Much of a comet, typically

ICE

Think of the frozen core that gives comets their bright tails when they near the sun.

Comets are often called "dirty snowballs" because they're mostly made of frozen gases, dust, and ice. The clue hints at this by calling out the main component—ice—which makes up the bulk of a comet’s nucleus. It’s a straightforward definition with no wordplay, just a nod to basic astronomy. Think of the bright tail as the comet melts near the sun, but the core stays icy.