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Astronomy

The Composition and Structure of Cometary Nuclei

Quick fact

The nucleus of a comet is typically only a few kilometres across – smaller than a city – yet it can produce a coma larger than the Sun.

Why this is interesting

Every so often, a cosmic snowball plunges toward the Sun, sprouting a glowing tail that stretches millions of miles. But what exactly is that ‘dirty snowball’ at its heart?