This lesson came from Arts and Activities. My second graders really enjoy creating all kinds of variations on these aliens. I have them fold a sheet of construction paper in half. Then draw half their alien away from the fold. Kids will often draw their alien along the side that opens up. This can cause unhappy results when they cut. Then the kids have to cut through both layers of the paper.
I also created a youtube video students would watch about the planets and I would tell a story about blasting off into space. Here is the video Warm & Cool Aliens. Here is a vide of me giving some of the instructions for the Symmetrical Aliens art lesson.
Mrs. Miller - Messy Art Teacher Blog 