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\hspace*{3.0in}Name:{\hrulefill} \\
\hspace*{3.25in}Date:{\hrulefill}

\begin{Large}
\section{\bf The History of Water on Mars}
\end{Large}

Scientists believe that for life to exist on a planet (or moon), there must
be liquid water available. Thus, one of the priorities for NASA has been
the search for water on other objects in our solar system. Currently,
these studies are focused on three objects: Mars, Europa (a moon of Jupiter),
and Enceladus (a moon of Saturn). It is believed that both Europa and 
Enceladus have liquid water below their surfaces. Unfortunately, it will
be very difficult to find out if their subsurface oceans harbor lifeforms,
as they are below very thick sheets of ice.
Mars is different. Mars was discovered to have polar ice caps more than
350 years ago. While much of the surface ice of these polar caps is ``dry 
ice'', frozen carbon dioxide, we believe there is a large quantity of frozen 
water in the polar regions of Mars.\\

Mars has many similarities to Earth. The rotation period of Mars is
24 hours and 37 minutes. Martian days are just a little longer than
Earth days. Mars also has seasons that are similar to those of the Earth. 
Currently, the spin axis of Mars is tilted by 25$^{\circ}$ to its orbital
plane (Earth's axis is tilted by 23.5$^{\circ}$). Thus, there are times during 
the Martian year when the Sun never rises in the northernmost and 
southernmost parts of the planet (winter above the ``arctic circles''). And 
times of the year in these same places where the Sun never sets (northern or 
southern summer). Mars is also very different from the Earth: its radius is 
about 50\% that of Earth, the average surface temperature is very cold, 
$-$63 $^{\circ}$C (= $-$81 $^{\circ}$F), and the atmospheric pressure at the 
surface is only 1\% that of the Earth. The low temperatures and pressures 
mean that it is hard for liquid water to currently exist on the surface of 
Mars. Was this always true?  We will find that out today.\\

In this lab you will be examining a notebook of images of Mars made by recent 
space probes and looking for signs of water. You will also be making 
measurements of some 
valleys and channels on Mars to enable you to distinguish the different 
surface features left by small, slow flowing streams and large, rapid 
outflows. You will calculate the volumes of water required to carve these 
features, and consider how this volume compares with other bodies of water.  
\\
\begin{figure}[htb]
\centerline{{\includegraphics[width=5cm]{yemendrainage.jpg}}{\includegraphics[width=8cm]{antamosing.jpg}}}
\caption{A dendritic drainage pattern in Yemen (left), and an anastomosing 
drainage in Alaska (right).}
\label{drainage}
\end{figure} 

\subsection{Water Flow Features on Mars}

The first evidence that there was once water on Mars was revealed by
the NASA spacecraft Mariner 9. Mariner 9 reached Mars in 1971, and after
waiting-out a global dust storm that obscured the surface of Mars, started 
sending back images in December of that year. Since that time a flotilla of 
spacecraft have been investigating Mars, supplying insight into the
history of water there.\\

\subsubsection{Warrego Valles}

The first place we are going to visit is called ``Warrego Valles'', where
the ``Valles'' part of its name indicates valleys (or canyons). The
singular of Valles is Vallis. The location of Warrego is indicated by the 
red dot on the map of Mars that is the first image (``Image \#1'') in the 
three ring binder.\\

{\it The following set of questions refer to the images of Warrego Valles. 
Image \#2 is a wide view of the region, while Image \#3 is a close-up.}

\begin{enumerate}

\item  By looking at the morphology, or shape, of the valley,
geologists can tell how the valley was formed. Does this valley
system have a dendritic pattern (like the veins in a leaf) or an 
anastomosing pattern (like an intertwined rope)? See Figure \ref{drainage}.
({\bf 1 point}) \\
\vspace{1in}

\item Overlay a transparency film onto the {\it \bf close-up} image. Trace 
the valley pattern onto the transparency. How does a valley like this form? 
Do you think it formed slowly over time, or quickly from a localized water 
source?  Why? ({\bf 3 points})
\vspace{2in}

\item  Now, on the wide-field view, trace the boundary between the uplands 
and plains on your close-up overlay (the transparency sheet) and label the 
Uplands and the Plains. Is Warrego located in the uplands or on the plains?  
({\bf 2 points}) 
\vspace{1.0in}

\item Which terrain is older?  Recall that we can use crater counting to help 
determine the age of a surface, so let's do some crater counting. {\it Overlay 
the transparency sheet on the wide-view image.}  Pick out 
two square regions on the wide view image (\#2), each 5~cm $\times$ 5~cm.
One region should cover the smooth plains (``Icaria Planum'') and the other 
should cover the upland
region.  Draw these two squares on the transparency sheet. Count all the 
impact craters greater than 1 millimeter in diameter within each of the two 
squares you have outlined.  Write these numbers below, with identifications.  
Which region is older?  What does this exercise tell you about when
approximately (or relatively) Warrego formed?  ({\bf 5 points})
\vspace{2in}

\item  To figure out how much water was required to form this valley, we first 
need to estimate its volume.  The volume of a rectangular solid (like a 
shoebox) is equal to $\ell \times w \times h$, where $\ell$ is the length of 
the box, $h$ is the height of the box, and $w$ is the width.  We will 
approximate the shape of the valley as one long shoebox and focus only on the 
main valley system.  {\it Use the close-up image for this purpose.}

First, we need to add up the total length of all the branches of the valley.  
Note that in the close-up image there are two well-defined valley systems.
A more compact one near the right edge, and the bigger one to the left of that.
Let's concentrate on the bigger one that is closer to the middle of the image.
Measure the length, in millimeters, of each branch and the main trunk.  Be 
careful not to count the same length twice.  Sometimes it is hard to tell 
where each branch ends.  You need to use your own judgment and be consistent 
in the way you measure each branch.  Now add up all your measurements and 
convert the sum to kilometers.  In this image 1~mm = 0.5~km. What is the 
total length $\ell$ of the valley system in kilometers?  \underline{ 
Show your work.}  ({\bf 3 points})\\

~\\
\vspace{1.0in}

\item Second, we need to find the average width of the valley.  Carefully 
measure
the width of the valley (in millimeters) in several places.  What is the 
average width?  Convert this to kilometers.  \underline{Show your 
work.} ({\bf 2 points})
\vspace{1.5in}

\item Finally, we need to know the depth.  It is hard to measure depths from
photographs, so we will make an estimate.  From other evidence that we will not
discuss here, the depth of typical Martian valleys is about 200 meters.  
Convert this to kilometers.  ({\bf 1 point})
\vspace{0.5in}

\item Now find the total valley volume in $\rm km^3$, using the relation 
$V = \ell \times w \times h$. This is the amount of sediment and rocks that 
was removed by water erosion to form this valley.  We do not know for sure how 
much water was required to remove each cubic kilometer, but we can guess.  
Let's assume that $100\,\rm km^3$ of water was required to erode $1\,\rm km^3$ 
of Mars.  How much water was required to form Warrego Valles? 
\underline{Show your work.} ({\bf 5 points})
\vspace{2in}
\end{enumerate}

Image \#4 is a recent image of one small ``tributary'' of the large valley
network you have just measured (it is the leftmost branch that drains into
the big valley system you explored). In this image the scientists have made
identifications of a number of features that are much too small to see in 
image \#3. Note that these researchers traced the valley network for this
tributary and note where dust has filled-in some of the valley, or
where ``faults'', cracks in the crust of the planet (orange line segments), 
have occurred. In addition, in the drawing on the right the dashed circles 
locate very old craters that have been eroded away. Using all of this 
information, you can begin to make good estimates of the age, and the 
sequences of events. Near the bottom they note a ``crater with lobate ejecta 
that postdates valleys.'' This crater, which is about 2 km in diameter, 
was created by a meteorite impact that occurred after the valley formed. 
{\it By doing this all along all of the tributaries of the Warrego Valles} 
the age of this feature can be estimated. Ansan \& Mangold (2005) 
conclude that the Warrego valley network began forming 3.5 billion years ago, 
from a period of rain and snow that may have lasted for 500 million years.\\

{\bf Clean-off transparency for the next section!}\\

\subsubsection{Ares and Tiu Valles}

We now move to a morphologically different site, the Ares and Tiu Valles.
These valleys are found near the equator of Mars, in the ``Margaritifer
Terra''. This region can be found in the upper right quadrant of image \#5 and 
is outlined in red. Note that the famous ``Valles Marineris'', the ``grand 
canyon'' of Mars (which dwarfs our Grand Canyon), is connected to the 
Margaritifer Terra by a broad, complicated canyon. In the close up, image \#6, 
the two valles are identified (ignore the numbered white boxes, as they are 
part of a scientific study of this region). In this false-color image,
elevation is indicated where the highest features are in white and brown, and 
the lowest features are pale green.\\

{\it 
The next set of questions refer to Ares and Tiu Valles. On the wide scale 
image, the spot where the {\rm Mars Pathfinder} spacecraft landed is indicated.
Can you guess why that particular spot was chosen? }\\

\begin{enumerate}
\setcounter{enumi}{8}
\item  First, which way did the water flow that carved the Ares and Tiu
Valles? Did water flow south-to-north, or north-to-south? How did you
decide this? [Note that the latitude is indicated on the right hand side of 
image \#6.]  ({\bf 2 points})
\vspace{1in}

\item In our first close-up image (\#7), there are two ``teardrop islands''. 
These two features can be found close to the ``l'' in the Pathfinder landing 
site
label in image \#6. There are other features with the same shape elsewhere 
in the channel. In image \#8, we provide a wide field view of the ``flood 
plains'' of Tiu and Ares centered on the two teardrop islands of image \#7. 
{\it Lay the transparency on this image and make a sketch of the pattern of 
these channels.} {\bf Now add arrows to show the path and direction the 
flowing water took.} Look at the pattern of these channels. Are they dendritic 
or anastomosing? ({\bf 3 points})
\vspace{1in}

~\\

\item  Now we want to get an idea of the volume of water required to form Ares 
Valles. Measure the length of the channel from the top end of the biggest
``island'' above the Pathfinder landing site (note there are two islands here, 
a smaller one with a deep crater, and a bigger one with a shallow crater. We 
want you to measure the channel that goes by this smaller island on the right 
side and to the left of the big island, and the channel that goes around the 
bigger island on the right to where they both join-up again at 
the top of this big island) to the bottom right corner of the image. In this 
image, 1~mm = 10~km. What is the total length of these channels?  
\underline{Show your work} ({\bf 3 points})
\vspace{1.75in}

\item Measure the channel width in several places and find the average width.
On average, how wide is the channel in km? \underline{Show your work} ({\bf 2 
points})
\vspace{1.0in}

\item The average depth is about 200 m. How much is that in km? ({\bf 1 point})
\vspace{0.5in}

\item Now multiply your answers (in units of km) to {\bf find the volume of 
the channel in km$^3$.} Use the same ratio of water volume to
channel volume that we used in Question 3 to find the volume
of water required to form the channel. Lake Michigan holds 5,000 km$^{\rm 3}$
of water, how does it compare to what you just calculated? 
Show your work. ({\bf 4 points})\\

~ \\
\vspace{1.3in}

\item Obviously, the Ares and Tiu Valles formed in a different fashion than
Warrego. We now want to examine the feature named ``Hydaspis Chaos'' in
image \#6. This feature ``drains into'' the Tiu Vallis. In image \#9, we 
present a wide view image of this feature. In image \#10, we show a close up 
of a small part of Hydaspis. Why do you think such features were given
the name ``Chaos'' regions? ({\bf 2 points})
\vspace{1.5in}

\item Scientists believe that Chaos regions are formed by the sudden
release of large amounts of groundwater (or, perhaps, the sudden melting
of ice underneath the surface), causing massive, and rapid flooding. Does such
an idea make sense to you? Why? What evidence for this hypothesis is present 
in these images to support this idea? ({\bf 4 points})
\vspace{1.8in}

~\\

\item In image \#11 is a picture taken at the time of the disembarkation 
of the little Pathfinder rover (named ``Sojourner'') as it drove down the ramp 
from its lander. Is the surrounding terrain consistent with its location in 
the flood plain of Ares Vallis? Why/why not? ({\bf 3 points})
\vspace{1.8in}

\item Recent research into the age of the Ares and Tiu Valles suggest that,
while they began to form around 3.6 billion years ago (like Warrego), water
still flowed in these channels as recently as 2.5 billion years ago. Thus,
the flood plains of Ares and Tiu are much younger than Warrego. Do you
agree with this assessment? How did you arrive at this conclusion?
 ({\bf 4 points})
\vspace{2.3in}

\item  You have now studied Warrego and Ares Valles up close.  {\bf Compare
and contrast the two different varieties of fluvial (water-carved) landforms 
in as many ways as you can think of (at least three!).} Do you think they 
formed the same way?  How does the volume of water required to form Ares 
Valles compare to the volume of water required to form Warrego Valles?  
({\bf 5 points})
\end{enumerate}
~\\

\vspace{2.5in}
\subsection{The Global Perspective}

In image \#12 is a topographic map of Mars that is color-coded to show
the altitude of the surface features where blue is low, and white is
very high. Note that the northern half of Mars is lower than the southern
half, and the North pole is several km lower than the South pole. The
Ares and Tiu Valles eventually drain into the region labeled ``Chryse
Planitia'' (longitude 330$^{\circ}$, latitude 25$^{\circ}$). 

\begin{enumerate}
\setcounter{enumi}{19}
\item If there was an abundance of water on Mars, what would the planet
look like? How might we prove if this was feasible? For example, scientists
estimate the age of the northern plains as being formed between 3.6 and 
2.5 billion years ago. How does this number compare with the ages of the
Ares and Tiu Valles? Could they be one source of water for this ocean? 
({\bf 5 points})
\vspace{2.5 in}
\end{enumerate}
One way to test the hypothesis that the northern region of Mars
was once covered by an ocean is to look for similarities to Earth. Over the
history of Earth, oceans have covered large parts of the current land
masses/continents (as one once covered much of New Mexico). Thus, there
could be ancient shoreline features from past Earth oceans that we can compare 
to the proposed ``shoreline'' areas of Mars. In image \#13 is a comparison of
the Ebro river basin (in Spain) to various regions found on Mars that
border the northern plains. The Ebro river basin shown in the upper left
panel was once below sea level, and a river drained into an ancient
ocean. The sediment laid down by the river eventually became sedimentary
rock, and once the area was uplifted, the softer material eroded away,
leaving ridges of rock that trace the ancient river bed. The other three 
panels show similar features on Mars.\\

If the northern part of Mars was covered by an ocean, where did the water
go? It might have evaporated away into space, or it could still be present
frozen below the surface. In 2006, NASA sent a spacecraft named Phoenix
that landed above the ``arctic circle'' of Mars (at a latitude of 68$^{\circ}$
North). This lander had a shovel to dig below the surface as well as
a laboratory to analyze the material that the shovel dug up. Image \#14
shows a trench that Phoenix dug, showing sub-surface ice and how chunks of 
ice (in the trench shadow) evaporated (technically ``sublimated'', ice
changing directly into gas) over time.  The slow sublimation
meant this was water ice, not carbon dioxide ice. This was confirmed
when water was detected in the samples delivered to the onboard laboratory.\\

\begin{enumerate}
\setcounter{enumi}{20}
\item Given all of this evidence presented in the lab today, Mars certainly
once had abundant surface water. We still do not know how much there
was, how long it was present on the surface, or where it all went. But 
explain why discovery of large amounts of subsurface water ice might be 
important for astronauts that could one day visit Mars ({\bf 5 points})
\vspace{3 in}
\end{enumerate}
\newpage
\hspace*{3.0in}Name:{\hrulefill} \\
\hspace*{3.25in}Date:{\hrulefill}\\

\subsection{Take Home Exercise (35 points total)}

Answer the following questions on a separate sheet of paper, and turn it in 
with the rest of your lab.\\

\begin{enumerate}
\item  What happened to all of the water that carved these valley systems?  We 
do not see any water on the surface of Mars when we look at present-day images 
of the planet, but if our interpretation of these features is correct, and 
your calculated water volumes are correct (which they probably are), then 
where has all of the water gone?  Discuss two possible (probable?) fates that 
the water might have experienced.  Think about discussions we have had in 
class about the atmospheres of the various planets and what their fates have 
been.  Also think about how Earth compares to Mars and how the water 
abundances on the two planets now differ. ({\bf 20 points})\\

\item Scientists believe that life (the first, primitive, single cell 
creatures) on Earth 
began about 1 billion years after its formation, or 3.5 billion years ago. 
Scientists also believe that liquid water is essential for life to exist. 
Looking at the ages and lifetimes of the Warrego, Ares and Tiu Valles, what 
do you think about the possibility that life started on the planet Mars at the 
same time as Earth? What must have Mars been like at that time? What would 
have happened to this life? ({\bf 15 points})
\end{enumerate}

\subsection{Possible Quiz Questions}
\begin{enumerate}

\item Is water an important erosion process on Mars?

\item What does ``dendritic'' mean?

\item What does ``anastomosing'' mean?

\end{enumerate}
\clearpage

\subsection{Extra Credit (ask your TA for permission before attempting, 5 points)}

In this lab you have found that dendritic and anastomosing ``river''
patterns are found on Mars, suggesting there was free flowing water at some
time in Mars' history. Use web-based resources to investigate our current
ideas about the history of water on Mars. Then find images of both 
dendritic and anastomosing features on the Earth (include them in your
report). Describe where on our planet those particular patterns were found, 
and what type of climate exists in that part of the world. What does this 
suggest about the formation of similar features on Mars?
\newpage
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