The Planet Mars

As a result, this has fueled much speculation about life on Mars. Here are a few highlights and outcomes:

• The book: The 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 aqueducts 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).

This imaginative and highly inaccurate speculation about Mars has sparked the desire to explore the Red planet with several missions to Mars...including the most current one aptly named "Curiosity".

• 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

  
  

In the past 15 years, Mars has been the target of several missions from NASA/JPL with the global mission of finding evidence of water existing in the past and present as well as life or having the potential for life. The first of these missions, Mars Global surveyor and Pathfinder were preliminary experiments to look for optimal areas on the surface for further study and to test the use of a robotic rover on Mars. The next successful mission, Phoenix lander sought evidence of water by analyzing soil samples with an onboard laboratory. Spirit and Opportunity rovers sent back several images of the soil and overall geology of Mars. Curiosity has recently landed and like Phoenix, has an onboard laboratory to analyze soil samples and look for amino acids - the building blocks of life. You may wonder why so many similar missions have been sent to Mars, well the answer is simply that Mars is a big place. It requires survey satellite missions to efficiently scan regions for optimal water discovery sites and more than one rover is needed to investigate the planet. The rovers that have landed have exceeded their lifetimes, but there are some conditions, such as sub zero temperatures, that make it hard on instruments to survive many years. They can only travel so far in their limited life times. Also, one location will not give the entire picture of the planets geologic history, therefore several rovers are sent - Earthlings invading Mars!

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. In terms of familiar places, this is approximately the distance from Portland Oregon to Chicago and over 4 times deeper than the Grand Canyon. 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. They lie on the Tharsis region, an uplifted area about 4000km in diameter and 10km high. 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 eroded 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 largest being Olympus Mons. Tharsis Montes and Elysium Planitia regions are rich in old cone volcanos, 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 Mars' 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 dating 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:
  • Valles Marineris: Looks like a huge rift valley on Mars as if crustal separation was occurring

  • Tharsis Volcanic Region: Region of 3 to 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 impact 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
    

    Recent studies have pieced together the following theory: Mars' interior was molten long enough for volcanic activity and potentially a global magnetic field. The event that created the Tharsis region effected the crust of the entire planet by causing it to rotate 20 degrees about it's core. Imagine if you could remove the peel of an orange in one piece and then place it back on the orange. Now rotate it around the fruit. That's what happened to Mars.

    There isn't conclusive evidence as to what happened to Mars' magnetic field. The planet could have simply cooled and solidified or large impacts could have disrupted the dynamo effect. Whatever the cause, Mars presently has small magnetic fields in various regions around the planet.