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<td>
<img width=800
src="http://pages.uoregon.edu/~imamura/121/images/ss.jpg">
</td>
<td>
<h2><center>
Topic 4:<br><p> The Solar System
</center>
<br>
<p>
Reading:<br>
<ul>
Formation of The Solar System, Chapter 6 <br>
</ul>
</h2>
</td>
</tr>
</table>
</center>
<h3><p>
For the rest of the quarter we will concentrate on trying to understand
how the Solar System formed, how it has evolved since its formation, and
its (our)place in the Universe. In this context, at some
point, we will address the questions of whether the Solar System
and life is unique
or whether there are other examples of these things in the
Universe.
<p><hr><p><center><table cell border=10 cellpadding=10 bgcolor=green><tr>
<td><img src="http://pages.uoregon.edu/~imamura/121/images/milky-way-sun.jpg"></td>
<td><h3><font color=yellow>
The Solar System is located in the grouping of stars (galaxy) known as
the Milky Way galaxy.
The Milky Way is a
just one of many billions of
galaxies in the Universe. The Milky Way galaxy is a <i> spiral
(barred spiral?) galaxy</i> which contains roughly 200 billion stars
(e.g., see
<a href="
http://pages.uoregon.edu/~imamura/121/images/m51_chanrda.jpg">here</a>
for the external spiral galaxy M51 and an edge-on view of the
<a href="http://apod.nasa.gov/apod/ap000228.html">Sombrero galaxy</a>, M104).
The visible material of the Milky Way is
contained in a thin, rotating disk
(<a href="http://antwrp.gsfc.nasa.gov/apod/ap990224.html">
optical image</a> and
<a href="
http://pages.uoregon.edu/~imamura/121/images/mway_ir.jpg">
infrared image</a>).
The diameter of the disk is on
the order 100,000 - 300,000 light years (1 light year = 6 trillion
miles = 9.3 trillion kilometers)
and has a thickness of several thousands of light years.
</td>
<td>
<a href="http://pages.uoregon.edu/~imamura/121/images/hst_deep_field.jpg">
<img width=300
src="http://pages.uoregon.edu/~imamura/121/images/hst_deep_field.jpg"></a>
</td>
</tr></table></center>
<P>
The appearance of the Milky Way is striking. In the
center of the disk there is a <b> bulge</b> out of which extends
several <b> spiral arms</b>. The Solar System is located in one of the
arms, roughly one-half of the way from the center of the disk.
The Solar System orbits the center of our Galaxy with a speed of roughly
220 kilometers per second or 800,000 kilometers per hour!
<P>
<b> Comment</b> -- The Milky Way galaxy has another component (in addition
to the visible disk). There is a large spherical component to the
Milky Way which is made up of nonluminous material (<i> Dark Matter</i>).
The Milky Way is dominated by this <i> Dark Matter</i> component. Perhaps
90 % of the Milky Way is nonluminous. This is also true for the
Universe where as much as 95-96 % of the Universe may be nonluminous!!
<P>
The average mass of a star in the Milky Way galaxy is 30 % that of the Sun.
The Sun is thus
slightly larger than average, but not
really that far out of line. The Sun is just 1 out of the two-hundred
billion stars which make up the Galaxy. Given
this, it is not unreasonable to suspect that the Solar System is
not unique. We return to this issue a little later.
<P><hr><hr><p>
<center><h2>GENERAL FEATURES OF THE SOLAR SYSTEM</h2></center><p>
The Solar System displays a
seemingly incomprehensible amount of diversity.
However, on closer inspection,
we see many regularities and patterns in the Solar
System. <center><p><table><tr>
<td><center>
<a target="_blank" href="https://www.youtube.com/watch?v=zR3Igc3Rhfg">
<img src="solar-system-lrg.png"></a><p>
Terrestrial, Jovian, and
<a href="http://pages.uoregon.edu/~imamura/121/lecture-4/dwarf_planets.html">
Dwarf planets</a> (and other objects in the asteroid and Kuiper belts).
Click on the above picture to see a nice video on the scale of the Solar
System: Youtube.<p>
<img width=505 src="Dwarf-Planets-1.jpg"> <img src="kbos.jpg"><p>
Dwarf Planets and Some Kuiper Belt Objects. An interesting object is Sedna.</center></td>
</tr></table><p><img src="Sedna_orbit.jpeg"><p><h4> Sedna is a likely
member of the Oort Cloud, the hypothesized reservoir for
the comets of our Solar System. Sedna's
furthest distance from the Sun (aphelion) is estimated as 937 AU
with its closest (perihelion) only 76 AU.
Here, AU is astronomical unit, the average distance of the Earth from the Sun.
Sedna has an orbital period of around 11,000 years (apply Kepler's 3rd Law
of planetary motion). Interestingly, the Voyager 2 spacecraft found
what we consider the edge of our Solar System (the heliopause)
at 121 AU (Nov 2018); Sedna ventures into interstellar space
at the furthest points in its orbit.
</h4></center>
<p><hr><p>
<center>
<table cell border=10 cellpadding=20 bgcolor=magenta>
<tr>
<td>
<img width=300 src="http://pages.uoregon.edu/~imamura/121/images/mercury2.jpg"></td>
<td>
<img width=350 src="http://pages.uoregon.edu/~imamura/121/images/venus_pvo2.jpg"></td>
<td>
<img width=350 src="http://pages.uoregon.edu/~imamura/121/images/earth2.jpg"></td>
</tr><tr>
<td>
<img width=300 src="http://pages.uoregon.edu/~imamura/121/images/jupiter2.jpg"></td>
<td>
<img width=350 src="http://pages.uoregon.edu/~imamura/121/images/Saturn2.jpg"></td>
<td>
<img width=350 src="http://pages.uoregon.edu/~imamura/121/images/Neptune,_Earth_size_comparison.jpg"></td>
</tr></table></center>
<p><hr><hr><p>
<center>
DYNAMICAL REGULARITIES
<p>
</center>
I have already mentioned
the
dynamical regularities
of the Solar System.
<p>
<center>
<img src="http://pages.uoregon.edu/~imamura/121/images/FG06_005.jpg">
</center>
<p>
<font color=red>
The principal ones are:
<P>
<UL>
<LI> All planetary orbits are roughly in the same plane -- low inclinations
<LI> All planetary orbits are roughly circular -- small eccentricities
<LI> All planetary orbits are in the same sense -- CCW as viewed from the North
</UL>
</font>
<p>
Secondary regularities are:
<p>
<UL>
<LI> Most planets rotate in the same sense as they orbit
<LI> The rotation axes of most planets are roughly
perpendicular to the ecliptic
</UL>
<P>
There are also some vexing properties which need to be explained, e.g.,
<p>
<UL>
<LI> The Sun contains over 99 % of the mass of the Solar System, but contains
less than
1 % of the angular momentum (why does the Sun rotate so slowly?)
<li> The Earth-Moon system
<li> The senses of rotation of Uranus, Pluto, and Venus
</UL>
<P><hr><p>
<center>
DYNAMICAL REGULARITIES
<P>
<table width=1000 border=8 cellpadding=6 bgcolor=magenta>
<tr><td><h2><h2>Planet</td><td><h2>a(A.U.)</td><td><h2>P<sub>orb</sub>(y)</td>
<td><h2><center>ε</td><td><h2>i(<sup>o</sup>)</td>
<td><h2>P<sub>rot</sub>(d)</td>
<td><h2>Obliquity(<sup>o</sup>)</td></tr>
<tr>
<td><h2>Mercury</td><td><h2>0.39</td><td><h2>0.24</td><td><h2>0.206</td><td><h2>7</td><td><h2>58.65d</td><td><h2>2</td>
</tr>
<tr>
<td><h2>Venus</td><td><h2>0.72</td><td><h2>0.62</td><td><h2>0.007</td><td><h2>3.4</td><td><h2>243.01d</td><td><h2>177.3</td>
</tr>
<tr>
<td><h2>Earth</td><td><h2>1</td><td><h2>1</td><td><h2>0.017</td><td><h2>0</td><td><h2>23h56m4.091s</td><td><h2>23.5</td>
</tr>
<tr>
<td><h2>Mars</td><td><h2>1.52</td><td><h2>1.88</td><td><h2>0.093</td><td><h2>1.8</td><td><h2>24h37m22s</td><td><h2>25.2</td>
</tr>
<tr>
<td><h2>Jupiter</td><td><h2>5.2</td><td><h2>11.9</td><td><h2>0.048</td><td><h2>1.3</td><td><h2>9h50m28s-
9h55m30s</td><td><h2>3.1</td></tr>
<td><h2>Saturn</td><td><h2>9.54</td><td><h2>29.5</td><td><h2>0.056</td><td><h2>2.5</td><td><h2>10h13m59s-10h38m25s</td><td><h2>26.7</td></tr>
<tr>
<td><h2>Uranus</td><td><h2>19.2</td><td><h2>84</td><td><h2>0.046</td><td><h2>0.8</td><td><h2>17.24h</td>
<td><h2>97.9</td>
</tr>
<tr>
<td><h2>Neptune</td><td><h2>30.1</td><td><h2>164.8</td><td><h2>0.010</td><td><h2>1.8</td><td><h2>16.11h</td>
<td><h2>29.6</td>
</tr>
<tr>
<td><h2>Pluto</td><td><h2>39.53</td><td><h2>248.5</td><td><h2>0.248</td><td><h2>17.1</td><td><h2>6.387d</td>
<td><h2>122</td>
</tr>
</table>
</center>
<center>
<font color=red><h2>
Any successful theory for the origin of the Solar System must
explain the principal facts listed above.</font></h2>
</center>
<P><hr><hr><p>
<center>
TYPES OF AND PROPERTIES OF THE TYPES OF THE PLANETS
</center>
<p>
The planets show <i> regularities</i> in that they
can be divided into distinct classes:<p>
<center><table cell border=10 cellpadding=10 bgcolor=green>
<tr><td>
<a href=
"http://pages.uoregon.edu/~imamura/121/images/terrestrials.gif">
<img width=400 src=
"http://pages.uoregon.edu/~imamura/121/images/terrestrials.gif"></td>
<td><center><h2><font color=yellow>Terrestrial Planets:</center><p>
The four planets closest to the Sun, Mercury, Venus, Earth, and Mars,
are considered Earth-like in nature, solid with higher densities than the
Jovian planets, smaller sizes, and smaller masses than the Jovian planets.
The Terrestrials have similar interior chemical make-ups; their masses are
dominated by silicates,
iron, nickel, and other heavier elements. The Terrestrial planets
are solid with atmospheres, excluding Mercury which, at best, has a
transient atmosphere.
</td></tr>
<tr><td>
<a href=
"http://pages.uoregon.edu/~imamura/121/images/jovian_worlds.gif">
<img width=400 src=
"http://pages.uoregon.edu/~imamura/121/images/jovian_worlds.gif"></a></td>
<td><center><h2><font color=yellow>Jovian Planets:</center><p>
The next four planets moving
away from the Sun, Jupiter, Saturn, Uranus, and Neptune,
are considered Jupiter-like
in nature, gaseous with larger sizes and larger masses than the Terrestrial
planets. The Jovians have fairly similar chemical compositions, compositions
more similar to the Sun (roughly 85-90 % hydrogen and 10-15 % helium)
than to the Terrestrial planets. The Jovian planets are
not solid, all with extensive atmospheres.</td></tr>
<tr><td><center><img width=200 src=
"http://pages.uoregon.edu/~imamura/121/images/pluto4.gif">
<img width=200 src=
"http://pages.uoregon.edu/~imamura/121/images/triton.gif"></center></td><td>
<center><h2><font color=yellow>Rocky/Icy Objects:</center><p>
Pluto and the other dwarf planets,
Triton and some of the
other large moons of the Jovian planets, and objects in the Kuiper and
asteroid (some, {\it e.g.}, Ceres) belts.
These objects combinations of rocky
material (silicates).
They are solid with densities in-between those
of the Terrestrial and Jovian planets. They are smaller in size and mass
than the Terrestrials.
</td></tr></table></center>
<p><hr><p>
In tabular form, we have for the general properties
of the planets:
<p>
<center>
Planetary Properties. I
<P>
<IMG ALIGN=BOTTOM ALT="" SRC="table2.gif">
<P>
<table width=1000 border=8 cellpadding=6 bgcolor=magenta>
<tr><td><h2><h2>Class</td><td><h2>Planet</rd>
<td><h2>a(A.U.)</td><td><h2>M(M<sub>E</sub>)</td>
<td><h2><center>R(R<sub>E</sub>)</td><td><h2>ρ(g-cm<sup>-3</sup>)</td></tr>
<tr><td><bgcolor=re><h2>Terrestrials</td></tr>
<tr>
<td><h2></td><td><h2>Mercury</td><td><h2>0.39</td>
<td><h2>0.055</td><td><h2>0.382</td><td><h2>5.4</td>
</tr>
<tr>
<td><h2></td><td><h2>Venus</td><td><h2>0.72</td><td><h2>0.815</td>
<td><h2>0.949</td><td><h2>5.2</td>
</tr>
<tr>
<td><h2></td><td><h2>Earth</td><td><h2>1</td><td><h2>1</td><td><h2>1</td>
<td><h2>5.5</td>
</tr>
<tr>
<td><h2></td><td><h2>Mars</td><td><h2>1.52</td><td><h2>0.107</td><td><h2>0.532</td><td><h2>3.9</td>
</tr>
<tr><td><h2>Jovians</td></tr>
<tr>
<td><h2></td><td><h2>Jupiter</td><td><h2>5.2</td><td><h2>318</td><td><h2>10.4-11.2</td><td><h2>1.3</td></tr>
<td><h2></td><td><h2>Saturn</td><td><h2>9.54</td><td><h2>95.2</td><td><h2>9.45</td><td><h2>0.7</td></tr>
<tr>
<td><h2></td><td><h2>Uranus</td><td><h2>19.2</td><td><h2>14.5</td><td><h2>4.01</td><td><h2>1.3</td>
</tr>
<tr>
<td><h2></td><td><h2>Neptune</td><td><h2>30.1</td><td><h2>17.2</td><td><h2>3.88</td><td><h2>1.7</td>
</tr>
<tr><td><h2>Rock/Ice</td></tr>
<tr>
<td><h2></td><td><h2>Pluto</td><td><h2>39.5</td><td><h2>0.0025</td><td><h2>0.18</td><td><h2>2.03</td>
</tr>
<td><h2></td><td><h2>Triton</td><td><h2>30.06</td><td><h2>0.04</td><td><h2>0.21</td><td><h2>2.07</td>
</tr>
</table>
</center>
<P>
</center>
For the scale of things:
<P>
<ul>
<li>Mass of the Earth = 6.0x10<sup>24</sup> kilograms
<li>Mass of the Sun = 2.0x10<sup>30</sup> kilograms = 330,000 Earths
<li>Diameter of the Sun = 1,400,000 kilometers = 109 Earths
<P>
</ul>
By adding up the masses of the planets (and including the asteroids
which are less than 0.001 Earths, we see that the Sun is more than 99 % of the
mass of the Solar System.
<P>
<center>
Random Comments
<P>
</center>
<UL>
<LI> the Jovian planets have extensive satellite systems
<LI> the Jovian planets have ring systems
<li> the existence of the comets (Kuiper Belt, Oort Cloud)
<li> the existence of the asteroids (as an amusing note, consider the
<a href="http://pages.uoregon.edu/~imamura/121/lecture-3/titius.html">
Titius-Bode relation</a>).
<LI> ...
</UL>
<P>
The regularities in the properties of the planets are tied to how far they are
from the Sun.
<font color=magenta><i>The Terrestrial planets are closer to the Sun
than are the Jovian planets</i></font>.
In general, <font color=magenta><i>the Terrestrial planets are
also smaller in diameter, less massive,
and more dense than the Jovian planets.</i></font>
Let's look at the
<a href="http://pages.uoregon.edu/~imamura/121/lecture-4/density.html">
density</a> for a second (to see why this is an important observation).
<P>
<i><font color=green>
What do the observed properties of the planets imply about the chemical
compostions of the interiors of the planets and the atmospheres
of the planets?
</i></font>
<center>
<p>
Planetary Properties. II
<P>
<IMG ALIGN=BOTTOM ALT="" SRC="table3.gif">
<P>
</center>
<i>
There are clear distinctions between the <b> Terrestrials</b>, <b>
Jovians</b>,
and <b> Rocky/Icy Planets</b></i> in their:
<p>
<UL>
<LI> distances from the Sun
<LI> masses and radii
<LI> interior compositions (inferred from their densities)
</ul>
<p>
There are differences in the <a href="atm.html">atmospheric pressures</a>
and <a href="escape.html">escape velocities</a>
of the Terrestrial and Jovian planets. What do these properties tell us
about the planets?
</ul>
</UL>
<p>
<p>
<center>
<a href="http://pages.uoregon.edu/~imamura/121/lecture-3/lecture-3.html">
<img width=100
src="http://pages.uoregon.edu/~imamura/122/images/shinkansen-back.jpg"></a>
<a href="http://pages.uoregon.edu/~imamura/121/lecture-5/lecture-5.html">
<img width=100
src="http://pages.uoregon.edu/~imamura/122/images/shinkansen-forward.jpg"></a>
</center>