Thank you for all your kind and helpful comments. I did have some ideas for more enemy spaceships and wanted something to happen when you left click but unfortunately I reached the limit of events.
Some enemy ships I wanted to add are one that could shoot at different angles that targets the asteroids closest, and an enemy ship that could magnetically push asteroids away (you'd want to keep close to those ones).
When designing the game I did experiment by hiding the cursor and having another object in its place but I found it to be distracting, and just decided to let players get a feel for it, I agree it is definitely a good idea to have the option to display a cursor and the lines though as there are some players who might prefer that.
My record time is 141 seconds which is achievable with a bit of practice. Encase you don't know the asteroids are randomly generated, they continuously get faster and spread apart over time and will eventually travel faster than the enemy ships which never change speed. You will definitely start noticing the change in speed / challenge after one minute, and if you do want to reach a high score you will need to put yourself in more danger ie further left.
Thank for playing and I look forward to hearing further comments and ideas.