Tenth Planet and Nibiru are references to Sumerian astronomy and legends.
Mike Dewitt dubbed the superhero on the 10th Planet Springfield rashguard "Nibiru" - it did not exist as a character previously. It's a nice touch as 10th Planet Springfield operates within the Superhero Academy.
10th Planet Rochester also has Sumerian Imagery, and the 10th Planet BioMech rashguards feature Sumerian glyphs. While not directly related, the 10th Planet West LA Darkside merch stems from Sumerian legends - Star Wars is full of Sumerian references.