(1) (a) Familiarize yourself with just how LARGE and MASSIVE the giant planets are by filling out the table below.

(b) HOW do we measure the density of planets? We measure the orbital period and orbital distance of a moon and then use Newton's version of Kepler's third law to get the mass of the planet. We then use the angular size and distance to the planet to obtain the planet's radius - hence volume. Finally, we divide the mass by the volume to get the planet's density.

(c) Why is hydrogen the main composition of the giant planets? This table of cosmic abundances will give you a clue. Yes, hydrogen is the most abundant element - the most abundant element of the solar nebula from which the giant planets were formed.

(2) (a) Taking an approximate value for the radii of Jupiter and Saturn (compared to the Earth) - to one significant figure - pick a single number that is a reasonable approximation for both planets (e.g. it could be 1, 5 10, 20 - we only need a rough estimate). Use this approximate radius to calculate an approximate value for the volume of Jupiter and Saturn compared to the volume of the Earth. Taking the radius of Jupiter and Saturn to be approximately 10 times that of the Earth, then their volume will be (10)³ = 1000 times the volume of the Earth. (Volume is proportional to (radius)³ )

(b) Do the same for Uranus and Neptune. Let's take Uranus and Neptune to be approximately 4 times the radius of the Earth. Their volume is approximately 4³= 64 times that of the Earth.

(3) What is (a) the temperature and (b) the pressure at the center of Jupiter? Write the pressure in millions of atmospheres. The temperature at the center of Jupiter is 20,000K. The pressure is 100,000,000 bars or 100 million times the atmospheric pressure of the Earth.

(4) (a) Look at the table of cosmic abundances and find the elements that are most abundant after hydrogen and helium - since we are looking for elements that will make compounds, ignore the "inert" elements. Oxygen is the next abundant after hydrogen and helium. Next is Carbon. We will ignore neon because it is an inert gas. The next element which can react with hydrogen is nitrogen.

(b) Next, write down the chemical formulae for the hydrogen compounds: water, ammonia and methane - that are believed to be important in the interiors of Uranus and Neptune. (Make a guess!) Water = H₂O. Ammonia = NH₄. Methane = CH₄

(5) The tail of the magnetosphere of Jupiter extends well beyond the orbit of Saturn. How many AU long is Jupiter's magnetosphere? Saturn's orbit is 9.53 AU, Jupiter's is at 5.20. So, the magnetosphere of Jupiter extends for 9.53-5.2 = 4.3 AU.

(6) WHY do the giant planets have thick atmospheres? Hint: Think about why the Moon and Mercury have such little atmosphere. The giant planets have thick atmospheres because they are massive and therefore have strong gravity which is able to hold in the light gases of hydrogen and helium.

(7) (a) What are the spin (rotation) periods of the giant planets? Jupiter? 0.41 day = 10 hours. Uranus?- 0.72 day = 17.3 hours. Saturn? 0.44 day = 10.6 hours. Neptune? 0.67 day = 16.1 hours.

(b) Use a ruler to measure the polar and equatorial diameters of Jupiter and Saturn in Figure 11.1. What are the ratios of equatorial to polar radii for (i) Jupiter and (ii) Saturn? Jupiter I get very close to 1 - it is hard to get a good measurement of the equatorial diameter because the left limb is in shadow. For Saturn I get 4.7cm/4.2cm = 1.11

(8) Check back to Session 13 on Light. What part of sunlight is being absorbed and what part is reflected to make Mars look red? Sunlight is in the visible part of the spectrum - for Mars to look red, the other parts of the visible spectrum - violet, blue, green - must be absorbed by the rock and dust on Mars. Similarly, what makes Venus look white? Venus looks white because the clouds in Venus' atmosphere reflect all parts of the visible spectrum equally.

(9) Look at pictures of Jupiter and Saturn and compare the range of colors of the two planets. Watch out! Sometimes the pictures are in "false color" where the colors have been distorted to show some feature. You will find images in Chapter 11 of the textbook and at The Nine Planets and Views of the Solar System. Describe the range of colors that you see in the images of each planet. In figure 11.1, the colors look a little dark. Figure 11.7 shows a better, more realistic color for Jupiter. Nevertheless, it is clear from all these pictures that the RANGE of colors is much greater for Jupiter than for Saturn. The colors look more washed out on Saturn - there is a layer of haze through which we have to look to see the colored clouds.

(10) (a) If a planet's atmosphere contains a gas that absorbs red light, which part of the visible spectrum remains after the sunlight is reflected by the planet? If the red part of the visible spectrum is absorbed then the planet will reflect mostly the violet/blu/green part of the visible spectrum.

(b) What color will the planet with the red-absorbing atmosphere appear to be? The planet will appear to be blue/green.

(11) Compare Jupiter to Saturn, and Uranus to Neptune. Which planet of EACH PAIR seems to have a layer of haze over the planet and which planet of each pair seems to have a clear atmosphere so that you can see through it down to a layer of thick clouds? (This is not supposed to be a subtle question - just look at the pictures and judge which planet looks "fuzzier"!) Jupiter and Neptune seem to have clearer atmospheres while Saturn and Uranus seem to have a layer of haze.

(12) Go to the website on the Galileo Probe and find descriptions of the measurements that were made. Describe 3 properties of the atmosphere and how they were measured. The Galileo probe measured Jupiter's atmospheric temperature (using a thermometer sticking out of the probe), pressure (using a barometer sticking out of the probe), composition (using mass analysers), cloud density (using a 'nephelometer' which sends out a laser beam and measures the about of laser light scattered by cloud particles), a lightning detector, the fluxes of energetic particles, the planet's magnetic field - and, finally, by tracking the probe as it was carried in the atmosphere: the wind speeds.

(13) The Galileo orbiter has taken many images of Jupiter's atmosphere to study the atmospheric structure and the weather on Jupiter. Go to these sites that show Great Red Spot , White Ovals, and latitude bands (these are just a selection of Galileo atmospheric images ). (a) How do false color pictures compare with true color pictures? Can you see more detail with false color? Yes, generally, the false color images enhance the detail in the atmospheric structure that you can see.

(b) If you look at higher resolution do you see more detail? Generally, yes - at smaller and smaller scales there is finer and finer stucture.

(c) To measure wind speeds you need to track cloud motions. This means taking a series of images. Look for images sequences or movies that show cloud motions.

Great Red Spot, white ovals, merging white ovals,

BUT - the Cassini movies are better - and more recent!

(d) Look for (i) wind shear, - see Cassini movies (ii) merging ovals, (iii) up- or down-welling.

(14) (a) What the cause of the seasons on earth? The tilt of the Earth's spin axis (which points to Polaris, you will remember) causes the Sun to be more directly overhead in June for the northern hemisphere and in December for the southern hemisphere - so these solstices are the northern and southern summers respectively.

(b) The diagram below shows the tilts of the giant planets' spin axes with respect to the plane of their orbits--the ecliptic. Which planets do you expect to have

(i) very strong seasons, - Uranus - it has the biggest tilt

(ii) moderate seasons, - Neptune, Saturn and Earth have similar, moderate tilts.

(iii) very little season effects? - Jupiter it has very little tilt.