Characteristics and Origins of the Solar System
Lecture 15
October 3, 2000
Today’s class will deal with the discoveries we have made with unmanned spacecraft over the past 30 years. These findings are fascinating feats of discovery in their own right, but they also provide the empirical groundwork and basis we need for obtaining insight into the geological history of Mars, and deal with the intriguing question of life (ancient or modern) on Mars.
Let’s begin with a look at Mars and how it stacks up relative to the Earth
http://mars.jpl.nasa.gov/science/index.html
A good collection of Mars images is contained at
http://mars.jpl.nasa.gov/gallery/images.html
After looking at these images, go outside tonight and look at Mars, 0.87 au distant, due south in the early evening.
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. There are also ambitious plans for the future, but I will wait to describe those at the end, when we can understand why they would be so scientifically desirable.
As a result of these missions, we found an amazing variety of landforms and surface
Geology were discovered.
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.
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 9.12 and 9.15 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 9.24, 9.25, and 9.26. 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. The book states fairly categorically that the runoff channels were a result of rainfall in an ancient Martian climate. However, I have read and heard objections to this interpretation, so I believe this question is more controversial than is presented in the book. An exciting new development this summer was evidence that water has very recently flowed on the surface 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.
http://www.msss.com/mars_images/moc/science_paper/f2/index.html
8. The Surface of Mars: The Viking landers and Mars Pathfinder 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.
http://antwrp.gsfc.nasa.gov/apod/ap000514.html
Next time I will discuss how all of this fits into our view of the geological history of Mars.