杏吧原创

Moonwalking astronauts often , but they weren鈥檛 clumsy 鈥� it was gravity鈥檚 fault. It turns out that the moon鈥檚 gravity is not enough to help them distinguish up from down.

of York University in Toronto, Canada, and his colleagues spun volunteers on a giant rotating arm to simulate different strength gravitational fields. As the volunteers spun, they saw images of a landscape or the letter 鈥減鈥�, which they read as a 鈥減鈥� or a 鈥渄鈥�, depending on which way they felt was up.

The study shows that humans need to feel at least 15 per cent of the gravitational force on Earth to figure out which way is up. The moon鈥檚 gravity is 17 per cent of Earth鈥檚, but it is also a strange environment; low gravity and unusual scenery explain why astronauts fell down even though they didn鈥檛 report feeling out of sorts.

It鈥檚 good news for future missions to Mars, where astronauts will experience gravity about 38聽per cent of that on Earth. Knowing which way is up will help Mars visitors stay safe, correctly estimate the angle of hills or turn the correct way towards an escape hatch. It could also be of use for more prosaic purposes.

鈥淪uppose you have a North American-style light switch, where pressing the 鈥榯op鈥� portion of the switch indicates 鈥榦n鈥�. If we don鈥檛 know which way 鈥榰p鈥� is off Earth, how do we know if the switch is 鈥榦n鈥� or 鈥榦ff鈥�?鈥� says Harris鈥檚 colleague . 鈥淥f all the challenges associated with manned missions to Mars, the gravity field should provide a sufficiently strong cue to allow for a good sense of the direction of up.鈥�

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