Good question! The planets in our solar system seem to be floating, but they are actually orbiting around the sun. The sun is a massive star and exerts a strong gravitational pull on the planets in our solar system. If the planets did not “feel” the sun’s gravity, they would fling off into space. Likewise, if the planets were not moving when they initially formed, they would be pulled right into the sun. Planets’ orbits are a result of the balance of their momentum (trying to fling them out into space) and the sun’s gravity (trying to pull them in).

All of the planets are falling into space. There is no "up" or "down" in space; there is only toward objects with mass, and away from them. The most massive thing in our solar system is the sun, which has about 99.8% of the solar system's mass. The planets orbit the sun because they are moving, but the sun's gravity causes them to arc over and circle the sun instead of just flying off into space, which is what they would do if the sun weren't there.