All of these topics are grist for the filler mill. A billion other galaxies whirl around in space with potentially millions of planets that contain life. Do mark down the date of your mailing. If there is no response after 90 days, send another copy to another market. Do some groundwork by thumbing through some of your favorite magazines to see what types of short material they use.
Many publications have a news section filled with short items.
Contact the editors of those sections. Writing fillers is fun and can be profitable. It's a good way to get started in a writing career, or to help support yourself while you're working on your next poetry collection or novel.