Directions: Read the passage and answer the question.

A comet is an icy small solar system body made up of ices mixed with smaller amounts of dust and rock. It is no larger than a few kilometers across. The main structure of a comet is know as the nucleus. Comets are composed primarily of many varieties of ice including water, methane and other gases. Comets usually orbit the sun. While planets have a circular orbit, comets' orbits are usually very elliptical. As a comet moves closer to the Sun, the ices begin to fizz. The closest point in its orbit to the Sun is known as “perihelion” and the farthest one is known as “aphelion”. Comets are not any kind of spaceship or alien base. They are bits of solar system material.

Comets consist of lesser amounts of ______.