Overview - page 3


Humans and Atmospheric Pressure


Atmospheric pressure is the amount of force exerted over a surface area, caused by the weight of air above it. Since fewer air molecules are present at higher elevations, atmospheric pressure decreases as altitude increases. The most common unit of measure for atmospheric pressure is the millibar (mb). On Earth, the average atmospheric pressure at sea level is 1,013 mb, while on Mars it is only 7.5 mb. At pressures lower than 700 mb, many humans become susceptible to altitude sickness, but they have also been known to survive conditions with much lower atmospheric pressure. For example, some climbers have reached the summit of Mount Everest, where the atmospheric pressure is only about 300 mb, without the aid of oxygen tanks. But they typically undergo a month-long period of acclimatization, during which time their bodies gradually become accustomed to the lower oxygen levels and atmospheric pressure. Despite this process, they are still unable to remain at the summit for very long. Because the atmospheric pressure on Mars is still much lower than even the summit of Mount Everest, astronauts visiting Mars would require pressurized spacesuits to venture out into the Martian environment.

Global Dust Storms on Mars

Extravehicular Mobility Unit (EMU)
Because of Mars' low atmospheric pressure, visitors there would need to wear a pressurized space suit. This one is called an extravehicular mobility unit (EMU) and consists of three major components: (1) the upper torso, (2) the lower torso, and (3) the portable life-support system. (Image Credit: NASA)
Satellite imagery of Mars has revealed that huge, swirling dust storms periodically cover nearly the entire planet, and measurements taken during the Viking Lander missions in the 1970s showed that wind gusts of up to 95 kilometers (60 miles) per hour occur during these dust storms. In addition, the low gravity conditions on Mars enable sand and dust grains to saltate (jump or leap) up to a meter (3.25 feet) high and then travel 3 to 10 meters (9 to 30 feet) downwind. These observations and measurements tell scientists that sand and dust are routinely transported across the Martian surface in massive amounts. When Mariner 9 arrived at Mars in 1971, the first images to arrive back at Mission Control revealed a huge dust storm that covered the entire surface of Mars. It was nearly a month before the dust settled and scientists were able to begin mapping the planet. Then in June 2001, the Hubble Space Telescope detected a dust storm brewing in Hellas Basin, a huge impact crater in Mars' southern hemisphere. Within a day, the dust storm enshrouded the
Mars Orbiter Pictures
The Mars Orbiter Camera onboard the Mars Global Surveyor captured these two images in June and July 2001. The view from June shows the Tharsis volcanic region (left), Valles Marineris chasms (right), and the late winter south polar cap (bottom). The view from July shows the same regions, but most of the details are hidden by a global dust storm that enshrouded nearly the entire planet. (Image Credit: NASA/JPL/Malin Space Science Systems)
entire planet and was so large that amateur astronomers could see it from Earth with their telescopes. Although dust storms occur on Earth, they don't come close to reaching the size of dust events on Mars. First, because Mars is a global desert, it offers plenty of fuel for feeding and sustaining dust storms. Second, because dust absorbs sunlight, it can substantially heat Mars' dry, thin atmosphere, which then increases winds. Earth's atmosphere, however, contains water vapor, which helps control atmospheric temperatures. During the 2001 dust storm, the global air temperature on Mars was about 30 degrees C (86 degrees F) warmer than before the storm began.

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