Thanks for the help everybody, here's how I ended up solving the problem.

function Update () 
{

}

function OnTriggerStay (other : Collider)
{
    other.attachedRigidbody.useGravity = false;

    var direction = -(other.attachedRigidbody.transform.position - transform.position);

    if (other.attachedRigidbody)
    {
        other.attachedRigidbody.constantForce.force = direction;
    }
}

function OnTriggerExit (other : Collider)
{
    other.attachedRigidbody.useGravity = true;
    other.attachedRigidbody.constantForce.force = Vector3.zero;
}

I saw your post and think this is worth taking a look at on the Unify Wiki page. It has a Simulation section on the scripts page.

Quote from page: "Gravity.js- Provides a relatively accurate simulation of body-to-body gravity (i.e. plantary gravity)."

Here is the link: http://www.unifycommunity.com/wiki/index.php?title=Gravity

I'm new too, hope it helps.

I am no expert by any means, but my first thought would be to have a sphere with sphere collider that would represent the reach of the gravitational pull. set the collider to be a trigger. Then you would need a script on the object that is going to be acted upon by the gravity that would register that it is in range to be under the gravitational pull and then calculate the distance from the planet to work out how much gravity should be applied. This is where I would start, but that doesn't necessarily mean that it would be the best way.

To add to that, the way I would apply the gravity in the script would probably be to alter the rotation and transforms, so every second the ship should be moved some amount closer, or something along those lines.