Is a little-known property of cat purrs the key to keeping astronauts healthy during long trips in space? Judge for yourself!


Purring is one of the least objectionable sounds a cat can make. It's much better than the common alternatives; hissing, meowing for attention, and that disturbing squelching sound they make when they're gnawing at something stuck in their butt fur. A true purr is the property of the smaller cats, such as your domestic cat. Although big cats make a thrumming breath sound, it is not, according to the experts at the National Wildlife Federation, a true purr. Why? Physics! The purr begins in the larynx of the cats, with a vibration of the vocal cords. To resonate correctly, at the established freqency of 25 to 150 cycles per second, the hyoid bone has to vibrate along with the larynx. The hyoid bone is a rough half-circle of bone under the chin. The small cat's hyoid bone is loose, and hums along with the vibration of the vocal cords. The big cats have a system of ligaments that run along the bone, keeping it in place. They trade this vibration for the greater movement of the larynx, which allows them to roar. The only larger cat to retain its purring ability is the cheetah. No other animal can make the sound that cats do. Which begs the question, why do cats do it?

The most common theory is that they purr to bond with other cats, since kittens start purring at about the second week, but cats have been known to purr under stressful or painful conditions. Dr. Elizabeth Von Muggenthaler, who is the president of Fauna Communications Research, and, judging by her name, a fully-qualified instructor at Hogwarts, suggests that the vibration can heal injuries and has been shown to increase bone density. Bones respond to pressure by building themselves up. Constant low pressure vibrations could work to the same degree that more occasional high-impact motion does. Cats might have adapted to purr to help keep their muscles, tendons, and bones healthy despite their astounding napping ability.

A sedentary lifestyle isn't the only way to earn frail bones and sad, weak muscles. Going into space will do the same thing. Astronauts come back from orbiting the earth only to head into physical rehab. Microgravity, the kind that people experience on the space station, can result in one percent bone loss per month. Without the ability to regularly exercise muscles, astronauts also lose muscle mass and strength, especially in their legs. One suit, which simulates the way gravity causes our body to exert pressure on our lower extremities, has already been designed to cope with the damage that space does to people. Maybe a different suit could be designed - one that simulated the frequency and tone of a cat's purr to help astronauts keep their bones and muscles strong in microgravity. All we need to do is explain that astronauts need to be fitted with vibrating catsuits.

Image: MacPhreak


Via Everyday Mysteries, Scientific American twice, and The National Wildlife Federation.