Luke Boggs, Will Abney, Matt Bestic, Paristu Alizadeh, Neal Amos, Guthrie Akins

Notes for 3/26/12

The Air Pressure differences between the terrestrial still need to be explained. ’ air pressure is far higher than it should be, in comparison to ’s. Mars’ is much less than it should be, compared to Earth’s. The CO₂ in Earth’s is removed, into the soil through the water. This can explain why there is less CO₂ in Earth’s atmosphere, compared with the other two planets – and it has to do with the “Goldilocks” idea that water can be liquid on Earth, but not on Venus or Mars. The rise of life on Earth got rid of the rest of the CO₂ (most of it) in their photosynthetic processes, thereby increasing the O₂ content in the atmosphere. Taking away all of the CO₂ from the atmosphere lessened the air pressure on Earth. Since it didn’t happen on Venus, the air pressure there has increased even more.

This increase in CO₂ also causes the surface of Venus to reach temperatures of 800 K.

What about Mars? At one point, there was liquid water (we have evidence of it), which means that there must have been higher temperatures and higher pressures. But Mars today has lost about 90% of its atmosphere, and now the only water on its surface is frozen. Since Mars is smaller than the Earth, it cooled off more quickly than Earth. As it did so, the cycle for removing the water and replenishing it broke down. The water was removed, but it stopped being replenished.

But things are more complicated. One of the primary mechanisms from stripping planetary is the Solar Wind. Since Mars doesn’t have a strong magnetic field, it can’t protect itself from the Solar Winds, which tear the atmosphere away.

How does this work? The basic idea: the atmospheric molecules need to be going fast enough to escape the gravity of the . Higher temperature = higher velocity.

Notes for 3/28/12

For a given temperature, you can figure out how fast something is moving. Temperature is a measure of the total kinetic energy of a system. It is 3/2 k T = ½ mv² – so, the velocity is the thing that really increases temperature (v is squared).

Terrestrial planets supposedly cannot hold Hydrogen because the gravity is not strong enough to keep in the fast-moving Hydrogen atoms. It turns out that, at room temperature, a Hydrogen molecule moves at 1.9 km/s. The escape velocity for something moving on the Earth is 11 km/s. So, the velocity of Hydrogen is not the reason why the atmosphere has so little Hydrogen. In this case, the reduction of the concept into simplistic ideas has shown that there must be something else at work. In fact, the 1.9 km/s mentioned above is the average velocity of the Hydrogen molecules. The molecules that move faster than the escape velocity does send some out into space. Collisions between the remaining molecules cause some to speed up, others to slow down. The average is reestablished, and the faster molecules escape again. This process Luke Boggs, Will Abney, Matt Bestic, Paristu Alizadeh, Neal Amos, Guthrie Akins

repeats itself until they are all gone. And this is why Earth’s primary atmosphere was different than the current one.

[We are not responsible for pages 229-37 in the textbook – stuff about climate.]

Greenhouse Gases – they absorb infrared radiation from the Earth’s surface because they are opaque, serving as blackbodies. Nitrogen doesn’t absorb radiation as well as Greenhouse Gases. For photons, the nitrogen looks transparent because they don’t vibrate at the right frequencies to absorb the photons. Greenhouse Gases do absorb those photons because they have energy levels in the infrared.

Primary Greenhouse Gases (in order of importance): Water Vapor Carbon Dioxide Methane Chlorofluorocarbons Nitric Oxide

We have always had Greenhouse Gases on Earth, though the last 2 listed above are anthropogenic (not occurring in nature). The reason Venus has a runaway Greenhouse is because it has a larger concentration of the 2 top gases listed above. Earth doesn’t have as much of them, so that’s why we don’t have as much of an effect (at least not yet).

The Stratification of an Atmosphere: each layer of the atmosphere is trying to reach an equilibrium. So, there’s a lot of energy is being absorbed at the surface, which means that there is a lot of energy being emitted at the surface. Close to the surface, infrared radiation is being absorbed by the Greenhouse Gases. Above this level, UV light is being absorbed in the Stratosphere. Most of the UV light never reaches the ground. Ozone is most abundant in this layer, and it absorbs UV light very well. Above this, in the Mesosphere, X-rays are being absorbed by a layer of charged particles. This is also called the Ionosphere because of the charged particles (radio waves projected from the Earth’s surface bounce back from this Ionosphere).

Summary Luke Boggs, Will Abney, Matt Bestic, Paristu Alizadeh, Neal Amos, Guthrie Akins

Planet Pressure Composition State of Water Surface Temperature

Venus 100 96% CO2, 3% N2 Gas 800K

Earth 1 77% N2, 21% O2 Water 290K

Mars .01 96% CO2, 3% N2 Ice

Ice: H2O, CO2, CH4 (Methane), NH3 (Ammonia)

Goldilocks Hypothesis: Earth is the only planet where liquid water is possible. However there are holes in the theory. Magnetic fields however are very important.

Reductionism vs Complexity: The battle between making things simple and being able to fully explain them.

1/2 mv^2 = 3/2 kT Luke Boggs, Will Abney, Matt Bestic, Paristu Alizadeh, Neal Amos, Guthrie Akins

Escape velocity of Earth 11 kilometers per second.

The average velocity of hydrogen is much lower than this; 1.9 kilometers per second. Eventually you’ll loose all of it because many are going faster and the faster ones speed up the slower ones.

What are the Greenhouse Gases?

• Water Vapor: H20

• Carbon Dioxide: CO2

o The amount of CO2 is being increased heavily by human activity.

o Methane: CH4

o Chlorofluorocarbons or CFCs (This one isn’t natural)

An incorrect Theory, but good starting point: The Jovian planets begin with a metal core, that starts to pull in rocks and metal. Once it gets five times the size of Earth of ice around it, which is a huge amount, it begins to pull in gas.

Better Theory:

• and o Metallic Core, with liquid H2 in the middle, then H, He gas on the outside. • Neptune: Liquid H2 and metallic core, which is surrounded by Ice, then by H and He.

What we know about the planets.

• Mass: Yes • Size: Yes • Composition: Yes, through spectroscopically o Iron and Nickel? No, the mass isn’t big enough o Hydrogen? Yes if you squeeze it hard enough, high enough pressure. • Magnetic Fields: • Obliqueness: Will help tell you the composition.

Jovian Planets Luke Boggs, Will Abney, Matt Bestic, Paristu Alizadeh, Neal Amos, Guthrie Akins

• Rings • More satellites o Four of Jupiter’s are huge; two of them are around the size of Mercury. . Europa, one of these satellites may have life. o Saturn’s Moon Titan has an atmosphere, of Nitrogen and bigger than the planet Mercury.