Polar Regions - page 6

Mars Up Close

NASA's Mariner Missions marked the beginning of a new phase in Mars exploration: for the first time, we could see pictures of what the Martian surface looked like. In 1964, Mariner 4 became the first spacecraft to fly past Mars and take close-up photos of the planet. Although the images were blurry, they revealed the presence of many impact craters on the Martian surface. This was followed by Mariners 6 and 7 in 1969, a dual mission that flew over the equator and south polar regions. Ironically, both spacecraft missed the large northern volcanoes and the great equatorial canyon system, but they obtained photos that showed much more geologic detail than those from Mariner 4. In 1971, Mariner 9 was the first probe to orbit Mars. The mission succeeded in mapping the entire planet and revealed many of Mars' most interesting features, such as Valles Marineris, Olympus Mons, and ancient, dry riverbeds.


In 1976, Vikings 1 and 2 were the first robotic spacecraft to orbit and land on Mars. Viking 1 landed on a cratered, volcanic plain called Chryse Planitia, and Viking 2 landed on Utopia Planitia, another rocky, desert area about 6460 km (4014 miles) away from Viking 1's landing site. Both landers acquired color, panoramic views of the Martian surface, and they also monitored the Martian weather.

1997 was a banner year for Mars exploration, with the Mars Pathfinder arriving on Mars on July 4, and the Mars Global Surveyor (MGS) entering elliptical orbit over Mars on September 12. Pathfinder obtained more than 16,000 images, and its six-wheel rover named Sojourner returned about 550 images and 15 chemical analyses of rocks. The MGS produced a topographic map of Mars, with its Mars Orbiter Laser Altimeter (MOLA), and over 100,000 photos.

The 2001 Mars Odyssey arrived at Mars on October 24, 2001. Its primary science mission - to map the distribution of chemical elements and minerals on the Martian surface - took place from February 2002 through August 2004. One of its primary instruments is the Thermal Emission Imaging System (THEMIS), which determines the presence of minerals that can only form in the presence of water. In 2002, the Gamma Ray Spectrometer instrument aboard Odyssey detected large amounts of subsurface water ice in the Martian arctic regions.

In December 2003, the European Space Agency's Mars Express entered the Martian orbit. In early 2004, researchers confirmed that the spacecraft had detected evidence of water ice throughout the south polar cap. Still in the process of carrying out its mission, it has returned impressive images of Valles Marineris and some of the planet's other notable features. Its lander, Beagle 2, failed during entry/landing on December 25, 2003.


Dubbed the "twin robot geologists," the Mars Exploration Rovers (MER), Spirit and Opportunity, launched on June 10 and July 7, 2003, and landed on the Martian surface on January 3 and 24, 2004. Within weeks of landing, Opportunity returned data that showed clear evidence of water in Mars' history. Spirit and Opportunity have now been trekking over Martian ground for over two Earth years, returning over 58,000 images as of December 2005. With an original estimated mission life of 90 days, MER has far exceeded expectations.

Cottage Cheese, Swiss Cheese, and Pancakes

Different rates of seasonal changes in ice can create interesting landforms at the Martian poles. In the southern polar region, "Swiss cheese" terrain forms when a flat plane of polar ice develops rimmed depressions due to varying rates of ice sublimation. Satellite imagery shows that the Swiss cheese "holes" have been growing during the past few years, and many scientists see this as evidence that Mars is in a period of rapid climate change.

There's cheese at the North Pole, too. The north polar cap has a flat, pitted surface that resembles cottage cheese in some places. In other areas, the pits and the flat areas are spaced slightly farther apart, so that the surface looks more like a kitchen sponge. Scientists believe the pits form over thousands of years as water ice changes from a solid to a gas.

Close-up mapping by the Mariner 9 mission in 1971-72 revealed strange, sedimentary pancake-like layers at both poles that had the color of soil. Based on data from both the Mariner and Viking projects, it is believed that the layers are a mixture of dust and ice, and that the differing strata could be an indication of climate change cycles on Mars - much like Earth's ice ages.


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