Download - Mars is the Fourth Planet From the Sun in the Solar System

8/2/2019 Mars is the Fourth Planet From the Sun in the Solar System

1/28

Mars is the fourthplanet from theSunin the Solar System. Named after the Romangod of war,Mars, it is often described as the "Red Planet" as theiron oxide prevalent on its surface gives it areddish appearance.[13] Mars is a terrestrial planetwith a thinatmosphere, having surface featuresreminiscent both of the impact craters of the Moon and the volcanoes, valleys, deserts, andpolarice capsofEarth. The rotational period and seasonal cycles of Mars are likewise similar to those

of Earth, as is the tilt that produces the seasons. Mars is the site ofOlympus Mons, the highestknown mountain within the Solar System, and ofValles Marineris, the largest canyon. ThesmoothBorealis basin in the northern hemisphere covers 40% of the planet and may be a giantimpact feature.[14][15]

Until the first successful flyby of Mars occurred in 1965, by Mariner 4, many speculated aboutthe presence of liquid water on the planet's surface. This was based on observed periodicvariations in light and dark patches, particularly in the polarlatitudes, which appeared to be seasand continents; long, darkstriations were interpreted by some as irrigation channels for liquidwater. These straight line features were later explained asoptical illusions, though geologicalevidence gathered by unmanned missions suggest that Mars once had large-scale water coverageon its surface.[16] In 2005, radar data revealed the presence of large quantities of water ice at the

poles,[17]

and at mid-latitudes.[18][19]

The Mars roverSpiritsampled chemical compoundscontaining water molecules in March 2007. ThePhoenix lander directly sampled water ice inshallow Martian soil on July 31, 2008.[20]

Mars has two moons, Phobos andDeimos, which are small and irregularly shaped. These may becaptured asteroids, similar to5261 Eureka, a Martian trojan asteroid. Mars is currently host tothree functional orbiting spacecraft: Mars Odyssey, Mars Express, and the Mars ReconnaissanceOrbiter. On the surface are the Mars Exploration RoverOpportunity and its recentlydecommissioned twin, Spirit, along with several other inert landers and rovers, both successfuland unsuccessful. ThePhoenix lander completed its mission on the surface in 2008.Observations byNASA's now-defunctMars Global Surveyorshow evidence that parts of thesouthern polar ice cap have been receding.[21] Observations by the Mars Reconnaissance Orbiter

have revealed possible flowing water during the warmest months on Mars.

[22]

Mars can easily be seen from Earth with the naked eye. Itsapparent magnitude reaches 3.0[7] abrightness surpassed only by Jupiter, Venus, the Moon, and the Sun. Optical ground basedtelescopes are typically limited to resolving features about 300 km (186 miles) across when Earthand Mars are closest, because of Earth's atmosphere.[23]

Contents[hide]

1 Physical characteristics

1.1 Geology

1.2 Soil

1.3 Hydrology

1.3.1 Polar caps

1.4 Geography

1.4.1 Impact topography
http://en.wikipedia.org/wiki/Planethttp://en.wikipedia.org/wiki/Sunhttp://en.wikipedia.org/wiki/Sunhttp://en.wikipedia.org/wiki/Sunhttp://en.wikipedia.org/wiki/Solar_Systemhttp://en.wikipedia.org/wiki/Roman_mythologyhttp://en.wikipedia.org/wiki/God_of_warhttp://en.wikipedia.org/wiki/Mars_(mythology)http://en.wikipedia.org/wiki/Iron(III)_oxidehttp://en.wikipedia.org/wiki/Iron(III)_oxidehttp://en.wikipedia.org/wiki/Mars_surface_colorhttp://en.wikipedia.org/wiki/Mars_surface_colorhttp://en.wikipedia.org/wiki/Terrestrial_planethttp://en.wikipedia.org/wiki/Terrestrial_planethttp://en.wikipedia.org/wiki/Atmospherehttp://en.wikipedia.org/wiki/Atmospherehttp://en.wikipedia.org/wiki/Impact_craterhttp://en.wikipedia.org/wiki/Moonhttp://en.wikipedia.org/wiki/Polar_ice_capshttp://en.wikipedia.org/wiki/Polar_ice_capshttp://en.wikipedia.org/wiki/Polar_ice_capshttp://en.wikipedia.org/wiki/Polar_ice_capshttp://en.wikipedia.org/wiki/Earthhttp://en.wikipedia.org/wiki/Earthhttp://en.wikipedia.org/wiki/Rotational_periodhttp://en.wikipedia.org/wiki/Olympus_Monshttp://en.wikipedia.org/wiki/Olympus_Monshttp://en.wikipedia.org/wiki/Valles_Marinerishttp://en.wikipedia.org/wiki/Borealis_basinhttp://en.wikipedia.org/wiki/Borealis_basinhttp://en.wikipedia.org/wiki/Mariner_4http://en.wikipedia.org/wiki/Mariner_4http://en.wikipedia.org/wiki/Latitudehttp://en.wikipedia.org/wiki/Striation_(geology)http://en.wikipedia.org/wiki/Optical_illusionhttp://en.wikipedia.org/wiki/Optical_illusionhttp://en.wikipedia.org/wiki/Spirit_roverhttp://en.wikipedia.org/wiki/Phoenix_(spacecraft)http://en.wikipedia.org/wiki/Moons_of_Marshttp://en.wikipedia.org/wiki/Phobos_(moon)http://en.wikipedia.org/wiki/Deimos_(moon)http://en.wikipedia.org/wiki/Deimos_(moon)http://en.wikipedia.org/wiki/Asteroidhttp://en.wikipedia.org/wiki/5261_Eurekahttp://en.wikipedia.org/wiki/5261_Eurekahttp://en.wikipedia.org/wiki/List_of_Mars_trojan_asteroidshttp://en.wikipedia.org/wiki/Spacecrafthttp://en.wikipedia.org/wiki/Mars_Odysseyhttp://en.wikipedia.org/wiki/Mars_Expresshttp://en.wikipedia.org/wiki/Mars_Expresshttp://en.wikipedia.org/wiki/Mars_Reconnaissance_Orbiterhttp://en.wikipedia.org/wiki/Mars_Reconnaissance_Orbiterhttp://en.wikipedia.org/wiki/Mars_Exploration_Roverhttp://en.wikipedia.org/wiki/Opportunity_roverhttp://en.wikipedia.org/wiki/NASAhttp://en.wikipedia.org/wiki/Mars_Global_Surveyorhttp://en.wikipedia.org/wiki/Mars_Global_Surveyorhttp://en.wikipedia.org/wiki/Apparent_magnitudehttp://en.wikipedia.org/wiki/Apparent_magnitudehttp://en.wikipedia.org/wiki/Jupiterhttp://en.wikipedia.org/wiki/Venushttp://en.wikipedia.org/wiki/Marshttp://en.wikipedia.org/wiki/Sunhttp://en.wikipedia.org/wiki/Solar_Systemhttp://en.wikipedia.org/wiki/Roman_mythologyhttp://en.wikipedia.org/wiki/God_of_warhttp://en.wikipedia.org/wiki/Mars_(mythology)http://en.wikipedia.org/wiki/Iron(III)_oxidehttp://en.wikipedia.org/wiki/Mars_surface_colorhttp://en.wikipedia.org/wiki/Terrestrial_planethttp://en.wikipedia.org/wiki/Atmospherehttp://en.wikipedia.org/wiki/Impact_craterhttp://en.wikipedia.org/wiki/Moonhttp://en.wikipedia.org/wiki/Polar_ice_capshttp://en.wikipedia.org/wiki/Polar_ice_capshttp://en.wikipedia.org/wiki/Earthhttp://en.wikipedia.org/wiki/Rotational_periodhttp://en.wikipedia.org/wiki/Olympus_Monshttp://en.wikipedia.org/wiki/Valles_Marinerishttp://en.wikipedia.org/wiki/Borealis_basinhttp://en.wikipedia.org/wiki/Mariner_4http://en.wikipedia.org/wiki/Latitudehttp://en.wikipedia.org/wiki/Striation_(geology)http://en.wikipedia.org/wiki/Optical_illusionhttp://en.wikipedia.org/wiki/Spirit_roverhttp://en.wikipedia.org/wiki/Phoenix_(spacecraft)http://en.wikipedia.org/wiki/Moons_of_Marshttp://en.wikipedia.org/wiki/Phobos_(moon)http://en.wikipedia.org/wiki/Deimos_(moon)http://en.wikipedia.org/wiki/Asteroidhttp://en.wikipedia.org/wiki/5261_Eurekahttp://en.wikipedia.org/wiki/List_of_Mars_trojan_asteroidshttp://en.wikipedia.org/wiki/Spacecrafthttp://en.wikipedia.org/wiki/Mars_Odysseyhttp://en.wikipedia.org/wiki/Mars_Expresshttp://en.wikipedia.org/wiki/Mars_Reconnaissance_Orbiterhttp://en.wikipedia.org/wiki/Mars_Reconnaissance_Orbiterhttp://en.wikipedia.org/wiki/Mars_Exploration_Roverhttp://en.wikipedia.org/wiki/Opportunity_roverhttp://en.wikipedia.org/wiki/NASAhttp://en.wikipedia.org/wiki/Mars_Global_Surveyorhttp://en.wikipedia.org/wiki/Apparent_magnitudehttp://en.wikipedia.org/wiki/Jupiterhttp://en.wikipedia.org/wiki/Venushttp://en.wikipedia.org/wiki/Marshttp://en.wikipedia.org/wiki/Planet


2/28

1.4.2 Tectonic sites

1.4.3 Caves

1.5 Atmosphere

1.6 Climate

2 Orbit and rotation

3 Moons

4 Search for life

5 Exploration missions

5.1 Current missions

5.2 Past missions

5.3 Future missions

5.4 Manned mission goals

6 Astronomy on Mars

7 Viewing

7.1 Closest approaches

7.1.1 Relative

7.1.2 Absolute, around the present time

7.2 Historical observations

7.3 Martian "canals"

8 In culture

8.1 Intelligent "Martians" 9 Surface details

10 Exploration timeline

11 See also

12 Notes

13 References

14 External links

Physical characteristics


3/28

Size comparison ofEarth and Mars.

Mars has approximately half the diameterof Earth. It is less dense than Earth, having about 15%of Earth's volume and 11% of the mass. Its surface area is only slightly less than the total area ofEarth's dry land.[6] While Mars is larger and more massive than Mercury, Mercury has a higherdensity. This results in the two planets having a nearly identical gravitational pull at the surfacethat of Mars is stronger by less than 1%. The red-orange appearance of the Martian surface iscaused by iron(III) oxide, more commonly known as hematite, or rust.[24]

Geology

Main article: Geology of Mars

Mars is a terrestrial planetthat consists of minerals containing siliconandoxygen, metals, andother elements that typically make up rock. The surface of Mars is primarily composed oftholeiiticbasalt,[25]although parts are more silica-rich than typical basalt and may be similar toandesitic rocks on Earth or silica glass. Regions of low albedoshow concentrations ofplagioclase feldspar, with northern low albedo regions displaying higher than normalconcentrations of sheet silicates and high-silicon glass. Parts of the southern highlands includedetectable amounts of high-calciumpyroxenes. Localized concentrations ofhematite and olivinehave also been found.[26]Much of the surface is deeply covered by finely grainediron(III) oxide

dust.[27][28]

Like Earth, this planet has undergone differentiation, resulting in a dense, metallic core regionoverlaid by less dense materials.[29]Current models of the planet's interior imply a core regionabout 1794 65 km in radius, consisting primarily ofiron and nickel with about 1617%sulfur.[30] This iron sulfide core is partially fluid, and has twice the concentration of the lighter elementsthan exist at Earth's core. The core is surrounded by a silicate mantle that formed many of thetectonic and volcanic features on the planet, but now appears to be dormant. Besides silicon andoxygen, the most abundant elements in the martian crust are iron, magnesium, aluminum,calcium, and potassium. The average thickness of the planet's crust is about 50 km, with amaximum thickness of 125 km.[31]Earth's crust, averaging 40 km, is only one third as thick asMars crust, relative to the sizes of the two planets.

Although Mars has no evidence of a current structured global magnetic field,[32] observationsshow that parts of the planet's crust have been magnetized, and that alternating polarity reversalsof its dipole field have occurred in the past. Thispaleomagnetismof magnetically susceptibleminerals has properties that are very similar to thealternating bands found on the ocean floors ofEarth. One theory, published in 1999 and re-examined in October 2005 (with the help of theMars Global Surveyor), is that these bands demonstrateplate tectonicson Mars fourbillionyearsago, before the planetary dynamo ceased to function and the planet's magnetic field faded away.[33]
http://en.wikipedia.org/wiki/Earthhttp://en.wikipedia.org/wiki/Diameterhttp://en.wikipedia.org/wiki/Diameterhttp://en.wikipedia.org/wiki/Masshttp://en.wikipedia.org/wiki/Surface_areahttp://en.wikipedia.org/wiki/Mercury_(planet)http://en.wikipedia.org/wiki/Mercury_(planet)http://en.wikipedia.org/wiki/Iron(III)_oxidehttp://en.wikipedia.org/wiki/Geology_of_Marshttp://en.wikipedia.org/wiki/Terrestrial_planethttp://en.wikipedia.org/wiki/Terrestrial_planethttp://en.wikipedia.org/wiki/Siliconhttp://en.wikipedia.org/wiki/Siliconhttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Metalhttp://en.wikipedia.org/wiki/Metalhttp://en.wikipedia.org/wiki/Rock_(geology)http://en.wikipedia.org/wiki/Tholeiitic_magma_serieshttp://en.wikipedia.org/wiki/Basalthttp://en.wikipedia.org/wiki/Silicahttp://en.wikipedia.org/wiki/Andesitichttp://en.wikipedia.org/wiki/Albedohttp://en.wikipedia.org/wiki/Albedohttp://en.wikipedia.org/wiki/Plagioclase_feldsparhttp://en.wikipedia.org/wiki/Pyroxeneshttp://en.wikipedia.org/wiki/Pyroxeneshttp://en.wikipedia.org/wiki/Hematitehttp://en.wikipedia.org/wiki/Olivinehttp://en.wikipedia.org/wiki/Iron(III)_oxidehttp://en.wikipedia.org/wiki/Iron(III)_oxidehttp://en.wikipedia.org/wiki/Planetary_differentiationhttp://en.wikipedia.org/wiki/Ironhttp://en.wikipedia.org/wiki/Ironhttp://en.wikipedia.org/wiki/Nickelhttp://en.wikipedia.org/wiki/Sulfurhttp://en.wikipedia.org/wiki/Sulfurhttp://en.wikipedia.org/wiki/Iron(II)_sulfidehttp://en.wikipedia.org/wiki/Mantle_(geology)http://en.wikipedia.org/wiki/Magnetic_fieldhttp://en.wikipedia.org/wiki/Paleomagnetismhttp://en.wikipedia.org/wiki/Paleomagnetismhttp://en.wikipedia.org/wiki/Paleomagnetismhttp://en.wikipedia.org/wiki/Magnetic_stripinghttp://en.wikipedia.org/wiki/Magnetic_stripinghttp://en.wikipedia.org/wiki/Magnetic_stripinghttp://en.wikipedia.org/wiki/Mars_Global_Surveyorhttp://en.wikipedia.org/wiki/Plate_tectonicshttp://en.wikipedia.org/wiki/Plate_tectonicshttp://en.wikipedia.org/wiki/1000000000_(number)http://en.wikipedia.org/wiki/1000000000_(number)http://en.wikipedia.org/wiki/Dynamo_theoryhttp://en.wikipedia.org/wiki/File:Mars_Earth_Comparison.pnghttp://en.wikipedia.org/wiki/File:Mars_Earth_Comparison.pnghttp://en.wikipedia.org/wiki/Earthhttp://en.wikipedia.org/wiki/Diameterhttp://en.wikipedia.org/wiki/Masshttp://en.wikipedia.org/wiki/Surface_areahttp://en.wikipedia.org/wiki/Mercury_(planet)http://en.wikipedia.org/wiki/Iron(III)_oxidehttp://en.wikipedia.org/wiki/Geology_of_Marshttp://en.wikipedia.org/wiki/Terrestrial_planethttp://en.wikipedia.org/wiki/Siliconhttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Metalhttp://en.wikipedia.org/wiki/Rock_(geology)http://en.wikipedia.org/wiki/Tholeiitic_magma_serieshttp://en.wikipedia.org/wiki/Basalthttp://en.wikipedia.org/wiki/Silicahttp://en.wikipedia.org/wiki/Andesitichttp://en.wikipedia.org/wiki/Albedohttp://en.wikipedia.org/wiki/Plagioclase_feldsparhttp://en.wikipedia.org/wiki/Pyroxeneshttp://en.wikipedia.org/wiki/Hematitehttp://en.wikipedia.org/wiki/Olivinehttp://en.wikipedia.org/wiki/Iron(III)_oxidehttp://en.wikipedia.org/wiki/Planetary_differentiationhttp://en.wikipedia.org/wiki/Ironhttp://en.wikipedia.org/wiki/Nickelhttp://en.wikipedia.org/wiki/Sulfurhttp://en.wikipedia.org/wiki/Iron(II)_sulfidehttp://en.wikipedia.org/wiki/Mantle_(geology)http://en.wikipedia.org/wiki/Magnetic_fieldhttp://en.wikipedia.org/wiki/Paleomagnetismhttp://en.wikipedia.org/wiki/Magnetic_stripinghttp://en.wikipedia.org/wiki/Magnetic_stripinghttp://en.wikipedia.org/wiki/Mars_Global_Surveyorhttp://en.wikipedia.org/wiki/Plate_tectonicshttp://en.wikipedia.org/wiki/1000000000_(number)http://en.wikipedia.org/wiki/Dynamo_theory


4/28

During the Solar System's formation, Mars was created as the result of a stochastic process ofrun-away accretion out of theprotoplanetary diskthat orbited the Sun. Mars has many distinctivechemical features caused by its position in the Solar System. Elements with comparatively lowboiling points such as chlorine, phosphorus and sulphur are much more common on Mars thanEarth; these elements were probably removed from areas closer to the Sun by the young star'senergetic solar wind.[34]

After the formation of the planets, all were subjected to the so-called "Late HeavyBombardment". About 60% of the surface of Mars shows a record of impacts from that era,[35][36][37] while much of the remaining surface is probably underlain by immense impact basins causedby those events. There is evidence of an enormous impact basin in the northern hemisphere ofMars, spanning 10,600 km by 8,500 km, or roughly four times larger than the Moon's South Pole Aitken basin, the largest impact basin yet discovered.[14][15] This theory suggests that Mars wasstruck by a Pluto-sized body about four billion years ago. The event, thought to be the cause ofthe Martian hemispheric dichotomy, created the smooth Borealis basin that covers 40% of theplanet.[38][39]

The geological history of Mars can be split into many periods, but the following are the three

primary periods:[40][41]

Noachian period (named afterNoachis Terra): Formation of the oldest extant surfaces ofMars, 4.5 billion years ago to 3.5 billion years ago. Noachian age surfaces are scarred bymany large impact craters. The Tharsisbulge, a volcanic upland, is thought to haveformed during this period, with extensive flooding by liquid water late in the period.

Hesperian period (named after Hesperia Planum): 3.5 billion years ago to 2.93.3billion years ago. The Hesperian period is marked by the formation of extensive lavaplains.

Amazonian period (named afterAmazonis Planitia): 2.93.3 billion years ago topresent. Amazonian regions have few meteorite impact craters, but are otherwise quitevaried. Olympus Mons formed during this period, along with lava flows elsewhere onMars.

Top down view ofOlympus Mons, the highest known mountain in the solar system

Some geological activity is still taking place on Mars. The Athabasca Valles is home to sheet-like lava flows up to about 200 Mya. Water flows in the grabens called the Cerberus Fossaeoccurred less than 20 Mya, indicating equally recent volcanic intrusions. [42] On February 19,
http://en.wikipedia.org/wiki/Formation_and_evolution_of_the_Solar_Systemhttp://en.wikipedia.org/wiki/Stochastic_processhttp://en.wikipedia.org/wiki/Protoplanetary_diskhttp://en.wikipedia.org/wiki/Protoplanetary_diskhttp://en.wikipedia.org/wiki/Solar_windhttp://en.wikipedia.org/wiki/Solar_windhttp://en.wikipedia.org/wiki/Late_Heavy_Bombardmenthttp://en.wikipedia.org/wiki/Late_Heavy_Bombardmenthttp://en.wikipedia.org/wiki/South_Pole_%E2%80%93_Aitken_basinhttp://en.wikipedia.org/wiki/South_Pole_%E2%80%93_Aitken_basinhttp://en.wikipedia.org/wiki/Plutohttp://en.wikipedia.org/wiki/Martian_hemispheric_dichotomyhttp://en.wikipedia.org/wiki/Borealis_basinhttp://en.wikipedia.org/wiki/Noachis_Terrahttp://en.wikipedia.org/wiki/Tharsishttp://en.wikipedia.org/wiki/Tharsishttp://en.wikipedia.org/wiki/Amazonis_Planitiahttp://en.wikipedia.org/wiki/Impact_eventhttp://en.wikipedia.org/wiki/Olympus_Monshttp://en.wikipedia.org/wiki/Olympus_Monshttp://en.wikipedia.org/wiki/Athabasca_Valleshttp://en.wikipedia.org/wiki/Mya_(unit)http://en.wikipedia.org/wiki/Cerberus_Fossaehttp://en.wikipedia.org/wiki/File:Olympus_Mons_alt.jpghttp://en.wikipedia.org/wiki/File:Olympus_Mons_alt.jpghttp://en.wikipedia.org/wiki/Formation_and_evolution_of_the_Solar_Systemhttp://en.wikipedia.org/wiki/Stochastic_processhttp://en.wikipedia.org/wiki/Protoplanetary_diskhttp://en.wikipedia.org/wiki/Solar_windhttp://en.wikipedia.org/wiki/Late_Heavy_Bombardmenthttp://en.wikipedia.org/wiki/Late_Heavy_Bombardmenthttp://en.wikipedia.org/wiki/South_Pole_%E2%80%93_Aitken_basinhttp://en.wikipedia.org/wiki/South_Pole_%E2%80%93_Aitken_basinhttp://en.wikipedia.org/wiki/Plutohttp://en.wikipedia.org/wiki/Martian_hemispheric_dichotomyhttp://en.wikipedia.org/wiki/Borealis_basinhttp://en.wikipedia.org/wiki/Noachis_Terrahttp://en.wikipedia.org/wiki/Tharsishttp://en.wikipedia.org/wiki/Amazonis_Planitiahttp://en.wikipedia.org/wiki/Impact_eventhttp://en.wikipedia.org/wiki/Olympus_Monshttp://en.wikipedia.org/wiki/Olympus_Monshttp://en.wikipedia.org/wiki/Athabasca_Valleshttp://en.wikipedia.org/wiki/Mya_(unit)http://en.wikipedia.org/wiki/Cerberus_Fossae


5/28

2008, images from the Mars Reconnaissance Orbitershowed evidence of an avalanche from a700 m high cliff.[43]

Soil

Main article: Martian soil

ThePhoenix lander returned data showing Martian soil to be slightly alkaline and containingelements such as magnesium, sodium,potassium and chloride. These nutrients are found ingardens on Earth, and are necessary for growth of plants.[44]Experiments performed by theLander showed that the Martian soil has abasicpHof 8.3, and may contain traces of the saltperchlorate.[45][46]

Annotated image of Tharsis Tholus dark streak, as seen by Hirise. It is located in the middle leftof this picture. Tharsis Tholusis just off to the right.

Streaks are common across Mars and new ones appear frequently on steep slopes of craters,troughs, and valleys. The streaks are dark at first and get lighter with age. Sometimes the streaksstart in a tiny area which then spreads out for hundreds of metres. They have also been seen tofollow the edges of boulders and other obstacles in their path. The commonly accepted theoriesinclude that they are dark underlying layers of soil revealed after avalanches of bright dust ordust devils.[47]Several explanations have been put forward, some of which involve wateror eventhe growth of organisms.[48][49]

Hydrology

Main article: Water on Mars
http://en.wikipedia.org/wiki/Mars_Reconnaissance_Orbiterhttp://en.wikipedia.org/wiki/Martian_soilhttp://en.wikipedia.org/wiki/Phoenix_(spacecraft)http://en.wikipedia.org/wiki/Magnesiumhttp://en.wikipedia.org/wiki/Sodiumhttp://en.wikipedia.org/wiki/Sodiumhttp://en.wikipedia.org/wiki/Potassiumhttp://en.wikipedia.org/wiki/Chloridehttp://en.wikipedia.org/wiki/Base_(chemistry)http://en.wikipedia.org/wiki/PHhttp://en.wikipedia.org/wiki/PHhttp://en.wikipedia.org/wiki/PHhttp://en.wikipedia.org/wiki/Salt_(chemistry)http://en.wikipedia.org/wiki/Perchloratehttp://en.wikipedia.org/wiki/Hirisehttp://en.wikipedia.org/wiki/Tharsis_Tholushttp://en.wikipedia.org/wiki/Tharsis_Tholushttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Water_on_Marshttp://en.wikipedia.org/wiki/File:Tharsis_Tholus_block.JPGhttp://en.wikipedia.org/wiki/File:Tharsis_Tholus_block.JPGhttp://en.wikipedia.org/wiki/Mars_Reconnaissance_Orbiterhttp://en.wikipedia.org/wiki/Martian_soilhttp://en.wikipedia.org/wiki/Phoenix_(spacecraft)http://en.wikipedia.org/wiki/Magnesiumhttp://en.wikipedia.org/wiki/Sodiumhttp://en.wikipedia.org/wiki/Potassiumhttp://en.wikipedia.org/wiki/Chloridehttp://en.wikipedia.org/wiki/Base_(chemistry)http://en.wikipedia.org/wiki/PHhttp://en.wikipedia.org/wiki/Salt_(chemistry)http://en.wikipedia.org/wiki/Perchloratehttp://en.wikipedia.org/wiki/Hirisehttp://en.wikipedia.org/wiki/Tharsis_Tholushttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Water_on_Mars


6/28

Microscopic photo taken by Opportunity showing a gray hematiteconcretion, indicative of thepast presence of liquid water

Liquid water cannot exist on the surface of Mars due to low atmospheric pressure, except at thelowest elevations for short periods.[50][51] The two polar ice caps appear to be made largely ofwater.[52][53] The volume of water ice in the south polar ice cap, if melted, would be sufficient tocover the entire planetary surface to a depth of 11 meters.[54] Apermafrost mantle stretches fromthe pole to latitudes of about 60.[52]

Large quantities of water iceare thought to be trapped underneath the thickcryosphere of Mars.Radar data from Mars Expressand the Mars Reconnaissance Orbitershow large quantities ofwater ice both at the poles (July 2005) [17][55] and at mid-latitudes (November 2008).[18] ThePhoenix lander directly sampled water ice in shallow Martian soil on July 31, 2008.[20]

Landforms visible on Mars strongly suggest that liquid water has at least at times existed on theplanet's surface. Huge linear swathes of scoured ground, known as outflow channels, cut across

the surface in around 25 places. These are thought to record erosion which occurred during thecatastrophic release of water from subsurface aquifers, though some of these structures have alsobeen hypothesised to result from the action of glaciers or lava.[56][57] The youngest of thesechannels are thought to have formed as recently as only a few million years ago.[58] Elsewhere,particularly on the oldest areas of the martian surface, finer-scale, dendriticnetworks of valleysare spread across significant proportions of the landscape. Features of these valleys and theirdistribution very strongly imply that they were carved by runoffresulting from rain or snow fallin early Mars history. Subsurface water flow andgroundwater sapping may play importantsubsidiary roles in some networks, but precipitation was probably the root cause of the incisionin almost all cases.[59]

There are also thousands of features along crater and canyon walls that appear similar to

terrestrial gullies. The gullies tend to be in the highlands of the southern hemisphere and to facethe Equator; all are poleward of 30 latitude. A number of authors have suggested that theirformation process demands the involvement of liquid water, probably from melting ice,[60][61]

although others have argued for formation mechanisms involving carbon dioxide frost or themovement of dry dust.[62][63] No partially degraded gullies have formed by weathering and nosuperimposed impact craters have been observed, indicating that these are very young features,possibly even active today.[61]
http://en.wikipedia.org/wiki/Opportunity_roverhttp://en.wikipedia.org/wiki/Hematitehttp://en.wikipedia.org/wiki/Concretionhttp://en.wikipedia.org/wiki/Concretionhttp://en.wikipedia.org/wiki/Concretionhttp://en.wikipedia.org/wiki/Permafrosthttp://en.wikipedia.org/wiki/Permafrosthttp://en.wikipedia.org/wiki/Evolution_of_water_on_Mars_and_Earthhttp://en.wikipedia.org/wiki/Evolution_of_water_on_Mars_and_Earthhttp://en.wikipedia.org/wiki/Cryospherehttp://en.wikipedia.org/wiki/Mars_Expresshttp://en.wikipedia.org/wiki/Mars_Expresshttp://en.wikipedia.org/wiki/Mars_Reconnaissance_Orbiterhttp://en.wikipedia.org/wiki/Geomorphologyhttp://en.wikipedia.org/wiki/Outflow_channelshttp://en.wikipedia.org/wiki/Valley_networks_(Mars)http://en.wikipedia.org/wiki/Valley_networks_(Mars)http://en.wikipedia.org/wiki/Surface_runoffhttp://en.wikipedia.org/wiki/Groundwater_sappinghttp://en.wikipedia.org/wiki/Groundwater_sappinghttp://en.wikipedia.org/wiki/Gullieshttp://en.wikipedia.org/wiki/File:Nasa_mars_opportunity_rock_water_150_eng_02mar04.jpghttp://en.wikipedia.org/wiki/File:Nasa_mars_opportunity_rock_water_150_eng_02mar04.jpghttp://en.wikipedia.org/wiki/Opportunity_roverhttp://en.wikipedia.org/wiki/Hematitehttp://en.wikipedia.org/wiki/Concretionhttp://en.wikipedia.org/wiki/Permafrosthttp://en.wikipedia.org/wiki/Evolution_of_water_on_Mars_and_Earthhttp://en.wikipedia.org/wiki/Cryospherehttp://en.wikipedia.org/wiki/Mars_Expresshttp://en.wikipedia.org/wiki/Mars_Reconnaissance_Orbiterhttp://en.wikipedia.org/wiki/Geomorphologyhttp://en.wikipedia.org/wiki/Outflow_channelshttp://en.wikipedia.org/wiki/Valley_networks_(Mars)http://en.wikipedia.org/wiki/Surface_runoffhttp://en.wikipedia.org/wiki/Groundwater_sappinghttp://en.wikipedia.org/wiki/Gullies


7/28

Other geological features, such as deltasandalluvial fans preserved in craters, also argue verystrongly for warmer, wetter conditions at some interval or intervals in earlier Mars history.[64]

Such conditions necessarily require the widespread presence of craterlakes across a largeproportion of the surface, for which there is also independent mineralogical, sedimentologicaland geomorphological evidence.[65] Some authors have even gone so far as to argue that at timesin the martian past, much of the low northern plains of the planet were covered with a true oceanhundreds of meters deep, though this remains controversial.[66]

Further evidence that liquid water once existed on the surface of Mars comes from the detectionof specific minerals such ashematite and goethite, both of which sometimes form in the presenceof water.[67]Some of the evidence believed to indicate ancient water basins and flows has beennegated by higher resolution studies by the Mars Reconnaissance Orbiter.[68] In 2004,Opportunity detected the mineraljarosite. This forms only in the presence of acidic water, whichdemonstrates that water once existed on Mars.[69]

Polar caps

Northern ice cap of Mars in 1999

South polar cap in 2000Mars has two permanent polar ice caps. During a pole's winter, it lies in continuous darkness,chilling the surface and causing thedeposition of 2530% of the atmosphere into slabs ofCO2ice (dry ice).[70] When the poles are again exposed to sunlight, the frozen CO2sublimes, creatingenormous winds that sweep off the poles as fast as 400 km/h. These seasonal actions transportlarge amounts of dust and water vapor, giving rise to Earth-like frost and largecirrus clouds.Clouds of water-ice were photographed by theOpportunityrover in 2004.[71]
http://en.wikipedia.org/wiki/River_deltahttp://en.wikipedia.org/wiki/River_deltahttp://en.wikipedia.org/wiki/Alluvial_fanshttp://en.wikipedia.org/wiki/Alluvial_fanshttp://en.wikipedia.org/wiki/Lakeshttp://en.wikipedia.org/wiki/Liquidhttp://en.wikipedia.org/wiki/Hematitehttp://en.wikipedia.org/wiki/Hematitehttp://en.wikipedia.org/wiki/Goethitehttp://en.wikipedia.org/wiki/Jarositehttp://en.wikipedia.org/wiki/Jarositehttp://en.wikipedia.org/wiki/Deposition_(phase_transition)http://en.wikipedia.org/wiki/Deposition_(phase_transition)http://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Dry_icehttp://en.wikipedia.org/wiki/Sublimation_(physics)http://en.wikipedia.org/wiki/Sublimation_(physics)http://en.wikipedia.org/wiki/Cirrus_cloudhttp://en.wikipedia.org/wiki/Cirrus_cloudhttp://en.wikipedia.org/wiki/Cirrus_cloudhttp://en.wikipedia.org/wiki/Opportunity_roverhttp://en.wikipedia.org/wiki/Opportunity_roverhttp://en.wikipedia.org/wiki/Opportunity_roverhttp://en.wikipedia.org/wiki/File:South_Polar_Cap_of_Mars_during_Martian_South_summer_2000.jpghttp://en.wikipedia.org/wiki/File:Martian_north_polar_cap.jpghttp://en.wikipedia.org/wiki/River_deltahttp://en.wikipedia.org/wiki/Alluvial_fanshttp://en.wikipedia.org/wiki/Lakeshttp://en.wikipedia.org/wiki/Liquidhttp://en.wikipedia.org/wiki/Hematitehttp://en.wikipedia.org/wiki/Goethitehttp://en.wikipedia.org/wiki/Jarositehttp://en.wikipedia.org/wiki/Deposition_(phase_transition)http://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Dry_icehttp://en.wikipedia.org/wiki/Sublimation_(physics)http://en.wikipedia.org/wiki/Cirrus_cloudhttp://en.wikipedia.org/wiki/Opportunity_rover


8/28

The polar caps at both poles consist primarily of water ice. Frozen carbon dioxide accumulates asa comparatively thin layer about one metre thick on the north cap in the northern winter only,while the south cap has a permanent dry ice cover about eight metres thick. [72] The northern polarcap has a diameter of about 1,000 kilometres during the northern Mars summer,[73] and containsabout 1.6 million cubic km of ice, which if spread evenly on the cap would be 2 km thick.[74]

(This compares to a volume of 2.85 million cubic km (km3) for theGreenland ice sheet.) Thesouthern polar cap has a diameter of 350 km and a thickness of 3 km.[75] The total volume of icein the south polar cap plus the adjacent layered deposits has also been estimated at 1.6 millioncubic km.[76] Both polar caps show spiral troughs, which recent analysis ofSHARAD icepenetrating radar has shown are a result ofkatabatic winds that spiral due to theCoriolis Effect.[77][78]

The seasonal frosting of some areas near the southern ice cap results in the formation oftransparent 1 metre thick slabs of dry ice above the ground. With the arrival of spring, sunlightwarms the subsurface and pressure from subliming CO2 builds up under a slab, elevating andultimately rupturing it. This leads to geyser-like eruptionsof CO2 gas mixed with dark basalticsand or dust. This process is rapid, observed happening in the space of a few days, weeks ormonths, a rate of change rather unusual in geologyespecially for Mars. The gas rushingunderneath a slab to the site of a geyser carves a spider-like pattern of radial channels under theice.[79][80][81][82]

Geography

Main article: Geography of MarsSee also: Category:Surface features of Mars

Volcanic plateaus (red) and impact basins (blue) dominate this topographic map of Mars

Although better remembered for mapping the Moon, Johann Heinrich Mdlerand Wilhelm Beerwere the first "areographers". They began by establishing that most of Mars surface features

were permanent, and more precisely determining the planet's rotation period. In 1840, Mdlercombined ten years of observations and drew the first map of Mars. Rather than giving names tothe various markings, Beer and Mdler simply designated them with letters; Meridian Bay (SinusMeridiani) was thus feature "a."[83]

Today, features on Mars are named from a variety of sources. Albedo features are named forclassical mythology. Craters larger than 60 kilometres (37 mi) are named for deceased scientistsand writers and others who have contributed to the study of Mars. Craters smaller that 60 km are
http://en.wikipedia.org/wiki/Greenland_ice_sheethttp://en.wikipedia.org/wiki/Greenland_ice_sheethttp://en.wikipedia.org/wiki/SHARADhttp://en.wikipedia.org/wiki/SHARADhttp://en.wikipedia.org/wiki/Katabatic_windhttp://en.wikipedia.org/wiki/Katabatic_windhttp://en.wikipedia.org/wiki/Coriolis_Effecthttp://en.wikipedia.org/wiki/Coriolis_Effecthttp://en.wikipedia.org/wiki/Martian_geyserhttp://en.wikipedia.org/wiki/Martian_geyserhttp://en.wikipedia.org/wiki/Geography_of_Marshttp://en.wikipedia.org/wiki/Category:Surface_features_of_Marshttp://en.wikipedia.org/wiki/Johann_Heinrich_M%C3%A4dlerhttp://en.wikipedia.org/wiki/Wilhelm_Beerhttp://en.wikipedia.org/wiki/File:MarsTopoMap-PIA02031_modest.jpghttp://en.wikipedia.org/wiki/File:MarsTopoMap-PIA02031_modest.jpghttp://en.wikipedia.org/wiki/Greenland_ice_sheethttp://en.wikipedia.org/wiki/SHARADhttp://en.wikipedia.org/wiki/Katabatic_windhttp://en.wikipedia.org/wiki/Coriolis_Effecthttp://en.wikipedia.org/wiki/Martian_geyserhttp://en.wikipedia.org/wiki/Geography_of_Marshttp://en.wikipedia.org/wiki/Category:Surface_features_of_Marshttp://en.wikipedia.org/wiki/Johann_Heinrich_M%C3%A4dlerhttp://en.wikipedia.org/wiki/Wilhelm_Beer


9/28

named for towns and villages of the world with populations of less than 100,000. Large valleysare named for the word mars or star in various languages, small valleys are named for rivers.[84]

Large albedo features retain many of the older names, but are often updated to reflect newknowledge of the nature of the features. For example, Nix Olympica (the snows of Olympus) hasbecome Olympus Mons (Mount Olympus).[85]The surface of Mars as seen from Earth is divided

into two kinds of areas, with differing albedo. The paler plains covered with dust and sand rich inreddish iron oxides were once thought of as Martian 'continents' and given names like ArabiaTerra (land of Arabia) orAmazonis Planitia(Amazonian plain). The dark features were thoughtto be seas, hence their names Mare Erythraeum, Mare Sirenum andAurorae Sinus. The largestdark feature seen from Earth is Syrtis Major Planum.[86] The permanent northern polar ice cap isnamed Planum Boreum, while the southern cap is called Planum Australe.

Mars equator is defined by its rotation, but the location of its Prime Meridian was specified, aswas Earth's (at Greenwich), by choice of an arbitrary point; Mdler and Beer selected a line in1830 for their first maps of Mars. After the spacecraft Mariner 9 provided extensive imagery ofMars in 1972, a small crater (later calledAiry-0), located in the Sinus Meridiani("Middle Bay"or "Meridian Bay"), was chosen for the definition of 0.0 longitude to coincide with the original

selection.[87]

Since Mars has no oceans and hence no 'sea level', a zero-elevation surface also had to beselected as a reference level; this is also called the areoid[88]of Mars, analogous to the terrestrialgeoid. Zero altitude is defined by the height at which there is 610.5 Pa (6.105 mbar) ofatmospheric pressure.[89]This pressure corresponds to thetriple point of water, and is about 0.6%of the sea level surface pressure on Earth (0.006 atm).[90] In practice, today this surface is defineddirectly from satellite gravity measurements.

An approximate true-color image, taken by Mars ExplorationRover Opportunity, shows theview ofVictoria Craterfrom Cape Verde. It was captured over a three-week period, fromOctober 16 November 6, 2006.

Impact topographyThe dichotomy of Martian topography is striking: northern plains flattened by lava flows contrastwith the southern highlands, pitted and cratered by ancient impacts. Research in 2008 haspresented evidence regarding a theory proposed in 1980 postulating that, four billion years ago,the northern hemisphere of Mars was struck by an object one-tenth to two-thirds the size oftheMoon. If validated, this would make the northern hemisphere of Mars the site of an impact crater10,600 km long by 8,500 km wide, or roughly the area of Europe, Asia, and Australia combined,surpassing the South Pole Aitken basin as the largest impact crater in the Solar System.[14][15]
http://en.wikipedia.org/wiki/Albedohttp://en.wikipedia.org/wiki/Arabia_Terrahttp://en.wikipedia.org/wiki/Arabia_Terrahttp://en.wikipedia.org/wiki/Amazonis_Planitiahttp://en.wikipedia.org/wiki/Amazonis_Planitiahttp://en.wikipedia.org/wiki/Mare_Erythraeumhttp://en.wikipedia.org/wiki/Mare_Erythraeumhttp://en.wikipedia.org/wiki/Aurorae_Sinushttp://en.wikipedia.org/wiki/Aurorae_Sinushttp://en.wikipedia.org/wiki/Syrtis_Major_Planumhttp://en.wikipedia.org/wiki/Syrtis_Major_Planumhttp://en.wikipedia.org/wiki/Planum_Boreumhttp://en.wikipedia.org/wiki/Planum_Australehttp://en.wikipedia.org/wiki/Prime_Meridianhttp://en.wikipedia.org/wiki/Greenwichhttp://en.wikipedia.org/wiki/Mariner_9http://en.wikipedia.org/wiki/Airy-0http://en.wikipedia.org/wiki/Airy-0http://en.wikipedia.org/wiki/Sinus_Meridianihttp://en.wikipedia.org/wiki/Sinus_Meridianihttp://en.wikipedia.org/wiki/Geoidhttp://en.wikipedia.org/wiki/Pascal_(unit)http://en.wikipedia.org/wiki/Bar_(unit)http://en.wikipedia.org/wiki/Triple_pointhttp://en.wikipedia.org/wiki/Triple_pointhttp://en.wikipedia.org/wiki/Opportunity_roverhttp://en.wikipedia.org/wiki/Opportunity_roverhttp://en.wikipedia.org/wiki/Victoria_Craterhttp://en.wikipedia.org/wiki/The_Moonhttp://en.wikipedia.org/wiki/The_Moonhttp://en.wikipedia.org/wiki/South_Pole_%E2%80%93_Aitken_basinhttp://en.wikipedia.org/wiki/File:Victoria_Crater,_Cape_Verde-Mars.jpghttp://en.wikipedia.org/wiki/File:Victoria_Crater,_Cape_Verde-Mars.jpghttp://en.wikipedia.org/wiki/Albedohttp://en.wikipedia.org/wiki/Arabia_Terrahttp://en.wikipedia.org/wiki/Arabia_Terrahttp://en.wikipedia.org/wiki/Amazonis_Planitiahttp://en.wikipedia.org/wiki/Mare_Erythraeumhttp://en.wikipedia.org/wiki/Aurorae_Sinushttp://en.wikipedia.org/wiki/Syrtis_Major_Planumhttp://en.wikipedia.org/wiki/Planum_Boreumhttp://en.wikipedia.org/wiki/Planum_Australehttp://en.wikipedia.org/wiki/Prime_Meridianhttp://en.wikipedia.org/wiki/Greenwichhttp://en.wikipedia.org/wiki/Mariner_9http://en.wikipedia.org/wiki/Airy-0http://en.wikipedia.org/wiki/Sinus_Meridianihttp://en.wikipedia.org/wiki/Geoidhttp://en.wikipedia.org/wiki/Pascal_(unit)http://en.wikipedia.org/wiki/Bar_(unit)http://en.wikipedia.org/wiki/Triple_pointhttp://en.wikipedia.org/wiki/Opportunity_roverhttp://en.wikipedia.org/wiki/Victoria_Craterhttp://en.wikipedia.org/wiki/The_Moonhttp://en.wikipedia.org/wiki/The_Moonhttp://en.wikipedia.org/wiki/South_Pole_%E2%80%93_Aitken_basin


10/28

Mars is scarred by a number ofimpact craters: a total of 43,000 craters with a diameter of 5 kmor greater have been found.[91]The largest confirmed of these is theHellas impact basin, a lightalbedo featureclearly visible from Earth.[92] Due to the smaller mass of Mars, the probability ofan object colliding with the planet is about half that of the Earth. Mars is located closer to theasteroid belt, so it has an increased chance of being struck by materials from that source. Mars isalso more likely to be struck by short-period comets, i.e., those that lie within the orbit of Jupiter.[93] In spite of this, there are far fewer craters on Mars compared with the Moon because theatmosphere of Mars provides protection against small meteors. Some craters have a morphologythat suggests the ground became wet after the meteor impacted.[94]

Tectonic sites

The shield volcano,Olympus Mons (Mount Olympus), at 27 km is the highest known mountainin the Solar System.[95]It is an extinct volcano in the vast upland region Tharsis, which containsseveral other large volcanoes. Olympus Mons is over three times the height ofMount Everest,which in comparison stands at just over 8.8 km.[96]

The large canyon, Valles Marineris (Latin forMarinerValleys, also known as Agathadaemon inthe old canal maps), has a length of 4,000 km and a depth of up to 7 km. The length of Valles

Marineris is equivalent to the length of Europe and extends across one-fifth the circumference ofMars. By comparison, the Grand Canyon on Earth is only 446 km long and nearly 2 km deep.Valles Marineris was formed due to the swelling of the Tharsis area which caused the crust in thearea of Valles Marineris to collapse. Another large canyon is Ma'adim Vallis (Ma'adim isHebrew for Mars). It is 700 km long and again much bigger than the Grand Canyon with a widthof 20 km and a depth of 2 km in some places. It is possible that Ma'adim Vallis was flooded withliquid water in the past.[97]

Caves

THEMIS image of probable Mars cave entrances, informally named (A) Dena, (B) Chloe, (C)Wendy, (D) Annie, (E) Abby (left) and Nikki, and (F) Jeanne.

Images from the Thermal Emission Imaging System(THEMIS) aboard NASA's Mars Odyssey

orbiterhave revealed seven possible cave entrances on the flanks of the Arsia Monsvolcano.

[98]

The caves, named after loved ones of their discoverers, are collectively known as the "sevensisters."[99] Cave entrances measure from 100 m to 252 m wide and they are believed to be atleast 73 m to 96 m deep. Because light does not reach the floor of most of the caves, it is likelythat they extend much deeper than these lower estimates and widen below the surface. "Dena" isthe only exception; its floor is visible and was measured to be 130 m deep. The interiors of thesecaverns may be protected from micrometeoroids, UV radiation, solar flares and high energyparticles that bombard the planet's surface.[100]
http://en.wikipedia.org/wiki/Impact_craterhttp://en.wikipedia.org/wiki/Hellas_Planitiahttp://en.wikipedia.org/wiki/Hellas_Planitiahttp://en.wikipedia.org/wiki/Albedo_featurehttp://en.wikipedia.org/wiki/Albedo_featurehttp://en.wikipedia.org/wiki/Comethttp://en.wikipedia.org/wiki/Shield_volcanohttp://en.wikipedia.org/wiki/Shield_volcanohttp://en.wikipedia.org/wiki/Olympus_Monshttp://en.wikipedia.org/wiki/Tharsishttp://en.wikipedia.org/wiki/Mount_Everesthttp://en.wikipedia.org/wiki/Valles_Marinerishttp://en.wikipedia.org/wiki/Mariner_programhttp://en.wikipedia.org/wiki/Grand_Canyonhttp://en.wikipedia.org/wiki/Ma'adim_Vallishttp://en.wikipedia.org/wiki/Hebrewhttp://en.wikipedia.org/wiki/THEMIShttp://en.wikipedia.org/wiki/Thermal_Emission_Imaging_Systemhttp://en.wikipedia.org/wiki/Thermal_Emission_Imaging_Systemhttp://en.wikipedia.org/wiki/2001_Mars_Odysseyhttp://en.wikipedia.org/wiki/2001_Mars_Odysseyhttp://en.wikipedia.org/wiki/Cavehttp://en.wikipedia.org/wiki/Arsia_Monshttp://en.wikipedia.org/wiki/Arsia_Monshttp://en.wikipedia.org/wiki/Solar_flarehttp://en.wikipedia.org/wiki/File:Mars_caves_from_NASA_orbiters.jpghttp://en.wikipedia.org/wiki/File:Mars_caves_from_NASA_orbiters.jpghttp://en.wikipedia.org/wiki/Impact_craterhttp://en.wikipedia.org/wiki/Hellas_Planitiahttp://en.wikipedia.org/wiki/Albedo_featurehttp://en.wikipedia.org/wiki/Comethttp://en.wikipedia.org/wiki/Shield_volcanohttp://en.wikipedia.org/wiki/Olympus_Monshttp://en.wikipedia.org/wiki/Tharsishttp://en.wikipedia.org/wiki/Mount_Everesthttp://en.wikipedia.org/wiki/Valles_Marinerishttp://en.wikipedia.org/wiki/Mariner_programhttp://en.wikipedia.org/wiki/Grand_Canyonhttp://en.wikipedia.org/wiki/Ma'adim_Vallishttp://en.wikipedia.org/wiki/Hebrewhttp://en.wikipedia.org/wiki/THEMIShttp://en.wikipedia.org/wiki/Thermal_Emission_Imaging_Systemhttp://en.wikipedia.org/wiki/2001_Mars_Odysseyhttp://en.wikipedia.org/wiki/2001_Mars_Odysseyhttp://en.wikipedia.org/wiki/Cavehttp://en.wikipedia.org/wiki/Arsia_Monshttp://en.wikipedia.org/wiki/Solar_flare


11/28

Atmosphere

Main article: Atmosphere of Mars

The tenuous atmosphere of Mars, visible on the horizon in this low-orbit photo

Mars lost itsmagnetosphere 4 billion years ago,[101] so the solar wind interacts directly with theMartian ionosphere, lowering the atmospheric density by stripping away atoms from the outerlayer. Both Mars Global Surveyorand Mars Express have detected these ionised atmosphericparticles trailing off into space behind Mars.[101][102] Compared to Earth, the atmosphereof Mars isquite rarefied. Atmospheric pressureon the surface ranges from a low of 30Pa (0.030kPa) onOlympus Mons to over 1,155 Pa (1.155 kPa) in the Hellas Planitia, with a mean pressure at thesurface level of 600 Pa (0.60 kPa).[103] The surface pressure of Mars at its thickest is equal to thepressure found 35 km[104] above the Earth's surface. This is less than 1% of the Earth's surfacepressure (101.3 kPa). The scale height of the atmosphere is about 10.8 km,[105] which is higherthan Earth's (6 km) because the surface gravity of Mars is only about 38% of Earth's, an effectoffset by both the lower temperature and 50% higher average molecular weight of theatmosphere of Mars.

The atmosphere on Mars consists of 95%carbon dioxide, 3% nitrogen, 1.6% argon and containstraces ofoxygen and water.[6] The atmosphere is quite dusty, containing particulates about1.5 min diameter which give the Martian sky a tawny color when seen from the surface.[106]

Methane map

Methane has been detected in the Martian atmosphere with amole fraction of about 30ppb;[12][107]

it occurs in extended plumes, and the profiles imply that the methane was released from discrete
http://en.wikipedia.org/wiki/Atmosphere_of_Marshttp://en.wikipedia.org/wiki/Magnetospherehttp://en.wikipedia.org/wiki/Magnetospherehttp://en.wikipedia.org/wiki/Solar_windhttp://en.wikipedia.org/wiki/Ionospherehttp://en.wikipedia.org/wiki/Mars_Global_Surveyorhttp://en.wikipedia.org/wiki/Celestial_body_atmospherehttp://en.wikipedia.org/wiki/Celestial_body_atmospherehttp://en.wikipedia.org/wiki/Atmospheric_pressurehttp://en.wikipedia.org/wiki/Atmospheric_pressurehttp://en.wikipedia.org/wiki/Pascal_(unit)http://en.wikipedia.org/wiki/Pascal_(unit)http://en.wikipedia.org/wiki/Pascal_(unit)http://en.wikipedia.org/wiki/Pascal_(unit)http://en.wikipedia.org/wiki/Olympus_Monshttp://en.wikipedia.org/wiki/Hellas_Planitiahttp://en.wikipedia.org/wiki/Hellas_Planitiahttp://en.wikipedia.org/wiki/Scale_heighthttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Nitrogenhttp://en.wikipedia.org/wiki/Nitrogenhttp://en.wikipedia.org/wiki/Argonhttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/%CE%9Cmhttp://en.wikipedia.org/wiki/%CE%9Cmhttp://en.wikipedia.org/wiki/Tawny_(color)http://en.wikipedia.org/wiki/Methanehttp://en.wikipedia.org/wiki/Mole_fractionhttp://en.wikipedia.org/wiki/Mole_fractionhttp://en.wikipedia.org/wiki/Ppbhttp://en.wikipedia.org/wiki/Ppbhttp://en.wikipedia.org/wiki/File:Martian_Methane_Map.jpghttp://en.wikipedia.org/wiki/File:Martian_Methane_Map.jpghttp://en.wikipedia.org/wiki/File:Mars_atmosphere.jpghttp://en.wikipedia.org/wiki/File:Mars_atmosphere.jpghttp://en.wikipedia.org/wiki/Atmosphere_of_Marshttp://en.wikipedia.org/wiki/Magnetospherehttp://en.wikipedia.org/wiki/Solar_windhttp://en.wikipedia.org/wiki/Ionospherehttp://en.wikipedia.org/wiki/Mars_Global_Surveyorhttp://en.wikipedia.org/wiki/Celestial_body_atmospherehttp://en.wikipedia.org/wiki/Atmospheric_pressurehttp://en.wikipedia.org/wiki/Pascal_(unit)http://en.wikipedia.org/wiki/Pascal_(unit)http://en.wikipedia.org/wiki/Olympus_Monshttp://en.wikipedia.org/wiki/Hellas_Planitiahttp://en.wikipedia.org/wiki/Scale_heighthttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Nitrogenhttp://en.wikipedia.org/wiki/Argonhttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/%CE%9Cmhttp://en.wikipedia.org/wiki/Tawny_(color)http://en.wikipedia.org/wiki/Methanehttp://en.wikipedia.org/wiki/Mole_fractionhttp://en.wikipedia.org/wiki/Ppb


12/28

regions. In northern midsummer, the principal plume contained 19,000 metric tons of methane,with an estimated source strength of 0.6 kilogram per second.[108][109] The profiles suggest thatthere may be two local source regions, the first centered near 30 N, 260 W and the second near0, 310 W.[108] It is estimated that Mars must produce 270 ton/year of methane.[108][110]

The implied methane destruction lifetime may be as long as about 4 Earth years and as short as

about 0.6 Earth years.[108][111]

This rapid turnover would indicate an active source of the gas on theplanet. Volcanic activity,cometaryimpacts, and the presence ofmethanogenicmicrobial lifeforms are among possible sources. Methane could also be produced by a non-biological processcalledserpentinization[b] involving water, carbon dioxide, and themineralolivine, which isknown to be common on Mars.[112]

Climate

Mars from Hubble Space Telescope October 28, 2005 with dust storm visible.Main article: Climate of Mars

Of all the planets in the Solar System, the seasons of Mars are the most Earth-like, due to thesimilar tilts of the two planets' rotational axes. The lengths of the Martian seasons are abouttwice those of Earth's, as Mars greater distance from the Sun leads to the Martian year beingabout two Earth years long. Martian surface temperatures vary from lows of about 87 C(125 F) during the polar winters to highs of up to 5 C (23 F) in summers.[50]The wide rangein temperatures is due to the thin atmosphere which cannot store much solar heat, the lowatmospheric pressure, and the lowthermal inertia of Martian soil.[113]The planet is also 1.52times as far from the sun as Earth, resulting in just 43% of the amount of sunlight.[114]

If Mars had an Earth-like orbit, its seasons would be similar to Earth's because its axial tilt issimilar to Earth's. The comparatively large eccentricity of the Martian orbit has a significanteffect. Mars is nearperihelionwhen it is summer in the southern hemisphere and winter in thenorth, and nearaphelion when it is winter in the southern hemisphere and summer in the north.As a result, the seasons in the southern hemisphere are more extreme and the seasons in thenorthern are milder than would otherwise be the case. The summer temperatures in the south canreach up to 30 C (86 F) warmer than the equivalent summer temperatures in the north.[115]

Mars also has the largestdust storms in our Solar System. These can vary from a storm over asmall area, to gigantic storms that cover the entire planet. They tend to occur when Mars isclosest to the Sun, and have been shown to increase the global temperature.[116]
http://en.wikipedia.org/wiki/Volcanismhttp://en.wikipedia.org/wiki/Comethttp://en.wikipedia.org/wiki/Comethttp://en.wikipedia.org/wiki/Comethttp://en.wikipedia.org/wiki/Methanogenhttp://en.wikipedia.org/wiki/Methanogenhttp://en.wikipedia.org/wiki/Microorganismhttp://en.wikipedia.org/wiki/Serpentinitehttp://en.wikipedia.org/wiki/Mineralhttp://en.wikipedia.org/wiki/Mineralhttp://en.wikipedia.org/wiki/Olivinehttp://en.wikipedia.org/wiki/Hubble_Space_Telescopehttp://en.wikipedia.org/wiki/Climate_of_Marshttp://en.wikipedia.org/wiki/Volumetric_heat_capacityhttp://en.wikipedia.org/wiki/Volumetric_heat_capacityhttp://en.wikipedia.org/wiki/Axial_tilthttp://en.wikipedia.org/wiki/Apsishttp://en.wikipedia.org/wiki/Apsishttp://en.wikipedia.org/wiki/Apsishttp://en.wikipedia.org/wiki/Apsishttp://en.wikipedia.org/wiki/Dust_stormhttp://en.wikipedia.org/wiki/Dust_stormhttp://en.wikipedia.org/wiki/File:2005-1103mars-full.jpghttp://en.wikipedia.org/wiki/File:2005-1103mars-full.jpghttp://en.wikipedia.org/wiki/Volcanismhttp://en.wikipedia.org/wiki/Comethttp://en.wikipedia.org/wiki/Methanogenhttp://en.wikipedia.org/wiki/Microorganismhttp://en.wikipedia.org/wiki/Serpentinitehttp://en.wikipedia.org/wiki/Mineralhttp://en.wikipedia.org/wiki/Olivinehttp://en.wikipedia.org/wiki/Hubble_Space_Telescopehttp://en.wikipedia.org/wiki/Climate_of_Marshttp://en.wikipedia.org/wiki/Volumetric_heat_capacityhttp://en.wikipedia.org/wiki/Axial_tilthttp://en.wikipedia.org/wiki/Apsishttp://en.wikipedia.org/wiki/Apsishttp://en.wikipedia.org/wiki/Dust_storm


13/28

Orbit and rotation

Mars average distance from the Sun is roughly 230 million km (1.5 AU) and its orbital period is687 (Earth) days as depicted by the red trail, with Earth's orbit shown in blue.(Animation)

Mars average distance from the Sun is roughly 230 million km (1.5 AU) and its orbital period is687 (Earth) days. The solar day (orsol) on Mars is only slightly longer than an Earth day: 24hours, 39 minutes, and 35.244 seconds. A Martian year is equal to 1.8809 Earth years, or 1 year,320 days, and 18.2 hours.[6]

The axial tilt of Mars is 25.19 degrees, which is similar to the axial tilt of the Earth.[6] As a result,Mars has seasons like the Earth, though on Mars they are nearly twice as long given its longeryear. Currently the orientation of the north pole of Mars is close to the starDeneb.[9] Mars passeditsaphelion in March 2010[117] and itsperihelion in March 2011.[118] The next aphelion comes inFebruary 2012[118] and the next perihelion in January 2013.[118]

Mars has a relatively pronounced orbital eccentricityof about 0.09; of the seven other planets inthe Solar System, only Mercury shows greater eccentricity. It is known that in the past Mars hashad a much more circular orbit than it does currently. At one point 1.35 million Earth years ago,Mars had an eccentricity of roughly 0.002, much less than that of Earth today .[119] The Mars cycleof eccentricity is 96,000 Earth years compared to the Earth's cycle of 100,000 years.[120] Marsalso has a much longer cycle of eccentricity with a period of 2.2 million Earth years, and thisovershadows the 96,000-year cycle in the eccentricity graphs. For the last 35,000 years the orbitof Mars has been getting slightly more eccentric because of the gravitational effects of the otherplanets. The closest distance between the Earth and Mars will continue to mildly decrease for thenext 25,000 years.[121]
http://en.wikipedia.org/wiki/Timekeeping_on_Marshttp://en.wikipedia.org/wiki/North_polehttp://en.wikipedia.org/wiki/Denebhttp://en.wikipedia.org/wiki/Denebhttp://en.wikipedia.org/wiki/Aphelionhttp://en.wikipedia.org/wiki/Aphelionhttp://en.wikipedia.org/wiki/Perihelionhttp://en.wikipedia.org/wiki/Orbital_eccentricityhttp://en.wikipedia.org/wiki/Orbital_eccentricityhttp://en.wikipedia.org/wiki/Mercury_(planet)http://en.wikipedia.org/wiki/File:Marsorbitsolarsystem.gifhttp://en.wikipedia.org/wiki/File:Marsorbitsolarsystem.gifhttp://en.wikipedia.org/wiki/Timekeeping_on_Marshttp://en.wikipedia.org/wiki/North_polehttp://en.wikipedia.org/wiki/Denebhttp://en.wikipedia.org/wiki/Aphelionhttp://en.wikipedia.org/wiki/Perihelionhttp://en.wikipedia.org/wiki/Orbital_eccentricityhttp://en.wikipedia.org/wiki/Mercury_(planet)


14/28

Images comparing Mars' orbit with Ceres, adwarf planet in the asteroid belt. The left is shownfrom the north ecliptic pole. The right is shown from the ascending node. The segments of orbitssouth of the ecliptic are plotted in darker colors. Theperihelia (q) and aphelia (Q) are labelledwith the date of nearest passage. The orbit of Mars is red, Ceres is yellow.

MoonsMain articles: Moons of Mars,Phobos (moon), andDeimos (moon)

Phobos in color byMars Reconnaissance OrbiterHiRISE, on March 23, 2008
http://en.wikipedia.org/wiki/Ceres_(dwarf_planet)http://en.wikipedia.org/wiki/Dwarf_planethttp://en.wikipedia.org/wiki/Dwarf_planethttp://en.wikipedia.org/wiki/Asteroid_belthttp://en.wikipedia.org/wiki/Ecliptichttp://en.wikipedia.org/wiki/Perihelionhttp://en.wikipedia.org/wiki/Aphelionhttp://en.wikipedia.org/wiki/Moons_of_Marshttp://en.wikipedia.org/wiki/Moons_of_Marshttp://en.wikipedia.org/wiki/Phobos_(moon)http://en.wikipedia.org/wiki/Deimos_(moon)http://en.wikipedia.org/wiki/Deimos_(moon)http://en.wikipedia.org/wiki/Mars_Reconnaissance_Orbiterhttp://en.wikipedia.org/wiki/Mars_Reconnaissance_Orbiterhttp://en.wikipedia.org/wiki/HiRISEhttp://en.wikipedia.org/wiki/File:Phobos_colour_2008.jpghttp://en.wikipedia.org/wiki/File:ThePlanets_Orbits_Ceres_Mars.svghttp://en.wikipedia.org/wiki/File:ThePlanets_Orbits_Ceres_Mars_PolarView.svghttp://en.wikipedia.org/wiki/Ceres_(dwarf_planet)http://en.wikipedia.org/wiki/Dwarf_planethttp://en.wikipedia.org/wiki/Asteroid_belthttp://en.wikipedia.org/wiki/Ecliptichttp://en.wikipedia.org/wiki/Perihelionhttp://en.wikipedia.org/wiki/Aphelionhttp://en.wikipedia.org/wiki/Moons_of_Marshttp://en.wikipedia.org/wiki/Phobos_(moon)http://en.wikipedia.org/wiki/Deimos_(moon)http://en.wikipedia.org/wiki/Mars_Reconnaissance_Orbiterhttp://en.wikipedia.org/wiki/HiRISE


15/28

Deimos in color on February 21, 2009 by the same (not to scale)

Mars has two relatively small natural moons, Phobos and Deimos, which orbit close to theplanet. Asteroid capture is a long-favored theory but their origin remains uncertain.[122] Bothsatellites were discovered in 1877 byAsaph Hall, and are named after the characters Phobos(panic/fear) and Deimos (terror/dread) who, in Greek mythology, accompanied their fatherAres,god of war, into battle. Ares was known as Mars to the Romans.[123][124]

From the surface of Mars, the motions of Phobos and Deimos appear very different from that ofour own moon. Phobos rises in the west, sets in the east, and rises again in just 11 hours. Deimos,being only just outside synchronous orbitwhere the orbital period would match the planet'speriod of rotationrises as expected in the east but very slowly. Despite the 30 hour orbit ofDeimos, it takes 2.7 days to set in the west as it slowly falls behind the rotation of Mars, then justas long again to rise.[125]

Because the orbit of Phobos is below synchronous altitude, the tidal forces from the planet Marsare gradually lowering its orbit. In about 50 million years it will either crash into Mars surfaceor break up into a ring structure around the planet.[125]

The origin of the two moons is not well understood. Their low albedo andcarbonaceouschondritecomposition have been regarded as similar to asteroids, supporting the capture theory.The unstable orbit of Phobos would seem to point towards a relatively recent capture. But bothhave circular orbits, very near the equator, which is very unusual for captured objects and therequired capture dynamics are complex. Accretion early in the history of Mars is also plausiblebut would not account for a composition resembling asteroids rather than Mars itself, if that isconfirmed.

A third possibility is the involvement of a third body or some kind of impact disruption.[126] Morerecent lines of evidence for Phobos having a highly porous interior[127] and suggesting acomposition containing mainlyphyllosilicates and other minerals known from Mars,[128] pointtoward an origin of Phobos from material ejected by an impact on Mars that reaccreted in

Martian orbit,[129]

similar to theprevailing theoryfor the origin of Earth's moon. While the VNIRspectra of the moons of Mars resemble those of outer belt asteroids, the thermal infrared spectraof Phobos are reported to be inconsistent with chondritesof any class.[128]

Search for lifeMain article: Life on Mars
http://en.wikipedia.org/wiki/Phobos_(moon)http://en.wikipedia.org/wiki/Deimos_(moon)http://en.wikipedia.org/wiki/Deimos_(moon)http://en.wikipedia.org/wiki/Asaph_Hallhttp://en.wikipedia.org/wiki/Asaph_Hallhttp://en.wikipedia.org/wiki/Phobos_(mythology)http://en.wikipedia.org/wiki/Deimos_(mythology)http://en.wikipedia.org/wiki/Greek_mythologyhttp://en.wikipedia.org/wiki/Areshttp://en.wikipedia.org/wiki/Synchronous_orbithttp://en.wikipedia.org/wiki/Tidal_forcehttp://en.wikipedia.org/wiki/Carbonaceous_chondritehttp://en.wikipedia.org/wiki/Carbonaceous_chondritehttp://en.wikipedia.org/wiki/Carbonaceous_chondritehttp://en.wikipedia.org/wiki/Carbonaceous_chondritehttp://en.wikipedia.org/wiki/Circular_orbithttp://en.wikipedia.org/wiki/Phyllosilicateshttp://en.wikipedia.org/wiki/Giant_impact_hypothesishttp://en.wikipedia.org/wiki/Giant_impact_hypothesishttp://en.wikipedia.org/wiki/VNIRhttp://en.wikipedia.org/wiki/Thermal_infraredhttp://en.wikipedia.org/wiki/Chondritehttp://en.wikipedia.org/wiki/Chondritehttp://en.wikipedia.org/wiki/Life_on_Marshttp://en.wikipedia.org/wiki/File:Deimos-MRO.jpghttp://en.wikipedia.org/wiki/Phobos_(moon)http://en.wikipedia.org/wiki/Deimos_(moon)http://en.wikipedia.org/wiki/Asaph_Hallhttp://en.wikipedia.org/wiki/Phobos_(mythology)http://en.wikipedia.org/wiki/Deimos_(mythology)http://en.wikipedia.org/wiki/Greek_mythologyhttp://en.wikipedia.org/wiki/Areshttp://en.wikipedia.org/wiki/Synchronous_orbithttp://en.wikipedia.org/wiki/Tidal_forcehttp://en.wikipedia.org/wiki/Carbonaceous_chondritehttp://en.wikipedia.org/wiki/Carbonaceous_chondritehttp://en.wikipedia.org/wiki/Circular_orbithttp://en.wikipedia.org/wiki/Phyllosilicateshttp://en.wikipedia.org/wiki/Giant_impact_hypothesishttp://en.wikipedia.org/wiki/VNIRhttp://en.wikipedia.org/wiki/Thermal_infraredhttp://en.wikipedia.org/wiki/Chondritehttp://en.wikipedia.org/wiki/Life_on_Mars


16/28

Viking Lander 2site May 1979

Viking Lander 1site February 1978.

The current understanding ofplanetary habitabilitythe ability of a world to develop and sustainlifefavors planets that have liquid water on their surface. This most often requires that the orbitof a planet lie within the habitable zone, which for the Sun currently extends from just beyondVenus to about the semi-major axisof Mars.[130] During perihelion Mars dips inside this region,but the planet's thin (low-pressure) atmosphere prevents liquid water from existing over largeregions for extended periods. The past flow of liquid water demonstrates the planet's potential forhabitability. Some recent evidence has suggested that any water on the Martian surface may havebeen too salty and acidic to support regular terrestrial life.[131]

The lack of a magnetosphere and extremely thin atmosphere of Mars are a challenge: the planethas little heat transferacross its surface, poor insulation against bombardment of the solar windand insufficient atmospheric pressure to retain water in a liquid form (water instead sublimates toa gaseous state). Mars is also nearly, or perhaps totally, geologically dead; the end of volcanicactivity has apparently stopped the recycling of chemicals and minerals between the surface and

interior of the planet.[132]

Evidence suggests that the planet was once significantly more habitable than it is today, butwhether living organisms ever existed there remains unknown. The Viking probesof the mid-1970s carried experiments designed to detect microorganisms in Martian soil at their respectivelanding sites and had positive results, including a temporary increase of CO2 production onexposure to water and nutrients. This sign of life was later disputed by some scientists, resultingin a continuing debate, with NASA scientistGilbert Levin asserting that Viking may have foundlife. A re-analysis of the Viking data, in light of modern knowledge ofextremophile forms of
http://en.wikipedia.org/wiki/Viking_2http://en.wikipedia.org/wiki/Viking_2http://en.wikipedia.org/wiki/Viking_1http://en.wikipedia.org/wiki/Viking_1http://en.wikipedia.org/wiki/Planetary_habitabilityhttp://en.wikipedia.org/wiki/Semi-major_axishttp://en.wikipedia.org/wiki/Semi-major_axishttp://en.wikipedia.org/wiki/Heat_transferhttp://en.wikipedia.org/wiki/Solar_windhttp://en.wikipedia.org/wiki/Organismhttp://en.wikipedia.org/wiki/Viking_probeshttp://en.wikipedia.org/wiki/Viking_probeshttp://en.wikipedia.org/wiki/Gilbert_Levinhttp://en.wikipedia.org/wiki/Gilbert_Levinhttp://en.wikipedia.org/wiki/Extremophilehttp://en.wikipedia.org/wiki/File:Mars_Viking_11h016.pnghttp://en.wikipedia.org/wiki/File:Mars_Viking_21i093.pnghttp://en.wikipedia.org/wiki/Viking_2http://en.wikipedia.org/wiki/Viking_1http://en.wikipedia.org/wiki/Planetary_habitabilityhttp://en.wikipedia.org/wiki/Semi-major_axishttp://en.wikipedia.org/wiki/Heat_transferhttp://en.wikipedia.org/wiki/Solar_windhttp://en.wikipedia.org/wiki/Organismhttp://en.wikipedia.org/wiki/Viking_probeshttp://en.wikipedia.org/wiki/Gilbert_Levinhttp://en.wikipedia.org/wiki/Extremophile


17/28

life, has suggested that the Viking tests were not sophisticated enough to detect these forms oflife. The tests could even have killed a (hypothetical) life form.[133]Tests conducted by thePhoenix Mars lander have shown that the soil has a veryalkalinepHand it contains magnesium,sodium, potassium and chloride.[134] The soil nutrients may be able to support life but life wouldstill have to be shielded from the intense ultraviolet light.[135]

At the Johnson Space Center lab, some fascinating shapes have been found in themeteoriteALH84001, which is thought to have originated from Mars. Some scientists propose that thesegeometric shapes could be fossilized microbes extant on Mars before the meteorite was blastedinto space by a meteor strike and sent on a 15 million-year voyage to Earth. An exclusivelyinorganic origin for the shapes has also been proposed.[136]

Small quantities ofmethaneand formaldehyderecently detected by Mars orbiters are bothclaimed to be hints for life, as thesechemical compoundswould quickly break down in theMartian atmosphere.[137][138] It is remotely possible that these compounds may instead bereplenished by volcanic or geological means such asserpentinization.[112]

Exploration missions

Main article: Exploration of Mars

Western rim of Endeavour Crater

Mars can be observed from Earth, but the latest detailed information comes from four activeprobes on or in orbit around Mars as of 2012: Mars Odyssey, Mars Express, Mars ReconissanceOribter, and Opportunity rover. The public can request photos of the Mars surface at 25 cm apixel with the HiWish program, which uses a 50 cm diameter telescope in Mars orbit.

In the past dozens ofspacecraft, including orbiters, landers, and rovers, have been sent to Marsby the Soviet Union, the United States,Europe, and Japan to study the planet's surface, climate,and geology. In 2008, the price of transporting material from the surface ofEarth to the surfaceof Mars is approximately US$309,000 perkilogram.[139]

Current missions

The NASA Mars Odyssey orbiter entered Mars orbit in 2001.[140] Odyssey'sGamma RaySpectrometerdetected significant amounts of hydrogen in the upper metre or so ofregolithonMars. This hydrogen is thought to be contained in large deposits of water ice.[141]

The Mars Expressmission of the European Space Agency(ESA) reached Mars in 2003. Itcarried the Beagle 2lander, which failed during descent and was declared lost in February, 2004.[142] In early 2004 the Planetary Fourier Spectrometerteam announced the orbiter had detectedmethane in the Martian atmosphere. ESA announced in June 2006 the discovery ofauroraeonMars.[143]
http://en.wikipedia.org/wiki/Alkalinehttp://en.wikipedia.org/wiki/Alkalinehttp://en.wikipedia.org/wiki/PHhttp://en.wikipedia.org/wiki/PHhttp://en.wikipedia.org/wiki/PHhttp://en.wikipedia.org/wiki/Johnson_Space_Centerhttp://en.wikipedia.org/wiki/Johnson_Space_Centerhttp://en.wikipedia.org/wiki/Meteoritehttp://en.wikipedia.org/wiki/Meteoritehttp://en.wikipedia.org/wiki/ALH84001http://en.wikipedia.org/wiki/Methanehttp://en.wikipedia.org/wiki/Methanehttp://en.wikipedia.org/wiki/Formaldehydehttp://en.wikipedia.org/wiki/Formaldehydehttp://en.wikipedia.org/wiki/Chemical_compoundhttp://en.wikipedia.org/wiki/Chemical_compoundhttp://en.wikipedia.org/wiki/Chemical_compoundhttp://en.wikipedia.org/wiki/Serpentinizationhttp://en.wikipedia.org/wiki/Serpentinizationhttp://en.wikipedia.org/wiki/Serpentinizationhttp://en.wikipedia.org/wiki/Exploration_of_Marshttp://en.wikipedia.org/wiki/HiWish_programhttp://en.wikipedia.org/wiki/Spacecrafthttp://en.wikipedia.org/wiki/Orbiterhttp://en.wikipedia.org/wiki/Lander_(spacecraft)http://en.wikipedia.org/wiki/Rover_(space_exploration)http://en.wikipedia.org/wiki/Soviet_space_programhttp://en.wikipedia.org/wiki/Soviet_space_programhttp://en.wikipedia.org/wiki/NASAhttp://en.wikipedia.org/wiki/NASAhttp://en.wikipedia.org/wiki/ESAhttp://en.wikipedia.org/wiki/JAXAhttp://en.wikipedia.org/wiki/Earthhttp://en.wikipedia.org/wiki/Earthhttp://en.wikipedia.org/wiki/US$http://en.wikipedia.org/wiki/Kilogramhttp://en.wikipedia.org/wiki/Mars_Odysseyhttp://en.wikipedia.org/wiki/Gamma_Ray_Spectrometerhttp://en.wikipedia.org/wiki/Gamma_Ray_Spectrometerhttp://en.wikipedia.org/wiki/Gamma_Ray_Spectrometerhttp://en.wikipedia.org/wiki/Regolithhttp://en.wikipedia.org/wiki/Regolithhttp://en.wikipedia.org/wiki/Mars_Expresshttp://en.wikipedia.org/wiki/Mars_Expresshttp://en.wikipedia.org/wiki/European_Space_Agencyhttp://en.wikipedia.org/wiki/European_Space_Agencyhttp://en.wikipedia.org/wiki/Beagle_2http://en.wikipedia.org/wiki/Beagle_2http://en.wikipedia.org/wiki/Planetary_Fourier_Spectrometerhttp://en.wikipedia.org/wiki/Aurora_(astronomy)http://en.wikipedia.org/wiki/Aurora_(astronomy)http://en.wikipedia.org/wiki/File:PIA14508_-_West_Rim_of_Endeavour_Crater_on_Mars.jpghttp://en.wikipedia.org/wiki/File:PIA14508_-_West_Rim_of_Endeavour_Crater_on_Mars.jpghttp://en.wikipedia.org/wiki/Alkalinehttp://en.wikipedia.org/wiki/PHhttp://en.wikipedia.org/wiki/Johnson_Space_Centerhttp://en.wikipedia.org/wiki/Meteoritehttp://en.wikipedia.org/wiki/ALH84001http://en.wikipedia.org/wiki/Methanehttp://en.wikipedia.org/wiki/Formaldehydehttp://en.wikipedia.org/wiki/Chemical_compoundhttp://en.wikipedia.org/wiki/Serpentinizationhttp://en.wikipedia.org/wiki/Exploration_of_Marshttp://en.wikipedia.org/wiki/HiWish_programhttp://en.wikipedia.org/wiki/Spacecrafthttp://en.wikipedia.org/wiki/Orbiterhttp://en.wikipedia.org/wiki/Lander_(spacecraft)http://en.wikipedia.org/wiki/Rover_(space_exploration)http://en.wikipedia.org/wiki/Soviet_space_programhttp://en.wikipedia.org/wiki/NASAhttp://en.wikipedia.org/wiki/ESAhttp://en.wikipedia.org/wiki/JAXAhttp://en.wikipedia.org/wiki/Earthhttp://en.wikipedia.org/wiki/US$http://en.wikipedia.org/wiki/Kilogramhttp://en.wikipedia.org/wiki/Mars_Odysseyhttp://en.wikipedia.org/wiki/Gamma_Ray_Spectrometerhttp://en.wikipedia.org/wiki/Gamma_Ray_Spectrometerhttp://en.wikipedia.org/wiki/Regolithhttp://en.wikipedia.org/wiki/Mars_Expresshttp://en.wikipedia.org/wiki/European_Space_Agencyhttp://en.wikipedia.org/wiki/Beagle_2http://en.wikipedia.org/wiki/Planetary_Fourier_Spectrometerhttp://en.wikipedia.org/wiki/Aurora_(astronomy)


18/28

In January 2004, the NASA twin Mars Exploration Roversnamed Spirit(MER-A) andOpportunity (MER-B) landed on the surface of Mars. Both have met or exceeded all theirtargets. Among the most significant scientific returns has been conclusive evidence that liquidwater existed at some time in the past at both landing sites.Martian dust devilsand windstormshave occasionally cleaned both rovers' solar panels, and thus increased their lifespan.[144]SpiritRover(MER-A) was active until 2010, when it stopped sending data.

On March 10, 2006, the NASA Mars Reconnaissance Orbiter(MRO) probe arrived in orbit toconduct a two-year science survey. The orbiter began mapping the Martian terrain and weatherto find suitable landing sites for upcoming lander missions. The MRO snapped the first image ofa series of active avalanches near the planet'snorth pole, scientists said March 3, 2008.[145]

The Mars Science Laboratory, named Curiosity, launched on November 26, 2011, and isexpected to reach Mars in August 2012. It is larger and more advanced than the MarsExploration Rovers, with a movement rate of 90 m/h. Experiments include a laser chemicalsampler that can deduce the make-up of rocks at a distance of 13 m.[146]

Past missions

Attempted Martian missions

Decade

1960s 13

1970s 11

1980s 2

1990s 8

2000s 8

2010s 2

Mars 3 lander on a 1972 Soviet stamp.

The first successful fly-by of Mars was on July 1415, 1965, by NASA'sMariner 4.[citation needed]

On November 14, 1971 Mariner 9 became the first space probe to orbit another planet when itentered into orbit around Mars.[147] The first objects to successfully land on the surface were two
http://en.wikipedia.org/wiki/Mars_Exploration_Rovershttp://en.wikipedia.org/wiki/Mars_Exploration_Rovershttp://en.wikipedia.org/wiki/Spirit_roverhttp://en.wikipedia.org/wiki/Opportunity_roverhttp://en.wikipedia.org/wiki/Spirit_Roverhttp://en.wikipedia.org/wiki/Spirit_Roverhttp://en.wikipedia.org/wiki/Spirit_Roverhttp://en.wikipedia.org/wiki/Mars_Reconnaissance_Orbiterhttp://en.wikipedia.org/wiki/Mars_Reconnaissance_Orbiterhttp://en.wikipedia.org/wiki/Avalanchehttp://en.wikipedia.org/wiki/North_polehttp://en.wikipedia.org/wiki/North_polehttp://en.wikipedia.org/wiki/Mars_Science_Laboratoryhttp://en.wikipedia.org/wiki/Metre_per_hourhttp://en.wikipedia.org/wiki/Mars_3http://en.wikipedia.org/wiki/Mariner_4http://en.wikipedia.org/wiki/Mariner_4http://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Mariner_9http://en.wikipedia.org/wiki/File:Soviet_Union-1972-Stamp-0.16._Mars_3.jpghttp://en.wikipedia.org/wiki/File:Soviet_Union-1972-Stamp-0.16._Mars_3.jpghttp://en.wikipedia.org/wiki/Mars_Exploration_Rovershttp://en.wikipedia.org/wiki/Spirit_roverhttp://en.wikipedia.org/wiki/Opportunity_roverhttp://en.wikipedia.org/wiki/Spirit_Roverhttp://en.wikipedia.org/wiki/Spirit_Roverhttp://en.wikipedia.org/wiki/Mars_Reconnaissance_Orbiterhttp://en.wikipedia.org/wiki/Avalanchehttp://en.wikipedia.org/wiki/North_polehttp://en.wikipedia.org/wiki/Mars_Science_Laboratoryhttp://en.wikipedia.org/wiki/Metre_per_hourhttp://en.wikipedia.org/wiki/Mars_3http://en.wikipedia.org/wiki/Mariner_4http://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Mariner_9


19/28

Soviet probes: Mars 2[citation needed] on November 27 and Mars 3 on December 2, 1971, but bothceased communicating within seconds of landing. The 1975 NASA launches of the Vikingprogram consisted of two orbiters, each having a lander; both landers successfully touched downin 1976. Viking 1 remained operational for six years, Viking 2 for three. The Viking landersrelayed color panoramas of Mars[148] and the orbiters mapped the surface so well that the imagesremain in use.

The Soviet probes Phobos 1 and 2 were sent to Mars in 1988 to study Mars and its two moons.Phobos 1 lost contact on the way to Mars. Phobos 2, while successfully photographing Mars andPhobos, failed just before it was set to release two landers to the surface of Phobos.[149]

Roughly two-thirds of all spacecraft destined for Mars have failed in one manner or anotherbefore completing or even beginning their missions, including the difficult late 20th centuryperiod of early pioneers and first-timers. Mission failures are typically ascribed to technicalproblems, and missions planners balance technology and mission goals.[150] Failures since 1995include Mars 96 (1996), Mars Climate Orbiter(1999), Mars Polar Lander(1999), Deep Space 2(1999),Nozomi (2003), Beagle 2 (2003), and Fobos-Grunt (2011).

Following the 1992 failure of the Mars Observerorbiter, the NASA Mars Global Surveyor

achieved Mars orbit in 1997. This mission was a complete success, having finished its primarymapping mission in early 2001. Contact was lost with the probe in November 2006 during itsthird extended program, spending exactly 10 operational years in space. The NASA MarsPathfinder, carrying a robotic exploration vehicleSojourner, landed in the Ares Vallison Mars inthe summer of 1997, returning many images.[151]

Spirit's lander on Mars, 2004

View from thePhoenixlander, 2008

The NASA Phoenix Mars lander arrived on the north polar region of Mars on May 25, 2008. [152]

Its robotic arm was used to dig into the Martian soil and the presence of water ice was confirmedon June 20.[153][154][154] The mission concluded on November 10, 2008 after contact was lost.[155]

The Dawnspacecraft flew by Mars in February 2009 for a gravity assist on its way to investigateVestaand then Ceres.[156]
http://en.wikipedia.org/wiki/Soviethttp://en.wikipedia.org/wiki/Mars_2http://en.wikipedia.org/wiki/Mars_2http://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Mars_3http://en.wikipedia.org/wiki/Viking_programhttp://en.wikipedia.org/wiki/Viking_programhttp://en.wikipedia.org/wiki/Viking_1http://en.wikipedia.org/wiki/Viking_2http://en.wikipedia.org/wiki/Phobos_programhttp://en.wikipedia.org/wiki/Mars_96http://en.wikipedia.org/wiki/Mars_Climate_Orbiterhttp://en.wikipedia.org/wiki/Mars_Climate_Orbiterhttp://en.wikipedia.org/wiki/Mars_Polar_Landerhttp://en.wikipedia.org/wiki/Mars_Polar_Landerhttp://en.wikipedia.org/wiki/Deep_Space_2http://en.wikipedia.org/wiki/Nozomi_(spacecraft)http://en.wikipedia.org/wiki/Beagle_2http://en.wikipedia.org/wiki/Fobos-Grunthttp://en.wikipedia.org/wiki/Mars_Observerhttp://en.wikipedia.org/wiki/Mars_Global_Surveyorhttp://en.wikipedia.org/wiki/Mars_Pathfinderhttp://en.wikipedia.org/wiki/Mars_Pathfinderhttp://en.wikipedia.org/wiki/Sojourner_(rover)http://en.wikipedia.org/wiki/Sojourner_(rover)http://en.wikipedia.org/wiki/Ares_Vallishttp://en.wikipedia.org/wiki/Ares_Vallishttp://en.wikipedia.org/wiki/Spirit_roverhttp://en.wikipedia.org/wiki/Phoenix_(spacecraft)http://en.wikipedia.org/wiki/Phoenix_(spacecraft)http://en.wikipedia.org/wiki/Phoenix_(spacecraft)http://en.wikipedia.org/wiki/Dawn_Missionhttp://en.wikipedia.org/wiki/Dawn_Missionhttp://en.wikipedia.org/wiki/4_Vestahttp://en.wikipedia.org/wiki/4_Vestahttp://en.wikipedia.org/wiki/Ceres_(dwarf_planet)http://en.wikipedia.org/wiki/File:PhoenixSolarPanelandRoboticArm.pnghttp://en.wikipedia.org/wiki/File:MER_Spirit_Lander_Pan_Sol16-A18R1_br2.jpghttp://en.wikipedia.org/wiki/Soviethttp://en.wikipedia.org/wiki/Mars_2http://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Mars_3http://en.wikipedia.org/wiki/Viking_programhttp://en.wikipedia.org/wiki/Viking_programhttp://en.wikipedia.org/wiki/Viking_1http://en.wikipedia.org/wiki/Viking_2http://en.wikipedia.org/wiki/Phobos_programhttp://en.wikipedia.org/wiki/Mars_96http://en.wikipedia.org/wiki/Mars_Climate_Orbiterhttp://en.wikipedia.org/wiki/Mars_Polar_Landerhttp://en.wikipedia.org/wiki/Deep_Space_2http://en.wikipedia.org/wiki/Nozomi_(spacecraft)http://en.wikipedia.org/wiki/Beagle_2http://en.wikipedia.org/wiki/Fobos-Grunthttp://en.wikipedia.org/wiki/Mars_Observerhttp://en.wikipedia.org/wiki/Mars_Global_Surveyorhttp://en.wikipedia.org/wiki/Mars_Pathfinderhttp://en.wikipedia.org/wiki/Mars_Pathfinderhttp://en.wikipedia.org/wiki/Sojourner_(rover)http://en.wikipedia.org/wiki/Ares_Vallishttp://en.wikipedia.org/wiki/Spirit_roverhttp://en.wikipedia.org/wiki/Phoenix_(spacecraft)http://en.wikipedia.org/wiki/Phoenix_(spacecraft)http://en.wikipedia.org/wiki/Dawn_Missionhttp://en.wikipedia.org/wiki/4_Vestahttp://en.wikipedia.org/wiki/Ceres_(dwarf_planet)


20/28

Future missions

In 2008, NASA announced MAVEN, a robotic mission in 2013 to provide information about theatmosphere of Mars.[157] In 2018 the ESA plans to launch its first Rover to Mars; the ExoMarsrover will be capable of drilling 2 m into the soil in search of organic molecules.[158]

The Finnish-Russian MetNet, is mission concept where multiple small vehicles on Mars toestablish a widespread observation network to investigate the planet's atmospheric structure,physics and meteorology.[159] MetNet was considered for a piggyback launch on the RussianFobos-Grunt mission, but not selected.[160] It may be included on a future Mars-Net mission.[161]

Another Russian mission concept is Mars-Grunt, a Mars sample return mission.[161]

InSight (formerly GEMS) is a Mars lander mission proposed under NASA's Discovery program,to place a geophysical lander on Mars to study its deep interior, and understand the processesthat shaped the rocky planets of the inner solar system.[162]

Manned mission goals

Main article: Manned mission to Mars

The ESA hopes to land humans on Mars between 2030 and 2035.[163] This will be preceded bysuccessively larger probes, starting with the launch of theExoMars probe[164] and a joint NASA-ESA Mars sample return mission.[165]

Manned exploration by the United States was identified as a long-term goal in the Vision forSpace Explorationannounced in 2004 by then US President George W. Bush.[166] The plannedOrion spacecraft would be used to send a human expedition to Earth's moon by 2020 as astepping stone to a Mars expedition. On September 28, 2007, NASA administratorMichael D.Griffin stated that NASA aims to put a man on Mars by 2037.[167]

Mars Direct, a low-cost human mission proposed by Robert Zubrin, founder of the Mars Society,would use heavy-lift Saturn V class rockets, such as the Space XFalcon X, or, theAres V, toskip orbital construction, LEO rendezvous, and lunar fuel depots. A modified proposal, called

"Mars to Stay", involves not returning the first immigrant explorers immediately, if ever (seeColonization of Mars).[168]

Astronomy on MarsMain article: Astronomy on Mars
http://en.wikipedia.org/wiki/MAVENhttp://en.wikipedia.org/wiki/ExoMarshttp://en.wikipedia.org/wiki/MetNethttp://en.wikipedia.org/wiki/MetNethttp://en.wikipedia.org/wiki/InSighthttp://en.wikipedia.org/wiki/Discovery_programhttp://en.wikipedia.org/wiki/Manned_mission_to_Marshttp://en.wikipedia.org/wiki/ExoMarshttp://en.wikipedia.org/wiki/ExoMarshttp://en.wikipedia.org/wiki/Mars_sample_return_missionhttp://en.wikipedia.org/wiki/Vision_for_Space_Explorationhttp://en.wikipedia.org/wiki/Vision_for_Space_Explorationhttp://en.wikipedia.org/wiki/Vision_for_Space_Explorationhttp://en.wikipedia.org/wiki/George_W._Bushhttp://en.wikipedia.org/wiki/Orion_(Constellation_program)http://en.wikipedia.org/wiki/Michael_D._Griffinhttp://en.wikipedia.org/wiki/Michael_D._Griffinhttp://en.wikipedia.org/wiki/Michael_D._Griffinhttp://en.wikipedia.org/wiki/Mars_Directhttp://en.wikipedia.org/wiki/Robert_Zubrinhttp://en.wikipedia.org/wiki/Mars_Societyhttp://en.wikipedia.org/wiki/Mars_Societyhttp://en.wikipedia.org/wiki/Saturn_Vhttp://en.wikipedia.org/wiki/Space_Xhttp://en.wikipedia.org/wiki/Falcon_Xhttp://en.wikipedia.org/wiki/Falcon_Xhttp://en.wikipedia.org/wiki/Ares_Vhttp://en.wikipedia.org/wiki/Ares_Vhttp://en.wikipedia.org/wiki/Mars_to_Stayhttp://en.wikipedia.org/wiki/Colonization_of_Marshttp://en.wikipedia.org/wiki/Astronomy_on_Marshttp://en.wikipedia.org/wiki/File:15-ml-06-phobos2-A067R1.jpghttp://en.wikipedia.org/wiki/File:15-ml-06-phobos2-A067R1.jpghttp://en.wikipedia.org/wiki/MAVENhttp://en.wikipedia.org/wiki/ExoMarshttp://en.wikipedia.org/wiki/MetNethttp://en.wikipedia.org/wiki/InSighthttp://en.wikipedia.org/wiki/Discovery_programhttp://en.wikipedia.org/wiki/Manned_mission_to_Marshttp://en.wikipedia.org/wiki/ExoMarshttp://en.wikipedia.org/wiki/Mars_sample_return_missionhttp://en.wikipedia.org/wiki/Vision_for_Space_Explorationhttp://en.wikipedia.org/wiki/Vision_for_Space_Explorationhttp://en.wikipedia.org/wiki/George_W._Bushhttp://en.wikipedia.org/wiki/Orion_(Constellation_program)http://en.wikipedia.org/wiki/Michael_D._Griffinhttp://en.wikipedia.org/wiki/Michael_D._Griffinhttp://en.wikipedia.org/wiki/Mars_Directhttp://en.wikipedia.org/wiki/Robert_Zubrinhttp://en.wikipedia.org/wiki/Mars_Societyhttp://en.wikipedia.org/wiki/Saturn_Vhttp://en.wikipedia.org/wiki/Space_Xhttp://en.wikipedia.org/wiki/Falcon_Xhttp://en.wikipedia.org/wiki/Ares_Vhttp://en.wikipedia.org/wiki/Mars_to_Stayhttp://en.wikipedia.org/wiki/Colonization_of_Marshttp://en.wikipedia.org/wiki/Astronomy_on_Mars


21/28

Phobostransits the Sun, as seen by Mars RoverOpportunityon March 10, 2004

With the existence of various orbiters, landers, and rovers, it is now possible to study astronomyfrom the Martian skies. While Mars moon Phobos appears about one third theangular diameterof the full Moon as it appears from Earth, Deimos appears more or less star-like, and appearsonly slightly brighter than Venus does from Earth.[169]

There are various phenomena, well-known on Earth, that have been observed on Mars, such asmeteors andauroras.[143] Atransit of the Earth as seen from Marswill occur on November 10,2084.[170] There are also transits of Mercury andtransits of Venus, and the moons Phobos andDeimos are of sufficiently smallangular diameterthat their partial "eclipses" of the Sun are bestconsidered transits (see Transit of Deimos from Mars).[171][172]

Viewing

Animation of the apparent retrograde motion of Mars in 2003 as seen from Earth

Because the orbit of Mars is eccentric itsapparent magnitude at opposition from the Sun can

range from 3.0 to 1.4. The minimum brightness is magnitude +1.6 when the planet is inconjunction with the Sun.[7] Mars usually appears a distinct yellow, orange, or reddish color; theactual color of Mars is closer tobutterscotch, and the redness seen is just dust in the planet'satmosphere; considering thisNASA's Spirit rover has taken pictures of a greenish-brown, mud-colored landscape with blue-grey rocks and patches of light red colored sand.[173]When farthestaway from the Earth, it is more than seven times as far from the latter as when it is closest. Whenleast favorably positioned, it can be lost in the Sun's glare for months at a time. At its mostfavorable timesat 15- or 17-year intervals, and always between late July and late September
http://en.wikipedia.org/wiki/Astronomical_transithttp://en.wikipedia.org/wiki/Astronomical_transithttp://en.wikipedia.org/wiki/Sunhttp://en.wikipedia.org/wiki/MER-Bhttp://en.wikipedia.org/wiki/MER-Bhttp://en.wikipedia.org/wiki/Astronomyhttp://en.wikipedia.org/wiki/Angular_diameterhttp://en.wikipedia.org/wiki/Angular_diameterhttp://en.wikipedia.org/wiki/Meteorhttp://en.wikipedia.org/wiki/Aurorashttp://en.wikipedia.org/wiki/Aurorashttp://en.wikipedia.org/wiki/Transit_of_Earth_from_Marshttp://en.wikipedia.org/wiki/Transit_of_Earth_from_Marshttp://en.wikipedia.org/wiki/Transit_of_Earth_from_Marshttp://en.wikipedia.org/wiki/Transit_of_Mercury_from_Marshttp://en.wikipedia.org/wiki/Transit_of_Venus_from_Marshttp://en.wikipedia.org/wiki/Transit_of_Venus_from_Marshttp://en.wikipedia.org/wiki/Angular_diameterhttp://en.wikipedia.org/wiki/Angular_diameterhttp://en.wikipedia.org/wiki/Transit_of_Deimos_from_Marshttp://en.wikipedia.org/wiki/Apparent_magnitudehttp://en.wikipedia.org/wiki/Apparent_magnitudehttp://en.wikipedia.org/wiki/Butterscotchhttp://en.wikipedia.org/wiki/NASAhttp://en.wikipedia.org/wiki/NASAhttp://en.wikipedia.org/wiki/File:Apparent_retrograde_motion_of_Mars_in_2003.gifhttp://en.wikipedia.org/wiki/File:Apparent_retrograde_motion_of_Mars_in_2003.gifhttp://en.wikipedia.org/wiki/Astronomical_transithttp://en.wikipedia.org/wiki/Sunhttp://en.wikipedia.org/wiki/MER-Bhttp://en.wikipedia.org/wiki/Astronomyhttp://en.wikipedia.org/wiki/Angular_diameterhttp://en.wikipedia.org/wiki/Meteorhttp://en.wikipedia.org/wiki/Aurorashttp://