Pretty stones, pretty necklaces by Etsy seller Chrysalism.

They are described as a way to , “Wear your favorite planet around your neck!  These simple galactic adornments perfectly compliment just about any outfit- add geeky flair to your everyday attire, or use as the finishing touch to your epic steampunk cosplay ensemble! The perfect gift for any space geek! One of a kind jasper stone world, wire-wrapped inside a copper ring and orbited by a tiny pyrite “moon”. 18-inch aged brass chain with lobster clasp for a mixed metal look.”

These sell for a Pluto (or if you are picky about your astronomy Mercury)-sized USD$24.