IntroductionWith their extreme environmental conditions, the unspoiled territories of the Arctic and Antarctica can inspire awe, yet still push humans to the brink of survival. Although the earliest humans appeared on Earth about two million years ago, it is only during the past 200 years that explorers have reached Earth's poles. We have learned much from the successful expeditions, as well as from the tragic ones, as each has contributed to our discovery of what lies in the polar regions, and also to our understanding of how these regions interact with the rest of our planet.
Now, for the first time in human history, we are embarking on the exploration of polar regions on other planets. This new phase in exploration begins with our closest planetary neighbor - Mars. Recent orbiter missions to Mars show that Mars' polar regions display many similarities to those on Earth, but they also harbor many unique features. In May 2008, Phoenix will touch down in the northern arctic plains of Mars to look for signs of liquid water and to assess the potential habitability of the Martian polar environment. The Phoenix mission will represent the first spacecraft to safely land in the polar regions of another planet.
Earth's Polar Regions
The Ross Ice Shelf extends to the Bay of Whales in the Ross Sea, Antarctica. This is the southern-most navigable point on the planet and the location where Roald Amundsen started his successful trek to the South Pole. (Image Credit: NOAA; Michael Van Woert, photographer)
Earth's polar regions are the lands and waters surrounding the geographic North and South Poles. Defined simply, geographic poles are the northernmost and southernmost points on any planet. More precisely, the geographic poles (also known as True North and True South) are the northern and southern points at which a planet's axis of rotation meets the surface.
Earth's geographic North Pole sits at 90° North, at a point in the Arctic Ocean where the depth is about 4090 meters (13,400 feet). The geographic South Pole, located at 90° South, is presently located in Antarctica.
The polar regions are characterized by extreme climate conditions, which means bitterly cold temperatures, heavy glaciation, and seasonal variations in the number of daylight hours. At winter solstice (around December 21) the North Pole is pointed away from the Sun and experiences 24 hours of darkness, while the South Pole is pointed towards the Sun and has 24 hours of daylight. At summer solstice (around June 21), the situation is reversed, with the North Pole in constant daylight and the South Pole in darkness.
Both poles have polar ice caps that expand and shrink seasonally as the amount of sunlight changes. The South Pole is dominated by the Antarctic Ice Sheet, which contains about 30 million square km (11.6 million square miles) of ice and holds 90% of the fresh water on the Earth's surface. During the winter, up to 18 million square km (6.9 million square miles) of the ocean surrounding Antarctica is covered by sea ice (frozen ocean water), which eventually floats into warmer waters towards the equator and melts. At the North Pole, however, the Arctic Ocean is almost completely surrounded by land (parts of Europe, Asia, Greenland, and North America), so sea ice that forms there is not as mobile and tends to stay in the Arctic region for a long time.
The main difference between Earth's northern and southern polar regions is that very little land area exists in the Arctic, whereas Antarctica is a continental land mass that covers about 13 million square km (about 5 million square miles). Most of Antarctica's land lies beneath layers of ice and snow up to 2 km (1.2 miles) thick, and the Antarctic interior is a cold desert with few signs of life.
Because of the extreme dry, cold conditions in Earth's polar regions, scientists have discovered some locations in both Antarctica and the Arctic where the environmental conditions closely match those on Mars. Antarctica's dry valleys, which cover about 3100 square km (1200 square miles), harbor some of the coldest places on Earth - but they receive no precipitation or snow. Scientists believe this region to be an excellent location for Mars analog studies. In the Canadian High Arctic, Devon Island offers researchers not only climatic conditions that are similar to Mars, but also an impact crater that resembles many of those seen on the Martian surface.
The Phoenix Mars Lander mission marks the first time that humans are exploring the polar regions on another planet. In fact, it is only within the last 200 years or so that explorers and scientists have reached the Earth's poles.