The human body is built to move relying on the Earth's gravitation pull but gravity is not the same in the lunar surface or in space. The difference in the level of gravity on Earth and on the moon is apparently also the reason why astronauts have trouble telling which way is "up" when they are in a low-gravity environment.

Losing a sense of direction particularly in space has crucial and even troubling implications. Astronauts, for instance, could wrongly flip a switch or go to the wrong way when an emergency arises. They could also tip over and miscalculate what could happen to an object when it is thrown or dropped. A new research, however, reveals what largely contributes to this directional dilemma.

In a new study published in the journal PLOS ONE on Sept. 3, Michael Jenkin, from the Department of Electrical Engineering and Computer Science at the York University in Toronto, Canada, and colleagues, involved 10 participants in an experiment conducted at the Arm Centrifuge Facility of the European Space Agency (ESA) in Cologne, Germany, to determine how much gravity is required to affect a person's perception of up and down.

The researchers simulated different levels of gravity by using a Short-Arm Centrifuge and then used a perceptual test to measure the effectiveness of different levels of gravity on the participants' perception of up. They found that the gravity needed to effectively influence a person's sense of up and down is about 0.15 g, which is very close to the gravity level on the moon.

"Our data suggest that a gravitational field of about 0.15 g is necessary to provide effective orientation information," Jenkin and colleagues wrote. "This value is compatible with the results of studies that have varied g using parabolic flight and is close to the gravitational force on the Moon of 0.17 g."

The researchers have likewise found that the gravity on Mars, which is at 38 percent of the level found on Earth, should be enough for the astronauts to orient themselves and keep their balance during future manned missions on the Red Planet.

"It's crucial to understand how the direction of up is established and to establish the relative contribution of gravity to this direction before journeying to environments with gravity levels different to that of Earth," Jenkin said.

NASA is already making preparations for a planned manned mission in Mars, which some experts believe could possibly happen by 2030.

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