Apple Motion 2 Tutorials - Manual (Page 211)

Tutorial 4 Working With Particles 211
To set the particles to orbit the Big Star object:
1 Press F7 or D to display the Dashboard.
2 Drag the Big Star object from the Layers tab to the Object well in the Inspector.
Important: When selecting the Big Star object, be sure to click and drag in one
movement. If you click the object and release the mouse button, the object is selected
and its Inspector appears.
The particles now orbit the Big Star object.
3 In the Layers tab, select Big Star.