|Volume: 01, Issue: 10||08/13/2003|
See Mars MeltMars enthusiasts, listen up: The ice cap on the southern hemisphere of Mars is melting, and if you can find a telescope, you can watch. Seasonal polar caps composed of carbon dioxide (CO2) from Martian air are experiencing sublimation, which means they’re changing directly from a solid form to a gas without ever becoming a liquid.
The melting is occurring during a month of optimal Mars viewing. The planet glows brightly in the southern sky, as can be seen by the naked eye between midnight and sunrise on nights when skies are clear. As the planet draws closer to Earth, making its closest brush with our planet on August 27, sky watchers can use ordinary telescopes to spot Martian volcanoes, craters, dust clouds, and polar caps. The ice on the Red Planet’s southern pole reflects sunlight, making the meltdown particularly easy to see.
Both seasonal and permanent polar caps are present on Mars. Seasonal caps are composed of CO2 from the atmosphere that becomes solid during the Martian winter. These areas are wide and shallow, reaching only about one meter deep. Scientists estimate almost 25% of the Martian atmosphere freezes during the winter. Besides these significant caps, there is also a permanent cap of frozen water lurking below the CO2. When the seasonal caps melt, the permanent ice cap appears as a defined white spot close the pole. It lies within a compact area and reaches a depth of about three kilometers.
Mars is currently experiencing the later stages of spring, so thawing of the seasonal cap has begun. "The polar cap is receding because the sun is shining on it,” said planetary scientist Dave Smith of Goddard Space Flight Center. “Southern summer on Mars begins September 29th; by then much of the polar cap will be gone."
As the polar caps melt, their appearances change. Their borders become jagged, and rifts and dark spots appear. NASA’s Mars Global Surveyor infra-red cameras have also detected a vast dark region on the southern pole that spans hundreds of kilometers. This spot, which scientists have dubbed the “Cryptic Region,” stays at an extremely low temperature even as the cap thaws.
A side effect of the melting is a change in air pressure across the planet. As the CO2 changes from solid to gas, air pressure increases. Northern and southern polar caps thaw at different times, causing air pressure to fluctuate by as much as 25%. To envision such a change, imagine being an airplane that’s taking off and ascending thousands of feet in the air.
"While the south polar cap is vaporizing the north polar cap is growing. It's a balancing act,” Smith explained. “Overall air pressure will be greatest when there's the least amount of CO2 on the ground."
When Mars is in the early stages of summer and late stages of fall, the planet reaches the height of overall air pressure. The pressure increase may make it possible for liquid water to flow freely in some regions, which is normally impossible due to extremely low air pressure.
While this exciting possibility exists due to the air pressure change, a consequence is that higher air pressure provides a more favorable environment for dust storms. These chronic storms impair the vision of researchers trying to study the planet.
Barring a planet-eclipsing dust storm, researchers will have plenty of opportunities to study the Red Planet more closely as it moves toward Earth. Between melting polar caps, a “Cryptic Region,” and ever-problematic dust storms, scientists should have plenty to research.
For more information about Mars and for other space information, visit http://www.nasa.gov.
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