You have to pass an array to the view. CodeIgniter automatically makes $planet
available to you.
$data = array('planet' => $planet);
$this->load->view('main_view', $data);
With this you can use $planet
in your view.
E.g., if you do the following:
$data = array('foo' => 'Hello', 'bar' => 'world');
$this->load->view('main_view', $data);
$foo
and $bar
will be available in your view. The key-value pairs in the array are automatically converted to variables in the view.