If we approximate the orbit of the planets around the Sun to circular orbits with a uniform circular motion, where the velocity [tex]\vec{V}[/tex] is a vector, whose direction is perpendicular to the radius [tex]r[/tex] of the trajectory; the acceleration [tex]\vec{a}[/tex] is directed towards the center of the circumference (that's why it's called centripetal acceleration).
Now, according to Newton's 2nd law, the force [tex]\vec{F}[/tex] is directly proportional and in the same direction as the acceleration:
[tex]\vec{F}=m.\vec{a}[/tex]
Therefore the net force resulting from the movement of a planet orbiting the Sun points towards the center of the circle, this is called Centripetal Force which is a central force that in this case is equal to the gravity force.
