Could move the alien and planet to outside on the ship, then use as picture frame. Cute spaceship porthole craft w/ paper plates, aluminum foil, pipe cleaners. Could pre-make some aliens and planets for the little ones, if needed?
Comet craft: First, have kids use black construction paper with crayons and draw planets and stars. Cut styrofoam balls in half, cover in foil and glue to paper. Use glitter glue pens (or glue with sprinkled glitter) for the tail of comet.