On Tuesday, NASA's New Horizons probe will become the first spacecraft ever to visit Pluto.

When it arrives, it'll be carrying state quarters from Maryland (where the craft was built) and Florida (where it was launched), as well as the ashes of Clyde Tombaugh — the man who discovered Pluto in 1930.

Universe Today points out that, like many spacecraft, New Horizons is carrying a number of small keepsakes along with scientific instruments. Here's the full list, from NASA:

1) A portion of Pluto discoverer Clyde Tombaugh’s ashes and an inscription 2) The "Send Your Name to Pluto" CD-ROM with more than 434,000 names of people who wanted to participate in this great journey of exploration 3) A CD-ROM with project personnel pictures 4) A Florida state quarter, for the state New Horizons was launched from 5) A Maryland state quarter, for the state New Horizons was built in 6) A cutout piece of the historic SpaceShip One and an inscription 7) U.S. Flag 1 8) U.S. Flag 2 9) The 1991 U.S. stamp proclaiming, "Pluto: Not Yet Explored"

While it's certainly interesting (and perhaps a little morbid) that New Horizons is carrying Tombaugh's ashes, my favorite item is #9: the Pluto stamp.

It's a reminder that, even though Pluto seems very familiar to us, we know far less about it than any of the planets in our solar system. Two of its moons (Kerberos and Styx) were actually discovered after New Horizons left Earth in 2006 — back when Pluto was still officially considered a planet. (At the time, astronomers only knew about Charon, Nix and Hydra.)

In the 1960s and '70s, the Mariner missions showed us Mars, Venus, and Mercury for the first time. And in the 1970s and '80s, the Voyager missions showed us Jupiter, Saturn, Neptune, and Uranus.

In much the same way, New Horizons is about to give us a close-up view of Pluto for the first time.