Attach this script to the mercury movie clip:

onClipEvent(load) {
speed = .4;
radius = 40;
orbit = 0;
}
onClipEvent(enterFrame) {
orbit += speed;
this._x = Math.cos(orbit) * radius + _root.sun._x;
this._y = Math.sin(orbit) * radius + _root.sun._y;
}

The

`load` event

sets the speed of the planet and the distance it remains from the sun. The speed determines how much of the circumference of the circle the planet travels in each frame. A speed of 6.28 would mean that the planet would move completely around the sun in one frame. A speed of .4 would mean that it would take 15.7 frames (6.28/.4) to orbit the sun.

Every

`enterFrame`, the orbital position is increased by

`speed`, and the new position is calculated. Both x and y positions are adjusted by the location of the sun so that the planet's orbit is centered on the sun.