The encounter will make space history — completing the initial
reconnaissance of our classical solar system — and, because the
stamp is onboard, it will make some postal history, too. Not only
is it thought to be the first time that a U.S. postage stamp has
been present for the event that effectively made its design
outdated, but it is also the farthest that any stamp has ever
traveled before.

"We're honored to have the 'Not Yet Explored' stamp travel the
billions of miles to
Pluto," Mary-Anne Penner, the U.S. Postal Service's acting
director of stamp services, said in an interview with
collectSPACE.com. "We are hoping that the New Horizons mission
provides Pluto with a 'stamp of approval,' regardless of its
status in the solar system."

The United States Postal Service (USPS) didn't just issue a stamp
in 1991 to highlight the fact that Pluto had never been explored.
Instead, it was part of a 10-stamp "Space Exploration" set that
was first proposed by Howard Paine, the postal service's art
director, and artist Ron Miller.

As released, each stamp depicted one of the planets (the 10th
stamp was for Earth's moon) and a NASA robotic spacecraft that
had been sent to study it.

"Paine had been a fan of my first space art book, 'The Grand
Tour,' and thought the subject of the planets would make an
interesting stamp set," Miller recalled in an email to
collectSPACE.com. "The original idea was to just focus on the
worlds themselves. It was only later that spacecraft were added
[because] the stamp committee thought there should be an American
connection with each planet."

And so Miller went about designing the art for the stamps that,
for example, paired Mariner 10 with Mercury, Viking with Mars and
Voyager with
Saturn, Uranus and Neptune.

All of the planets (and Earth's moon) had a partner probe to go
with them — all, that is, except Pluto.

On Oct. 1, 1991, when the stamps were released for sale, Pluto
was still some 15 years from losing its planethood in a decree by
the International Astronomical Union (IAU). But even then it was
the odd planet out, having never had a spacecraft visit.

Miller doesn't remember who came up with the tagline "Not Yet
Explored," although he suspects it was Paine.

As it turned out, among the people who took notice of the Pluto
stamp and its "not yet explored" taunt were a group of engineers
working at NASA's Jet Propulsion Laboratory (JPL) in Pasadena,
California. JPL had been, and continues to be, responsible for
managing most of the space agency's planetary missions (though
New Horizons is based out of Johns Hopkins University's Applied
Physics Laboratory in Baltimore, Maryland).

"Some JPL'ers saw that stamp and decided it would be a great idea
to go to Pluto," said Alan Stern, New Horizons' principal
investigator, of the Southwest Research Institute in Boulder,
Colorado, in an interview with collectSPACE.

The JPL engineers were able to run their ideas for sending a
probe to Pluto by the NASA Administrator but neither he nor they
were aware at the time that a group of scientists had been
formulating such a mission since
Voyager 2 flew by Neptune in 1989.

"The stamp motivated [the engineers], but the scientific
community doesn't work that way," Stern said. "You don't advocate
for a billion-dollar mission because some stamp says 'not yet
explored.'"

Still, the stamp's three-word inscription eventually took on
meaning for the New Horizons mission.

"That stamp was often used as a sort of rallying cry," said
Stern. "And when we launched New Horizons, I made sure a copy of
that stamp was on the spacecraft
being flown to Pluto."

And so now, in what may be the ultimate of self-correcting acts,
a "Not Yet Explored" stamp is about be a part of the first
exploration of Pluto.

"It was correct at the time we printed the stamp," Penner noted,
"[but] we are very excited about this, and we're glad to be part
of this mission."

After a 9.5-year journey speeding through space, the New Horizons
probe is set to make its closest approach to the dwarf planet at
about 7:50 a.m. EDT (1150 GMT) on July 14. It will point its
cameras and science instruments at the small world, providing the
first up-close look at Pluto.

"I'm very proud to have been a part — however small — of this
project," shared Miller. "It gives me a very proprietary interest
in the planet Pluto!"