The inset shows details of the central coma . The unseen nucleus itself is essentially a chunk of dirty ice about ten kilometers in diameter. Comets usually originate in the Oort cloud in the distant Solar System - well past Pluto , most never venturing into the inner Solar System. As a comet approaches the Sun, rocks, ice-chunks, gas, and dust boil away, sometimes creating impressive looking tails . In fact, debris from Comet Swift-Tuttle is responsible for the Perseids meteor shower visible every July and August.
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