NASA cut short a spacewalk outside the International Space Station Tuesday after water began building up inside the helmet of the Italian astronaut making the walk.
Luca Parmitano was conducting his second career spacewalk when he reported feeling water on the back of his head. As large quantities of liquid collected inside his helmet, NASA called off the spacewalk. Parmitano, along with fellow astronaut American Christopher Cassidy, made it back into the space station after one hour, 32 minutes outside the research lab.
NASA said it initially suspected that Parmitano's drinking water supply might have escaped into his helmet. But the U.S. space agency later said an investigation has ruled out that possibility.
The agency is now investigating whether a leak in the spacesuit's cooling system, which contains about four liters of water, could be responsible.
NASA said Parmitano and the rest of the ISS crew are unharmed. It praised them for performing admirably under pressure.