Exciting to see more low-level devs here! This is a very cute game, and easy to pick up. One thing I would suggest is having some sort of auditory feedback about incoming aliens, in addition to the little indicators on the sides of the screen (if it were me, I would have one sound to indicate an incoming alien, and then another droning sound that gets louder as you get closer to them, as a way to help people gauge how quickly they should be spinning while the alien is still offscreen).
All-in-all, though, this was a fun little game and a nice jam entry. Kudos! I had fun playing to the end. I made it, but unfortunately only 7 of my cows survived :\