Comets get the “dirty snowball” nickname from their composition: they are a little bit of rocky dust, a good amount of chunks of ice, and a pinch of more complex compounds. Spectra analysis reveals the presence of hydrogen compounds within comets, and the existence of hydrogen compounds like water and the presence of carbon dioxide and carbon monoxide confirm that Comets form in the outer portion of the solar system. This is because these compounds and gases can only condense in the most distant and coldest corners of the solar system. In fact, comets have been discovered to contain organic compounds, supporting the theory that comets could have played a crucial role in the emergence of life on Earth by providing our planet with the organic compounds needed for life to take root.
There have been a multitude of spacecraft missions to comets that have revealed fascinating insights about these celestial objects. The most remarkable findings, in my opinion, occurred in 2004, when NASA’s Stardust spacecraft visited Comet Wild 2. The mission used a material called aerial to gather dust particles from the comet, providing us with the first ever direct sample of comet dust. The findings have perplexed scientists, the composition of the dust suggests that the comet formed in the inner portion of the solar system and combined with other cometary material formed in the outer solar system. This finding completely uprooted the scientific theory of comet composition and caused many scientists to rethink how comets are formed.