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\rhead{Earth, Moon, and Planets Lab (Wed 6-9pm)}
\chead{}
\lhead{Lab 1: Solar System Taxonomy}
\renewcommand{\rightmark}{}
\lfoot{Roban Hultman Kramer} \cfoot{\thepage} \rfoot{Fall 2006}

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\begin{document}
\begin{center}
\huge Solar System Taxonomy
\end{center}

\section*{Introduction}

There's recently been quite a bit of publicity about the definition of
a planet, and in particular, how to categorize Pluto and its companion
Charon. In this lab you will come up with your own categories for
solar system objects, and in the process learn a little about what
kinds of objects are out there.

Remember to record what you do in your lab notebooks. To remind you,
I've put things that are particularly important to write down in
\textbf{bold}.

\section{Creating a classification scheme}

\subsection*{Materials} table of solar system object properties, graph paper

\subsection*{Instructions}

The debate about revising the definition of a planet has actually
gotten quite heated at times. To aid your detachment from the
emotional side of the argument, you've been given a table of solar
system objects without their names. You will find, however, some
properties that might be relevant in classifying them.

Work with your group to come up with your own classification scheme
for the objects listed in the table. The steps listed below will walk
you through some things that might help you develop your scheme.

You will make several graphs in this exercise. Don't think about
drawing a straight line though the points, but look, rather, for
natural groups of objects.

\subsubsection*{Composition and distance from the sun}

The ``Composition'' column indicates in which form most of the mass in
the body is found. \textbf{Find the average distance from the Sun for
objects of each composition (i.e. ``rock'', ``ice'', etc.). Are there
any bodies who do not seem to fit in with the others of the same
composition? If so, list them, then recalculate the average distance
for that class again without this/these member(s). Does the
composition of an object seem to correlate with its distance from the
Sun?}

\subsubsection*{Orbital eccentricity}

Orbital eccentricity tells us how the orbit is shaped. Very eccentric
orbits ($e \approx 1$) are much longer in one direction than they are
in the other. Orbits that are almost circular have low eccentricities
($e \approx 0$). Identify the bodies that have the most eccentric
orbits --- you can set your own ``cutoff'' value. Look at the other
properties of the eccentric bodies. Is there anything they have in
common?

\subsubsection*{Mass and distance from the sun}

\textbf{Make a scatter plot of object mass $m$ versus distance from the
Sun $r$}. The x-axis will be $\log_{10}(r)$ in units
of AU and the y-axis will be $\log_{10}(m)$ in units of
Earth masses ($M_E$). \textbf{Do massive bodies tend to be farther or
closer?  What about low-mass bodies? What exceptions are there to
this?}

\subsubsection*{Density versus distance from the sun}

\textbf{Make a scatter plot of object density versus orbital radius.}  The
x-axis will again be $\log_{10}(r)$ and the y-axis will be
density. \textbf{Does there seem to be any relationship between
density and distance from the Sun?}

\subsubsection*{Number of moons versus mass}

\textbf{Make a scatter plot of number of moons versus mass $m$ of the
object.} Let your x-axis be $\log_{10}(m)$ in units of Earth masses
($M_E$) and your y-axis will be the number of moons.  \textbf{How do
these two quantities tend to relate to each other?}

\subsubsection*{Orbital zone clearing}

The $\mu$ (Greek letter ``mu'') column tells us how much the body has
``cleared out'' its orbital zone --- that is, collected stuff along
its path around the Sun and accumulated it. More precisely, $\mu$ is
the ratio of the mass of the body to the total mass of all objects in
the orbital zone. Identify the objects with the lowest $\mu$ (define
your own reasonable cutoff value). Look at the other properties of
these low-$\mu$ objects. \textbf{Is there anything that these objects
share in common?}

\subsubsection*{Make your groups}

Now you should come up with your own classification scheme. You can
use or ignore any of the plots or numbers in the table. Ideally each
object would belong uniquely and unambiguously to one category. Of
course, this isn't always possible in the real world, and opinions can
differ (especially among experts) about what properties are most
important and should therefore form the basis of a classification
system. As long as you can explain your reasoning, I'll be happy with
anything you come up with.

\textbf{Record your scheme in your lab notebooks, along with what
objects fall into what categories, and a few sentences explaining the
reasoning behind your groupings. Are there bodies that don't seem to
fit into any of your groups?} \textbf{Which of these groups do you
think should be deemed ``planets'' (it can be more than one), and
why?}

\subsection*{Discussion}

Once everyone has completed their classification each group will
present their scheme to the class and we'll discuss any differences
among your systems and if there is even any point in having these
categories. Then I will reveal the identities of the mystery objects,
and we can see if that changes how you feel about your schemes.

\section{Evaluating other proposals}

\subsection*{Materials} Copies of the IAU draft and final versions of
the IAU resolutions on the definition of a planet.

\subsection*{Instructions}

The International Astronomical Union recently tackled the question of
how to define a ``planet''. Several proposals were put forward before
a definition was finally agreed upon. It should be noted that, while
Astronomers overwhelmingly defer to the IAU in the area of
nomenclature of solar system objects, there are still many in the
astronomical community who are unsatisfied by the final definition. I
have given you the first draft resolution proposed at this years IAU
meeting, and the resolutions that were finally adopted.

Read both resolutions and discuss them with your group. How do they
differ from your scheme? \textbf{Think of some advantages and
disadvantages of each resolution and record them in your lab
notebook.}

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