$~~~~$Gravity has been at the top of the science agenda since the start of Mars missions. In the earlier days of space travel, scientists tried to overcome the force of gravity so that a rocket could shoot 16 Earth’s pull in order to land humans on the moon. Today, they are more interested in how reduced gravity affects the astronauts’ 17 condition.
$~~~~$Our bodies have evolved to exist within Earth’s gravity (1 g), not in the weightlessness of space (0 g) or the microgravity of Mars (0.3 g). When on Earth, we have more fluids in our lower body because they are pulled down by Earth’s gravity. However, with the absence of gravity in the outer space, our body fluids
18 , shifting toward the upper body and the head. As a result, the astronauts have swollen, puffy faces, very much resembling that of the round-headed Charlie Brown in the famous comic strip. This “Charlie Brown effect” will be more 19 when the astronauts go on their Mars missions, which will take about three years to complete, much longer than missions to the moon. Moreover, the effect is often 20 space motion sickness, headaches, and nausea. Such a syndrome is considered the top health risk for the astronauts, and scientists are still trying to figure out how it may be prevented.