Astronomy Chapter 10

Mars Atmosphere

-95% CO2 , and 5% of N,Ar,O2 -Thin, 0.6% the pressure of Earth -Gravity of Mars strong enough to hold down these compounds, but too weak to keep water -All martial atmospheric H2O fits into one great lake Great oceans have now evaporated -Red atmosphere from iron oxide dust (rust)

Thermosphere

X rays and UV heat and ionize gases

Stratosphere

Heated by UV light, no convection

Troposphere

Greenhouse gases trap infrared radiation from ground, convection important

Exosphere

Heated by X rays and UV, fast-moving atoms and molecules can escape to space

Today's Atmosphere

-Atmosphere pulled towards Earth by gravity -Most of the atmosphere content is within 11km of the surface of the Earth Layers: --Troposphere - Weather (11km) --Stratosphere - Ozone O3 (11-50km) ---Holes can replenish themselves within a century if production of CFCs stopped. --Mesosphere - 50-70km --Ionosphere - atoms are ionized by Sun's radiation and charged particles are produced. 70-150km --Exosphere - very thin

Atmospheres can...

-Create pressure on surface -absorb and scatter light -create wind and weather patterns -create a climate on the planet -can be responsible for greenhouse effect

Mars: Water in Ice Form

-Estimations: there might have been enough water to cover Mars in 500m thick -Most water left today on the surface of Mars is found in the polar ice caps

Venus: Effect of Atmosphere

-Heated by the greenhouse effect --750K (460oC hotter than Mercury) --CO2 is transparent to optical light, but absorbs infrared --Day and night sides about the same T -Too hot for liquid water -Any water from ice-bearing bodies would have evaporated

Venus Atmosphere

-Like Mercury, Venus has no moon --no tides -Similar mass, size and density as Earth -30% closer to the Sun --INHOSPITIBLE to life -Very thick clouds hide the surface --Reflect sunlight significantly (albedo=0.6) --Intrinsically bright in the night sky -Cloud cover causes a pressure of 90 bar! -Cloud layer is... --20km thick --50-60km above surface -Composition: --96% CO2 + 4% N (similar to early Earth) --CO2 and sulfuric acid vented through volcanoes --Yellow/Orange clouds due to sulfuric acid!

Van Allen Radiation Belts

-Some charged particles get trapped in the earth's field zones called the Van Allen belts -filled with charged particles -belt extends from an altitude of about 1,000 to 60,000 km above surface -feed some of lightning of earth -unstable -reflect am radio waves -sometimes overloaded -escaping particles can collide with molecules in upper atmosphere causing a florescence and aurora (northern lights)

Mercury's Atmosphere

-Thinnest atmosphere of all terrestrial planets -10^17 times less dense than air -Gravity is too weak to hold gases onto planet -Traces of H, He (coming from Sun) -Na, K (from outgassing) -Oxygen (melting polar ice?) -Most extreme temperature range in the solar system -Slow rotation, proximity to the Sun, and lack of atmosphere ΔT~700-100K (cf. ΔT~11K on Earth)

Atmospheric Structure of Venus

-Yellow-Orange color of clouds due to sulfuric acid and related molecules -Clouds are made of droplets of concentrated sulfuric acid (H2SO4)

Atmospheric Pressure

-force applied by all atoms and molecules -force is created by particles in motion -it's air pressure that keeps a ballon from collapsing on itself

Atmosphere

-layer of gas surrounding a world -often very thin -gas is made of atoms and or molecules -temperature is usually low enough to allow for molecules to form

Greenhouse Effect

1. sun arrives at earth 2. 39% of sunlight is reflected by clouds and surface 3. sunlight that isn't reflected is absorbed by surface, heating it 4. Heated surface emits infrared radiation 5. some of infrared radiation is trapped by atmosphere, heating both atmosphere and surface 6. remaining infrared radiation "leaks" into space EVENTUALLY WILL ESCAPE

Earth's Atmosphere

Atmosphere has changed over the last few billion years -1st Atm : --H and He were left over from SS formation. They escape quickly --No free oxygen -2nd Atm: --New gas came from inside of Earth --Composed of CO2, N and water vapor -Present day: --Contains about 4-to-1 N to O --O and N are rare on other planets -Volcanoes expelled CO, H2O and some N --Oceans precipitated out --Comets also added to oceans --CO absorbed into oceans --Rocks formed from sea shells --Plants absorbed remaining CO O --UV broke up CO to create more O Greenhouse Effect -This happened when Earth was between ~0.3 to 2 billion years old

Auroras Colors

Auroras result from emissions of photons from -ionized N atoms regaining an electron -O and N atoms returning fro an excited state to ground state -Atoms first ionized or excited by collision of solar wind particles being funneled down and accelerated along the magnetic field lines - oxygen emissions: green or brownish-red -nitrogen emissions: blue if atom regains an electron after it has been ionized, red if returning to ground state from excited state

Moon's Atmosphere

Average daytime abundances of elements in lunar atmosphere(atoms per cm^3): -Argon: 40,000 -Helium: 2,000-40,000 -Sodium: 70 -Potassium: 17 -Hydrogen: fewer than 17 -Continually flying away (low gravity) -Continually replenished by sunlight releasing more gas from the rocks.

Magnetosphere

Magnetic field of a planet affects its atmosphere -generated by dynamo effect -lines deflect charged particles from space -charged particles are re-directed towards magnetic poles -earth has relatively strong magnetic field -venus and mars have weak fields -mercury and moon have no field

Importance of Magnetic Field for life

Protects from bombardment of energetic space particles originating form solar wind -charged particles moving at 400 km/s get deflected

Seasons on Mars

Rotation axis 24.9 degrees