What’s the difference between an asteroid and a comet? A comet is basically a dirty iceball composed of rock and ice. The classic image is of a bright “star” in the night sky with a long curved tail extending into space. This is what happens when they approach the Sun and start emitting gases and releasing dust. It normally continues until there’s nothing left but rock or until they fragment into dust.
Asteroids, on the other hand, are primarily just rocks. They might conjure up notions of Hans Solo steering the Millennium Falcon through an implausibly dense “asteroid field” to escape a swarm of TIE Fighters, but mostly they just quietly orbit the Sun, minding their own business.
Yet these two space objects are not always as mutually exclusive as this would suggest. Let me introduce Phaethon, a “rock comet” that blurs the definitions between asteroid and comet, and let me tell you why it will be worth paying attention to this fascinating object in the coming years.
