A New Planet Astronomers have found evidence of what could be a ninth planet in the outer solar system. They say that the planet, probably a gas giant like Jupiter or Saturn, was thrown off the Sun's ecliptic plane thousands of years ago. All the planets in our solar system orbit the Sun in this plane or zone, however the new planet, named Planet 9, has a slightly elongated orbit. This planet's orbit lies very far away from the Sun. In fact, it would take Planet 9 between 10,000 and 20,000 years to go around the Sun just one time. Astronomers have not actually seen Planet 9, but other sources of research have convinced them that such a planet definitely exists. Because Planet 9 has a mass that is 10 times that of Earth's, astronomers are certain that Planet 9 will indeed be classified as a planet rather than a dwarf planet, like Pluto. In the process of Planet 9's discovery, researchers also discovered a cluster of smaller KBOs or Kuiper Belt Objects. These are a very large band of rocky and icy objects found beyond the orbit of Neptune in the solar system. This belt is comparable to the large body of rocks of different shapes and size ranging from dwarf planets to dust particles found between Mars and Jupiter called the asteroid belt. Astronomers believe that Planet 9 herds these KBOs, because their perihelion, or closest point to the Sun, in their course (or orbit) matches that of Planet 9's.

Based on the context of this passage,
A. an orbit is the time taken by a planet to revolve around the Sun
B. the distance between Jupiter and Saturn
C. the shape of the path taken by a planet
D. the periodic path taken by a planet or space object