The "Pluto - Explored!" series features an image of the probe itself and a photo it took of the celestial body that shows its famous heart-shaped region. Cute, but they still got nothing on that one lucky piece of paper that's now on its way to Kuiper Belt object 2014 MU69. By the time it reaches the icy rock that might be one of the oldest objects in our solar system, the stamp would have added a billion more miles to its journey.

While it took almost a decade for the stamp to reach Pluto, it still got there at an incredible speed: New Horizons went past the moon within nine hours, whereas the Apollo 11 took three days to get to its destination. Guinness World adjudicator Jimmy Coggins said that if the Pony Express tried to deliver a letter to a destination 3 billion miles away, "they would be swapping ponies out for the next 47,000 years..."