When You are making a game, such as super mario galaxy, you need the gravity code, right? well, here it is!
Mario Man654321 already posted this code, but he didn't explain it good enough. When you want to use the code for all the gravity, then that would be a STEP action. let me show you.
1. Create a sprite of a planet or sompething.
2. Make an object. (to make things less confusing, name it object_parent)
3. Make a CREATE event.
4. Go to the tab that says: Control.
5. Drag the EXECUTE CODE thing onto the board.
6. Put in THIS code (be sure the code is in the CREATE event.)
7. (the code) 
rotation=0;
rotation_previous=0;
rot_speed=0;
8. Now, after you have put in that code, make a STEP event.
9. REPEAT STEP 5.
10. Put in THIS code (make sure you are in the STEP event.)
11. (the code)
if place_meeting(x,y,whatever_your_player_is_called) and rot_speed>0
{
var dist,ang;
dist=point_distance(x,y,player.x,player.y);
ang=point_direction(x,y,player.x,player.y);
player.x=x+lengthdir_x(dist-2,ang+rot_speed);
player.y=y+lengthdir_y(dist-2,ang+rot_speed);
}
image_angle+=rot_speed;
12. Now, after you've completed ALL OF THESE STEPS, Make another object (can be a different sprite, doesn't matter. to make things less confusing, name it either planet1, planet 1, or object_child)
13. make the PARENT (for this object) the first planet (a.k.a. object_parent)