For 10 points, name these astronomical bodies, which are commonly called "dirty snowballs."
The Giotto probe studied one body of this type, and confirmed that they typically have albedos below 4%. An early model for the composition of these bodies is the "Gravel Bank" model, and their composition was studied by the (*) "Deep Impact" probe. The cloud of gas around them is known as a coma, and their tails point in the direction of the solar wind. Many of these objects originate in the Oort Cloud. For 10 points, name these astronomical bodies, which are commonly called "dirty snowballs."
The Giotto probe studied one body of this type, and confirmed that they typically have albedos below 4%.
comets