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
- 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.
- Alleged shorelines on an ancient ocean
style="mso-spacerun: yes">
- 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.
- 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.
- Clearly
water flowed in large volumes.
Where did it come from (particularly if rainfall is ruled out, and
where did it go?
- What
formed the valley networks?
- How
could outflows have occurred as late 1 to 2 billion years ago, as they
seem to have done?
- 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