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Comet cooking 101

Use these instructions to make your own versions of these celestial visitors.
Comet
In my February story, “What Halley’s Comet taught us,” I mentioned that astronomers characterized the makeup of the famous celestial visitor as a “dirty snowball.” Once Halley made its most recent close approach, in 1986, the suite of probes that studied it in detail confirmed this view ⎯ mostly. It turns out that the comet’s nucleus is actually less volatile than scientists had suspected, meaning it was made up of more inert material than they thought, making it more of a “snowy dirtball.”

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