Gradually, the cloud became differentiated into light and heavy components, and eddies appeared in it where the matter was concentrated. Eventually, these eddies produced large numbers of proto-planets which collided and stuck together to form larger bodies. Most of the large bodies were concentrated in a disk revolving around the proto-sun. In that case, the Sun would be part of a double star system. Smaller objects such as Pluto, the asteroids, and the planetary moons are solid like the inner planets.
Vertical elevation is shown with contour lines , which join points of equal altitude.
The top of the diagram to the right is a topographic map of a hill. The bottom is a picture of the hill it represents. Assuming that the numbers on the map refer to feet, note that The contour line with the highest elevation is 100 ft. The contour line with the lowest elevation is 20 ft. Not every point lies on a contour line.