Ann: Half Yearly Report and Accounts, page-99

some facts I didn't know - might indicate why the crack wasn't so easy to spot or fix

Researchers have known for decades that if you cool liquid helium just a few degrees below its boiling point of –452 degrees Fahrenheit (–269 degrees Celsius) it will suddenly be able to do things that other fluids can't, like dribble through molecule-thin cracks, climb up and over the sides of a dish, and remain motionless when its container is spun.

No longer a mere liquid, the helium has become a superfluid—a liquid that flows without friction. "If you set [down] a cup with a liquid circulating around and you come back 10 minutes later, of course it's stopped moving," says John Beamish, an experimental physicist at the University of Alberta in Edmonton. Atoms in the liquid will collide with one another and slow down. "But if you did that with helium at low temperature and came back a million years later," he says, "it would still be moving."