Quick Facts:

Mars is relatively small, having only about 10% the mass of the Earth

Mars has an atmosphere made up mostly of Carbon Dioxide but its pressure is only 1% of the Earth's atmospheric pressure. Thus Mars has 10,000 times less Carbon Dioxide in its atmosphere than Venus

Mars is tilted on its axis by 25 degrees, very similar to the Earth and hence Mars has seasonal variations

These seasonal variations cause frozen carbon dioxide to sublime from the Polar Caps thus giving Mars a seasonal atmospheric pressure

Surface featurs of Mars are continually augmented and eroded by Wind and periodic dust storms.

Humans have always had a fascination with Mars and have pondered. mostly in a science fiction manner, the possibility of their being life on Mars. Visual observations of Mars made by astronomers through telescopes in the period 1880-1920 fueled speculation for of a civlization on Mars. The Italian astronomy Schiaparelli first made detail maps of the surface of Mars from visual inspection through a telescope in 1877. Over the next decade he worked to refine these maps, some of which are reproduced below:

The distinguishing feature of these maps are the apparent linear structures, orginally interpreted by Schiaparelli to be "channels" (maybe carved by water). These would be later interpreted by American Astronomer Percivall Lowell (see more in the next lecture) as artificial canals designed to deliver water from the polar regions to where the civilization lived.

As a result, this has fueled much speculation about Life On Mars. Here are a few highlights:

• War of the Worlds by HG Wells in the late 19th century (this is actually an entertaining social commentary instead of a book about Martians invading the Earth even though Hollywood disagrees)

• Percival Lowell (late 1920s): A semi-deranged astronomer who thought he saw canals which connected the polar cap regions to the equatorial regions. He also saw changing patterns on Mars which he attributed to seasonal vegetation growth. He made up an elaborate story that Agrarian Martians built a network of aqeducts to bring water from the polar regions to irrigate equatorial crops. The New York Times believed him.

• Orson Wells: On Halloween night 1939 he gave a radio broadcast announcing that the Martians were landing in New Jersey. People believed him (must be how Rush Limbaugh got his start) - totally amazing. See the movie "Buckaroo Banzai" for more details on Cherry Hill New Jersey and John Bigbooty.

With all this is a backdrop, curiousity about Mars began to drive several space craft missions:

Early Spacecraft Encounters with Mars:

• Mariner 4 crash landed on the surface in July 1965. Limited images revealed a cratered surface

• Mariner 6 and 7 in 1969 took additional images (before crashing) which indicated the surface was not uniformly cratered like the lunar surface. Hence, Mars must have a younger surface

• Mariner 9 in 1971 was the first orbiter mission. Approaching mars revealed a surface that appeared suprisingly smooth and uniform with a few black dots. At the time of the approach, Mars was engulfed in one of its periodic global dust storms and the black dots were the tops of huge volcanoes sticking above the dust storm. These dust storms account for the shifting large scale patterns on Mars that Percival Lowell thought were agriculturual fields. Mariner 9 returned the first evidence that periodic massive floods (of water) occur on Mars.

• Viking Landers and Orbiters in 1976 took extensive images of Mars at fairly high resolution (like a few cm in the case of the Landers). These pictures are quite striking and should be inspected here

Surface Geology and Features on Mars:

This image is a mosaic of the Valles Marineris hemisphere of Mars. It is a view similar to that which one would see from a spacecraft. The center of the scene shows the entire Valles Marineris canyon system, more than 3,000 kilometers long and up to 8 kilometers deep. Many huge ancient river channels begin from the chaotic terrain and north-central canyons and run north. Many of the channels flowed into a basin called Acidalia Planitia, which is the dark area in the extreme north of this picture. The three Tharsis volcanoes (dark red spots), each about 25 kilometers high, are visible to the west. Very ancient terrain covered by many impact craters lies to the south of Valles Marineris.

Although Valles Marineris originated as a tectonic structure, it has been modified by other processes.

This image shows a close-up view of a landslide on the south wall of Valles Marineris. This landslide partially removed the rim of the crater that is on the plateau adjacent to Valles Marineris. Note the texture of the landslide deposit where it flowed across the floor of Valles Marineris. Several distinct layers can be seen in the walls of the trough.

This image of the head of Ravi Vallis shows a 300-kilometer long portion of a channel. Like many other channels that empty into the northern plains of Mars, Ravi Vallis originates in a region of collapsed and disrupted ("chaotic") terrain within the planet's older, cratered highlands. Structures in these channels indicate that they were carved by liquid water moving at high flow rates. The abrupt beginning of the channel, with no apparent tributaries, suggests that the water was released under great pressure from beneath a confining layer of frozen ground. As this water was released and flowed away, the overlying surface collapsed, producing the disruption and subsidence shown here.

The water that carved the channels to the north and east of the Valles Marineris canyon system had tremendous erosive power. One consequence of this erosion was the formation of streamlined islands where the water encountered obstacles along its path. This image shows two streamlined islands that formed as the water was diverted by two 8-10 kilometer diameter craters lying near the mouth of Ares Vallis in Chryse Planitia. The water flowed from south to north (bottom to top of the image). The height of the scarp surrounding the upper island is about 400 meters, while the scarp surrounding the southern island is about 600 meters high. There is a great deal of evidence of the existence of liquid water on Mars, at least in the far past. A secondary atmosphere for all terrestrial worlds is rich in CO2, H2O and SO2. On Earth, the temperature is just right for H2O to rain out and form oceans. On Venus, the temperature is too hot and H2O stays as a vapor to be destroyed by photodisintegration. On Mars, it is too cold for liquid water. All the H2O is locked up in permafrost under the soil and subsurface ice reservoirs. Notice that most of the water flow features are near the base of old volcanoes or impact craters. These early events heated the subsurface ice to produce a short-lived flow of liquid H2O.

There is also much evidence for wind features on Mars in the form of sand dunes and wind eroded craters. The current atmospheric pressure on Mars is low, about 1% that of the Earth's but that is still sufficient to generate wind and substanial air borne dust. As a result, Mars has relatively few impact craters visible on its surface as most of them have been aroded away. Ultimately the sand blasting nature of the winds, coupled with very low temperatures at night limit the operational lifetime of any equipment that we place on Mars for surface monitoring and measurements.

There are very large shield volcanoes on Mars. The Tharsis and Elysium are rich in old cone volcanoes, averaging over 500 km across and 25 km high. These are ``hotspot'' volcanoes like the Hawaii Islands. The extreme size is due to the fact that there is no tectonic plate motion on Mars and the lower gravitational field strength of Mars allows volcanic ejecta to reach higher distances above the surface.

In addition to these features, Mars shows examples of chaotic terrain in the form of highlands and broken hills. These are probably old tectonic regions. There are also numerous canyons and long fractured regions. These may be mostly tectonic in origin as well.

Atmosphere and Climate:

Mars is another example of a secondary atmosphere from outgassing (therefore, we know that Mars had an early epoch of tectonic activity). However, unlike the Earth or Venus, the atmosphere is very thin, about 1% the mass of Earth's atmosphere. Its composition is 95% CO2, 3% N2, 2% Ar and less than 1% O2. A high noble gas content implies that Mar's atmosphere was much thicker in the past (noble gases do not react with other elements and are heavy enough to stay within the gravitational field of Mars). The climate on Mars is very desert-like due to its thin atmosphere. There is too little mass in the atmosphere to hold in heat so the warmest daytime temperatures are around 50 degrees F, but the nighttime temperatures are -170 degrees F. Other weather features are massive dust storms and occasional CO2 fog in the canyons.

Summary of Likely Surface Geological Evolution on Mars:

• No age dataing is available time sequencing of events is still speculative

• Crater erosion is occuring as over time the craters are filled in with wind-blown dust

• Some evidence exists for primitive plate tectonics:
  • Valley Marineris: Looks like a huge rift valley on Mars as if crustal separation was occurring

  • Tharsis Volcanic Region: Region of 3--4 large shield volcanoes. Very reminiscent of the Hawaiian Islands as being on a moving plate over a stationary hot spot (magma source) deep in the interior of the earth. The large size of these Volcanoes is probably related to the low surface gravity on Mars (40% of the Earth's)

• Fluvial Erosion (running water) from two sources. Note that the current atmospheric pressure on Mars is insufficient for water to exist as a liquid. However, during volcanic episodes the atmospheric pressure (mostly provided by carbon dioxide) is sufficient for liquid water to exist for a short time.
  • Much of the Martian topsoil is supported by permafrost. Periodic melting would cause this support to collapse and on Mars there does appear to be large scale collapse features (jumbled up terrain if you want a technical term)

  • Many fluvial features are associated with large impact craters. This suggest that the heat dissipated during the impace melts much of the permafrost causing a large scale flood. This flooding events are similar to what occurred in the massive flood 15,000 years ago that shaped much of Eastern Washington