A small piece of flying space debris has hit the International Space Station (ISS), but it’s deemed just a diminutive piece of the space junk problem.

In April, the tiny space junk flew at the space station’s Cupola, which is a European-built element installed in 2010. It provides the best views of Earth, and it is where astronauts have taken stunning images and videos of the planet.

“I am often asked if the International Space Station is hit by space debris. Yes – this is the chip in one of our Cupola windows, glad it is quadruple glazed!” said British astronaut Tim Peake, who took the photo of the damaged window.

The photo shows a 7-millimeter circular chip with potentially a paint flake or tiny metal fragment. The eerie blackness of space serves as the crack’s background.

The Cupola also serves as an observation and work desk when the space crew operates the robotic arms of the ISS. The window to fascinating Earth and celestial views, while made of fused silica and borosilicate glass, can sometimes suffer impacts from space debris or tiny artificial matter.

Minor strikes like this are considered a non-threat, given that the ISS has an extensive shielding around important crew and technical locations. Strikes from larger debris, however, are an entirely different story.

While an object measuring 1 centimeter in size could disarm an instrument or flight system on a satellite, anything bigger could get through the shields of the crew modules. An object bigger than 10 centimeters, though, could shatter a whole spacecraft or satellite into pieces.

The European Space Agency (ESA), a partner in the ISS mission, said it has established guidelines for debris mitigation so as to stop orbital-debris problems before they occur. The said guidelines, including discharging batteries and dumping fuel tanks at the end of every mission to prevent explosions, are deemed applicable to all new ESA missions.

NASA tracks more than 500,000 space junk the size of a marble or bigger, sometimes commanding the ISS to alter its orbit to stay out of the way of a harmful space element. Millions other debris, however, may be too small to be monitored – including the one that struck the space station window.

In 2007, Chinese authorities fired a missile at a defunct weather satellite, something that created over 3,000 new junk pieces. While in 2009, a worn-out Russian satellite hit an operational satellite, damaging it and producing 2,000 pieces.