Tiny planet spotted, 3x as distant as Pluto

NASA

Astronomers have spied a cold world three times as distant from the Sun as Pluto.

The unexcitingly-named V774104 is at least 500km across and the most faraway dwarf planet yet spotted. Operators of the Japanese Subaru telescope will now track its movements in hopes to learn more about the behavior of such distant bodies, which tend to have strange orbits.

Models for Solar System formation suggest that such objects were probably not created in these weird, eccentric orbits.
One explanation is that they have been perturbed gravitationally and pulled on to their strange trajectories by a passing planet - perhaps one that was expelled from our Solar System early in its history.
Some scientists even speculate that such objects could have been stolen from a star that formed from the same "nursery" of gas and dust as our Sun 4.6 billion years ago.

It's about 3/4 as far out as the Voyager probe, which may or may not have left the solar system, depending on your point of view.