The old phrase of “I remember when…” can readily be applied to the solar system. For example, “I remember when Pluto was a planet”. This T-shirt make bring back memories of “I remember when Jupiter had 13 moons” (which was as late as 1979 btw). Now the count is 67 as celebrated in this T-shirt.
The full list of moons as appearing on the shirt is: Io, Europa, Ganymede, Callisto, Amalthea, Himalia, Elara, Pasiphae, Sinope, Lysithea, Carme, Ananke, Leda, Themisto, Metis, Adrastea, Thebe, Callirrhoe, S/2000 J 11, Iocaste, Praxidike, Harpalyke, Taygete, Chaldene, Erinome, Kalyke, Isonoe, Megaclite, Euporie, Euanthe, Orthosie, Hermippe, Thyone, Aitne, Kale, Eurydome, Pasithee, Arche, Sponde, Autonoe, Carpo, S/2003 J 12, S/2003 J 3, S/2003 J 18, Thelxinoe, Helike, S/2003 J 16, Mneme, Herse, S/2003 J 19, S/2003 J 15, S/2003 J 10, Aoede, Kallichore, Kore, Cyllene, Eukelade, S/2003 J 4, Hegemone, S/2003 J 9, S/2003 J 5, S/2003 J 2, S/2003 J 23, S/2010 J 2, S/2010 J 1, S/2011 J 1, S/2011 J 2
The link to Redbubble: Moons of Jupiter T-shirt