In microgravity, says astronaut Chris Hadfield, "your eyes make tears but they stick as a liquid ball."

In May 2011, astronaut Andrew Feustel, in the midst of a seven-hour spacewalk, got something in his eye.

Feustel and fellow astronaut Mike Fincke had just finished running power cables from the U.S. side of the International Space Station to the Russian, and -- at the EVA's five-hour mark -- some anti-fogging solution from the inside of Feustel's helmet had begun to flake. One of those flakes, swirling in the modified snow globe that is a spacesuit helmet, ended up in precisely the place you wouldn't want it to.

"Just as an FYI, my right eye is stinging like crazy right now," the astronaut announced to his team. "It's watering a lot. Must have gotten something in it."

Fincke's reply? "Sorry, buddy."

Which was an appropriately mellow response, because Feustel's liquid little plight wasn't an emergency: He managed to wiggle down far enough in his spacesuit to reach the spongy device typically used to block the nose in case of a pressure readjustment -- and to use that to rub his eye. Which did the trick. But the episode was a reminder that much of the science -- much of the experimentation in general -- being done on the orbiting lab of the space station is being conducted, by default, on the humans who call the vehicle home. Knowledge -- about zero-gravity's effect on the body, about space as a human environment -- reveals itself in fits and starts, through unexpected events like the flaking of anti-fogging solution in an astronaut's helmet. In this case, Feustel's tearjerker was a reminder of the fact that astronauts, technically, can't cry.

Astronauts can, certainly, tear up -- they're human, after all. But in zero gravity, the tears themselves can't flow downward in the way they do on Earth. The moisture generated has nowhere to go. Tears, Feustel put it, "don't fall off of your eye ... they kind of stay there." NASA spacewalk officer Allison Bollinger, who oversaw Feustel's EVA, confirmed this assessment. "They actually kind of conglomerate around your eyeball," she said. 

In other words, yep: There's no crying in space.

And now, courtesy of ISS Expedition 34, we know a little bit more about the brand-new phenomenon that is tears in heavens: Crying, without the crying part, actually kind of hurts. And that's so even when the tears in question aren't being formed by eye-stingingly errant chemical flakes. Chris Hadfield, current ISS denizen and prolific tweeter, replied to a student question on the subject with this description of space tears:

@dkiazyk Can you cry in space? Your eyes make tears but they stick as a liquid ball. In fact, they sting a bit. So - space tears don't shed.

-- Chris Hadfield (@Cmdr_Hadfield) January 8, 2013

Which is ... weird. Tears, in theory, shouldn't hurt. We don't know why, exactly, we cry, but we're pretty sure that the action, evolutionarily, has a palliative effect. Tears should soothe, not sting. But we know as well that life in near-zero-gravity can have a deleterious effect on human vision -- and one explanation for that could be fluids shifting toward the head during long-term stays in microgravity. It could be that space gives you a pretty wretched case of dry eye -- and that sudden moisture to the cornea, particularly when it takes the form of (eeesh) "a liquid ball," could sting rather than soothe. 

Then again -- fortunately for any sob-happy space explorers currently above us -- those eyeball-clinging orbs are easily dealt with. If you experience them in the space station itself, you can just wipe them away. Or, if you can put up with the stinging, you can wait for them to blow you away. According to shuttle astronaut Ron Parise, "When the tears get big enough they simply break free of the eye and float around." Meaning that, in space, you could ostensibly watch a show composed of your own weightless tears. Which sounds just beautiful and lyrical and haunting enough to make you want to ... well, you know.

Hat tip @faketv.