User:Sbandrews/Mars

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[edit] Geology

Main article: Geology of Mars
Rock strewn surface imaged by Mars Pathfinder
Rock strewn surface imaged by Mars Pathfinder

Based on orbital observations and the examination of the Martian meteorite collection, the surface of Mars appears to be composed primarily of basalt. Some evidence suggests that a portion of the Martian surface is silica-rich than typical basalt, and may be similar to andesitic stones on Earth. However, these observations may also be explained by silica glass. Much of the surface is deeply covered by a fine iron(III) oxide dust that has the consistency of talcum powder.[1]

Although Mars has no intrinsic magnetic field, observations show that parts of the planet's crust have been magnetized. This Paleomagnetism of magnetically-susceptible minerals has properties very similar to the alternating bands found on the ocean floors of Earth. One theory, published in 1999 and re-examined in October 2005 with the help of the Mars Global Surveyor, is that these bands demonstrate plate tectonics on Mars 4 billion years ago, before the planetary dynamo ceased to function.[2]

Current models of the planet's interior infer a core region approximately 1,480 km in radius, consisting primarily of iron with about 15-17% sulfur. This iron sulfide core is partially fluid, and has twice the concentration of lighter elements than exist at the Earth's core. The core is surrounded by a silicate mantle that formed many of the tectonic and volcanic features on the planet, but now appears to be inactive. The average thickness of the planet's crust is about 50 km, with a maximum thickness of 125 km.[3] Earth's crust, averaging 40km, is only a third as thick as Mars's crust relative to the sizes of the two planets.

The geological history of Mars is split into three broad epochs:

  • Noachian epoch (named after Noachis Terra): Formation of the oldest extant surfaces of Mars, 3.8 billion years ago to 3.5 billion years ago. Noachian age surfaces are scarred by many large impact craters. The Tharsis bulge volcanic upland is thought to have formed during this period, with extensive flooding by liquid water late in the epoch.
  • Hesperian epoch (named after Hesperia Planum): 3.5 billion years ago to 1.8 billion years ago. The Hesperian epoch is marked by the formation of extensive lava plains.
  • Amazonian epoch (named after Amazonis Planitia): 1.8 billion years ago to present. Amazonian regions have few meteorite impact craters but are otherwise quite varied. Olympus Mons formed during this period along with lava flows elsewhere on Mars.


[edit] Hydrology

Photo of microscopic rock forms indicating past signs of water, taken by Opportunity
Photo of microscopic rock forms indicating past signs of water, taken by Opportunity

Liquid water cannot exist on the surface of Mars with its present low atmospheric pressure, but water ice is in no short supply, with two polar ice caps made largely of water ice, and a water ice permafrost mantle stretching down from the pole to lattitudes of about 60°[4]. Much larger quantities of water are thought to be trapped underneath Mars' thick cryosphere, only to be released when the crust is cracked through volcanic action. The largest such relase of liquid water is thought to have occured when the Valles Marineris formed early in Mars' history, enough water being released to form river valleys across the planet. A smaller but more recent event of the same kind occurred when the Cerberus Fossae chasm opened about 5 million years ago, leaving a sea of frozen ice still visible today on the Elysium Planitia[5].

Further proof that liquid water once existed on the surface of Marscomes from the detection of specific minerals such as hematite and goethite, both of which sometimes form in the presence of water.[6]

Changing gully deposits on Mars
Changing gully deposits on Mars

More recently on December 6, 2006, NASA revealed photographs taken by Global Surveyor suggesting the ongoing existence of transient liquid water on the surface Mars. The two images, taken six years apart, show a pair of gullies on Mars with what appears to be new deposits of sediment. Michael Meyer, the lead scientist for NASA's Mars Exploration Program, said, "these observations give the strongest evidence to date that water still flows occasionally on the surface of Mars."[7] However, alternative scenarios have been suggested, including the possibility that the deposits were caused by carbon dioxide frost or by the movement of dust on the Martian surface.[8][9]

[edit] References

  1. ^ NASA Mars Page. Volcanology of Mars. Retrieved on 2006-06-13.
  2. ^ Goddard Space Flight Center. New Map Provides More Evidence Mars Once Like Earth. Retrieved on 2006-03-17.
  3. ^ Dave Jacqué. "APS X-rays reveal secrets of Mars' core", Argonne National Laboratory, 2003-09-26. Retrieved on 2006-07-01. (in English)
  4. ^ Kostama et al., V. P. (3 June), "Recent high-lattitude icy mantle in the northern plains of Mars", Geophysical Research Letters 33: L11201
  5. ^ Murray et al., John B. (17 March), "Evidence ... for a frozen sea close to Mars' equator", Nature 434: 352 - 355
  6. ^ NASA (2004-03-18). Mineral in Mars 'Berries' Adds to Water Story. Press release. Retrieved on 2006-06-13.
  7. ^ NASA Images Suggest Water Still Flows in Brief Spurts on Mars. NASA (06 December 2006). Retrieved on 2006-12-06.
  8. ^ Water flowed recently on Mars. BBC (06 December 2006). Retrieved on 2006-12-06.
  9. ^ Water May Still Flow on Mars, NASA Photo Suggests. NASA press release. Retrieved on 2006-04-30.
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