`destination` is a Cartographic, but you are passing `object` here directly.  You need to access the `object.position` property and get it's value (using `getValueCartographic`).  You also need to specify the time.  If the object is moving, you need to fly to where the object will be at the end of `duration`, not where the object is now.  This means you'll have to take the clock parameters into affect (which you can get from the `viewer.clock` property).