Two Different Stories

MARS:

The global properties of Mars can be found here. Things to note are the following:

• 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.
• The strangest thing about Mars atmospheric content is the high degree of residual Argon
• 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

Speculation about Life on Mars:

This has runned rampant for many years. 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.

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 Geological Evolution on Mars:

• No age dataing is available so everything is still a guess.
• Crater erosion is occuring as over time the craters are filled in with wind-blown dust
• Some evidence 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

Searching for Life in the Martian Top Soil:

The Viking Landers primary mission was to test for microbial life in the Martian soil. They landed at latitudes of 23 and 48 degrees. There were three identical experiments on board each lander designed to see if anything in the soil did the following:

• Ate
• Breathed
• Deposited Waste

The Three Experiments and the results are the following:

• Gas Exchange Experiment: Some soil was put in a small chamber on board the Viking spacecraft to which water was added. There was a change in the atmospheric composition in the chamber but this could be entirely explained via chemical reactions with peroxides (a peroxide molecule has 2 hydrogens and 2 oxygens and is highly chemically reacting).
• The labelled Release Experiment: This was designed to see if anything in the Martian soil would "eat" some nutrients that were mixed in. The results can again be explained entire via chemical reactions
• The Pryolictic Release Experiment: This was designed to detect photosynthesis. When illuminated with light, photosynthesis should deposit carbon in the soil in the chamber. There was a small increase in the amount of carbon fixed in the soil which can not be entirely explained through chemistry.

An excellent summary of the Viking Lander Experiments can be found in a article in Scientific American in 1977 by Horowitz. A brief summary is given below:

• No Martians were observed standing in front of the Camera and waving shouting "Hey, we are on TV!".
• Overall the results are ambiguous but most are consistent with a purely chemical reaction
• The soil of Mars is highly chemically reactive with a high oxidizing capacity (which of course is why the soil is red)
• A photochemically active surface is evident. However, due to low temperature and absence of water this surface is maintained in a state far from chemical equilibrium. Hence, the Viking lander experiments chemically woke-up some dormant top soil.
• The mass spectrometer aboard each lander carefully analyzed the topsoil of Mars and found no organic matter down to a level of 10 parts per billion.

The major flaw associated with the Viking Lander experiments is that they could only access the topsoil. As this is the product of wind blown dust, it is possible it has become sterile by this process. Hence, it is desireable to return to Mars and sample deep into the soil, down near the bedrock, to test for the presence of organic matter.

There is ample scientific motivation to return to Mars with a manned mission. Here's predicting it will happen before the year 2025.

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