One of the factors stopping the U.S. from eliminating its nuclear weapons stockpile is the potential of an asteroid hurtling towards the planet.

The finding comes from a Government Accountability Office report (pdf) on the National Nuclear Security Administration (NNSA), which oversees the dismantling of the nation's nuclear weapons.

The unusual tidbit from the April 2014 report was noted by Nuclear Watch New Mexico in June, but gathered more media attention this week following reporting by the Wall Street Journal.

In a section listing reasons why the NNSA is not disassembling some "canned subassemblies (CSA)—a major nuclear component that can contain highly enriched uranium (HEU)," it states:

For potential use in planetary defense against earthbound asteroids. NNSA officials told us that CSAs associated with a certain warhead indicated as excess in the 2012 Production and Planning Directive are being retained in an indeterminate state pending a senior-level government evaluation of their use in planetary defense against earthbound asteroids. While NNSA has declared these CSAs to be excess and, until March 2013, had scheduled them for disassembly beginning in fiscal year 2015, the national labs’ retention letter has also characterized the CSA associated with this warhead as an “irreplaceable national asset. ” The WDD program is coordinating NNSA’ s evaluation of their use in planetary defense with the support of LLNL, LANL, and Y-12.

As theoretical physicist and author Michio Kaku explained in a 2013 cover story for Newsweek, a large asteroid hitting the Earth is an unusual but potentially serious threat.

You can hear Kaku discuss the issue—including how a hydrogen bomb could be used—in this light-hearted interview on the Colbert Report: