Characteristics and Origins of the Solar System

Lecture 18

October 18, 2000

Mars: Latest Developments and Conclusions

 

            Here are some additional points to be made about Mars. 

 

The Viking Lander Biological Experiments

 

            The Viking landers contained sophisticated, automated laboratories to search for the presence of primitive life.  Read in your textbook about the results.  Although these experiments were not totally unambiguous, the general consensus was the there was not life at the sites of the Viking landers.

 

The Mars Rock

 

            One of the many intriguing developments in planetary science in the last decade has been the realization that a small number of the many meteorites recovered actually come from Mars.

            >>>>>>>Question for the august assembly: how the heck could you know (or even suspect ) such a thing?

 

            There are 14 such meteorites “in captivity”.  There are also meteorites believed to have come from the asteroid Vesta. 

 

            In 1997, the scientific world was electrified by the announcements that one of these Martian meteorites (the so-called SNC meteorites, or Shergottites) with the snazzy name of ALH84001 showed evidence of possible ancient life.

>>>>>>> Picture of ALH84001

 

            This remarkable claim was based on the fact that ALH84001 showed evidence of being submerged in water for a long time.  Furthermore, inside were some odd mineralogical deposits which were consistent with biological activity of microbes.  Controversy about the chemistry that went on in ALH84001 has continued for the past three years, with one camp maintaining that the rock showed evidence of biochemistry, while the other camp claimed that unusual inorganic chemistry, particularly at elevated temperatures, could have done the trick as well. 

 

            Recent evidence has seemed to support the inorganic school, but the issue will not be settled definitively until we have had the chance to make sophisticated analyses of more Mars rocks. 

 

Other Recent Developments

  1. About a year ago, researchers using the laser altimeter data claimed that there seemed to be evidence for an ancient ocean in the northern hemisphere of Mars.  The evidence (other than the suggestive flatness of this plain, with no evidence of cratering) was primarily the remarkable fact that a number of outflow channels that “flow into” this sea were at the same level, as would be river deltas of oceans throughout the world. The people proposing this also thought they saw geological evidence of ancient shorelines. >>>>>>> Picture of Mola data and Mars. This claim is not universally accepted.  The identification of “ancient shorelines” in particular has been criticized. >>>>> Images of putative shorelines.
  2. Alleged shorelines on an ancient ocean style="mso-spacerun: yes"> 
  3. Recent outflows from craters.  This summer, evidence was presented for additional water flows from the walls of craters.  These are a new type of water channels that have only been seen with the Mars Global Surveyor data.  What makes these data particularly intriguing is the claim that there is no evidence for Aeolian processes being active in modifying or erasing these features.  This implies that the channels are sufficiently recent that the Aeolian processes (wind erosion) have not had time to erase them.  This indicates that these water channels are very recent geologically speaking, and that the water is still there, not far below the surface of the planet.  >>>>>>> Web site with crater flow channels.
  4. In the textbook, it is strongly suggested that the valley networks or runoff channels  were formed by ancient rainfall. Exempli causa, on p206, there is the statement  “They are called runoff channels because they look like what geologists would expect from troughs that carried the surface runoff of ancient rainstorms”.  In the last year, evidence has emerged that casts doubt on this.  In the August, 2000 issue of the journal  Icarus, there is an article entitled “Meter-Scale Characteristics of Martian Channels and Valleys”.  It utilizes Mars Global Surveyor data to examine a number of the valley network channels with unprecedented high resolution.  The main conclusion is that they do not see the spiderweb of small tributaries that one would expect if the runoff channels had been fed by rainfall.  The authors claims that they aren’t there in anything like sufficient numbers.  This paper contains a number of intriguing quotes that plug in directly to what we have been discussing in this course: “Argments for warmer climatic conditions in the (Martian) past have been based mainly on the valley networks”, “Direct evidence for surface runoff from precipitation is sparse”, “there is almost no fine-scale dissection of the Martian surface, as would be expected if surface runoff played a major role in valley formation”.

 

What the Heck is Going On?

 

            At the present time, there are a number of real oddities about the geological history of Mars.  We are far from having a good understanding of the climatic history of Mars, and how the liquid water plugged into that history.  Here are some of the issues.

  1. Clearly water flowed in large volumes.  Where did it come from (particularly if rainfall is ruled out, and where did it go?
  2. What formed the valley networks? 
  3. How could outflows have occurred as late 1 to 2 billion years ago, as they seem to have done?
  4. Was the climate of Mars ever really like that of Earth?
Finally, what does the future hold? There is an ambitious plan of research for Mars, to be carried out by the WORLD FAMOUS JET PROPULSION LABORATORY