Updated

For years, Arkansas historians have searched for a valuable lunar rock from the Apollo 17 mission, one of the moon rocks NASA presented to each state in the 1970s.

While other states also continue to dig for the rocks that came to be known as the Goodwill Moon Rocks, the mystery in Arkansas was solved Wednesday -- sort of -- when an archivist discovered it in former President Bill Clinton's gubernatorial papers.

Still up in the air is how the moon rock got there.

Bobby Roberts, director of the Central Arkansas Library System, told Reuters the archivist opened a box previously archived as "Arkansas flag plaque." The tiny flag was also sent to space, Roberts said. The rock was inside.

"The moon rock, which is in a plastic container, had fallen off the plaque," Roberts said. "The archivist immediately knew what he had discovered."

Other states such as New Jersey and Alaska have also misplaced their Goodwill rocks, which some experts estimate could be worth millions of dollars.

Some states have found theirs in recent years, including Colorado, where former Governor John Vanderhoof confessed in 2010 he had the rock in his personal collection and agreed to give it back to the state.

Roberts, who worked for Clinton when he was governor, said the moon rock was presented to Governor David Pryor in 1976. He could only speculate about how Clinton ended up with it.

Roberts' theory is that when Clinton became governor in 1978, Pryor left the plaque in the office. When Clinton lost re-election in 1980, everything in his office was packed up and stored.

"Ironically, I moved those papers out," Roberts said. "I'm a historian and I never saw that plaque."

The Butler Center for Arkansas History and Genealogy, which is part of the library system, acquired the Clinton papers in 2004. The papers, photographs and memorabilia are contained in 2,000 boxes.

"We will talk to the Clinton Foundation and the Governor's office and determine where it should be," Roberts said. "It should definitely be in a museum."

Roberts said that the moon rock, which is now in a safe, will be re-attached to the plaque.