massive relative to the inner Solar System that we're more familiar with. It is also, like Sedna, not officially a dwarf planet as of yet according to the International Astronomical Union, though they are generally assumed by many scientists to be.
Here's an illustration of Biden's orbit, provided by the Carnegie Institute of Sciences:
That small white dot in the middle is the Sun. On this scale, the orbits of the inner planets like Earth are too small to see - instead, the four purple lines represent the orbits of Jupiter, Saturn, Uranus and Neptune, while the cloud of blue dots is the Kuiper Belt. That's where Pluto is, and where the New Horizons probe is currently heading - a probe that was launched in 2006, and which still isn't there yet. And much further out, beyond there, is the red dot of Biden and the orange dot of Sedna. The Earth orbits the Sun at one astronomical unit (AU), but by comparison the closest point between Biden and the Sun is a 80 times that distance. It is, to understate matters, far away.
Yet it's a fascinating discovery for what it lets us infer from the rest of the Oort Cloud, which was believed to extend from 5,000 to 10,000AU from the Sun. When Sedna was discovered it seemed to imply that there might be a further layer of objects orbiting in between the Kuiper Belt - which has objects with closest approaches of no more than 50AU from the Sun - and the Oort Cloud, a so-called inner Oort Cloud, which extended as far as 1,500AU from the Sun. Scientists were intrigued by the possibility of the objects they might find in the inner Oort Cloud, as they would represent a kind of fossilised early Solar System.
Most asteroids in the inner Solar System - from those in the Asteroid Belt to the Greeks and Trojans that chase and follow Jupiter around - have been perturbed out of their original, primordial orbits by the influence of planets, and are now locked into stable, regular orbits that resonate with the objects surrounding them. The stuff that's in the outer Oort Cloud is so far from the Sun that extremely slight tugs from outside the system, such as that from a passing star, can be enough to knock them around. Yet the inner Oort Cloud would be in a sweet spot, far enough from planets, Sun or passing stars to avoid getting disturbed, and as such reflect things pretty much as they were when the Solar System formed 4.5 billion years ago.
The surprise with Biden, though, is that it not only lends credence to the hypothesis that that inner Oort Cloud exists, but that the region has been affected by the gravity of an unknown large planet. Look again at the diagram above - Sedna and Biden both come to their closest approach to the Sun on the same side. Those two alone may just have been a coincidence, but so far there are 12 objects known to orbit out beyond Pluto, and they all cluster on the same side. It's too much to have been a coincidence. Here's National Geographic's Dan Vergano:
This orbital coincidence is what statistically suggests that a bigger planet tugged either long ago or continuously now at these smaller worlds' orbits to keep them clustered together. If the putative bigger planet is still there and is only a few times bigger than Earth, it would circle the sun about 250 times farther away than our planet does. A bigger one would circle even farther away.
It could still be there, it might not be. It might have been something like a rogue planet passing through, one lost by its home star and now wandering space. We just don't know, and it's only through further observation of this strange, distant, cold region of our part of the cosmos - which Shepherd and Trujiloo estimate could contain as many as 1,000 such objects, some of which will be as large as Mars - that we can narrow the options down. It would be wonderful if it turned out that all those astronomers who obsessivley searched for the so-called "Planet X", a planet with mass somewhere between the Earth's and Saturn's and assumed to lie beyond the orbit of Neptune, turned out to be correct.