By that I am referring to a 'Trojan' Asteroid, the first to be found orbiting the Sun along Earth's orbit. This particular asteroid is known as 2010 TK7 and was discovered when the WISE telescope had been scanning the entire sky from January 2010 to February of this year, this asteroid was spotted because it follows an unusual orbit and as such takes it farther away from the Sun than is typical for Trojans. Such Asteroids have been found in the solar system before but never following the orbit of the Earth, this is because they are extremely hard to detect due to them being relatively small and from the Earth's point of view they seem relatively close to the sun. Trojans remain stable due to circling around 'Lagrange Points' which are gravity wells situated near two large objects, in this case the Sun and the Earth. These Lagrangian points mark positions where the combined gravitational pull of the two large masses provide precisely the required centripetal force required to rotate upon that orbit. As they follow in or lead in the same orbit as a planet they therefore can never collide with that planet, so any of you who were worried needn't worry about a catastrophic collision with 2010 TK7.
The asteroid is roughly 300m in diameter, at a distance of about 80 million kilometres from the Earth. It has an unusual orbit that not only does it follow the orbit of earth with an extremely complex motion but that it also moves above and below the plane of orbit. The asteroid's orbit will most likely stay stable for the next 10,000 years therefore it shan't be disappearing into the vastness of space any time soon. A handful of other objects share an orbit similar to that of earth which may potentially be the aim of human or robotic exploration but 2010 TK7 is not one of these due to it's odd orbit travelling above and below the plane of orbit, therefore it would take a massive amount of fuel to reach.
