As most people know, there are nine planets in our solar system. They are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. The first four planets, also known as the inner planets, are the most dense planets. The rest, outer planets, are less denser because of their gaseous composition.

The planets seem to be on a circular path around the sun, but they are not. Their path's are described as ellipses. An ellipse can be described as a stretched circle with two center points. The Sun is always at one of the center points in a orbit's path. Since the Sun is at one center (focal) point, when a planet nears that focal point it travels faster. As it goes further away from the Sun, the planet travels slower. The reason for this change in velocity has to due with the Sun's gravitational pull. Now all ellipses are not the same. Some are more curved than others, and some are longer than others. Scientists use eccentricity to describe each planet's orbital path shape. Gravity also has a major role in each planets orbital path. Gravity is what keeps each planet on track and not flying all over the place. However, gravity is a two way street in space. Just as the Sun applies its gravity on all planets in our solar system, each planet applies its own gravity back on the Sun. Since the Sun is so massive, the planets can't move the Sun with their gravity and are forced to move around the Sun.

Since there is so much gravity, what keeps the planets from being pulled into the Sun?. The answer has to deal with a planets speed. All planets in our solar system move around the sun at their own speeds. They each move at different speeds because the Sun's gravity affects each planet at different distances. As mentioned before, when the a planet is closer to the Sun it travels faster than when it is further away. The closer to the Sun the stronger the gravity becomes resulting in more speed an object needs to escape its gravity. However, the planets work in a way that they don't have enough speed to escape the Sun's gravity, but enough not to be pulled in by the Sun's gravity. This state of equilibrium is what keeps the planets in orbit around the Sun.

Is there a possibility that planets will crash into each other? The answer is no. Our solar system was designed to be stable. There are many forces (such as gravity and velocity) that are acting on the planets to keep them stable. The planets move at their own pace and in their own paths. The only two planets that do cross paths are Neptune and Pluto and they have no chance of meeting. Also, if you noticed from above, each planet has a great deal of mass, which requires a great deal of energy to affect it. So far, there is no object with such energy in our solar system other than the Sun. In the end the Earth will not be destroyed by other planets.