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?