Rotate around object then leave at realistic angle

Hi, I'm trying to make a sphere being able to enter and leave an orbit of another object. Currently I am using transform.RotateAround to make the sphere rotate around the object. However, when I stop the rotation, I want to make the sphere leave the orbit in a streight line that would be realistic.

My problem is that I cant figure what method would make this possible. At the moment I'm using Rigidbody2D.AddForce to a straight "up" force. This obviously does not work because when the sphere leaves, it just gets an forced up velocity.

How can I achieve this? Is there a way to calculate the leaving angle and then apply force to that direction? Do i need to change transform.RotateAround with physics or something completely different?

Thanks!

My Code: (A bit werid at the "Orbiting" logic, I know :/ )

 using UnityEngine;
 using System.Collections;
 
 public class PlayerController : MonoBehaviour {
 
     public float playerSpeed = 1.5f;
     public bool Orbiting = false;
     GameObject Sphere;
     public Rigidbody2D Player_rb;
     public Transform center;
     public Vector3 axis = Vector3.forward;
     public Vector3 desiredPosition;
     public float radius = 1.2f;
     public float radiusSpeed = 2f;
     public float rotationSpeed = 80.0f;
 
     void Start() {
         /*
         Sphere = GameObject.FindWithTag("Sphere");
         center = Sphere.transform;
         transform.position = (transform.position - center.position).normalized * radius + center.position;
         radius = 1.2f;
         */
     }
 
     void Player_Movement() {
         if(Orbiting == true) {
             Player_rb.isKinematic = true;
 
             transform.RotateAround(center.position, axis, rotationSpeed * Time.deltaTime);
             desiredPosition = (transform.position - center.position).normalized * radius + center.position;
             transform.position = Vector3.MoveTowards(transform.position, desiredPosition, Time.deltaTime * radiusSpeed);
         } else {
             Player_rb.isKinematic = false;
 
             if(Player_rb.velocity.magnitude < playerSpeed) {
                 Player_rb.AddForce(transform.up * playerSpeed);
             } else {
                 return;
             }
         }
     }
 
     void Update() {
         if (Input.GetKey("space")) {
             Orbiting = true;
         } else {
             Orbiting = false;
         }
         Debug.Log(Player_rb.velocity.magnitude);
     }
 
     void FixedUpdate() {
         Player_Movement();
     }
 
 }