Gases in Atmospheres

• Volatiles in Molecular Form (ice or gas):– Carbon dioxide CO2 (molecular weight = 44)– Oxygen O2 (molecular weight = 32)– Nitrogen N2 (molecular weight = 28)– Water H2O (molecular weight = 18)

• Other gases:– Argon Ar (molecular weight = 40)– Neon Ne (molecular weight = 20)

• Jovian gases:– Ammonia NH3 (17), Methane CH4 (16), Helium He (4),

and Hydrogen H2 (2)

Light and Atmospheres

• Greenhouse gases absorb infrared light

• Scattering of visible wavelengths depends on wavelength

• Molecular dissociation by ultraviolet light

• Ionization by X-rays

Atmospheric Layers

Greenhouse Effect

Blue Sky: Scattered Light

UV and X-ray Light

• Ozone (O3) in stratosphere of Earth absorbs ultraviolet light.– Chemical balance between O3 and O2

– Chlorofluorocarbons (CFCs) destroy ozone

• X-rays ionize the upper layers of the atmosphere (ionosphere)– Charged particles reflect low frequency radio

waves (e.g., AM radio)

Temperature Profiles

Magnetosphere

Convection

Convection on Earth

Wind Patterns on Earth

Water Cycle on Earth

Creation of Terrestrial Atmosphere

Loss of Atmosphere

Thermal Escape of Gas

Retaining an Atmosphere

• Gas will have a lifetime of several billion years if the escape velocity is 10 times the rms velocity

Become Aware of Greenhouse Effect!