Tea - Mystery in a Cup of Tea

Using odds and ends from the space station pantry, researchers have learned something new about fluid physics.

Try this: In your kitchen at home, squirt a stream of warm honey into a cup of water or tea, and watch what happens. Sweet gooey rivulets, falling downward, twist themselves into curly-cues, filaments, and spinning "smoke rings." It's mesmerizing. But only for a split-second, then the honey splats into the bottom of the cup.

Gravity is such a brute.

What you need is a kitchen in space. Without gravity dragging everything down, spinning rings of honey in water could hang suspended for hours. Honey-ribbons would have more time to twist and turn, developing into … no one knows what.

"How fluids mix in weightlessness is not well understood," explains chemistry professor John Pojman of the University of Southern Mississippi. Here on Earth, he says, the physics is dominated by gravity. Dense fluids sink and light fluids rise; everything else is a side effect of that basic motion.

In space, the pull of gravity subsides and other, more subtle phenomena rule. Intermolecular forces can hold films or globs of fluid together that, on Earth, would be torn apart by their own weight. These delicate structures can last for a long time, simply because they float rather than crash into the floor of their container.

Honey and water in the author's kitchen.

That's not to say weightless fluids are still. On the contrary, in a container holding two different fluids, like honey and water, scientists expect strange and complicated currents to flow. "Tiny differences in fluid composition or temperature can, in theory, induce stresses that cause convection," explains Pojman. This effect, called "Korteweg stress," is unobservable on Earth because buoyant motions overwhelm it. But in space it could be important.