Researchers have sticky fingers when it comes to NASA's moon rocks and meteorites, and hundreds of samples have gone missing after being loaned out by the US space agency, an audit said Thursday.

NASA Inspector General Paul Martin issued a report detailing foibles such as the US space agency making loans to researchers who never used the samples, or simply losing track of rare pieces dating back to the first US trip to the Moon in 1969.

"According to NASA records, 517 loaned astromaterials have been lost or stolen between 1970 and June 2010," said the report.

Astromaterials include Moon rocks and soil; meteorites from asteroids, Mars, and the Moon; ions from the outer layers of the Sun; dust from comets and interstellar space; and cosmic dust from Earth's stratosphere.

"These samples constitute a rare and limited resource and serve an important role for research and education," it added.

"Specifically, we found that NASA records were inaccurate, and that researchers could not account for all samples loaned to them and held samples for extended periods without performing research or returning the samples to NASA."

NASA needs a better tracking system and should do an annual inventory to stop unnecessary sample loss, the audit said.

"NASA concurred with our recommendations and promised to take corrective action," it added.

As of March, NASA had more than 26,000 samples on loan, of a collection that totals 140,000 lunar samples, 18,000 meteorite samples and 5,000 solar wind, comet, and cosmic dust samples.

NASA has admitted to losing such materials in the past. One researcher lost 18 lunar samples in 2010.

In 2002, 218 samples from the Moon and meteorites were stolen from Johnson Space Center in Houston but later returned.

Earlier this year, one moon rock that had been given up for lost was discovered in a box of former president Bill Clinton's files and memorabilia, stored at an Arkansas library.

"It's a bit of a mystery solved," Bobby Roberts of Little Rock's Central Arkansas Library System was quoted as telling CNN in September. "It's kind of like, 'where'd I leave my wallet?'"