Exploration of the Solar System

Week  6,  Topic 8 (continued)

A Spacecraft Tour of the Planet Mars

 

            To understand what the big, contemporary issues about Mars are,  one first must get an idea of the geography of the planet.  One can get some ideas from telescope observations, but not all that much.  A set of pictures from Earth,  taken as the planet

Mars rotates, are shown in Figure 11.2 of the book,  which is copied below. 

 

 

Pictures like this show the dark areas,  the polar caps,  odd white areas, and a little more.  However,  to really get a good picture requires a spacecraft to go there and take images.  The first spacecraft to go to Mars was Mariner 4 in 1965.  It returned the picture shown in Figure 11.3,  shown below. 

 

 

Question:  Based on what we have learned in this class, and in particular what we have learned from studies of the Moon,   what would you conclude from a picture like this? 

 

The Flotilla of Mars Spacecraft

More spacecraft were sent to Mars following Mariner 4.  

The following spacecraft have successfully completed missions to Mars.

 

In addition to these, there were a number of other US and Russian missions to Mars, which were unfortunately lost when Martians hiding in “The Face” emerged to destroy the spacecraft. 

 

Some scientists,  carefully examining the photographs from Mariner 4,  saw some features that indicated Mars might be more interesting than indicated by the picture above.  These hunches were confirmed by Mariner 9,  which began to reveal terrain like that shown below,  which displays a kind of feature called a valley network. 

 

 

This made the whole enterprise seem a lot more interesting,  and was the impetus for the spacecraft missions named above.  There are also ambitious plans for the future, but I will wait to describe those at the end  of these lectures, when we can understand why they would be so scientifically desirable.  I will talk about these in Topic 9. 

 

 

Main Surface Features of Mars 

Let’s review the findings about the surface of Mars,  as permitted by the spacecraft missions of the past 40 years.  This will initially be a travelogue,  then we will consider all of this from the viewpoint of planetary science. 

                  

1.  North-South Asymmetry:  The southern hemisphere is higher in altitude than the northern, and heavily cratered.  The northern hemisphere is lower (like the lunar Maria) and has regions with few or no craters, and other evidence of geology or hydrology.

http://ltpwww.gsfc.nasa.gov/tharsis/global_paper.html

 

2. Impact craters:  Craters are seen all over the planet, so the surface retains information from the Age of Bombardment.  Interestingly, and importantly, some of these craters show evidence of liquid ejecta, or seepage from crater walls. A good example is Figure 11.6 of your book.  Below is a link showing scads of craters.  Gusev crater is where the robot Spirit has been since January.  This site was chosen because  since there seems to be an ancient river which flowed into the crater. 

http://www.msss.com/mars_images/moc/MENUS/crater_list.html

 

3. Volcanos: The northern hemisphere of Mars has prominent shield volcanos.  Some of them have slopes with numerous impact craters, so they have evidently been dormant since the early days of  the solar system.  However, the largest, Olympus Mons, has crater-free slopes, so it has been active well after the age of bombardment, and may still be active.

http://www.msss.com/mars_images/moc/MENUS/volcanic_list.html

 

4. Valles Marineris: There is a large crack in the crust of Mars, evidently caused by

tectonic forces, which stretches across most of one hemisphere. See Figures 11.13 in your book.  There have been observations of haze in the bottom of this canyon in the Martian morning, which is believe to be due to water ice below the surface.  A good picture of this is seen in the URL under section 1. above. 

5. Runoff  Channels and Outflow Channels:  Perhaps the most exciting development was the discovery of flow channels which are accepted to be ancient waterways.  These channels are therefore dry river beds. Excellent examples are shown in Figures 11.17 – 11.20 of your book.  The book divides these into outflow channels, which were apparently caused by huge eruptions of subsoil water, and runoff channels (also called valley networks) which have more of a network of tributaries, and are found in more heavily cratered  (and therefore older) parts of Mars.  Some scientists believe that the runoff channels were a result of rainfall in an ancient Martian climate.  However,  there are potent objections to this interpretation, so I believe this question is still open,  and deals with an important issue in the early history of the planet.

http://barsoom.msss.com/http/ps/channels/channels.html

 

6. Polar Caps. ..  The polar caps are a combination of water ice and carbon dioxide ice.  The seasonally-variable component is carbon dioxide, the permanent component is water ice.  The fact that water ice is known to be present was a reason the Mars Polar Lander was sent to this part of  the planet, but they got it too.

7. Hebes Chasma and Ancient Lakes:  There are a number of depressions and basins that have rock formations which appear to be sedimentary deposits.  This would then suggest that they were lakes in which standing water was present for long periods of time.  This suspicion has been strongly confirmed by the results of the Mars Exploration Rover spacecraft,  as we will be discussing in the next couple of lectures. 

http://www.msss.com/mars_images/moc/science_paper/f2/index.html

 

8. The Surface of Mars: The Viking landers, Mars Pathfinder,  and Mars Exploration Rovers returned abundant pictures from the surface of Mars.  These pictures show an eerily Earth-like scene.  Pathfinder was deliberately chosen to land in an ancient water channel, and the rocks appeared to have been deposited in an ancient flash-flood.  Spirit and Opportunity landed in very carefully chosen locations.  We will discuss the significance of those locations later.

http://antwrp.gsfc.nasa.gov/apod/ap040114.html

 

 

         Next time I will discuss how all of this fits into our view of the geological history of Mars.