Some sources ([wikipedia Italy](https://it.wikipedia.org/wiki/Cometa)) say that comets are mostly made of gas and “ice”. Other sources ([INAF](https://www.media.inaf.it/2017/08/22/comete/)) say that Rosetta has shown evidence that “ice” is no more than 20% of the mass of a comet. So which one is true?
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> So which one is true?
Both! Comets are usually made up of a combination of rock, dust, ice, and frozen gasses. But their ratio of those substances varies. One comet might be mostly gas and ice, while another is mostly rock with smaller proportions of gas and ice.
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