US 1991 29c Space Exploration Stamps

United States set of ten 29-cent booklet stamps (Scott 2568-77) issued October 1, 1991, honoring Voyager 2's passage of Neptune. Each stamp pairs a planet with a spacecraft that explored it, except Pluto, whose stamp reads "Pluto: Not Yet Explored". A copy of that stamp later flew aboard NASA's New Horizons spacecraft.

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