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Mars |
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Mars was empty before we came. That's not so say that nothing had ever happened.
The planet had accreted, melted, roiled and cooled, leaving a surface scarred by enormous geological
features: craters, canyons, volcanoes. But all of that happened in mineral unconsciousness, and
unobserved. There were no witnesses--except for us, looking from the planet next door, and that
only in the last moment of its long history. We are all the consciousness that Mars has ever had.
Kim Stanley Robinson's Red Mars |
Use the phase diagrams of water and carbon dioxide to explain the possible states of matter for these two substances.
Based strictly upon its location in the solar system, outline what we would predict would be the global characteristics of Mars; that is, its temperature, composition, size, atmosphere characteristics, etc.
Explain why Mars no longer has a global magnetic field (and thus no aurorae).
Outline what is meant by the highlands and plains dichotomy and give one feasible explanation for this difference.
List four ways Mars differs from the Earth because it lacks plate tectonics.
Explain why the tharsis volcanoes became so much larger than their terrestrial counterparts.
Itemize the major features of the runaway-refrigerator-effect at work on Mars.
Relate the major types of features on Mars that are given as evidence of past liquid water on the surface to similar structures on the Earth.
Contrast the impact craters on Mars to those on Earth.
Summarize the Pathfinder mission: why was the landing site chosen, and what were the major findings?
Geologic Processes
Take the Quiz!
In studying Mars, you will find that one or two lectures is simply not adequate. Because of the number of probes we have sent to this planet, and the level of success achieved with each, we have volumes of information--enough for years of study! The best initial approach is to look for what Mars and Earth have in common. Volcanoes, faults, craters, "river" tributaries, sand dunes, sand devils, land slides, ice poles, "islands," valley network, cyclical climatic variation, and an atmosphere (although quite different!).
You should return to the first lecture on the fundamentals of planetary science and review the phases of matter and the phase diagrams for water and carbon dioxide. What are the possible phases for water? For carbon dioxide? Why can't liquid water exist now on the surface of Mars? Would it make a difference if we somehow could increase the surface temperature of Mars to above freezing?
Differentiation and Interior Structure
Scientists and those who study or read about science must never forget the scientific method. Science does not set out to prove anything, nor to seek truths. It does set out to form and test hypotheses about why things are the way they are, why we observe what we do. We tend to talk today that past water on Mars is a foregone, unquestionable conclusion. It is not. We have no "proof" that there ever was water on Mars, and to keep us all honest, here is an argument against that theory.
The counter argument stresses the evidence that Mars NEVER had rivers, lakes or oceans, and probably never had liquid water flowing on its surface. Ever. The author makes predictions of what should be observed if there were surface water, and what is not observed. It is interesting reading. See summary of article by Nick Hoffman, White Mars and accompanying White Mars Image Gallery
Mars rotates in about 25 hours, and thus should have ample energy to drive a dynamo and create a magnetic field. But, Mars has only fossil remnants of a field it once had. What is missing? Where has the magnetic field gone? Without a strong magnetic field, Mars will lack the aurora (even though they would be extremely weak with the thin Martian atmosphere) that Earth has.
For information covered in class, see:
MGS Initial Results from the Magnetometer
More Results from the Magnetometer
If we take an overall look at the surface of Mars, we notice immediately that there
is a stark difference between the northern and southern hemispheres. Take a look
at this elevation map. What is going on?
Image from The Global Topography of Mars from MOLA
Mars has no plate tectonics. Mars has cooled--its crust is rigid and static. What
does the Earth have that Mars does not? Mountain chains, oceanic troughs, mid-ocean
ridges, and long lines of volcanoes. If plate tectonics is not the story of Mars,
then one huge fault is: Valles Marineris. It is theorized that the building of
the Tharsis bulge, huge flows of basalt, created so much stress on the surface of
Mars that it literally cracked. Check out the Mars images from the links given at
the end of these notes. You should examine the Tharsis volcanoes--the largest in the
whole solar system. Take a look at Valles Marineris--if overlaid on the United States,
you could drive from Los Angeles to New York along its length.
Ask any 4th grader and he or she will be able to tell you the largest volcano in the solar system is Olympus Mons. This volcano dwarfs all volcanoes on Earth. What's more, the other 3 Tharsis volcanoes are not that much smaller. If Olympus Mons were set on top of Washington State, it would cover everything. The Greater Seattle Area would nicely tuck into the caldera. (Now that we think about it, wouldn't this be remarkable? Seattle would have such world-wide respect, and think of the skiing on a volcano that is 25 km high!)
Why was Olympus Mons able to build to such huge dimensions? A) The lack of plate tectonics on Mars meant that the lava flow was located in one spot. Contrast this to the Hawai'ian Island chain. These islands are built as the Pacific plate passes over a hot spot--now building new land on the Big Island and also starting a totally new island deep under the ocean. B) Mars has lower surface gravity, and so material feels less force pulling it down. C) Mars has lower atmospheric pressure--less force pressing down. D) Faster cooling of the lava took place, so it did not flow as far. An interesting feature of Olympus Mons is its base that in places rises nearly vertical 2-4 km above the neighboring land. One theory for this unusual trait is that Mars (with no large moon to stabilize its tilt) wobbles significantly on its axis. It may be that the north pole of Mars was once where Olympus Mons is located, and the lava spilt out onto ice. The ice cap acted as a sort of circular dam, trapping the flow. Then, when Mars's wobble slowly moved the north pole to a different spot, the ice cap melted, leaving the huge cliffs we see today.
Currently, the greatest amount of erosion comes from the dust storms on Mars, storms that occasionally envelope and ravage the entire planet. The Mars Global Surveyor has many images showing dust devils, dust storms, craters filled with wind sediment, sand dunes. A comparison of some of the images have shown marked changes over a period of months to a few years.
Mars also has ample evidence of past erosion by water, evidence supported by observations of similar features on Earth. You will be comparing one example of this in the lab, Martian Topography, when you compare alcoves, channels, and aprons on Mars to those caused by outflowing water on Mt. St. Helens.
For the latest pictures from Malin Space Science Systems and the Mars Global Surveyor, Mars Orbiter Camera (MOC), go to The Latest Pictures from MOC. There you will find many, many high resolution images showing erosion on Mars (plus a whole lot more).
Cratering on Mars differs from that on Earth slightly. On Mars, the craters are formed under lower surface gravity and so the central peaks, if formed, are often quite large. The ejecta material can fly farther from the crater. Mars has suffered little resurfacing over the past 100 million years or so, and so craters are retained. Mars has a number of craters that exhibit a "flower petal" structure, or a lobate, layered ejecta blanket indicative of subsurface frost that was melted by the impact. Most impacts, however, are in regions with no subsurface ice. Cratering on the two planets have a few similarities: both suffer erosion by wind and dust, both have similar surface compositions.
The evidence is strong for Mars having had a much denser atmosphere in its past. The features that resemble those on Earth created by running water are suggestive of past, perhaps vast, bodies of water on Mars. Most of that atmosphere has disappeared today, with the surface pressure on Mars less than 1% that of Earth. Where did the atmosphere go? Mars has a lower escape velocity, to start with, because of its smaller size. Some scientists theorize that perhaps the atmosphere was "knocked" off by a gigantic impact. (Perhaps the same one that created the northern lower plains? Who knows.) Sun light would dissociate the molecules in the atmosphere--the carbon and hydrogen escape, the oxygen goes into rusting the rocks on the surface.
Once the atmosphere starts to
cool, the remaining water and carbon dioxide in the atmosphere freezes out, leaving
even lower amounts of these greenhouse gases in the atmosphere. This lowers the
temperature even more, causing additional gases to condense at the poles. There is
some circulation of the atmosphere during Mars's seasons. During the northern summer,
some of the ice sublimates and refreezes on the south pole. The opposite happens during
the summer in the southern hemisphere. The polar ice caps have an estimated 1.2 million
cubic kilometers of water. (From
www.space.com, 22 May 2002).
The freezing-out cycle continues, something we've called the runaway refrigerator effect. Seems as though Venus is too hot, Mars is too cold, but our Earth is just right.
| For a more in-depth discussion, be sure to read the following on-line article: Global Climatic Change on Mars" from Scientific American |
To answer the questions posed in the objectives for this lecture, visit the Mars Pathfinder web site at the End of the Mission and look up "science" and "geology." Recall, as you read through this material, the analogy with the scablands of eastern and central Washington, and how this region was formed--from the release of an enormous amount of water, all at once, when an ice dam broke and Lake Missoula flowed through Washington.
 Panoramic photo mosaic taken by the IMP camera on July 4, 1997: foreground is dominated by the lander with Ares Valles in the background. |
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Three classes of Martian rocks: Large rounded rocks with weathered coatings, small gray angular rocks lacking weathered coatings, and flat white rocks. |
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The rock Yogi: Yogi is taller than the rover. The soil around Yogi is the site of multiple soil experiments performed by Sojourner's cleated wheels. (Sojourner is still on Mars, all alone.) |
| There is tons of information at the JPL Mars Pathfinder Mission Pathfinder Web Sites. Take some time to visit and check out the images, especially those in 3-D (got your red and blue glasses?). | |
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the Quiz!
NOTE: If you get the message, "Catalyst Tools Error .... you are not authorized to use
this survey. (Error 628)" it means that you have no doubt used the convenient in-document
links I provide at the top to jump around the notes. Enter the on-line notes directly
from the calendar page and then use the spacebar or sidebar to get to the quiz link.
Relevant Links -- Must visit Mars sites:
The March, 2000, issue of Scientific American was devoted to Mars and the exploration of Mars. Start here: How to Go to Mars and continue to follow the imbedded links for a wonderful mental journey to the Red Planet.
Gallery of Images from Mars Orbiter Camera
Watch the Progression of the Dust Storm that overtook Mars in mid-July, 2001.
Review the information given at the SEDS site on Mars and the Views of the Solar System. Then, if you have a few extra hours for exploration (become a true traveler), then visit the Mars Global Surveyor home page at NASA.
The 3-D images seen in class were taken from a CD-ROM. Samples can be found at 3-D Tour of the Solar System
Clouds, Sunsets, and Sunrises on Mars from the Pathfinder.
3-D Sand Dunes
Face on Mars