Yeah, there should, but the artist prolly didn't think they were necessary.
*looks at the negative score*
I knew I was taking a huge risk by posting these images... Somebody wouldn't even bother looking at the tags then say, "why the fuck is an image of a planet here!?"
To me a planet pic isn't danbooru related even though is connected to a game. Your mileage may vary, but I'm not going to approve these. Don't know about other janitors/mods/admins.