Characteristics and Origins of the Solar System

Lecture 12

February 27, 2004

What the Martian Surface Tells Us About Martian History

 

 

Announcements:

  1. Read the rest of the Chapter on Mars to be ready for the exam on Monday
  2. Watch the Moon this weekend as it moves through the constellations of Taurus and Gemini

 

  1. Last time we discussed the evidence for water on the surface of Mars in the past.  The extreme suggestion of this is that the flat, northern plain is an ancient ocean bed.  This evidence for this shows up clearly on the image under “North-South Asymmetry” in the last lecture.  This suggestion,  that we are looking at an ancient ocean floor, is still very controversial. 
  2. All of this information presents a confusing story from the surface of Mars;  the current low atmospheric pressure and cold temperature preclude the existence of liquid water, yet evidence for water flows (some big).  In addition, there is evidence of possible bodies of water in the past and their sedimentary rocks (Hebes Chasma) and good evidence for underground reservoirs in the form of ice.  So what’s the answer?  Destination Check:  the point of all this is to ascertain Mars as a possible abode for life,  either now or in the remote past. 
  3. The scientific discussion of hydrology on Mars, & associated possibility of life,  concentrates on Mars in the remote past.  Mars, like the Earth, has been here for 4.5 Gyr  (billion years).  Although presently inhospitable, it may be that early in the history of the solar system it was more favorable to life.  In fact, the most intriguing features of the Martian surface, the valley networks, are found in some of the oldest terrain on Mars that was formed early in its history. 
  4. It is not presently known what the state of the Martian surface has been during the 4.5 Gyr history of the solar system.  The main goal of the NASA and European Space Agency Mars programs is to find out.  Scientists in this area divide into two camps.  There are those who believe in the warm,wet Mars scenario, in which early Mars had a dense atmosphere, a warm temperature, and active hydrology.  On the other side, are the spoil-sports who believe in the cold, dry Mars history,  in which Mars has always been more or less like we see it now,  and never had oceans, a hydrological cycle, warm temperatures, etc. 
  5. Let’s start with the “warm, wet Mars”  description, since it’s more fun to think about.  The best framework I have seen for discussing this is a figure from a 1989 article by Christopher McKay and Carol Stoker comparing the geological history of the Earth and Mars.  >>>>>>> transparency of history of two planets.
  6. (A) Start with the description of the history of Earth
  7. (B) Look at the corresponding history of Mars.
  8. This diagram provides the context for current Mars exploration.  Two thrusts  can be discerned.