Objects.object.Rotation = 1.5
local obj = game.CurrentScene.SceneObjects["asteroid"]
--obj.Scale = 0.5 -- is possible to define initial scale of object sprite / active animation
obj.RotationCenter = { x = -1, y = -1} -- -1, -1 = center of sprite / animation, define other coordinates if you don't want it to rotate via center.
obj:to(60000, {Rotation = math.rad(360)}, easeLinearOut, true, false) -- new to() tween function (simpler than startObjectTween function, however may not work in current public build).
Don't try to rotate objects that go outside of the viewport [...] Simon said he would fix this for future build, but I don't know whether he has gotten around to it or not.