Well that's a little unsettling.
Astronaut Tim Peake took to Twitter to share an image of a 7-mm crack in the window of the Cupola module of the International Space Station, caused by a bit of what he called "space debris."
"I am often asked if the International Space Station is hit by space debris," Peake wrote. "Yes -- this is the chip in one of our Cupola windows, glad it is quadruple glazed!"
NASA said a typical window on a home here on Earth is made of two panes of glass just 1/16th of an inch thick. ISS windows, on the other hand, are each made from four panes of glass between 0.5 and 1.25 inches thick, and there is an exterior aluminum shutter that can be closed for extra protection.
The European Space Agency said the fused-silica and borosilicate-glass windows of the space station are sometimes hit by tiny objects, but they pose no threat to the astronauts as there is "extensive shielding around all vital crew and technical areas."
However, the agency said larger debris would pose "a serious threat."
"An object up to 1 cm in size could disable an instrument or a critical flight system on a satellite," ESA said in a news release. "Anything above 1 cm could penetrate the shields of the Station’s crew modules, and anything larger than 10 cm could shatter a satellite or spacecraft into pieces."