What's the difference between a nebula and comet?

A comet is a small body composed of mostly ice in orbit around the Sun. When it approaches close enough, the heat causes the volatile ices to warm up and sublimate, which can give the comet a spectacular tail for a while before it heads back into the deep freeze of the outer solar system. read more

Here’s an infographic on the differences between asteroids, comets, meteors and meteoroids. Here’s NASA’s Lunar and Planetary Science Page on asteroids. And here’s Hubblesite’s News Releases about Asteroids. read more

The main difference between asteroids and comets is their composition, as in, what they are made of. Asteroids are made up of metals and rocky material, while comets are made up of ice, dust and rocky material. Both asteroids and comets were formed early in the history of the solar system about 4.5 billion years ago. read more