That Rosetta has wanted to see
And it looks like a duck
Though with plenty of luck
They’ll find water among the debris
Comets are astronomical objects consisting of a mixture of rocks, dust, water ice and frozen gases which orbit the sun in an extended orbit. When they approach the sun they heat up and some of the water and frozen gases evaporate, releasing some of the dust. The escaping material is blown by the solar wind (caused by plasma escaping from the sun) to form a tail which can sometimes be visible to the naked eye - although the central rocky body is too small to see. Every time it comes close to the sun it loses more material and may break up into fragments. Meteor showers can be associated with some comets - representing small fragment which have become detached and spread out along the orbit over millions of years.