This new sheet of four stamps, called “Pluto—Explored!,” shows an artist’s rendering of the New Horizons spacecraft and the spacecraft’s image of Pluto taken near its closest approach. In 2006, NASA placed a 29-cent 1991 “Pluto Not Yet Explored” stamp in the New Horizons spacecraft. In 2015, the spacecraft carried the stamp on its history-making mission to Pluto and beyond. Credit: ©2016 USPS