Changes

There is a dichotomy on the surface of Mars; the northern hemisphere consists of low-lying volcanic plains, with the southern hemisphere consists of ancient, heavily-cratered highland plains. Mars also has two volcanic regions: Tharsis and Elysium. Within the Tharsis region is the largest volcano in the solar system, [[Olympus Mons]]. Olympus Mons is approximately 500 km across and is about the same size as the state of Arizona. Its peak is 24 km above the surrounding plains and it is surrounded by a vertical scarp 6 km high. A large canyon system, Valles Marineris, is located along the Martian equator east of the Tharsis region. Valles Marineris is 2-6km deep and 200-600km wide and approximately 4,500 km long (approximately the distance from San Francisco to Boston). The eastern part of Valles Marineris appears to have a tectonic origin, but the western part is characterized by features such as teardrop islands and longitudinal grooves, indicating it may have been formed by catastrophic flooding in the past. Such flooding may be possible under current climate conditions. Run-off channels in the cratered highland indicate a thicker atmosphere or warmer climate in the past that would have allowed water to be stable on the surface.

There is a dichotomy on the surface of Mars; the northern hemisphere consists of low-lying volcanic plains, with the southern hemisphere consists of ancient, heavily-cratered highland plains. Mars also has two volcanic regions: Tharsis and Elysium. Within the Tharsis region is the largest volcano in the solar system, [[Olympus Mons]]. Olympus Mons is approximately 500 km across and is about the same size as the state of Arizona. Its peak is 24 km above the surrounding plains and it is surrounded by a vertical scarp 6 km high. A large canyon system, Valles Marineris, is located along the Martian equator east of the Tharsis region. Valles Marineris is 2-6km deep and 200-600km wide and approximately 4,500 km long (approximately the distance from San Francisco to Boston). The eastern part of Valles Marineris appears to have a tectonic origin, but the western part is characterized by features such as teardrop islands and longitudinal grooves, indicating it may have been formed by catastrophic flooding in the past. Such flooding may be possible under current climate conditions. Run-off channels in the cratered highland indicate a thicker atmosphere or warmer climate in the past that would have allowed water to be stable on the surface.

Recent satellite imagery has shown that Mars has a 3 kilometre deep ice cap around its polar regions. The northern polar region is surrounded by dune fields. During the Martian winter, a layer of carbon dioxide condenses at the poles and sublimates in the summer, leaving the water-ice and dust polar caps exposed. The ratio of dust to water-ice contained in the polar caps remains unknown.  

Recent satellite imagery has shown that Mars has a 3 kilometre deep ice cap around its polar regions. The northern polar region is surrounded by [[dune]] fields. During the Martian winter, a layer of carbon dioxide condenses at the poles and sublimates in the summer, leaving the water-ice and dust polar caps exposed. The ratio of dust to water-ice contained in the polar caps remains unknown.  

[[Image:F035a72_processed.jpg|thumb|100px|left|Cydonia Mensae, home of the alleged "face on Mars."]]

[[Image:F035a72_processed.jpg|thumb|100px|left|Cydonia Mensae, home of the alleged "face on Mars."]]

Persistent rumors tell of a "face on Mars," allegedly located in the Cydonia Mensae region at coordinates 40.9°N and 9.45°W. This alleged "face" is located in the midst of several pyramids and other mountains. Prevailing opinion at NASA is that the "face" is a trick of the eye due to the unusual lighting conditions.<ref name=faq>Williams, David R. "[http://nssdc.gsfc.nasa.gov/planetary/planetaryfaq.html#Mars Frequently Asked Questions - Planetary - Mars]." National Space Science Data Center, [[National Aeronautics and Space Administration|NASA]], January 2, 2008. Accessed May 27, 2008.</ref>

Persistent rumors tell of a "face on Mars," allegedly located in the Cydonia Mensae region at coordinates 40.9°N and 9.45°W. This alleged "face" is located in the midst of several pyramids and other mountains. Prevailing opinion at NASA is that the "face" is a trick of the eye due to the unusual lighting conditions.<ref name=faq>Williams, David R. "[http://nssdc.gsfc.nasa.gov/planetary/planetaryfaq.html#Mars Frequently Asked Questions - Planetary - Mars]." National Space Science Data Center, [[National Aeronautics and Space Administration|NASA]], January 2, 2008. Accessed May 27, 2008.</ref>