1、Comets are similar in composition to the gas giants.
2、Comets, by contrast, are relatively pristine - at least, below their outer crust.
3、 Comets are just as much members of the sun's family as (are) the other planets.
4、Comets were formed around the same time the Earth was formed.
5、Comets consist of "dirty ice", rather than solid rock, and so contain little iridium.
6、Comets are probably the most numerous astronomical bodies in the solar system aside from small meteor fragments and the asteroids.
7、Comets formed in circular orbits but were gravitationally flung into their present-day elliptical orbits when they ventured too close to planets.
8、Comets are conglomerations of ice, dust and rock from the early solar system, whose cores have remained physically and chemically unchanged ever since.
