Good job on this! Movement was smooth and I thought the harpoon feature was well executed. Overall, visuals and UI looked really clean and the variety of planets is great to see. This could be a fun little mobile game if you put more time into it.
I would say that your galaxy is too big for the amount of time you are given with the sun. There were quite a few runs where I was spawned with planets far away from the sun so I was basically done from the start. I would also make the planet/sun collision more meaningful. They kind of just melt into it and that's something that I would expect to have a lot of gusto behind since it's a pretty cataclysmic event.
I also noticed that it isn't formatted well for browser if you don't do full screen. I would take another look at your UI elements settings' within the Canvas to make sure they properly scale and reposition based on the screen resolution.