Q:

Move object along spline(circle) in Three.js

I'm pretty new to Three.js (1 day experience lol)
I want to create a model of Solar system so I got planets that should move along their trajectories (circles).
function render() { 
    requestAnimationFrame(render); 

    sun.rotation.y += 0.01;
    mercury.rotation.y +=0.03;

    renderer.render(scene, camera); 
} 
render();

I tried to use splines for this, but failed to animate because I don't get how to use
requestAnimationFrame with variables (only this simplest incremental stuff like +=0.03)
mercury.position = spline.getPoint(t);

Also tried to do it with math, but same result. Don't know how to animate variables.
mercury.position.x = 20*Math.cos(4) + 0;

But I don't have any experience in animating anything in JS. So my mind is blown away by this requestAnimationFrame thing, that I got from some tutorial, it's like a black box to me.

A:

var sunGeo = new THREE.SphereGeometry(12,35,35);
var sunMat = new THREE.MeshPhongMaterial(); 
    sunMat.map = THREE.ImageUtils.loadTexture("image/sunmap.jpg");
var sun = new THREE.Mesh(sunGeo, sunMat); 
sun.position.set(0,0,0);
scene.add(sun); // add Sun

var mercuryGeo = new THREE.SphereGeometry(2,15,15);
var mercuryMat = new THREE.MeshPhongMaterial(); 
    mercuryMat.map = THREE.ImageUtils.loadTexture("image/mercurymap.jpg");
var mercury = new THREE.Mesh(mercuryGeo, mercuryMat); 
scene.add(mercury); // add Mercury

var t = 0;
function render() { 
    requestAnimationFrame(render); 
    t += 0.01;          
    sun.rotation.y += 0.005;
    mercury.rotation.y += 0.03;

    mercury.position.x = 20*Math.cos(t) + 0;
    mercury.position.z = 20*Math.sin(t) + 0; // These to strings make it work

    renderer.render(scene, camera); 
} 
render();

Found a solution

