Comets are the rogue cousins of our solar system family, flashing about space with brilliant tails streaming behind them. Made up of rock, dust and ice, comets were formed with the rest of the solar system some 4.5 billion years ago. Unlike asteroids, which formed closer to the sun, comets came together in space so cold that their icy particles would not melt. They circle the sun just like planets but in an elongated, elliptical orbit.