The difference between meteors and meteroids is that meteroids don't burn up. Instead, they crash into the surface of Earth. From pieces of meteroids that have collided with Earth in the past, we know that most are composed of either iron or nickel.
Comets are like dusty balls of ice because they are composed of rock, ice, and dust. At there brightest, they can outshine stars. The tail on the comet form when the main part gets close to the sun and the ice begins to melt. The trail of melting ice gets pushed back by the foward motion of the comet. Some come periodically. For example Halley's comet appears every seventy-five years. The next appearance should be in 2061.
