Draw a custom shape on a gameobject

Hello,

I'm still newbie in unity and I'm sorry if this is a very obvious question. Actually, I'm trying to build a game where a thin object (the white stick in the figure below) is trying to touch a sphere object (the orange one in the image below). The red, green, blue and yellow lines are the raycasts fired from the top of the stick in different directions.

The main goal is to draw on the sphere a black shape illustrating the intersection points between the stick and the sphere. To better understand it, we see in the following image the scene from a top view perspective with how it should look like if the stick do the job properly.

To this end, I used this code to draw the raycast hit point but it is not working because rend.material.mainTexture is always null and I'm not sure why!!

        RaycastHit hit_down, hit_right, hit_forward,  hit_left;         
        if (Physics.Raycast(stick.transform.position, stick.transform.TransformDirection(Vector3.down), out hit_down))
       {             
                 Debug.DrawRay(stick.transform.position, stick.transform.TransformDirection(Vector3.down) * hit_down.distance, Color.yellow);              
               Debug.Log("Point of contact down: "  + hit_down.point + " on " + hit_down.collider.gameObject.tag);

               if (hit_down.collider.gameObject.tag == "sphere")             
               {
         Renderer rend = hit_down.transform.GetComponent<Renderer>();
                     MeshCollider meshCollider = hit_down.collider as MeshCollider;
 
             Debug.Log(rend.material.mainTexture);
                     if (rend == null || rend.sharedMaterial == null || meshCollider == null)
                            return;

                     Texture2D tex = rend.material.mainTexture as Texture2D;
                     Vector2 pixelUV = hit_down.textureCoord;
                     pixelUV.x *= tex.width;
                     pixelUV.y *= tex.height;

                     tex.SetPixel((int)pixelUV.x, (int)pixelUV.y, Color.black);
                     tex.Apply();             
               } 
     }

One last question, is it the proper way to achieve my goal? Is there any other more efficient way to accomplish this task?

Thanks in advance.