Comets - Visitors from the frozen edge of the Solar System
Crawford, C. (Carolin) (2014-03)
Millions of dirty icebergs orbit around the Sun in a huge cloud of debris almost a light-year in radius. These are all pristine relics of our primordial Solar nebula. Only when one tumbles towards the inner Solar system does it heat up to develop into the spectacular apparition known as a comet.