International Polar Year on Earth and Beyond
The International Polar Year (IPY) is an international effort to focus attention on the Earth's polar regions. 2007-2009 marks the fourth IPY, which was last held approximately fifty years ago. Numerous planned studies and events will cover not only science but sociology, geography, and culture. It is a truly global scale undertaking, to understand what lies in store for the future of Earth's Polar Regions. There is a particularly acute urgency for the fourth IPY, as wide scale climate change is affecting the extent and dynamics of ice cover at the poles, the degree of ozone thinning and local patterns of precipitation and wind flow. The Earth's poles are also affected by the solar wind and by changes in the Earth's magnetic field, all of which are under study and consideration by the global scientific community.
The most prominent feature of Earth's poles is ice. Ice preserves climate records, regulates weather, and shelters ocean-dwelling life forms from the extremes of winter cold. Earth is not the only object in our solar system which has ice. In fact, ice is a common and very important part of many different bodies in our solar system, including many icy moons and comets. Observance of IPY from the perspective of Earth reminds us that there are other bodies in the solar system that have polar regions worth exploring. Understanding these other icy worlds can help us gain a better understanding of our own planet Earth. Often their poles tell us about how the planet or moon evolved, what stresses it experiences today, and what weather patterns it may experience.
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Among the inner rocky planets, even Mercury, as close to the Sun as it is, appears to have ice in the shadowed craters of its north polar region. Earth's Moon may have water ice in the permanently shadowed regions of its south pole in the form of ice-rich soil. There is speculation that this may represent a major water source for a sustained human presence on the moon.
On Mars, as on Earth, the icy polar regions have an effect on global weather. The polar regions of Mars, have extensive ice caps made up of frozen water and carbon dioxide. There is also extensive subsurface ice in the form of Martian permafrost, a frozen mixture of soil and water. The Martian polar regions give rise to temperature gradients over the planet's surface and this is responsible, at least in part, for the strong winds which often sweep across the planet's surface. These winds lead to a global redistribution of small particle, aeolian weathering of rocks, and the burial of craters and other landforms. Clouds, not due to dust, have even been seen in the Martian sky and there is a global water cycle in which nightly frosts of water ice are deposited on boulders and other surfaces due to evaporation and condensation reactions driven by the water supplied by Mars' icy poles. This frost formation and melting as well as the strong winds has led to cleaning of the solar panels on the Mars Exploration Rovers, allowing them to regain power and keep moving for much longer than was expected. So, without icy poles on Mars, this mission may not have been as long lived!
The outer gas giant planets, Jupiter, Saturn, Uranus, and Neptune have many different kinds of ice associated with them-ammonia ice, methane ice, and nitrogen ice. The gaseous nature and rapid rotation of these planets has led to differentiation of atmospheric structure at their poles, but little is known of the solid rocky and icy cores that may be present underneath their thick atmospheres. However, their many moons have revealed complex structures composed of ice and rock-sometimes more ice, and sometimes more rock. A few of these, including Saturn's moons Enceladus and Titan, have been studied in detail and proven to be very interesting.
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Enceladus, a moon of Saturn, has a very complex structure despite its very small size, only 500 km in diameter. The poles of Enceladus are very different from each other. The north polar region is heavily cratered and therefore older than the south polar region. The south polar area is very smooth with complex patterns of ridges, scarps, and rifts. The south pole temperatures are the warmest of those on the entire moon, possibly due to the presence of a subsurface liquid water equivalent of a magma chamber on Earth. Occaisonally this water bursts forth, erupting to the surface as geysers or cryovolcanic plumes. This activity may be spurred by the presence of internal heat generated by radionuclides in the iron and silicate core. There may even be chambers of molten rock in the interior of Enceladus which contribute to heating of the moon. However, due to the tidal heating produced by its interaction with Saturn, and the pull of Saturn's gravity, this activity is concentrated in the south polar region, with Saturn's gravity effectively causing a relocation of the hotspot over time. The water vapor plumes produce a tenuous atmosphere around this small moon, which is thicker at the south pole where other components-carbon dioxide, methane, and nitrogen-have been detected in addition to water vapor.
Titan, another of Saturn's moons, has been extensively studied by the Cassini-Huygens mission. Cassini's visual and infrared mapping spectrometer has imaged a huge cloud system covering the north pole of Titan during a Dec. 29, 2006 flyby designed to observe the limb of the moon. Cassini's visual and infrared mapping spectrometer scanned the limb, revealing a spectacular cloud system which covers the north pole down to 62 degrees north latitude and at all observed longitudes. It was also recently reported that the high north latitude regions of Titan are dotted by numerous lakes of liquid hydrocarbons and these may drive a global cycle of evaporation-condensation-precipitation much as occurs with water on Earth. The condensates (probably methane) which make up the cloud may be the source of liquid that fills the lakes.
The fourth IPY will hopefully focus world attention on our Earth's poles and the capture the importance of their health on our planet's well-being. The study of poles and ice on other bodies in our solar system will also help us better understand our own polar system in the larger context of the solar system. This polar focus will hopefully also establish the importance of continued research on our Earth as well as other bodies in our solar system.
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