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We have had a long fascination with this:

• HG Welles wrote an interesting story about it
  

• The telescopic appearance of Mars can show "subtle" changes over time. This is due to wind blown dust changing the large scale features and reflective characteristics. In the late 19th century Schaperilli imagined he saw linear features which he called "canals"
  

• Schaperilli's atlas of Martian Canals captivated the imagination of Percival Lowell who greatly popularized the idea of Life on Mars. Lowell imagined a system of canals that the Martians would use to transport water from the Polar Caps to the more arid regions. He constructed an elaborate globe of mars to illustrate this:
  

  Orson Welles 1939 broadcast of Martians invading New Jersey only served to perpetuate the mythology of the Martians. Unfortunately, the media really does have a powerful effect on people.

So what is Mars really Like?

• Looking Around
• Looking around some more

The Viking Lander Mission on Mars (1976) sampled the soil and found evidence of a highly chemical reactive soil and environment. There was no unambiguous evidence for biological processes. Worse still was the mass spectrometer measurements which detected no organic molecules down to a concentraction of less than 1 part in 10 million.

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.

So what about the Martian Meteorite?

• Microscopic examination showed morphological peculiarites?

• once you find one you can find many
• Age dating suggests the following sequence
  • The rock itself is 4.6 billion years old (this by itself is highly unusual)
  • The concentration of carbonates is dated to between 3.6 -- 4.0 billion years ago. This suggests that carbonates were despoited inside the rock as liquid water found its way into cracks
  • 16 million years ago, the rock was part of a large cloud of Martian debris that was blasted off the surface by a large impact
  • 13,000 years ago it felt on the Antarctic Ice Sheet
  • 20 Years ago it was found

By analogy with the development of early life on the earth, starting which chemical processes that synthesized organic molecules and rained them into the oceans, we believe that oceans are required for the development of early life:

• Shields sensitive Organic Molecules from UV radiation
• Acts as a transport medium that facilitates interaction

Was there water on Mars?

• Yes, there is now
• There is evidence of flooding
• More evidence
• Agent for Water Production

The ability for liquid water to exist on the Martian surface depends upon the atmospheric pressure. Current atmospheric pressure is 1/1000 that of the earth - way to thin of atmosphere for water to exist.

Note that the most recent NASA radar measurements (from July 2007) indicate that there is enough frozen water on mars to flood it uniformly to a depth of 11 meters. This is approximately 10 times more available water than previously thought.

However, in the early history of Mars there was enough Carbon Dioxide present to form an atmosphere that was 2 times as thick as the present day atmosphere of the Earth (note the early earth's atmosphere was 50 times its present capacity).

At this pressure, water could exist as a liquid on the Surface. The question is, how long did these "oceans" exist. On earth we know it took 800 million -- 1 billion years for the first cells to evolve. It is highly unlikely that oceans on Mars existed for that long - it is mostly likely that they only existed for a few 10's of millions of years before the atmospheric pressure lowers to the point that liquid water can longer be sustained

Where does the atmosphere go?

• Freeze out at the Poles but the more recent measurements suggest very low concentration of frozen CO₂ in the Martian polar caps. This is a critical blow to the idea that Mars was once warm and wet.

• Gradual escape - Mars is a very small planet; has only 1/2 of the earth's gravity and therefore has difficulty holding on to atmospheric gases.

The most probably explanation of the morphological features seen in the Martian Meteorite is a chemical reaction. Factors that work against the biological interpretation are the following:

• The structures are 10--20 times smaller than similar "micro fossils" seen on the earth. This is a real problem - the structures aren't really big enough to "hold" DNA

• Carbonate concentrations in meteorites can easily be produced by chemical reactions that happen when the rock is shocked. This happens at high temperature (700 C) -->definitely not conducive for biology

• Magnetic fields have played a role in the evolution of bacteria on the earth. They use the magnetic field to sense their position. On Mars there is no magnetic field --> there might have be one in its early history (when the core was molten) but it would have been very weak.

• All of the evidence remains morphological and not physical.

Recent analysis of the Martian topsoil soil indicates that it is quite similar to that found in Antarctica's dry upper valleys and the salts it contains are another indication of the presence of water

The soil about one-inch into the surface layer is alkaline, with a pH between 8 and 9 and it appears to contain magnesium, sodium, potassium, and chloride this is highly similar to many soils on the Earth.

Overall, the soil appears to have sufficient nutrients to potentially support microbial life.

But the most encouraging aspect of potential microbial life on Mars comes from our increasing understanding that life thrives in hydrothermal ocean vents.

The principle energy source is the processing of hydrogen sulfide (H₂S) by bacteria. This leaves behind rich deposits of sulfur.

The most significant aspect of this is that its now clear that life can form in a way that is independent of the Energy of the Sun This is a Big Deal

But of course, its only true if its on YouTube.

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And this is very much an Alien world, on the Earth, which should remind us all that there is much more to know.