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Roger Weller, geology instructor

Marie Reid

Physical Geology
Spring 2005


Mars: The Red Planet

            The planet Mars is also known as the Red Planet or Red World.  Its surface is covered with an iron rich clay giving the planet that reddish color.  Mars is the only planet whose surface can be seen in detail from the Earth.  Even with the unaided eye, Mars appears redder than that of the other planets and stars in the night sky.  No telescope is needed to see Mars because it is most visible in the early morning sky from fall to early spring and in the evening sky from the spring to early summer.  You will notice the planet because it will be a small rust-colored light in the sky.


            Since Mars is a reddish-color, it was named after the god of war of the ancient Romans.  The Roman god of Mars was a god of agriculture before becoming associated with the Greek Ares; those in favor of colonizing.  Though the Roman god of war and agriculture don’t seem to go together, they really do.  Mars protected those who fought for their communities and stayed home to raise crops for food.  Most people don’t associate the fact that the month of March derives from Mars.


            Mars was explored by flybys by Mariner 4, 6 and 7 in the 1960’s.  We also had Mariner 9 orbiting Mars in 1971 before NASA mounted the ambitious Viking I and II missions, which launched two orbiters and two landers to the planet in 1975.  Both Viking landers landed on the smooth northern hemisphere.  The Viking I landing site is given on the left hemisphere and the Viking II landing site is on the right hemisphere.  Viking I landed on the edge of the highland, while Viking II landed in the middle of the lowland.  Both Viking I and II carried a mass-spectrometer for chemical analysis of the atmosphere, the soil, and there was a camera with many other scientific instruments on each lander.  The landers found no chemical evidence of life.  On the Viking I landing site, fine grain sands were clearly visible, there were an abundant angular rocks, and the gravel surface was probably formed by deflation.  The Aeolian processes obviously were operating in this area.  The Viking II landing site was a little bit different.  It revealed a vast plain littered with angular blocks and low drifts of sand.  These blocks might be ejected from nearby impact craters, or they might be the weathered remnants of a lava or debris flow.  Like those at the Viking I site, many of the rocks were pitted, as a result of wind erosion.  Another remarkable feature on both views was the bright sky in the background; this is very different from the surface pictures taken on the Moon, where the background sky is black.  The bright sky was a result of the atmosphere that scattered sunlight within itself.       


The first spacecraft to visit Mars was Mariner 4 in 1965.  Several others followed including Mars 2, the first spacecraft to land on Mars and the two Viking landers in 1976.  Ending a long 20 year hiatus, Mars Pathfinder landed successfully on Mars on 4 July 1997, delivering a mobile robot rover which explored the immediate vicinity.  In early 2004, the Spirit and Opportunity rovers landed in two different locations on the surface of Mars.  Like robotic geologists, Spirit and Opportunity are currently exploring the Martian surface, taking samples of the soil and rocks and sending back many incredible images.  Some of the pictures sent back clearly show the surface of Mars which closely resemble a desert environment found on Earth.  The Odyssey and Mars Global Surveyor continue to orbit the planet, studying geology, weather and climate from above.  They perform an important role in the Martian missions, relaying commands from Earth to the rovers and data from the rovers to Earth.  Mars Global Surveyor is creating the highest resolution map of the planets surface, but the European Space Agency’s Mars Express has taken the first pictures of the red planet.  Photos taken by the probes High Resolution Stereo Cameras (HRSC) on 1 December 2003 shows Mars from about 3.4 million miles away.  They were very unusual views because the planet is illuminated in a way never before seen from Earth.  The sun shines on part of the western hemisphere, but more than a third of the Martian disk lies in the dark.  The dark features at the top are part of the northern lowlands of Mars, where oceans might have existed billions of years ago. 


Mars is the seventh largest planet in the Solar System and the fourth planet from the Sun. It is located between Earth and Jupiter and is the last of the inner, terrestrial planets.  Mars has two satellites or moons, Phobos and Deimos.  These are considered the two smallest moons in the solar system.  Phobos is approximately 18 miles in diameter, while Deimos is approximately 9 miles in diameter.  They are actually two asteroids, which are small, rocky bodies which were scattered throughout our solar system.  They became moons when they became close enough to Mars that they were “captured” by Mars’ gravity and they have been circling ever since.   


Mars rotation period is about 24 hours and 37 minutes.  Because its spinning axis is tilted with respect to the ecliptic plane by 24.5 degrees similar to the Earth’s, the surface of Mars should experience seasonally variations just like the Earth.  The orbit or path which Mars takes around the Sun is called a mild ellipse or stretched circle.  The orbital path from which Mars has to take around the Sun is about 227,940,000 km from the Sun.  A Martian year compared to Earth is about one Earth year and ten and a half months.  Mars’ diameter is approximately 6796 Kms (4223 miles), a little more than half the size of Earth.  If Earth was a baseball, Mars would be a golf ball.  Though Mars is smaller than Earth, its surface area is about the same as the land surface area of Earth.  Mars’ mass is huge at 6.4219e23 kg.  It is about 128 million miles from the Sun at its closest and 154 million miles at its farthest.  The temperature of Mars seems to differ so much, I don’t think that people may never be able to survive on this harsh planet.  The temperature ranges around -140 to 20 degrees Celsius (-220 to -60 degrees Fahrenheit) during the winter.  During the summer, it is 27 degrees Celsius (80 degrees Fahrenheit on the day side). 


People talked about how much they would weigh on the Moon and realized there was hardly any gravity on the Moon.  If you weighed 70 lbs on Earth, you would weigh about 27 lbs on Mars.  Its surface gravity is only about 38% of the surface gravity of Earth.  I am assuming  most women would love to live on Mars with those kinds of numbers.


Mars’ atmosphere is made up mostly of carbon dioxide.  The breakdown of the atmosphere is as follows:

·         Carbon dioxide      ►95.3%

·         Nitrogen                 ►2.7%

·         Argon                     ►1.6%

·         Traces of Oxygen  ►.15%

·         Water                     ►.03%


The average pressure on the surface is only about 7 millibars (less than 1% of Earth’s), but it varies greatly with altitude from almost 9 millibars in the deepest basins to about 1 millibar at the top of the famous Olympus Mons mountain.  Mars has a very thin layer of atmosphere, but even though it is thin, it still has weather, including dust storms and clouds that can cover the entire planet at one time.  Mars’ thin atmosphere produces a greenhouse effect, but it is only enough to raise the surface temperature by 5 degrees, much less than the Earth’s.  A weak greenhouse effect is present because of the carbon dioxide.  There are cloud formations on Mars, but on Earth, clouds represent the condensation of water vapor in the air, on Mars, however, it could represent the condensation of either water vapor or carbon dioxide vapor.  Above the Polar Regions, clouds are expected to be mostly carbon dioxide clouds.  In latitudes closer to the equator, clouds are possibly water vapor clouds because of the higher temperature. 


A lot of people ask or wonder what Mars is really made up of.  At this point, we can only speculate at some of our findings.  We think  it has a core of iron, just like Earth’s.  The core is dense, about 1,700 km in radius with a molten, rocky mantle and thin crust.  Mars’ crust and mantle are composed of silicates.  Mars’ relatively low density indicates that its core probably contains a relatively large fraction of sulfur in addition to iron (iron and iron sulfide).  On top of the iron core is a layer of rock (like Earth), but layers of rock are much thicker than that of Earth’s. 


We have seen lots of pictures of what the surface is like on Mars, but what does it really look like.  Except for Earth, Mars has the most highly varied and interesting terrain of any of the terrestrial planets, though some are quite spectacular.  Much of the Martian surface is very cold and cratered, but there are also much younger rift valleys, ridges, hills and plains.  Rocky, dusty surface, complete with clouds and dust storms (that can cover the whole planet at once) is strong enough to support very strong winds and vast dust storms that can last for months at a time.  Mars has many mountains, sandy deserts, canyons, and many, many inactive volcanoes.  Mars has much higher mountains and far deeper canyons than the Earth.  It has the biggest stretch of mountains, which is like going from New York City, New York to Los Angeles, California.  One amazing fact is Mars has the largest volcano in the whole Solar System.  Olympus Mons is over 45,000 feet tall and over 600 feet wide at the base and rimmed by a cliff at 20,000 feet high.  The Thearsis region contains the three mountains Arsia Mons, Pavonis Mons and Ascraeus Mons.  Mars has vast plains such as Utopia Planitia, Elysium Planitia and Hells Planitia.  In photos, it is clear the light-colored areas represent the heavily cratered highlands, whereas the dark areas are the relatively smooth lowlands.  One striking feature, however, is the light and dark areas take on a hemispheric distribution.  If the highlands are considered the equivalent of the continents on Earth, and the lowlands are the equivalent of ocean floors, one hemisphere of the Martian surface would become a continent and the other hemisphere would be covered by an ocean.  This is a very peculiar feature.  At present, no universally accepted explanation exists to account for the hemispheric distribution of these two distinct landforms.  


Close to the equator is a vast system of interconnected canyons called Valles Marineris. This canyon is visible from a global view of the planet, and is almost equivalent to the width of the continental United States.  The Valles Marineris is over 2,000 miles long and deep enough to hold a mountain range, with a system of canyons 4,000 km long and from 2 to 7 km deep.  Individual canyons can be as much as 200 km wide and 7 km deep, for comparison, the Grand Canyon on Earth is only about 1.6 km deep.  Looking at the numbers, you can see the huge difference in sheer size of the canyons.  We know that these canyons were not created by running water, but formed by the stretching and cracking of the crust associated with the creation of the Tharsis bulge. 


The Hellas Planitia is an impact crater in the southern hemisphere that is over 6 km deep and 2,000 km in diameter.  Cratering was an important process in shaping the Martian surface.  Crater morphology is extremely similar to that of the Moon and Mercury.  Small craters showed simple, bowl-shaped depressions with raised rims as well as smooth walls and floors.  Craters on Mars  appeared to experience more erosions or degradations then those seen on the Moon or Mercury.  This is believed to be the combined result of a dynamic atmosphere, more active volcanism throughout the history of the planet, and more weathering due to the processes associated with hydro-processes.  Crater density on Mars was significantly smaller than that of the Moon and Mercury, due to two reasons, first was the availability of asteroids and meteorites which decreases as a planet becomes farther away from the Sun and second, the subsequent geological processes on Mars such as the hydro-processes.  Aeolian processes and volcanism have significantly destroyed the earlier impact history of the planet.  The southern hemisphere is predominantly ancient cratered highlands, similar to the Moon. 


The northern hemisphere consists of plains which are much younger, lower in elevation and have a much more complex history.  Very few shield volcanoes can be found in the southern highlands, but are more prevalent in the northern hemisphere, in addition, some large channels  appear to have been carved by rivers or huge floods across this ancient battered surface can be recognized.   There is clear evidence of erosion in many places on Mars, including large floods and small river systems.  But there was at one point in the past some sort of fluid on the surface of Mars.  These flow channels give the Martian surface a decidedly different appearance from that of the Moon or Mercury.  Evidence suggests Mars once had rivers, streams, lakes, and even an ocean.  As the atmosphere slowly depleted into outer space, the surface water began to permanently evaporate.  Today, the only water on Mars is either frozen in the polar caps or underground.  The age of erosion channels is estimated to be about nearly 4 billion years old.   


Because of the lava flow and small conic structures, it is believed the plains most likely have a volcanic origin.  Dunes and wind streaks are also found on these areas, indicative of the Aeolian process operating in an environment covered with loose materials.  These materials may be derived from the deposits of the large flow channels emerging from the southern highlands.  Mars currently lacks active plate tectonics at the present.  There is no evidence Mars may have had tectonic activity in its early history, making comparison to Earth all the more interesting.  No recent evidence of horizontal motion of the surface, such as the folded mountain so common to Earth.  With no lateral plate motion, hot-spots under the crust stay in a fixed position relative to the surface.  Along with lower surface gravity, this may account for the Tharsis Bulge and its enormous volcanoes.  There is no evidence of current volcanic activity.   


Large, but not global, weak magnetic fields exists in various regions of Mars.  Probably remnants of an earlier global filed that has since disappeared.  This may have important implications for the structure of Mars’ interior and for the past history of its atmosphere and hence, for the possibility of ancient life.


Mars is a desert planet swept by frequent dust storms.  Dust storms are thought to occur every Martian year and begin in the southern hemisphere during the summer.  During the southern spring, many small local storms could be seen in areas where high winds develop.  It is thought a global dust storm could cut itself off when too much dust was in the atmosphere, such that sunlight was filtered out and temperatures at the surface would fall.  The wind speed would then drop and dust would settle out from the air.  This would usually take about three months for the atmosphere to become clear again.  The storms occur more frequently when Mars is closest to the Sun.  Wind blows from the east in the summer hemisphere and from the west in the winter hemisphere.  


Mars has permanent ice caps at both the North and South Poles, which are made from carbon dioxide (dry ice).  The ice caps exhibit a layered structure with alternating layers of ice with varying concentrations of dark dust.  In northern summer, the carbon dioxide completely sublimes, leaving a residual layer of water ice, but it’s not known if a similar layer of water ice exists below the southern cap since its carbon dioxide layer never completely disappears.  The mechanism responsible for the layering is unknown, but may be due to climatic changes related to long-term changes in the inclination of Mars’ equator to the plane of its orbit.  There may be water hidden below the surface of the lower latitudes.  Seasonal changes in the extent of solar caps changes the global atmospheric pressure by about 25%.  The south polar cap is permanent and is composed predominantly of solid carbon dioxide with some water.  It expands and contracts with the seasons as the dry ice vaporizes and sublimes.  The north cap is seasonal, so all the carbon dioxide is vaporized in the summer, leaving a residual cap of water ice only.  From telescopic observations, the polar ice caps of Mars can be identified, they are that predominant.  On both poles, there may be permanent water ice sheet spread over the surface, more often, carbon dioxide ice are detected in the Polar Regions.  Based on the Viking I and Viking II observations, strong winds existed frequently at both poles, most likely driven by large temperature variations between the poles and the equator.


I found some pictures of Mars that really show all the different land marks that makes this planet so different from ours, but so alike.


Fig. 1. This a global picture of Mars as a satellite passed by.


Fig. 2. This is the Martian atmosphere and you can really see the red from the iron content of the planet.


Fig. 3. Pictures captured from Viking I.


Fig. 4. Pictures captured from Viking II.



Fig. 5. Here, again is one of the many craters that cover the planet Mars.


Fig. 6. This a picture of Crater Yuty.


Fig. 7. It is so amazing to see all the craters that are on Mars.  Some are gigantic, while others are much smaller.


Fig. 8. With this crater, you can see the outer layers from the impact of the asteroid when it hit Mars.


Fig. 9. This is a multiple ring crater.



Fig. 10. The above picture is one of the many distinct channels on Mars



Fig. 11. Here is another picture of the huge channels that cover the planet Mars.


Fig. 12. This photo shows all the drainage systems thought to have had carried water at one time.


Fig. 13. This is also a global picture of Mars, but it shows the Valles Marineris.  This valley is over 2,000 miles long, deep enough to hold a mountain range.



Fig. 14. This is a sketch of the land mass of Mars.


Fig. 15. Here are clouds over the southern region of the poles.


Fig. 16. This is a picture of the Northern Ice Cap.


Fig. 17. This is unusual picture of the Northern Ice Caps.


Fig. 18. This is a storm of the South Pole Region


Fig. 19. This is an active cyclone on Mars.


Fig. 20. These are organisms were found on a meteorite from Mars, giving humans hopes of life on Mars.


Fig. 21. Of course, here is the famous picture of the “face” of Mars.


Works Cited

Mars. 17 March 2005.

Mars. Bill Arnett. 28 December 2000. 17 March 2005.


Mars Express Makes First Photo of Red Planet. Imaginova corp. Staff. 3 December

            2003. 17 March 2005. http:


Planet Mars. Hsui. 17 March 2005.


Solar System: Inner Planets – Mars. 17 March 2005.


Mars – from Eric Weisstein’s World of Astronomy. Eric W. Weisstein. 17 March 2005.


The Planet Mars – KidAstronomy.Com. 17 March 2005.


The Planet Mars – The Red Planet. Vic Stathopoulos. 8 August 2004. 17 March 2005.