No. The planets are held in orbit by forces balanced against each other: The force of gravity from the sun would pull the planet into the sun destroying it. The momentum of the planet making it travel in straight line would result in the planet travelling away from the solar system. There are also other forces involved such as the pull from other planets on each other. Combined, they balance each other resulting in a planets circular/elliptical path orbiting the sun. Otherwise, the planet would have fallen into the sun, collided with other planets or other objects, or just flown away from the solar system long ago and we would never have known about it.The force that holds objects in orbit is gravity. In the case of our solar system, the planets are held in orbit by the gravity generated by Sol, our sun (a sun is a star with a satellite system).The inertia of the planets combined with the Sun's gravity keeps the planets in orbit. So, there's only really one force, gravity. However, the effect of inertia is sometimes referred to as "centrifugal force", although its not a real force.Objects in our solar system are kept from falling into Sol, the sun, by their centripetal motion (inertia). They are kept from flying off into empty space by Sol's gravity, generated by spacial displacement.They are held in orbit by the gravity of a celestial body of a greater mass. For example, the planets in our solar system are held in orbit by the gravity of the sun.