Answer: Florida and Maryland

In mid-2015 when the New Horizons spacecraft went rocketing by Pluto, it had a full payload of scientific equipment as well as two quarters. Quarters, as in silver-colored U.S. coins, and not just any two quarters, but the state quarters of Florida and Maryland. Why quarters and why those two states?

The entire quarter-payload-plan was part of an idea put together by the principal investigator of the New Horizons team, Alan Stern. New Horizons is a nuclear-powered spacecraft and it required the governor of the state in which it was launched to sign off on the launch plans. To that end, and in a gesture of goodwill, Stern proposed to Jeb Bush (the governor of Florida at the time of the 2005 launch) that they put a Florida state quarter on the spacecraft. Bush loved the idea and signed off on the mission.

That accounts for the Florida quarter, but why Maryland? It turns out that the spacecraft was so precisely designed and so delicately balanced that they needed another quarter to put on the opposite side of the craft to balance out the weight, however small, of the Florida quarter. Maryland was selected in honor of where the New Horizons spacecraft was manufactured.

In addition to the coin payload, New Horizons also carries a more serious and very fitting payload. Aboard the spacecraft is a small vial of ashes from the cremation of Clyde Tombaugh, the American astronomer who discovered Pluto in 1930.