The Red Planet

Mars from Gustav Holst's The Planets

A Quick Summary...

Historical Notes

Mars has long been a prominent player in astronomy - a role far in excess of its relatively small size.

Planetary Characteristics

Early telescopic observations of Mars revealed an exciting world with polar caps and large green expanses that grew and shrank during the Martian year of 687 days. This helped fuel the speculation concerning life on Mars. Schiaparelli popularized the idea that the planet was criss-crossed by an elaborate canal system even though simple calculations showed that such canals would have to be enormously wide to be visible from earth. (example:1" seeing would be considered very good for earth based observations. If you clearly saw a canal stretching across Mars it would have to be on the order of 1" wide. Using the small angle formula the width in km would work out to be: width = (1"/206265) X 0.5 AU X 149, 500, 000 km = 350 km!). Wonderful maps were drawn up showing the intricate network of canals and numerous people "corroborated" Schiaparelli's work. This is really neat considering that

There are no canals on Mars!!!!

Because Mars is relatively close to us it moves around a great deal in the course of a season. Every other year we have Mars at its closest approach to us - during this time it is an easy object to observe even with a small telescope. During such times an observer is treated to a beautiful polar cap that grows and then shrinks as Martian summer sets in. Massive dust storms can be seen streaking across the planet for weeks on end. Wind speeds as high as 200 km/h have been reported. As well, cloud formations are occasionally seen. Prominent greenish areas wax and wane. Such observations reveal Mars as a potentially life sustaining world having an identifiable climate and seasons.

The high CO2 content of the Martian atmosphere favours the idea that the polar caps on Mars are primarily "dry ice" with some small content of water ice. Even though both poles have ice caps the northern polar cap loses its CO2 completely during its summer season and leaves behind the trace of water ice. This asymmetry is due to the ellipticity of the Martian orbit. The scarcity of water on Mars is an enigma. There is considerable reason to believe that Mars should have enough water to cover the planet to a depth of a few meters. This clearly is not the case and leads to a number of questions:

Why is Mars the "Red Planet"
Thanks to detailed soil analysis sent back from the Viking missions to Mars we know a great deal about the soil of Mars. Unlike the earth, Martian soil appears to consist primarily of igneous materials with abnormal concentrations of silicon and iron. It is the iron - in the form of rust - that gives Mars its ruddy appearance. The fact that the surface of Mars is laden with heavier elements suggests that the planet is not as highly differentiated as earth. This may be due to the cooler environment in which Mars formed - not allowing enough time for element differentiation to occur before the planet solidified. The interaction of wind and soil on Mars gives rise to extensive wind erosion and the formation of large dunes. Perhaps one of the most significant discoveries of recent years concerns the appearance of flow channels revealing that water once flowed in great volumes across the Martian landscape. It has been suggested that a great deal of water is trapped in a permafrost layer. During the heating of Martian summers some of this permafrost melts rapidly and flash-flooding results.

 

The Formation of Atmospheres and Why is Mars So Different?
A clear picture is beginning to emerge - atmospheres arise from volcanic activity . As we shall discuss soon Mars has been very active volcanically. A volcano releases trapped gases into the atmosphere. At this stage Earth and Mars would appear to be on equal footing. In their early histories both atmospheres probably started out in roughly the same way. But soon their paths diverge. On earth their is a continual interplay between:
  • atmosphere
  • ocean
  • continental plates

 


 

Oceans Play a BIG Role...

CO2 is being filtered by the oceans. This prevents a steady build up of CO2 in the atmosphere (Venus' problem). At the same time CO2 combines other materials and life forms to become tied up in rock and sediment on the ocean floor. Eventually some of this carbonate rock is cycled by tectonic activity back into volcanoes where CO2 is again returned to the atmosphere. This helps maintain a supply of CO2 in the atmosphere which enables greenhouse warming to occur on earth.
Earth case in which oceans provide an important C02 buffer and plate tectonics provides a return cycle while vegetation (green) provides an 02 source.

On Mars the situation is much different. Primarily because of the more rapid cool-down time, Mars has a very thick crust and shows no evidence of plate activity. The return cycle of CO2 to the atmosphere is thwarted and the CO2 level steadily drops. Greenhouse warming does not occur on the planet, remaining water freezes out. Most of the Martian CO2 is "locked" in the form of carbonate rock that has no chance of being recycled. Mars lost most of its atmosphere very early in its history. It now has a very thin atmosphere which is similar to earth's atmosphere (in terms of pressure) at an altitude of 30 km!

Magnetic fields, shields and the Solar Wind

A more subtle effect has to do with the interaction between the solar wind and the planetary atmosphere. Earth has probably always had a magnetic field and effective shield against the solar wind. Early in Martian history the core cooled, plate activity stopped and so did the Martian magnetic field. Without this protection from the solar wind, UV radiation could knock-apart water vapour molecules (H20). THe Hydrogen atoms would escape and the Oxygen would form oxides (rust-out!) on the surface. As well, C02in the atmosphere would be entrained with the solar wind and carried off. This, as well as a shut-down of vulcanism, all conspired to produce a thinning atmosphere.

 

Conclusion:

Mars suffers from a Reverse-Runaway Greenhouse Effect!

 
 

The Geology, Hydrology and History of Mars

The magnificent (probably extinct) volcano Olympus Mons is the size of Arizona and more than 25 km high. An example of a Shield Volcano, it dwarfs any similar geologic form on earth. The enormous size is probably due to two factors: In addition to shield volcanoes, Mars also has what are known as pyroclastic volcanoes. These literally explode on eruption and this may be linked to the presence of water or other volatiles trapped within the surface layers of the planet. Hot lava would cause rapid vapourization of these volatiles with explosive results. Other evidence that Mars either has or has had large quantities of water come from images of vast canyon systems. Shown below is a segment of Valles Marineris. This vast canyon stretches more than 4000 km across the planet, 600 km at its widest and 6 km in depth. Hundreds of Grand Canyons could fit in this vast chasm!
Images like this one reveal numerous dry river beds and flood plains - see if you can spot some. Mars is also heavily cratered - a trait shared by all of the Terrestrial planets (and Luna). Very little is known in detail about the interior of Mars. It seems that volcanic activity has ceased but we see evidence of enormous volcano remnants on the planet. The absence of a magnetic field and the inferred absence of tectonic activity suggest that Mars does not have a hot, molten core.

The Cratered Surface of Mars

Inspect the images on the Malin site to get an feel for the degree of cratering on Mars. What does this potentially tell us?

Searching for Life

Both Viking 1 and 2 carried on board experiments to test soil samples for life forms. They found none but the results were not conclusive. We now see that the Martian environment is a very harsh one. If life is present it would be at best in a microbial form and perhaps difficult to detect. Perhaps future missions to Mars will resolve this question.

Beginning in the late 1990's and early 2004 a series of very successful Mars rovers explored the Martian surface and finally found conclusive evidence that Mars was once much richer in liquid water than today. For more details follow this link to the JPL Mars Rovers site...

NEWS FLASH....

Elvis is on Mars!

The Martian Satellites: Phobos and Deimos

 

The tale takes a strange twist here. Mars has two small and very peculiar children. These moons are much more similar to asteroids than, for example, Earth's moon. It is possible that they were "captured" by the planet at an earlier epoch.
  Deimos is the smallest known moon in the solar system and orbits only 6000 km above Mars in a mere 7 hours! It moves so fast that you would see it rise in the west and set in the east - several times per day! The orbit of Deimos is decaying and it is expected that it will collide with Mars within the next 30 million years. Deimos has a density of 1.8 g/cc and is heavily cratered and scoured.
Phobos orbits Mars with a period of 1.26 Earth days. Like Deimos, it is small and low density (1.6 g/cc). It is quite possible that both Deimos and Phobos contain large quantities of water-ice. If so, this could be very important for the eventual establishment of space stations orbiting Mars.
Transit and eclipse of Deimos - Mars view!

 

Despite centuries of observation and numerous space missions to the "red Planet" it remains an enigma. 

To Summarize...

The Seven Ages of Man

The Four Ages of Planets

All the world's a stage,
    And all the men and women merely players:
    They have their exits and their entrances;
    And one man in his time plays many parts,
    His acts being seven ages At first the infant,
    Mewling and puking in the nurse's arms.
    And then the whining school-boy, with his satchel
    And shining morning face, creeping like snail
    Unwillingly to school. And then the lover,
    Sighing like furnace, with a woeful ballad
    Made to his mistress' eyebrow. Then a soldier,
    Full of strange oaths and bearded like the pard,
    Jealous in honour, sudden and quick in quarrel,
    Seeking the bubble reputation
    Even in the cannon's mouth. And then the justice,
    In fair round belly with good capon lined,
    With eyes severe and beard of formal cut,
    Full of wise saws and modern instances;
    And so he plays his part. The sixth age shifts
    Into the lean and slipper'd pantaloon,
    With spectacles on nose and pouch on side,
    His youthful hose, well saved, a world too wide
    For his shrunk shank; and his big manly voice,
    Turning again toward childish treble, pipes
    And whistles in his sound. Last scene of all,
    That ends this strange eventful history,
    Is second childishness and mere oblivion,
    Sans teeth, sans eyes, sans taste, sans everything.

Shakespeare - As You Like It, Act 2, Scene 7

All the solar system's a stage,
And all the planets, Terrestrial and Jovian merely players:
They have their exits and their entrances;
And one planet in its time plays many parts:

  • Differentiation - in this age the planet is very hot, cools and the heavier elements sink to the centre while the lighter elements are buoyed up to form a crust
  • Cratering - throughout its entire life but especially early in the history of the solar system impacts from asteroids and comets re-shapes the surface of the planet
  • Planetary flooding - in this phase earlier formations including impact craters are covered over through flooding of laval, liquid water or both. All of the terrestrial planets show evidence of this
  • Surface evolution - in this on-going phase the morphology of the surface changes over long periods of time. Change can occur because of tectonic activity or weathering.

 

 

Some Interesting Web Sites to Explore ...

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